TWI458397B - Magnet structure for particle acceleration - Google Patents

Description

Magnet structure for particle acceleration

The present invention relates to magnetic structures for particle acceleration.

A magnet structure containing a superconducting coil and a magnetic pole has been developed to generate a magnetic field in two cyclotrons (isochronous cyclotron and synchrocyclotron). Synchronous cyclotrons, like all cyclotrons, accelerate charged particles (ions) from a high-frequency alternating voltage in a helical path from a central axis that is introduced from the central axis. A further feature of the synchrocyclotron is that the frequency of the applied electric field is adjusted as the particles are accelerated, so that the particle mass is relatively increased as the speed is increased. Synchrotrons are also characterized by their volume being very small, and their size can be reduced almost in a cubic manner as the strength of the magnetic field generated between the poles increases.

When the magnetic poles are magnetically saturated, a magnetic field of about 2 Tesla can be generated between the magnetic poles. However, the use of superconducting coils in a synchrocyclotron has been shown to increase the magnetic field to about 5 Tesla as described in U.S. Patent No. 4,641,057, which is incorporated herein by reference. In X.Wu's PhD thesis "Conceptual Design and Orbit Dynamics in a 250Mev Superconducting Synchrocyclotron" published at the University of Michigan in 1990, the use of superconducting coils in a cyclotron produces up to about 5.5 Tesla. The magnetic field has been an additional conceptual discussion; in addition, J. Kim at the University of Michigan State University's doctoral thesis "An Eight Tesla Superconducting Magnet for Cyclotron Studies" in 1994 for the first-time cyclotron (where The magnetic field will increase with radius. The use of superconducting coils to generate 8 Tesla magnetic fields has been discussed. Both of the foregoing papers are available at http://www.nscl.msu.edu/ourlab/library/publications/index.php and are hereby fully incorporated by reference.

A delicate magnet structure includes a cold structure comprising at least two superconducting magnetic coils (i.e., superconducting coils for generating a magnetic field). The chilled structure defines an accelerating chamber, and an intermediate accelerating plane and a section central axis extend across the accelerating chamber. a yoke is wound around the cold structure and includes a pair of magnetic poles, the tapered inner surface defining a magnetic pole gap therebetween, wherein an interval between the magnetic spaces extends across the acceleration chamber, and wherein the magnetic The yoke radially defines a section of the central axis within the acceleration chamber. The inner surfaces of the poles are tapered (approximately symmetrical on opposite sides of the intermediate acceleration plane) whereby a peak gap from a greater radial distance from the central axis spans an inner stage, The gap of the inner pole tip adjacent the central axis is increased to more than double, and at a greater radial distance from the central axis, the gap on an outer stage is reduced from the peak gap to a separation, The separation system is smaller than one of the peak gaps at one of the pole ends of the pole fins.

The poles are thus shaped to provide a weak focus for the charged particles (ions) that accelerate within the accelerating chamber, as well as to provide phase stability for the accelerating particles. The weak focus will maintain the charged particles in the correct position as they accelerate through the magnetic field in an outward spiral. Phase stability ensures that the charged particles will acquire sufficient energy to maintain the desired acceleration in the acceleration chamber. In particular, it is necessary to always provide a higher voltage electrode in the acceleration chamber than is required to maintain ion acceleration; and the magnet structure is configured to provide sufficient for the electrodes in the acceleration chamber. Space and provide sufficient space for an extraction system to extract the accelerated ions from the acceleration chamber. The rapid reduction of the magnetic pole gap at the radial distance can be increased by increasing the external level to increase the magnetic pole diameter by increasing the energy gain relative to the radius.

The superconducting magnetic coil can be incorporated into a channel defined by the yoke and used to directly generate an extremely high magnetic field in an intermediate acceleration plane of the acceleration chamber. When activated, the superconducting magnetic coils "magnetize" the yoke so that the yoke also produces a magnetic field that can be considered to be different from the magnetic field directly generated by the magnetic coils. The two magnetic field components (i.e., the components directly produced by the superconducting magnetic coils and the components produced by the magnetized yokes) are all accelerated through the central axis about orthogonal to the central acceleration plane. flat. However, the magnetic field produced by the fully magnetized yoke at the central acceleration plane will be much smaller than the magnetic field produced by the coils at that plane. The tapered surface of the magnetic pole of the yoke can shape the magnetic field along the intermediate acceleration plane such that the magnetic field decreases as the radius from a central axis to the periphery of the acceleration chamber increases for use in a synchronization Among the cyclotrons.

In other embodiments, additional magnetic coils can be used to create a shaping magnetic field within the acceleration chamber, providing both weak focus and phase stability characteristics. These additional coils (now referred to as the "main" coils described in the previous paragraph) may be used instead of or in combination with the tapered magnetic pole surface, although the result is similar to the intermediate acceleration plane within the acceleration chamber. The magnetic field is shaped.

The two main superconducting coils are placed in a symmetrical manner on either side of an accelerating plane and are placed in a vacuum reel in a cold reel that is suspended by the tensioning element. A yoke around the cold structure is, for example, made of low carbon steel. The cold structure and the yoke together produce about 7 Tesla or more in an acceleration plane of a vacuum chamber between the poles (in a particular embodiment, 9 A combined magnetic field of Tesla or larger to accelerate ions. When the coils are in a superconducting state and a voltage is applied to the coils to initiate and maintain a continuous current flow through the coils, the superconducting coils produce substantially a substantial portion of the acceleration chambers The magnetic field, for example, is about 5 Tesla or larger (in a particular embodiment, it is about 7 Tesla or larger). The yoke is magnetized by the magnetic field generated by the superconducting coils and can contribute another two Tesla to the magnetic field generated in the acceleration chamber for ion acceleration.

With this high magnetic field, the magnet structure can become particularly small. In an embodiment having seven Tesla combined magnetic fields in the acceleration plane, the yoke has an outer diameter of 45 inches (~ 114 cm) or less. In a magnet structure designed for a higher magnetic field, the outer diameter of the yoke may be even smaller. A special additional embodiment of the magnet structure is designed such that the magnetic field used in the central acceleration plane is 8.9 Tesla or higher, 9.5 Tesla or higher, 10 Tesla or higher, Other magnetic fields between 7 and 13 Tesla, and magnetic fields above 13 Tesla.

The radii of the coils may be 20 inches (~51 cm) or less, and as such, even smaller for high magnetic fields. And the superconducting material in the coils may be Nb ₃ Sn, which may generate 9.9 Tesla or larger starting magnetic field in the magnetic pole gap for acceleration; or NbTi, which may be used for acceleration. A starting magnetic field of 8.4 Tesla or greater is generated in the magnetic pole gap. In a particular embodiment, each of the coils is comprised of an A15 Nb ₃ Sn type II superconductor. The coils may be formed by circularly ringing or winding a reacted Nb ₃ Sn synthetic conductor in the form of a set of concentric rings. The composite conductor may be a reacted Nb ₃ Sn cable soldered into a copper conduit or only the cable. The cable is assembled from a predetermined number of strands of copper and barrier material consisting of tin and ruthenium precursor components. Then, the wound strands are heated to react with the parent materials to form Nb ₃ Sn, wherein the closer to the cross section of the strand, the germanium content in the structure The higher it will be.

In addition, a conductive wire coupled to a voltage source may be wound around each of the coils. Then, when the coil begins to lose its superconductivity at its inner edge during operation, by applying a sufficient voltage to the wire, the wire can be used to "quench" the superconducting coil. (That is, keeping the entire coil in a "normal state" rather than a superconducting state), thereby maintaining the possibility of operation by using a local hot spot of high resistivity, the coil can be maintained. Alternatively, a strip of stainless steel or other conductor metal (such as copper or brass) may be attached around the coil or embedded in the coils such that when a current is passed through the strips, the coils are The superconducting state is quenched by heat and thereby protects the coil.

During operation, the coils can be maintained in "dry" conditions (i.e., not submerged in the liquid coolant); rather, the coils can be cooled by a cryocooler to The temperature below the critical temperature of the superconductor. Further, the cold structure may be coupled to a plurality of radial tension members that are used to concentrate the cold structure on the central axis during operation and the presence of a particularly high magnetic field. Around the place.

In addition, the ion accelerator may have a suitable compact beam chamber, D-shape, and resonator structure in which the plasma is formed, captured in an accelerated orbit, accelerated to final energy, It will then be extracted for use in several ion beam applications. The beam chamber, the resonator, and the D-shaped structure are present in an open space between the poles of the superconducting magnet structure, and the magnet structure is thus configured to receive the components ( However, special magnetic field shaping is still available). The beam chamber includes ion beam shaping. The plasma may be formed in an internal ion source or may be provided by an external ion source having an ion emitting structure. The beam chamber will be evacuated and will also act as a ground plane for the RF acceleration structure. The RF acceleration structure includes: a D-shaped object or a plurality of D-shaped objects; other surfaces or structures for defining an acceleration gap; and a transfer member for transmitting the RF waves from an external generator to the beam chamber In order to excite the D-shaped object or the plurality of D-shaped objects.

Still further, an integrated magnetic shield can be provided to surround the yoke and contain an external magnetic field generated therein. The integrated magnetic shield may be constructed of low carbon steel (similar to the yoke) and disposed outside of a contour of a 1,000 Gauss magnetic flux density that may be produced by the magnet structure during its operation. The shield may have a twisted shape such that a magnetic flux line extending outside the yoke intersects the integrated magnetic shield at a plurality of locations and at a plurality of angles to improve the effect of defining a magnetic field having various directions . The heads of the cryogenic coolers and other active elements that are susceptible to high magnetic fields are placed outside of the integrated magnetic shield.

