RU2288553C2 - Gas-filled diode with external magnetic insulation - Google Patents

Abstract

FIELD: acceleration engineering.

SUBSTANCE: proposed gas-filled diode with external magnetic insulation has annular anode and cylindrical cathodes, two cumulatively connected concentric coils disposed beyond external and internal radii of cylindrical cathodes, and power supply. Emissive surface of anode is provided with annular grooves coated with insulating material or with insulating inserts. Anode is made of high-conductivity material; turn number in windings W₁ and W₂ and radii centers of their ampere-turns R₁ and R₂ are disposed symmetrically to anode emissive surface, and their ratio is W₁·R₁ = W₂·R₂.

EFFECT: enhanced stability of generated pulses.

3 cl, 5 dwg

Description

The invention relates to accelerator technology and is intended for the generation of ion beams with their subsequent use to modify the surface of various materials, generate neutron flares, etc.

Several different schemes of ionic diodes are known (Patent RU 96113837, IPC 6 Н 05 Н 5/00 dated 1997.11.20), in which preliminary plasma production on the anode surface is performed due to the double-pulse mode, electrical breakdown on the surface of the dielectric coating of the anode (Nakagama Y. , Ariyosh T. // Rev. Sci. Justr. 1990, 61 (1) P.529-531) or injection of a gas jet before the formation of an accelerating pulse in a diode (Mekay PF, Bieg K.W., Olson RE, et al // Rev. Sci. Justr. 1990, 61 (1) P.559-561). To suppress the electronic component of the total current in the accelerated gap of the ion diode, a transverse magnetic field is created relative to the electric field vector.

The disadvantages of these devices include the fact that the repeatability and stability of the parameters of the generated ion beam from pulse to pulse is determined by the uniformity of the gas jet injection relative to the anode surface or the uniformity of plasma formation during surface breakdown of the anode dielectric, and many processes and actuators must be synchronized in time, which reduces the reliability these devices.

Closest to the claimed device is our chosen prototype ion diode with external magnetic isolation, described in (Davis HA, Johnston GP, Olson J.C. et. Al. // Appl. Phys. 1999, vol. 85 (2). R.713-721), consisting of two concentric coils, which are located at the surface of the annular anode. In a crossed magnetic and electric field, electrons in a preformed plasma make a closed drift parallel to the surface of the anode, and ions are accelerated in the gap of the diode in a small section of the Larmor circle, and in the subsequent drift space form a ring ion beam.

The disadvantage of this ion diode is the heterogeneity of the formed plasma in the radial section of the diode and significant local erosion of the surface of the dielectric along the edges of the anode since the plasma on the surface of the dielectric is formed mainly due to the creeping discharge initiated during the bombardment of the dielectric insert of the anode by electrons emitted from the sharp edges of the cathode rings. The efficiency of the prototype does not exceed 15-25%. In addition, with this method of plasma formation, additional measures are required to ensure increased accuracy of the installation of the diode gap to ensure plasma uniformity in the azimuthal direction.

The main technical result of the invention is to increase the stability of the generated ion current pulses due to a more uniform plasma formation on the surface of the anode and an increase in the efficiency of conversion of the electric energy stored in the drive into the kinetic energy of the ion beam. The proposed ionic diode allows, in comparison with the prototype, to increase the efficiency by at least 60%.

The technical result of the proposed solution is achieved by the fact that in an ion diode with external magnetic insulation containing a ring anode and cylindrical cathodes, two concentric according to the included coils located behind the outer and inner radii of the cylindrical cathodes, and switching power supplies, according to the proposed solution, the emission surface of the anode is equipped ring grooves with a dielectric coating or dielectric inserts, the anode is made of highly conductive material, and the number of turns in the winding W ₁ and W ₂ and the centers of their ampere-turns radii R ₁ and R ₂ are arranged symmetrically with respect to the emission surface of the anode and W at the ratio of ₁ · R ₁ = W ₂ · R _2.

In addition, the surface of the anode with a dielectric coating forms a spherical surface centered on the axis of symmetry of the ion diode and contains more than two concentric coils uniformly distributed along the emission surface of the anode.

It is advisable to provide cylindrical cathodes with short-circuited turns of a material with high electrical conductivity, and behind the short-circuited turns there is a grid or radially standing plates along the cross section of the ion beam.

Concrete example

Figure 1 shows the axial section of a conical ion diode with external magnetic insulation, figure 2 - axial section of a spherical ion diode, figure 3 - the course of the magnetic field lines without conductive short-circuited magnetic coils (screens) and, if any, and also the distribution of the electric field lines in the absence of an electron cloud and its presence in the anode-cathode gap, in Fig. 4 are diagrams of voltage and currents, in Fig. 5 is a photograph of the cathode assembly from the anode side.

The ion diode (figure 1) consists of a ring anode 1, which is made of a material with high electrical conductivity: copper, aluminum; the annular anode 1 is equipped with annular grooves filled with a dielectric 2, forming the emission surface of the ion diode, the annular anode 1 with the annular electrode 3 is attached to the high-voltage electrode 4 of the accelerator. Opposite the ring anode are the cathodes: external 5 and internal 6, made of a material with high resistivity: titanium, nichrome, stainless steel. The outer cathode 5 is attached to the supporting disk 7, and the inner 6 is attached to the supporting disk 7 using studs 8 and a short-circuited ring 9, a disk 10 of well-conducting material.