The apparatus and method of the present invention can generate extremely high magnetic fields from a very delicate structure to produce a punctiform head beam having high energy (and short wavelength) particles (i.e., having a small spatial profile). . Furthermore, the integrated magnetic shield of the present invention is excellently limited to the magnetic field generated there. The delicate structure of the present invention can be used in a wide variety of particle accelerators, where the accelerator may have a portable type, for example, can be used on a vehicle or in a vehicle and can be repositioned. To provide a temporary source of energetic ions for diagnostic or risk detection, for example, in a security system at a port or other type of transportation center. Therefore, the accelerator can be used where it is needed, rather than being used only in a dedicated accelerator facility. Still further, for example, the accelerator can also be placed on a retractor for moving the accelerator in a single room system with a fixed target (eg, a patient) as a reference. The object is illuminated by accelerated ions emanating from the accelerator from a variety of different source locations.

The numerous inventions described herein are widely available beyond their implementation in synchrocyclotrons (for example, in isochronous cyclotrons and in applications using superconductors and/or other applications for generating high magnetic fields). Medium) and can be easily applied in other fields. However, for the sake of reference, the description begins with an explanation of the basic principles and features in the field of synchrocyclotrons.

In general, a synchrocyclotron has the following characteristics: charge of an ion species (Q); mass of an accelerated ion (M); acceleration voltage V ₀ ; final energy E; a final radius R spaced from a central axis; Central magnetic field B ₀ . The parameters B ₀ and R are both related to the final energy, so only one of them needs to be specified. In particular, a synchrocyclotron can be characterized by the parameter sets Q, M, E, V ₀ , and B ₀ . The high magnetic field superconducting cyclotron of the present invention comprises several important features and components whose functions follow the principle of synchronous acceleration for creating, accelerating, and extracting a special Q, M, E, V ₀ , and B. ₀ ions. In addition, when the central magnetic field is raised individually and all other key parameters are maintained constant, the final radius of the accelerator is seen to be scaled down; and the synchrocyclotron becomes very compact. As the central magnetic field B ₀ increases, the overall compactness is roughly identifiable by the cube of the final radius, R ³ , and the results are shown in the following table, where greatly increasing the magnetic field greatly reduces the The approximate volume of the synchrocyclotron.

The last row in the above table represents the volume reduction factor, where R ₁ is the magnetic pole radius. When B ₀ is 1 Tesla, the radius is 2.28 m; and R is the central magnetic field B ₀ in each column. Corresponding radius. In this example, M = ρ _iron V and E = K(RB ₀ ) ² = 250 MeV, where V is the volume.

One of the factors that will vary greatly as the central magnetic field B ₀ increases is the cost of the synchrocyclotron, which will decrease. Another factor that can change significantly is the portability of the synchrocyclotron; that is, it should be easier to reposition the synchrocyclotron; for example, the synchrocyclotron can be placed together on a retractor and wound a patient movement for radiation therapy of cancer; or the synchrocyclotron can be placed on a vehicle or a truck for use in mobile applications, for example, in the use of energy-like dots The particle beam is used in the inlet channel security monitoring application. Another factor that changes as the magnetic field increases is the size; that is, all of the features of the synchrocyclotron and the important components and ion acceleration characteristics are substantially reduced in size as the magnetic field increases. The manner described herein greatly reduces the overall size of the synchrocyclotron (for a fixed ion species and final energy) by utilizing a superconducting magnetic structure that produces such magnetic fields to boost the magnetic field.

For a given energy E, charge Q, mass M, and acceleration voltage V ₀ , the synchrocyclotron has a structure for generating the required magnetic energy when the magnetic field B ₀ is raised. The magnetic structure provides stability and protection for the superconducting elements of the structure, reduces the large electromagnetic force accompanying the increase of the central magnetic field B ₀ , and provides cooling for the superconducting cold structure, and The necessary total magnetic field and magnetic field shape characteristics of the synchronized particle acceleration are generated.

Shown in Figure 1 is a yoke of a 9.2 Tesla, 250 MeV proton superconducting cyclotron 36, a D-shape 48, and a resonator structure 174 having a function of 11.2 Tesla. The superconducting coil of Nb ₃ Sn is mainly used in the peak magnetic field (not shown). In X.Wu's PhD thesis "Conceptual Design and Orbit Dynamics in a 250Mev Superconducting Synchrocyclotron" published by the University of Michigan in 1990, a novel calibration method was used in the solution obtained at 5.5 Tesla. Method) will predict the synchrocyclotron solution; Xianwen Wu's paper has proposed the highest central magnetic field (B ₀ ) level in the design of the synchronous cyclotron at that time - it has been confirmed in detail or experimentally Was proposed.

The high magnetic field calibration rule does not require that these new ionic species must be identical to the specific examples presented herein (ie, the calibration laws are common and not limited to 250Mev and protons); Above, the charge Q and the mass M may not be the same; and a certain standard solution may be determined for a new species for a different Q and M. For example, in another embodiment, the plasma removes electrons having a +6 charge carbon atom (ie, ¹² C ⁶⁺ ); compared to a lower mass, lower charge particle, this embodiment Only a smaller final shaping magnetic field is required (for example, the contours of the magnetic pole surfaces will be relatively flat). In addition, the new calibration energy E may be different from the previous final energy. Further, B ₀ can also be changed. With each of the aforementioned changes, the accelerated synchrocyclotron mode can be maintained.

A ferromagnetic yoke 36 surrounds the beam chamber, the D-shaped object 48, and the acceleration region where the resonator structure 174 is located; the yoke 36 also encloses the space of the magnet cryostat, from the upper magnet cryostat chamber 118 and below The magnet cryostat chamber 120 is shown. The beam acceleration system chamber, D-shaped material 48, and the size of the resonator structure 174 is designed to train a proton beam with E = 250MeV lower than V ₀ 20kV accelerating voltage at the (Q = 1, M = 1 ) . The ferromagnetic core and the yoke 36 are designed as a separate structure to aid assembly and maintenance; and the outer diameter is less than 35 inches (~89 cm) and the total height is less than 40 inches (~100 cm). The quality is less than 25 tons (~23,000kg). The yoke 36 is maintained at room temperature. This special solution can be used in any of the aforementioned applications that have been identified to work with a sophisticated high magnetic field superconducting cyclotron, such as being placed on a retractor, placed on a platform, or placed on a truck. Or placed in a fixed location at an application location.

For the sake of clarity, numerous other features of the ferromagnetic yoke structure 36 for high magnetic field synchrocyclotron operation are not shown in FIG. These features will now be shown in Figure 2. The structure of the synchrocyclotron is approximately 360 degrees of rotational symmetry centered on its major axis 16 to allow for separate turns and other discrete features at particular locations. The synchrocyclotron also has a central acceleration plane 18 which is the mirror symmetry plane of the ferromagnetic yoke 36 and the intermediate plane of the pair of split coils 12, 14; the central accelerating plane is also the beam chamber ( It is defined between the poles 38 and 40, the D-shape 48, and the vertical center of the resonator structure 174 and the vertical center of the particle track during acceleration. The ferromagnetic yoke structure 36 of the high magnetic field synchrocyclotron is composed of a plurality of components. The poles 38 and 40 define an upper intermediate passage 142 and a lower intermediate passage 144 which are aligned about the central axis 16 of the synchrocyclotron and each having a diameter of about 3 inches (~7.6). Cm), they are available for placement and removal of an ion source on the main axis 16 at a central plane 18 that is placed in the central region of the acceleration chamber 46.

A fine magnetic field structure is used to stabilize the plasma. The fine magnetic field configuration is provided by designing the shape of the ferromagnetic yoke 36; designing the magnetic pole tip contour 122 and the lower pole tip contour 124 and the upper pole contour 126 and lower pole contour for initial acceleration. The shape of 128; and the shape of the upper magnetic pole contour 130 and the lower magnetic pole contour 132 designed to accelerate the high magnetic field. In the embodiment of FIG. 2, the maximum magnetic pole gap between the upper magnetic pole contour 130 and the lower magnetic pole contour 132 (adjacent to the upper magnetic pole 134 and the lower magnetic pole 136) is greater than the upper magnetic contour 126 The maximum pole gap between the lower pole contours 128 is twice as large and five times larger than the minimum pole gap at the upper pole tip contour 122 and the lower pole tip contour 124. As shown, the slope of the upper pole tip contour 122 and the lower pole tip contour 124 is steeper than the slope of the adjacent upper pole contour 126 and lower pole contour 128 for initial acceleration. After the relatively smaller slope of the upper magnetic pole contour 126 and the lower magnetic pole contour 128, the slope of the upper magnetic pole contour 130 and the lower magnetic pole contour 132 for high magnetic field acceleration will again rise again (contour 130) and fall. (Contour 132) to increase the rate at which the pole gap expands as the radial distance from the central (main) axis 16 increases.

Moving outward rapidly, the slope of the surfaces of the upper pole 134 and the lower pole 136 may be steeper (and opposite) than the slope of the upper pole contour 130 and the lower pole contour 132. The size of the pole gap is rapidly reduced as the radius between the pole wings 134 and 136 increases (the reduction factor is greater than five times). Accordingly, the structures of the pole wings 134 and 136 substantially block the magnetic fields generated by the coils 12 and 14 by trapping the internal magnetic field lines adjacent to the coils 12 and 14 to prevent them from facing the acceleration chamber. The periphery moves so that the magnetic field outside the trapped magnetic field lines drops rapidly. The furthest gap, which is between the joint of the pole wing 134 having the surface 130 and the joint of the pole wing 136 having the surface 132, is about 37 cm. Then, the gap is suddenly (to form an angle between 80° and 90° with the central acceleration plane 18 - for example, at an angle of about 85°) narrowed to between the tips 138 and 140 About 6cm between. Accordingly, the gap between the pole wings 134 and 136 can be less than one-third (or even less than one-fifth) the size of the furthest gap between the poles. In this embodiment, the gap between the coils 12 and 14 is about 10 cm.

In embodiments where the magnetic fields originating from the coils are increased, the coils 12 and 14 contain more amperages and are further spaced apart from each other and are placed closer to the individual pole wings 134 and 136. The location. Furthermore, among the magnet structures designed for high magnetic fields, the magnetic pole gap between the contour lines 126 and 128 and between the contour lines 130 and 132 is increased, and the peripheral tips 138 and 140 are interposed. The inter-pole gap is narrowed (for example, narrowed to about 3.8 cm in a magnet structure designed for a 14 Tesla magnetic field) and the magnetic pole gap between the central tips 122 and 124. It will also narrow down. Still further, in these embodiments, the thickness of the pole wings 134 and 136 (as measured parallel to the acceleration plane 18) may increase. Furthermore, the applied voltage is relatively low, while the plasma track is more compact and larger; the axial and radial beam spacing is smaller.

The contour changes shown in Figure 2 are merely representative examples - for each high magnetic field synchrocyclotron calibration solution, there may be varying numbers of magnetic pole tapered changes to accommodate phase stabilization acceleration and weak focus; The surface may also have contour lines that vary smoothly. The ions will have a helical average orbit that expands along the radius r. The plasma also oscillates slightly orthogonally around this average orbit. The small oscillations around the average radius are known as betatron oscillations, and they define the special characteristics of the accelerated ions.

The upper and lower pole wings 134 and 136 will make the edge of the magnetic field for extraction sharper by moving the characteristic track damping, which will bring the finally achievable energy closer to the edge of the pole. The upper and lower pole wings 134, 136 are also used to block the internal accelerating magnetic field originating from the pair of strongly separated coils 12 and 14. An adequate non-axisymmetric edge is created by placing a ferromagnetic upper ferrule tip 138 and an additional localized component of the lower ferrule tip 140 around the faces of the upper and lower pole wings 134, 136. The magnetic field can be adapted to the conventional regenerative cyclotron extraction or self-extraction.

In a particular embodiment, the ferrous tips 138 and 140 are separated from each other by a gap therebetween through the respective upper and lower pole wings 134 and 136; thus, the ferrous tips 138 and 140 can be incorporated into the Inside the beam chamber, the walls of the beam chamber are passed through the gap. Although the ferrous tips 138 and 140 will be separately fixed, they will still be in the magnetic circuit.

In other embodiments, as shown in FIG. 3, the ferrous tips 138 and 140 or the pole wings 134 and 136 may be asymmetric with respect to the central axis 16 and include a slit 202 and an extension 204 for Reduce and increase the magnetic field at these locations, respectively. In other embodiments, the ferrous tips 138 and 140 are not continuous at the periphery of the poles 38 and 40, rather, they are in the form of different segments separated by a gap, wherein These gaps produce a lower local magnetic field. In yet another embodiment, by varying the composition of the ferrous tips 138 and 140 or by incorporating selected materials having different magnetic properties at different locations in the periphery of the tips 138 and 140 Different local magnetic fields. The composition elsewhere in the yoke can also be varied (for example, by providing different materials having different magnetic properties) to facilitate, if necessary, for providing weak focus and phase for the accelerated ions. Stable) The shape of the magnetic field is designed in a special area of the central acceleration plane.

A plurality of radial passages 154 defined in the ferromagnetic yoke 36 provide a proximal action on the central plane 18 of the synchrocyclotron. The central planar channels 154 are used for beam extraction and for invading the resonator inner conductor 186 and the resonator outer conductor 188 (see Figure 5). An alternative method for accessing the ion acceleration structure in the pole gap is via the upper axial RF channel 146 and via the lower axial RF channel 148.

The cold structure and cryostat (not shown) include a plurality of intrusions for use with leads, coolant, structural supports, and vacuum suction, and the invaders are passed through A pole cryostat passage 150 and a lower pole cryostat passage 152 are disposed within the ferromagnetic core and yoke 36. The cryostat is constructed of a non-magnetic material (for example, an INCONEL nickel-based alloy available from Special Metals Corporation of Huntington, West Virginia, USA).

The ferromagnetic yoke 36 includes a magnetic circuit that carries the magnetic flux generated by the superconducting coils 12 and 14 to the acceleration chamber 46. The magnetic circuit that passes through the yoke 36 also shapes the magnetic field at the upper pole tip 102 and at the lower pole tip 104 for the synchrotron weak focus. The magnetic circuit also enhances the magnetic field level in the acceleration chamber due to a majority of the magnetic flux comprising components other than the magnetic circuit, including the underlying ferromagnetic yoke element: an upper magnetic pole having a corresponding lower magnetic pole root 108 The root 106; and an upper yoke 110 having a corresponding lower yoke yoke 112. The ferromagnetic yoke 36 is made of a ferromagnetic substance that provides magnetic field shaping in the acceleration chamber 46 for ion acceleration even if it has been saturated.

The upper magnet cryostat chamber 118 and the lower magnet cryostat chamber 120 include the upper superconducting coil 12 and the lower superconducting coil 14 and a superconducting cold structure and a cryostat located around the coils (in the figure) Not shown).

For scaling a new synchrotron orbit solution for a given E, Q, M, and V ₀ , the position and shape of the coils 12 and 14 are equally important when B _{0 is} greatly increased. . The bottom surface 114 of the upper coil 12 will face the inverted top surface 116 of the bottom coil 14. The upper pole 134 will face the inner surface 61 of the upper coil 12; and likewise, the lower pole 136 will face the inner surface 62 of the lower coil 14.

If there is no additional shielding, (in the high magnetic field superconducting cyclotron or near the outer surface of the ferromagnetic yoke 36), the concentrated high magnetic field level will be adjacent to the person via magnetic attraction or magnetization. Equipment poses a potential hazard. A magnetic field derived from the synchrocyclotron can be minimized using an integrated outer shield 60 made of ferromagnetic material whose dimensions have been designed for the desired external magnetic field reduction. The shield 60 may have multiple layers or may have a convoluted surface for additional local shading and may have multiple channels for use with the synchrocyclotron and for use with the final external beam transport system remote from the cyclotron. .

Synchro cyclotron is a member of the circular grade particle accelerator. The beam theory of the circular particle accelerator has been developed very completely, and it is based on two key concepts: the balanced orbit and the beta oscillation around the balanced orbit. The principle of the equilibrium orbit (EO) can be described as follows: • A charge with a given momentum captured by a magnetic field will record a track; • A closed orbit represents the equilibrium state of the given charge, momentum, and energy; The stability of the magnetic field is analyzed to carry a set of smooth balanced orbits; and the acceleration can be considered to be transferred from one balance rail to another.

The weak focus principle of the perturbation theory can be described as follows: ● The particles will oscillate around an average orbit (also known as the midline); ● The oscillation frequencies (v _r , v _z ) will respectively characterize the diameter Movement in the direction (r) and the axial direction (z); ● the magnetic field is decomposed into a coordinate magnetic field component and a magnetic field index (n), and v _r = And v _z = And the resonance between the particle oscillations and the magnetic field components, especially the magnetic field error term, determine the acceleration stability and loss.

In the synchrocyclotron, the above-mentioned weak focus magnetic field index parameter n is defined as follows:

Where r is the radius of separation of the ions (Q, M) from the main axis 16; and B is the magnitude of the axial magnetic field at the radius. In the entire acceleration chamber, the weak focus magnetic field index parameter n ranges from zero to one (possibly exceptions are in the central region of the acceleration chamber close to the main central axis 16 where ions are introduced and where The radius approaches zero) to successfully accelerate the ions to full energy in the synchrocyclotron, wherein the magnetic field generated by the coils will control the magnetic field index. Specifically, a regenerative force is provided during reacceleration to keep the plasma oscillating around the average orbit. We can see that when n>0, this axial return force will exist, and it requires dB/dr<0 because B> and r>0 is true. The magnetic field of the synchrocyclotron is reduced with radius to match the magnetic field index required for acceleration. Alternatively, if the magnetic field index is known, we can specify a relatively precise electromagnetic circuit with the location and position of the features, as shown in Figure 2, for more detailed orbital and magnetic field calculations at these locations. Can provide an optimal solution. With the ready-made solution, the solution can then be adapted to a parameter set (B ₀ , E, Q, M, and V ₀ ).

In this regard, the rotational frequency ω of the ions rotating in the magnetic field of the synchrocyclotron is ω=QB/γ M

Where γ is the relative coefficient that the particle mass increases as the frequency increases. The decrease in frequency as a function of energy increases in a synchrocyclotron is the basis of the synchrotron acceleration mode of the circular particle accelerator, and in addition to the change in the magnetic field index required for the axial return force, And additionally reduce the magnetic field. The voltage V across the gap to provide a stable phase will be greater than the minimum required voltage V _min, that such particles may have an energy gap, a gap to make them more energy will be at crossed. In addition, synchrocyclotron acceleration also involves phase stability principles, characterized in that the available accelerating voltage almost always exceeds the voltage required for ion acceleration for full energy from the center of the accelerator to the outer edge. When the radius r of the ion is reduced, the acceleration electric field must be increased, and therefore, the acceleration voltage accompanying the increase of the magnetic field B may actually have a limit.

For a given set of known and operable high magnetic field synchrocyclotron parameters, the magnetic field index n (which, by itself, may depend on the aforementioned principle effect) may be used to infer the diameter in the magnetic field for acceleration. Change. This "B vs. r" curve can be further parameterized by dividing the magnetic field in the data set by the actual magnetic field value required at full energy and by using this "B vs. r" data set. The corresponding radius value is divided by the radius that will reach the full energy. This normalized data set can then be used to adapt to the synchrocyclotron acceleration solution at a higher central magnetic field B ₀ , and if at least the following is true, the overall accelerator reduction effect is achieved: (a) acceleration The resonance number h is a constant, wherein the resonance number refers to a multiple between the acceleration voltage frequency ω _RF and the ion rotation frequency ω in the magnetic field, and the relationship is as follows, ω _RF =h ω; and (b) each cycle The energy gain E _t will be limited to keep the ratio of E _t to another coefficient constant, specifically, the relationship is as follows: Wherein f(γ)=γ ² (1-0.25(γ ² -1)).

The characteristics of the superconducting coil will be further explored below to further develop a higher magnetic field synchrocyclotron using the superconducting coil. Several different types of superconductors can be used in superconducting coils; and among the many important engineering solution coefficients, the following three coefficients are commonly used to characterize superconductors: magnetic field, current density, and temperature. When the superconducting state is maintained at a specific utility engineering current density J _e and the operating temperature T _op , the maximum magnetic field that can be supported in the superconducting wire of the superconducting wire in the coils is B _max . For the purpose of comparison, superconducting coils in magnets (such as superconducting coils proposed for superconducting cyclotrons, especially the superconducting coils proposed in the high magnetic field synchrotron discussed in this paper) often use 4.5K. The operating temperature T _op . For the purpose of comparison, the engineering current density J _e of 1000 A/mm ^{2 is} a reasonable representative value. However, the true range of operating temperature and current density is greater than the aforementioned values.

NbTi superconducting material used in a superconducting magnet system and it may be at the 1000A / mm ² at 4.5K magnetic fields up to 7 Tesla operating level; Nb ₃ Sn may be in the 1000A / mm ² and 4.5K It operates at the magnetic field level of up to about 11 Tesla. However, the temperature of 2K can also be maintained in the superconducting magnet by a process called sub-cooling, and in this case, the performance of NbTi will reach about 11 Tesla operation at 2K and 1000 A/mm ² . The level of Nb ₃ Sn will reach about 15 Tesla operating levels at 2K and 1000A/mm ² . In fact, we have not designed the magnet to operate at the magnetic field limit of superconducting stability; in addition, the magnetic field level at the superconducting coil may be higher than the magnetic field level in the magnetic pole gap, therefore, the actual The operating magnetic field level will be lower. Furthermore, the difference in detail between specific members of the two conductor series described above extends this range as if it were operating at a lower current density. In addition to the previously proposed orbital calibration, the approximate range of the aforementioned known characteristics of the superconducting elements can also result in the selection of a desired operating magnetic field level in a compact high magnetic field superconducting cyclotron. Special superconducting wire and coil technology. Specifically, the operating magnetic field level of a superconducting coil made of NbTi conductor and Nb ₃ Sn conductor and operating at 4.5K ranges from a low magnetic field in a synchrocyclotron to a magnetic field exceeding 10 Tesla. Further reducing the operating temperature to 2K extends the range to at least 14 Tesla operating magnetic field levels.

The superconducting coil is also characterized by the level of magnetic forces in the winding and the need to quickly eliminate energy, and for a particular reason, a portion of the winding will become normally conductive at the fully operational current. Energy elimination is a known magnet quenching. There are several factors associated with the force and quenching protection of the split coil pairs 12 and 14 of a superconducting synchrotron for a calibrated high magnetic field superconducting cyclotron using a selected conductor type. Proposed to operate correctly. As shown in FIG. 4, the coil assembly includes a separate coil pair having an upper superconducting coil 12 and a lower superconducting coil 14. The upper superconducting coil 12 and the lower superconducting coil 14 axially wind the alternating current superconductor and the insulating element. There are several types and grades of superconductors that can be used with different compositions and characteristics.

The surface 168 in the upper superconducting coil 12 and the surface 170 in the lower superconducting coil 14 schematically represent the boundaries of the conductor level change in order to produce a better matching effect between the conductor and the coil design. At these and other locations, additional structures may be introduced for particular applications, such as assisting in quenching protection or increasing the structural strength of the winding. Therefore, each of the superconducting coils 12 and 14 may have a plurality of sections separated by boundaries 168 and 170. Although three segments are shown in Figure 4, this is only one of the embodiments, and in practice fewer or more segments may be used.

The upper coil 12 and the lower coil 14 are located within a cryogenic coil mechanical enclosure structure, referred to herein as the spool 20. The spool 20 will support both the radial and axial directions and contain the coils 12 and 14, because the upper coil 12 and the lower coil 14 have a very attractive suction load and a very large radial outward force. The spool 20 provides axial support to the respective surfaces 114 and 116 of the coils 12 and 14. To approximate the acceleration chamber 46, a plurality of radial passages 172 are defined in the spool 20 and pass through the spool 20. In addition, a plurality of attachment structures (not shown) may be provided on the spool 20 to impart a radial coupling for securing the coil/reel assembly in the correct position.

An approximate region of the highest magnetic field, shown at position 156 in upper superconducting coil 12 and at position 158 in lower superconducting coil 14; and this magnetic field level will set the design point for the selected superconductor, as discussed above . Further, the scribe line region 164 in the upper superconducting coil 12 and the region of the scribe line region 166 in the lower superconducting coil 14 are opposite to each other; and in the foregoing case, the radial force on the windings Will be inward and will decrease. Regions 160 and 162 are regions of low magnetic field or near zero overall magnetic field level, and such zones have the greatest resistance to quenching.

The compact high magnetic field superconducting cyclotron includes elements for phase stabilization acceleration, which are shown in Figures 5-8. Figures 5 and 6 provide a detailed engineering layout of one of the beam acceleration structure types for the 9.2 Tesla solutions of Figure 1, having a beam chamber 176 and a resonator 174, wherein the beam chamber 176 is Located in the magnetic gap space. Figure 5 is a front elevational view showing that only one of the D-shaped objects 48 is used to accelerate the plasma; and the side view shows that the D-shaped object 48 is separated from the top and bottom of the central plane. To allow the beam to pass through during acceleration. The D-shape 48 and the plasma are located in a volume under vacuum and defined by the beam chamber 176, the volume comprising a beam chamber substrate plate 178. Accelerating the gap defining the aperture 180 creates an electrical ground plane. Between the D-shaped object 48 and the acceleration gap ground plane defining the aperture 180, the plasma is accelerated by an electric field across the acceleration gap 180.

To establish the desired high magnetic field across the gap 182, the D-shapes 48 are coupled to a resonator inner conductor 186 and to a resonator outer conductor 188 via a D-resonator connector 184. The external resonator conductor 188 is coupled to the cryostat 200 of the high magnetic field synchrocyclotron (as shown in Figure 9) having a vacuum boundary maintained by the connecting line. The resonator frequency is varied by an RF rotating capacitor (not shown) that is coupled to the accelerating D-shape 48 via a resonator outer conductor swivel yoke 190 that passes through the coupling jaw 192. The inner conductor 186 and the outer conductor 188. Power is transferred to the RF resonant circuit via RF transmit line coupling 194.

In another embodiment, an alternative structure having two D-shaped and axial RF resonator elements would be incorporated into the delicate high magnetic field superconducting cyclotron, as shown schematically in FIG. This dual D-shape system can increase the acceleration rate or reduce the voltage V ₀ . Thus, this embodiment would use two D-shapes 48 and 49; the D-shapes 48 and 49 would be split into two halves on either side of the central plane, and by the upper axial resonators 195 and 196 and the lower shaft Energy is supplied to resonators 197 and 198 (in addition to the radial power feed via channel 154, as shown in Figure 2). The axial resonators are then powered by an external RF power source. Figure 9 also shows how a coil cryostat 200 is adapted to the ferromagnetic yoke structure 36.

A more complete and detailed diagram of a magnet structure 10 for particle acceleration is shown in Figures 10 and 11. For example, the magnet structure 10 can be used in a sophisticated synchrocyclotron (for example, in a synchrocyclotron featuring a synchrocyclotron disclosed in U.S. Patent No. 4,641,057). In an isochronal cyclotron, and in other types of cyclotrons that can accelerate ions (such as protons, deuterons, alpha particles, and other ions).

Within the broader magnetic structure, a high energy magnetic field is generated by a cold structure 21 comprising the pair of circular coils 12 and 14. As shown in FIG. 12, the pair of circular coils 12 and 14 are disposed within a separate copper thermal shield 78 located in a vacuum, and there is a tight relationship between the coils 12 and 14 and the copper thermal shield 78. Mechanical contact. Also placed in each of the copper heat shields 78 is a pressurized bladder 80 that exerts a radially inward force to counteract the action on each of the coils 12/14 during operation. High annular stretching force. The coils 12 and 14 are symmetrically arranged centered about a central axis 16 in an equidistant manner above and below the acceleration plane 18 on which the plasma can be accelerated. The coils 12 and 14 are separated by a sufficient distance to allow the RF acceleration system to extend into the acceleration chamber 46 therebetween. Each coil 12/14 includes a continuous path of conductor material that exhibits superconductivity at a designed operating temperature (typically 4 to 6K, but can also operate below 2K). State, additional superconducting performance and margins are achieved at this operating temperature. Each coil has a radius of approximately 17.25 inches (~43.8 cm).

As shown in Figure 13, the coils 12 and 14 comprise a superconductor cable or a cable-in-channel conductor having a cable strand 82 having a diameter of 0.6 mm and which is wound to provide Current carrying capacity between 2 million and 3 million total ampoules. In one embodiment, each of the cable strands 82 has a superconducting current carrying capacity of 2,000 amps, and 1,500 of the stranded wires are disposed in the coil to provide 3 million amps in the coil. The capacity of the cockroach. In general, the coil will be designed to have a plurality of windings to produce the desired number of ampere-turns for a desired magnetic field level without exceeding the critical current carrying capacity of the superconducting strand. The superconducting material may be a low temperature superconductor such as niobium titanium (NbTi), niobium tin (Nb ₃ Sn), niobium aluminum (Nb ₃ Al); in a special embodiment, the superconducting material is type II Superconductor - specifically, Nb ₃ Sn having an A15 crystal structure. High temperature superconductors such as Ba ₂ Sr ₂ Ca ₁ Cu ₂ O ₈ , Ba ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀ , or YBa ₂ Cu ₃ O _{7-x can also be used} .

The cable strands 82 are soldered to a U-shaped copper channel 84 to form a composite conductor 86. The copper channel 84 provides mechanical support, thermal stability during quenching; and provides a conductor path for current use when the superconducting material is in a normal state (ie, non-superconducting). The composite conductor 86 is then wound into the glass fibers and then wound into an outwardly facing relay. A strip heater 88 composed of stainless steel may also be interposed between the multilayer wound layers of the composite conductor 86 to perform rapid heating while quenching the magnet, and also after the quenching has been performed. Temperature balance is provided on the radial section of the coil to minimize thermal and mechanical stresses that may damage the coils. A vacuum is applied after winding, and the wound composite conductor structure is injected with an epoxy resin to form a fiber/epoxy synthetic filler 90 in the final coil structure. The resulting epoxy-glass composite in which the wound composite conductor 86 is embedded provides electrical insulation and mechanical rigidity. A wound insulating layer 96 composed of an epoxy resin-infused with glass fibers serves as a lining inside the copper heat shield 78 and surrounds the coil 12.

In one embodiment of the construction of Nb ₃ Sn for use in a cyclotron, the coil is constructed by loading a wound tin wire strand into a powder matrix. The wound strand and the precursor are then heated to a temperature of about 650 ° C for 200 hours to allow the tin wires to react with the ruthenium precursor and thereby form Nb ₃ Sn. After this heat treatment, each Nb ₃ Sn strand in the cable must carry a portion of the total current that has a sufficient current margin at the operating magnetic field and temperature to maintain the superconducting status. The copper channel profile and the specifications of the epoxy composite precursor allow the high field coil to maintain its superconducting state under greater mechanical stresses occurring in such delicate coils. This improved peak stress migration is also very advantageous for the coil to operate at higher current densities to increase the magnetic field produced, which is associated with greater forces acting on the superconducting coils. Unless all stress states in operation are properly limited, Nb ₃ Sn conductors are very fragile and can be damaged and lose specific superconducting properties. Forming an epoxy-composite mechanical structure on the windings following the winding and reaction process allows the Nb ₃ Sn coils to be used in other applications where superconductors are used or superconductors can be used. It may not be suitable for these applications due to the fragility of the standard Nb ₃ Sn coils in the previous embodiments.

The copper shields (which contain the coils 12 and 14) are disposed in a spool 20 of high strength alloy, for example, stainless steel or austenitic (austenitic). Nickel-chromium-iron alloy (commercial INCONEL 625, available from Special Metals Corporation, Huntington, West Virginia, USA). The reel 20 will invade between the coils 12 and 14, while the other portions are located outside of the coils 12 and 14. The thickness of the top end portion and the bottom portion (in accordance with the orientation of FIG. 12) of the reel 20 in the outer portion of the reel 20 (measured in the horizontal direction, according to the orientation of FIG. 12) is approximately equal to the coil 12/14. thickness of. The cold structure 21, which includes the coils 12 and 14 and the reel 20, is housed in an insulated and vacuumed stainless steel or aluminum casing 23, referred to as a cryostat, which can be The iron magnetic pole and the yoke 36 are disposed inside. The cold structure 21 defines (i.e., at least partially defines) a space for use by the acceleration chamber 46 (see FIG. 11) for accelerating ions and a section extending across the central axis 16 of the acceleration chamber 46.

As shown in Figure 11, the magnet structure 10 further includes a conductive wire 24 that surrounds each of the coils 12/14 (i.e., the spiral surrounds the coil, only a small portion of which is shown in Figure 11) (for example, , in the form of a cable, for quenching the coil 12/14 when it enters the "normal state" due to an increase in temperature. A voltage or current sensor is coupled to the coils 12 and 14 for monitoring whether the resistance in any of the coils 12/14 is increased, thereby indicating that a portion of the coil 12/14 is no longer super Guide state.

As shown in FIG. 10, a cryocooler 26 (which may use compressed helium in a Gifford-McMahon refrigeration cycle, or which may also have a pulse tube cryocooler design) is thermally coupled to the cold structure 21. . The coupling may be in the form of a low temperature superconductor (e.g., NbTi) current lead that contacts the coil 12/14. The cryocoolers 26 are capable of cooling each coil 12/14 to a temperature that causes it to assume a superconducting state. Accordingly, each of the coils 12/14 can be maintained in a dry condition during operation (i.e., not immersed in liquid helium or other liquid refrigerant), and in the cold structure 21 There is also no need to provide any liquid coolant in or near the vicinity to cool the cold or for the superconducting coils 12/14 to operate.

A second pair of cryocoolers 27 (which may have the same or similar design as the cryocooler 26) couple current leads 37 and 58 to the coils 12 and 14. The high temperature current lead 37 is composed of a high temperature conductor such as Ba ₂ Sr ₂ Ca ₁ Cu ₂ O ₈ or Ba ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀ , and is subjected to the low temperature cooler 27 at one end. The cold heads 33 at the end of the first stage are cooled, the cold heads are at a temperature of about 80K; at their other ends they are cooled by the cold heads 35 at the ends of the second stage of the cryogenic coolers 27. The temperature of the cold heads is about 4.5K. The high temperature current leads 37 are also electrically coupled to a voltage source. The low temperature current lead 58 is coupled to the high temperature current lead 37 for providing a path for current flow; and is also coupled to the cold head 35 at the end of the second stage of the low temperature cooler 27 for The low temperature current lead 58 is cooled to a temperature of about 4.5K. Each of the low temperature current leads 58 further includes a wire 92 attached to an individual coil 12/14; and a third wire 94 (which is also comprised of a low temperature superconductor) couples the two in series Coils 12 and 14. Each of these wires can be secured to the spool 20. Accordingly, current can flow from an external circuit having a voltage source to the first of the low temperature current leads 58 via the first one of the high temperature current leads 37 and enter the coil 12; It is then possible to flow through the coil 12 and exit via the wires that join the coils 12 and 14. The current then flows through the coil 14 and exits via the wire of the second low temperature current lead 58 and flows upward through the low temperature current lead 58 and then through the second high temperature current lead 37 and back to the voltage source.

The cryocoolers 29 and 31 can be used to operate a magnet structure remote from the source of the chilled cooling liquid, such as in an isolated disposal room or also on a mobile platform. The pair of cryocoolers 26 and 27 allow the magnet structure to be operated using only one of each pair of cryocoolers having the correct function.

At least one vacuum cylinder (not shown) is coupled to the acceleration chamber 46 via a resonator 28, wherein a current lead for the RF accelerator electrode is also placed. The other portion of the acceleration chamber 46 is sealed to create a vacuum in the acceleration chamber 46.

The radial tensioning connecting wires 30, 32, 34 are coupled to the coils 12 and 14 and the spool 20, and are configured such that the radial tensile connecting wires 30, 32, 34 are at a plurality of positions An outwardly facing annular force is provided on the spool 20 to place the spool 20 in a radially outwardly directed tension and to maintain the central axis 16 in the center of the coils 12 and 14 (i.e., such The coils 12 and 14 will be substantially symmetrical about the central axis 16). Therefore, the tensile connecting wires 30, 32, 34 provide radial support to counteract the magnetic eccentric force, so that the cold mass on one side of the iron material will see an exponentially rising force and will Closer to the iron. The radial tensioning links 30, 32, 34 include two or more elastic tensioning straps 64 and 70 having a linear section (for example, an approximate shape for a conventional track or runway) ) to join the end of the round head and have a right circular cross section. For example, the elastic bands are comprised of spirally wound glass or carbon-filled carbonaceous tape and are designed to minimize heat transfer from the high temperature outer frame to the low temperature coils 12 and 14. A low temperature elastic band 64 extends between the support pin 66 and the support pin 68. The low temperature support pin 66 (which will couple to the reel 20) is at a temperature of about 4.5 K, while the intermediate support peg 68 is at a temperature of about 80 K. A high temperature elastic band 70 extends between the intermediate support pin 68 and a high temperature support pin 72 (which is at a near ambient temperature of about 300K). An outward force can be applied to the high temperature support pin 72 for applying additional tension at any of the pull tabs 30, 32, 34 to effect a variety of eccentric forces on the coils 12 and Maintain the centering effect when it is above 14. The support pins 66, 68, and 72 can be constructed of stainless steel.

Similarly, similar pull tabs can be attached to the coils 12 and 14 along a vertical axis (in accordance with the orientation of Figures 10 and 12) to counteract an axial magnetic eccentric force to allow The positions of the equal coils 12 and 14 remain symmetrical to the intermediate plane 18. During operation, although the thick reel 20 section between the coils 12 and 14 will weaken the suction between the coils 12 and 14, the coils 12 and 14 will still strongly attract each other.

In addition to providing the necessary concentrated forces, the set of radial and axial tensile links also counteract gravity to support the quality of the coils 12 and 14 and the spool 20. The tensile connectors may be sized to allow a smooth or stepped three-dimensional translation or rotational movement of the entire magnet structure at a prescribed rate, such as for positioning the magnet structure together, a platform, or It is on the vehicle to move the proton beam in a room around a fixed target illumination position. Both the gravity support and the motion demand are tensile loads that do not exceed the magnetic eccentric forces. The dimensions of the pull tabs can be designed to move over and over many movement cycles and years of movement.

A yoke 36 of low carbon steel surrounds the coils 12 and 14 and the cryostat 23. Pure iron may be too weak and its modulus of elasticity may be too low; therefore, enough carbon and other elements can be used to dope the iron to provide sufficient strength or reduce its rigidity while maintaining the desired magnetic properties. Level. The yoke 36 will define the same section of the central axis 16 defined by the coils 12 and 14 and the cryostat 23. The radius at the outer surface of the yoke 36 (measured from the central axis) may be about 35 inches (~89 cm) or less.

The yoke 36 includes a pair of magnetic poles 38 and 40 having tapered inner surfaces 42 and 44 that define a magnetic pole gap 47 between the magnetic poles 38 and 40 and across the acceleration chamber 46. The contours of the tapered inner surfaces 42 and 44 will be functionally related to the positions of the coils 12 and 14. The tapered inner surfaces 42 and 44 are shaped such that when spaced apart from the central axis 16, the magnetic gap 47 (as measured by the reference line in Figure 10) will Defined to expand above an inner stage between the side surfaces 42; and when the distance from the central axis 16 is further increased, the pole gap 47 is shrunk above an outer stage defined between the side surfaces 44. . When used in a synchrocyclotron for proton acceleration, the internal stage establishes a correct weak focus requirement for ion (for example, proton) acceleration, and the external stage is configured to use The energy gain is increased relative to the radius to reduce the magnetic pole diameter, which helps to extract the plasma from the synchrocyclotron as it approaches the acceleration chamber 46.

The above-mentioned magnetic pole profile has several important acceleration functions, in other words, has the following functions: ion guiding at the center of the machine at low energy; capturing into a stable acceleration path; acceleration; axial and radial focusing; beam quality The beam loss is minimized; the final desired energy and intensity is achieved; and the final beam position is located for extraction. Specifically, among the synchrocyclotrons, it is possible to achieve both weak focus and accelerated phase stabilization. At the higher magnetic field achieved in the magnet structure, expanding the pole gap above the first stage provides sufficient weak focus and phase stability, and quickly closing the gap above the outer stage is to counteract such The adverse effect of the intense superconducting coil is to maintain a weak focus while correctly positioning the full energy beam near the edge of the pole to draw it out into the extraction channel. In an embodiment in which the magnetic field to be generated by the magnet is increased, the gap opening becomes larger as the radius above the inner stage increases, and the gap is closed to a narrower position above the outer stage. Separation distance. Since the iron in the poles is completely magnetically saturated at a magnetic pole strength above 2 Tesla, by using an additional set of nested superconducting coils 206 in the accelerating chamber (for example, in Superconducting states are present at a temperature of at least 4.5 K to replace the tapered surfaces of the poles and to optimize the currents in the nested coils to match the magnetic field contributions of the poles to the total accelerating magnetic field, The goal of this group synchronization can be achieved, as shown in Figure 16.

The radially distributed coil 206 can be embedded in the yoke 36 or placed (eg, latched) over the yoke 36. At least one of the additional superconducting coils 206 generates a magnetic field at a local reverse position of the two main superconducting coils 12 and 14. In this embodiment, the yoke 36 will also be cooled (for example, by one or more cryocoolers). Although not shown in the drawings, an insulating structure may be provided via the radial central planar passages 154 to allow the acceleration chamber to be contained within the insulating structure to maintain the acceleration chamber at a warm temperature. A reverse magnetic field is generated in the inner coils 206 by flowing current through the additional magnetic coils 206 in a direction opposite to the current passing through the primary coils 12 and 14. The use of the additional active coils 206 in the acceleration chamber may be particularly advantageous for accelerating the magnetic field in the plane 18 to greater than 12 Tesla and thus requiring greater magnetic field compensation to reduce the magnetic field with the radius while at the same time Maintain weak focus and phase stability. These higher field magnet structures will have a smaller outer diameter. For example, a magnet structure for generating a magnetic field of 14 Tesla in the central acceleration plane 18 can be constructed using a yoke having an outer diameter slightly larger than one foot (i.e., slightly larger than 30 cm).

In other embodiments, the yoke 36 can be omitted and the magnetic field can be generated entirely by the superconducting coils 12, 14, and 206. In another embodiment, the iron in the yoke 36 can be replaced with another strong ferromagnetic material, such as helium, which has a particularly high saturation magnetic force (for example, up to about 3 Tesla).

The iron yoke provides sufficient space for interposing a resonator structure 174 containing the radio frequency (RF) accelerator electrodes 48 (also referred to as "D-shaped objects"), the electrodes being constructed of a conductor metal . The electrodes 48 are part of a resonator structure 174 that extends through the sides of the yoke 36 and through the cryostat 23 and between the coils 12 and 14. The accelerator electrodes 48 include a pair of flat semi-circular parallel plates that are oriented parallel to the acceleration plane 18 within the acceleration chamber 46 and are oriented above and below the acceleration plane 18 (e.g., U.S. Patent No. 4,641,057) Said in the description with). The electrodes 48 are coupled to an RF voltage source (not shown) that generates an oscillating electric field for accelerating the ions from an extended orbital (helical) path in the acceleration chamber 46. The ions emitted at source 50. In addition, an emulation D can also be provided in the form of a planar sheet oriented in the plane of the central axis 16 (i.e., a plane intersecting the central axis and extending perpendicularly from the page in the direction of Figure 10). And a slit is defined therein for receiving the acceleration plane for the particles. Alternatively, although the simulated D-shaped object is coupled to an electrical ground instead of being coupled to a voltage source, the simulated D-shaped object may have exactly the same configuration as the electrodes 48.

An integrated magnetic shield 52 will define other components of the magnet structure 10. The integrated magnetic shield 52 can be in the form of a very thin sheet made of mild steel (for example, 2 cm thick). As shown in Figure 10, a plurality of sheets can be stacked together at selected locations to provide additional sensitive area masking effects as would be apparent from the stacking of the sheets along the sides of Figure 10. Alternatively, the shield 52 can have a twisted shape (for example, a collapsed accordion structure), as shown in Figures 14 and 15, and would be configured to be used by the coils 12 and 14 And the majority of the magnetic field generated by the yoke 36 must pass through the integrated magnetic shield 52 at a plurality of locations and at a plurality of angles formed with the local orientation of the shield 52. In the embodiment of FIG. 14, in the profile of the integrated magnetic shield 52, the direction will be perpendicular to the radial vector 56 originating from the central axis 16 and parallel to the radial vector 56 originating from the central axis 16. Gradually move back and forth. Each radial vector 56 will intersect the shield 52 at two or more different locations, including a near vertical angle and a near tangent angle. At the first intersection 74, the vector 56 will span the integrated magnetic shield 52 at a near vertical position, a vertical magnetic field component will be eliminated; and at the second intersection, the vector 56 will be at a near tangent position. Across the integrated magnetic shield 52, a tangential magnetic field component is eliminated.

The integrated magnetic shield 52 is disposed at a distance from the outer surface of the yoke 36 such that a voltage is applied to the superconducting coils 12 and 14 to create an eight-bit characteristic in the accelerating chamber 46. When the SLA is even larger, it will be positioned outside of the contour of a 1,000 Gauss magnetic flux density generated outside the yoke 36. Accordingly, the integrated magnetic shield 52 is positioned at a position far enough away from the yoke 36 so that it is not completely magnetized by the magnetic field, and it is used to suppress the ejectable from the magnet structure 10. Far magnetic field.

The heads 29 and 31 of the cryocoolers 26 and 27 are positioned outside of the integrated magnetic shield 52 to shield the heads 29 and 31 from magnetic fields (this may be due to The magnetic field limits in the heads 29 and 31 are equal to the operating capacity of the cryocooler). Accordingly, the integrated magnetic shield 52 defines individual turns therein such that the cryogenic coolers 26 and 27 can be inserted via the turns.

The magnet structure 10 described above will now be described in the following pages to produce a magnetic field for accelerating ions.

When the magnet structure 10 is in operation, the cryocoolers 26 are used to extract heat from the superconducting coils 12 and 14 to reduce the temperature of each to its critical temperature (which would be at that temperature) Below superconductivity). The temperature of the coil formed by the low temperature superconductor will drop to about 4.5K.

A voltage (in the embodiment described above having 1,500 windings in the coil, a current sufficient to generate 2,000 A flows through the current lead) is applied to each coil 12/14 through current lead 58 for A magnetic field of at least 8 Tesla is generated in the acceleration chamber 46 when the coil is 4.5K. In a particular embodiment using Nb ₃ Sn, a voltage is applied to the coils 12 and 14 to generate a magnetic field of at least about 9 Tesla within the acceleration chamber 46. Furthermore, as discussed above, by using the cryocoolers to further reduce the coil temperature to 2K, an additional 2 Tesla magnetic field can generally be increased. About two Tesla in the magnetic field are contributed by the fully magnetized iron poles 38 and 40; the remaining magnetic fields are generated by the coils 12 and 14.

This magnet structure is used to generate a magnetic field sufficient for ion acceleration. Ion (for example, a proton) pulse can be ejected from the ion source 50 (for example, as described in U.S. Patent No. 4,641,057 and the ion source shown). For example, a free proton can be generated by applying a voltage pulse to a cathode for releasing electrons from the cathode into the hydrogen gas; wherein, when the electrons collide with the hydrogen molecules, Shoot protons.

In this embodiment, the RF accelerator electrodes 48 will create a voltage difference of 20,000 volts across the plates. The frequency of the electric field generated by the RF accelerator electrodes 48 will coincide with the frequency of the cyclotron orbital frequency of the ions to be accelerated. When the plasma is closest to the central axis 16, the electric field generated by the RF accelerator electrodes 48 will oscillate at a frequency of 140 MHz; and when the plasma is farthest from the central axis 16 and closest to the acceleration chamber 46 When it is around, the frequency will drop to a low frequency of 100MHz. When the proton is accelerated, the frequency drops to compensate for the mass increase of the proton because the alternating frequency at the electrodes 48 alternately attracts and repels the plasma. When the plasma is thus accelerated in their orbit, the plasma will increase in velocity and the spiral will face outward.

When the accelerated ions reach an outer diameter orbit in the acceleration chamber 46, the plasma can be extracted (in the form of a pulsed beam) to the outside of the acceleration chamber 46 by: utilizing the acceleration A magnet near the periphery of chamber 46 magnetically directs the plasma into a linear beam extraction channel 60 extending from the acceleration chamber 46 via yoke 36 and then passes through a gap in the integrated magnetic shield 52. Move toward an external target. The radial tensioning links 30, 32, 34 are activated to impart an outward radial annular force on the cold structure 21 to maintain its correct position throughout the acceleration.

The integrated magnetic shield 52 contains magnetic fields generated by the coils 12 and 14 and the magnetic poles 38 and 40 to reduce external hazards associated with attracting pens, paper clips, and other metal objects to the magnet structure 10. These hazards can occur when the integrated magnetic shield 52 is not employed. When both the vertical magnetic field and the tangential magnetic field are generated by the magnet structure 10 and the optimum shielding direction for accommodating each is different by 90°, the magnetic field lines and the integrated magnetic shield 52 are at various angles. Interaction is very beneficial. This shield 52 is capable of limiting the intensity of the magnetic field transmitted to the outside of the yoke 36 via the shield 52 to less than 0.00002 Tesla.

When it is detected that the voltage rises or the current flowing through a coil 12/14 drops, it indicates that a part of the superconducting coil 12/14 is no longer superconducting, and thus a sufficient amount is applied. The voltage is applied to the quenched wire 24 that surrounds the coil 12/14. This voltage produces a first-rate current through the wire 24, which in turn produces an additional magnetic field for the individual conductors in the coil 12/14 that will keep them non-superconducting (i.e., "normal"). This approach solves a known problem because the internal magnetic field during operation of each superconducting coil 12/14 can be very high at its inner surface 62 (for example, 11 Tesla) and will The internal point is reduced to zero magnetic field. If quenching occurs, it may occur at a high magnetic field position, while a low magnetic field position may still maintain low cooling temperatures and superconductivity for an extended period of time. This quenching will generate heat (which is normal conductivity) in a portion of the superconductor of the coil 12/14; therefore, when its temperature rises, the edge will terminate superconductivity while the central region of the coil will remain low Cold temperature and superconductivity. The resulting thermal differential can cause damage to the stress in the coil due to differential thermal contraction. The purpose of this induced quenching example is to prevent or limit this difference, and thus the coils 12 and 14 can be used to generate a higher magnetic field without being destroyed by such stresses. Alternatively, current may flow through the heating strips 88 to raise the temperature of the heating strip to above 4.5 K and thereby locally heat the superconductors to minimize such internal temperature differences during a quenching period.

A cyclotron containing the above apparatus can be used in a variety of applications including: proton radiation therapy of the human body; etching (for example, micropores, filters, and integrated circuits); radioactive studies of materials; tribology; Basic science research; preservation (for example, monitoring proton scattering when using accelerated protons to illuminate target cargo); production of medical isotopes and trackers for medicine and industry; nanotechnology; cutting-edge biology; As well as a variety of other applications, it would be useful to generate a punctiform (i.e., small spatially distributed) beam of high energy particles from a compact source.

For the sake of clarity, specific techniques will be used in the description of the embodiments of the invention. For the purposes of this description, each specific term is intended to encompass at least all technical and functional equivalents that operate in a similar manner. Furthermore, in a particular embodiment of the invention, a particular embodiment of a plurality of system elements or method steps, the elements or steps may be replaced by a single element or step; likewise, a single element or step may also be plural Replacement of components or steps. Further, although the parameters of the various characteristics are specified herein for the embodiments of the present invention, unless otherwise mentioned, within the scope of the present invention, the parameters can be adjusted up and down by 1/20, 1/10. , 1/5, 1/3, 1/2, ..., etc., or choose their approximation. Furthermore, although the present invention has been shown and described with reference to the particular embodiments of the invention, those skilled in the art will appreciate that various modifications in form and detail can be made without departing from the scope of the invention. And other changes, other points, functions, and advantages are also within the scope of the invention. The contents of all of the references (including patents and patent applications) cited in the entire disclosure are hereby incorporated by reference. Suitable components and methods of these references can be screened for use in the present invention and its embodiments. Still further, the components and methods identified in the prior art paragraphs are integral to the present disclosure and may be used within the scope of the present invention in conjunction with the components and methods described elsewhere in this disclosure, or alternatively The components and methods described elsewhere in this disclosure.

10. . . Magnet structure

12. . . Superconducting coil

14. . . Lower superconducting coil

16. . . Central axis

18. . . Central acceleration plane

20. . . reel

twenty one. . . Cold structure

twenty three. . . Cryostat

twenty four. . . Conductive wire

26. . . Cryogenic cooler

27. . . Cryogenic cooler

28. . . Resonator

29. . . Cryogenic cooler

30. . . Radial tension cable

31. . . Cryogenic cooler

32. . . Radial tension cable

33. . . Cold head

34. . . Radial tension cable

35. . . Cold head

36. . . Yoke

37. . . Current lead

38. . . magnetic pole

40. . . magnetic pole

42. . . Tapered inner surface

44. . . Tapered inner surface

46. . . Acceleration room

47. . . gap

48. . . D shape

49. . . D shape

50. . . source of ion

52. . . Integrated magnetic shielding

56. . . Radial vector

58. . . Current lead

60. . . Integrated external shield

61. . . The inner surface

62. . . The inner surface

64. . . Elastic band

66. . . Support bolt

68. . . Support bolt

70. . . Elastic band

72. . . Support bolt

78. . . Copper heat shield

80. . . Pressure capsule

82. . . Cable strand

84. . . Copper channel

86. . . Synthetic conductor

88. . . Heater

90. . . Synthetic filler

92. . . wire

94. . . wire

96. . . Insulation

102. . . Upper pole tip

104. . . Lower pole tip

106. . . Upper magnetic pole

108. . . Lower magnetic pole

110. . . Upper yoke

112. . . Lower rotary yoke

114. . . Bottom surface

116. . . Top surface

118. . . Upper magnet cryostat chamber

120. . . Lower magnet cryostat chamber

122. . . Upper magnetic pole tip contour

124. . . Lower pole tip contour

126. . . Upper magnetic pole contour

128. . . Lower magnetic pole contour

130. . . Upper magnetic pole contour

132. . . Lower magnetic pole contour

134. . . Upper magnetic pole

136. . . Lower magnetic pole

138. . . Cutting edge

140. . . Cutting edge

142. . . Upper middle channel

144. . . Lower middle channel

146. . . Upper axial RF channel

148. . . Lower axial RF channel

150. . . Upper magnetic cryostat channel

152. . . Lower magnetic cryostat channel

154. . . Radial channel

156. . . Approximate area of the highest magnetic field

158. . . Approximate area of the highest magnetic field

160. . . region

162. . . region

164. . . region

166. . . region

168. . . surface

170. . . surface

172. . . Radial channel

174. . . Resonator structure

176. . . Beam chamber

178. . . Beam chamber substrate

180. . . Acceleration gap defining aperture

182. . . gap

184. . . D-shaped resonator connector

186. . . Resonator internal conductor

188. . . Resonator outer conductor

190. . . Resonator outer conductor swivel yoke

192. . . Coupling埠

194. . . RF transmission line coupling埠

195. . . Upper axial resonator

196. . . Upper axial resonator

197. . . Lower axial resonator

198. . . Lower axial resonator

200. . . Cryostat

202. . . Slit

204. . . Extension

206. . . Superconducting coil

In the drawings, the same component symbols in the different drawings represent the same or similar components. The drawings are not necessarily to scale, and the emphasis is on the particular principles of the method and apparatus having the features described in the embodiments.

Figure 1 is a perspective cross-sectional view showing the basic structure of a high magnetic field synchrocyclotron, in which the coil/low temperature thermostat assembly is omitted.

Figure 2 is a cross-sectional view of a ferromagnetic material and a magnetic coil for the high magnetic field synchrocyclotron.

Figure 3 shows a pair of iron tip rings extending from individual pole wings and sharing a common central directional axis for better graphical purposes, with the gap between the two extending in the plane.

Figure 4 is a cross-sectional view showing the characteristics of the high magnetic field and the separation of the superconducting coil set.

Figure 5 is a cross-sectional view of the synchrocyclotron beam chamber, the accelerated D-shape, and the resonator.

Figure 6 is a cross-sectional view of the apparatus of Figure 5 taken along the longitudinal axis shown in Figure 5.

Figure 7 is a cross-sectional view taken through the resonator conductor in the apparatus of Figure 5, which has twice the size.

Figure 8 is a cross-sectional view taken through the outer return yoke in the apparatus of Figure 5, which has twice the size.

Figure 9 shows an alternative RF configuration that uses two D-shapes and a shaft-oriented RF port.

Figure 10 is a cross-sectional view of a magnet structure as seen from the plane in which the central axis of the magnet structure is located.

Figure 11 is a cross-sectional view of the magnet structure of Figure 10 taken from a plane orthogonal to the central axis and parallel to the acceleration plane.

A cross-sectional view of the cold structure shown in Fig. 12, including the coils and the reel.

Figure 13 is a cross-sectional view showing the internal structure of a coil.

Fig. 13A is an enlarged view of the cross section shown in Fig. 13.

Figure 14 is a cross-sectional view of an integrated magnetic shield having a twisted shape.

Figure 15 is a perspective view of a cross section of the integrated magnetic shield of Figure 14.

Figure 16 is a cross-sectional view of a basic form of a magnet structure (with special details omitted) including additional active coils in the acceleration chamber for designing the shape of the magnetic field at the acceleration plane.

12. . . Superconducting coil

14. . . Lower superconducting coil

20. . . reel

twenty one. . . Cold structure

78. . . Copper heat shield

80. . . Pressure capsule

Claims (42)

A magnet structure for use in a synchrocyclotron, comprising: a cold structure comprising at least two coils, the coils comprising a continuous path of superconducting material at a nominal temperature of 4.5 K, a continuous path of the material and a diameter Defining an acceleration chamber and a section extending across a central axis of the acceleration chamber, wherein an intermediate acceleration plane extends orthogonally from the central axis across the acceleration chamber; and a yoke wrapped around the cold a structure, wherein the yoke is also radially surrounding a section of the central axis, wherein the yoke includes a pair of magnetic poles having a pole tip adjacent the central axis and a radial distance from the central axis being greater than the a magnetic pole tip pole, wherein the yoke has an outer diameter in the range of 30-114 cm, which is measured perpendicularly from the central axis, wherein the magnetic poles have a tapered internal surface to follow at an inner level The magnetic pole gap is gradually expanded as the radial distance increases, and the magnetic pole gap is gradually reduced as the radial distance increases on an outer stage, whereby the magnetic pole tip and the magnetic pole are A peak gap is created at a position between the wings that exceeds twice the magnetic pole gap between the poles of the poles and exceeds twice the magnetic pole gap between the poles, wherein the superconducting coils and poles are Constructed to produce a radially decreasing magnetic field to at least 7 Tesla for simultaneous cyclotron acceleration in an intermediate acceleration plane that decreases as the radius from the radius of the ion introduction to the radius of the ion exit increases And wherein the coils generate a magnetic field of at least 5 Tesla to reach the acceleration chamber. The magnet structure of claim 1, wherein the coils are dry, the magnet structure further comprising a cryocooler coupled The cold structure is used to cool the coils. The magnet structure of claim 2, wherein the cryocooler is a Gifford-McMahon cryocooler or a pulse tube cryocooler. The magnet structure of claim 2, further comprising a cryostat containing the coils therein. The magnet structure of claim 1, wherein the superconducting material is NbTi or Nb ₃ Sn. The magnet structure of claim 4, wherein the superconducting material is Nb ₃ Sn. The magnet structure of claim 1, wherein the superconducting material is an A15 class II superconductor. The magnet structure of claim 1, wherein the cold structure further comprises a reel in which the coils are mounted. The magnet structure of claim 1, further comprising a radial tension chain coupled to the cold structure, the radial tension links being set to apply an outward radial force to the cold Quality structure. The magnet structure of claim 1, wherein the coils have an outer radius that is measured from the central axis by no more than 51 cm in an orthogonal manner. The magnet structure of claim 1, wherein the peak gap between the magnetic poles is 37-55 cm. The magnet structure of claim 1, wherein the magnetic pole wings have an inner surface that is opposite to the intermediate acceleration plane. An angle of less than 90° is oblique to the intermediate acceleration plane as the distance from the central axis increases. The magnet structure of claim 12, wherein the inner surface of the magnetic pole wings is inclined at an angle greater than 80° with respect to the intermediate acceleration plane, and the radial distance from the central axis increases The intermediate acceleration plane. The magnet structure of claim 1, wherein the yoke includes a resonator structure including an electrode between the magnetic poles to generate a particle accelerating voltage in the accelerating chamber. The magnet structure of claim 1, wherein a weak focus magnetic field index parameter n is in a range from 0 to 1 on substantially all intermediate acceleration planes, wherein n=-(r/B) (dB/ Dr), and where dB/dr<0, where B is the magnetic field and r is the radius from the central axis. The magnet structure of claim 1, further comprising a voltage source coupled to the coils. A magnet structure for use in a synchrocyclotron, comprising: a cold structure comprising at least two superconducting coils, wherein the cold structure defines an acceleration chamber; a yoke wrapped around the cold structure and containing a pair of magnetic poles defining a magnetic pole gap between the magnetic poles and across the acceleration chamber; and an integrated magnetic shield surrounding the yoke external to the contour of the 1,000 Gauss magnetic flux density, the magnetic flux density being When a voltage is applied to the superconducting coils to generate a magnetic field of 8 Tesla within the accelerating chamber, the magnet structure is generated outside the yoke. The magnet structure of claim 17, wherein the integrated magnetic shield has a curved shape which is set such that a majority of the magnetic field lines extending from the yoke will be at a plurality of positions and in plural The angle intersects the integrated magnetic shield. The magnet structure of claim 17, wherein the integrated magnetic shield comprises iron. The magnet structure of claim 17, further comprising a cryocooler coupled to the cold structure to cool the coils. The magnet structure of claim 20, wherein the cryocooler comprises a head end positioned outside the boundary of the integrated magnetic shield. The magnet structure of claim 17, wherein the cold structure is positioned about a central axis, and wherein the integrated magnetic shield is thicker at a distance from the central axis. The magnet structure of claim 17, wherein the integrated magnetic shield is electrically isolated from the yoke. A method for fabricating a magnet structure comprising a Nb ₃ Sn superconducting coil, comprising: providing a tin line; providing a tantalum mold surrounding the tin lines; and the tin in the tantalum mold Heating the mass lines to cause the solder lines to react with the mold, and thereby forming a plurality of Nb ₃ Sn strands; inserting the Nb ₃ Sn strands into an electrically conductive conduit to form a composite conductor; The composite conductor; filling the wound composite conductor with a filler precursor to form a coil; and inserting the coil into a yoke containing a pair of magnetic poles defining a magnetic pole gap therebetween. The method of claim 24, wherein the electrically conductive conduit contains copper. The method of claim 25, further comprising insulating the Nb ₃ Sn strands with glass fibers. The method of claim 26, wherein the filler precursor comprises an epoxy resin. A method for generating a magnetic field for ion acceleration, comprising: providing a cold structure, which is located in a cryocooler and surrounding an acceleration chamber, the cold structure comprising: at least two superconductors a coil that is concentrated around a central axis; a cryocooler that is thermally coupled to the cold structure; a yoke that is positioned around the cold structure and that contains a pair of magnetic poles that are tied therebetween And defining a tapered magnetic pole gap across the acceleration chamber; and cooling the superconducting coils to or below a critical temperature of the superconductor, and applying a voltage to the cold structure to generate at least in the acceleration chamber A total magnetic field of 8 Tesla and decreases as the synchrocyclotron radius increases. The method of claim 28, wherein the superconducting coils comprise Nb ₃ Sn. The method of claim 29, wherein a total magnetic field of at least 9.9 Tesla is produced in the acceleration chamber. The method of claim 28, wherein the radial tension chain is coupled to the cold structure, the method further comprising applying an outward radial force to the cold structure to maintain the The positioning of the cold structure. The method of claim 31, wherein an integrated magnetic shield surrounds the yoke at a distance from the outer portion of the contour of the 1000 gaussian magnetic flux density produced by the cold structure and the yoke. The method of claim 28, wherein the magnetic pole gap increases at an inner level with increasing distance from the central axis, and wherein the magnetic pole gap is along an outer axis from the central axis The distance is further increased and reduced. The method of claim 33, wherein the magnetic pole gap is increased to a peak magnetic pole gap which is at least twice the minimum magnetic pole gap distance between the inner and outer stages. The method of claim 34, wherein the peak magnetic pole gap is 37-55 cm. The method of claim 34, wherein a minimum pole gap in the outer stage is between a pair of pole wings, and wherein the pole wings have an inner surface that is zero relative to the central axis The angle to 10° is oblique to each other as the radial radius increases. The method of claim 28, wherein the cold quality The structure and yoke produce a total magnetic field of at least 9 Tesla in the acceleration chamber. The method of claim 28, wherein the coils are maintained in a dry state in the cold structure when a magnetic field is generated. The method of claim 28, wherein the superconducting coils have an outer radius of no more than 51 cm. The method of claim 28, further comprising injecting a charged particle into the acceleration chamber. The method of claim 40, further comprising providing a resonator structure including a plurality of electrodes between the magnetic poles and applying a radio frequency voltage to the electrodes, thereby accelerating an outward spiral via the acceleration chamber The charged particles in the orbit. The method of claim 28, wherein an intermediate acceleration plane extends orthogonally from the central axis across the acceleration chamber, and wherein a weak focus magnetic field index parameter n is substantially across all intermediate acceleration planes From the range of 0 to 1, where n = - (r / B) (dB / dr), and where dB / dr < 0, where B is the magnetic field, and r is the radius from the central axis.