Coils for creating a magnetic field: external 11 and internal 12 are located in dielectric frames 13 and 14. The output of the winding of the internal coil 12 is in contact with the cathode 6, and the other output of the winding through the hollow pin 8 is connected to the winding of the external coil 11, the second output of which goes to switching power supply, the current of which creates a magnetic field. The ion diode is placed in a vacuum chamber 15, relative to which the supporting disk 7 is mounted and the cathode current circuits 5, 6 are provided. A grid 16 with high geometric transparency is installed on the short-circuited ring 9, which overlaps the cross section of the ion beam. Figure 1 is additionally indicated: Z is the axis of symmetry of the ion diode; Z ₁ is the optical axis of the ion beam, R ₁ , R ₂ are the radii of the centers of the ampere-turns of the windings of the coils 11 and 12; d is the position of the edge of the cathode 5 relative to the emission surface of the anode 1; F ₀ , F ₁ , F ₂ , F ₃ - focal lengths; α is the angle at the apex of the cone formed by the ion beam.

When using a spherical ionic diode (figure 2), the optical axis of the ion beam is directed along the radius R and the focus F ₀ is expressed in a point on the Z axis, and the surface of the anode has a spherical shape. To form a more uniform density of magnetic field lines along the spherical surface of the anode in the plane of symmetry R, an additional coil is installed in weakly conducting screens - cathodes or several coils symmetrically with respect to the plane of symmetry R of the ion beam. This ensures a large emission surface area and a uniform distribution of current density over the cross section of the generated ion beam.

Figure 3 shows the course of the magnetic field lines 17 (dashed lines) of the coils 11, 12 in a space free of conductive surfaces, and in the presence of a conductive anode and short-circuited turns 9, 10 by force lines 18. Dotted lines 19 show the distribution of electric field lines field in the absence of an electron cloud, and solid lines 20 - in the presence of an electronic cloud of drifting electrons 21 (shaded area) between the lines of force of the magnetic field 18. 22 - traces of drifting electrons on a dielectric Arkása 13, 14, coils 11, 12. The circles 23 indicate the direction of the currents in the coils 11,12, and 24 - in the body of the anode 1 and short-rings 9, 10. V _i - direction of the ion velocity.

Figure 4 shows the plot of the voltage at the anode 25 and currents: 26 - the total current of the accelerator, 27 - the ion current of the diode. The U _xx curve shows the anode potential in idle mode.

The principle of operation of an ion diode with external magnetic insulation is as follows: a voltage pulse is applied to the coils 11 and 12 connected in series, for example, by discharging a capacitance. Upon reaching the current in the coils 11, 12, sufficient to provide the conditions

Δ≤d _AK ,

where Δ is the thickness of the layer in which the electrons move in the presence of crossed electric and magnetic fields,

d _AK is the gap between the anode and cathode;

a high voltage pulse is supplied to the anode from the high-voltage generator of the accelerator.

The value of A is determined from the expression:

where Δ is the thickness of the electronic layer,

m _e is the mass of the electron,

B - magnetic field induction in the drift region,

E _⊥ - electric field strength,

V _II are the components of the electron velocity in the direction of the vectors B and E _⊥ at the time of injection from the explosive emission plasma.

At time t ₁ , explosive emission occurs from the sharp edges of the cathodes 5, 6 and the electrons of the explosive emission plasma begin to drift in the plane of the magnetic field lines 18 parallel to the surface of the ring anode 1. The current of the ion diode until time t ₂ has only a capacitive component associated with the accumulation charge in the electron cloud 21, the voltage at the annular anode 1 rises under conditions close to the idler of the accelerator (the load impedance significantly exceeds the output wave impedance of the high-voltage generator Dr. accelerator). The electric field strength increases and the thickness Δ of the drift electron layer increases. Electrons move in a layer parallel to the annular anode 1, with an average speed V = Е _⊥ / В along the cycloids whose vertices are directed towards the emission surface of the annular anode 1, and at time t ₂ begin to touch the dielectric and the annular protrusions of the metal of the annular anode 1, producing plasma. The alternation of the dielectric and metal regions in the presence of annular grooves on the surface of the anode along the electron drift path promotes more uniform plasma formation over the entire surface of the annular anode 1. In this case, the electron velocity is directed tangentially to the surface of the annular anode 1 and is equal to 2V.

In the time interval t ₃ -t _2, the accelerator generator is loaded with a current of ions, which also begin to drift at a speed V = E _⊥ / V, but their Larmor radius is m _i / m _e times larger than that of electrons. In the gap d, which is the distance from the surface of the ring anode 1 to the center of gravity of the charge of drifting electrons, ion acceleration occurs. The direction of the drift velocity of ions is the same as that of electrons, but the directions of deviation of the vertices of the cycloid of ions and electrons are opposite, and the acceleration of ions occurs almost along the lines of force of the electric field 19 in a small segment of the curve described by the Larmor radius of the ions.

The appearance of the transfer current in the ionic diode causes a voltage drop at the internal resistance of the switching power supply, voltage 25 stops increasing, the electrons do not reach the surface of the ring anode 1 and the diode gap formed by the surface density of positive charges on the ring anode 1 and the bulk density of electrons in the region of thickness Δ, loaded only by ion current with a density according to

Where

ε ₀ = 8.85 · 10 ^-12 f / m;

e is the elementary charge (electron charge),

m _i is the mass of the ion,

Z is the ionization ratio,

U is the potential of the anode,

d is the accelerating gap.

Thus, a rigid negative feedback is formed between the number of produced ions and the impedance of the high-voltage source.

As the ion current decreases, the anode potential rises again, since the voltage drop across the internal resistance of the accelerator’s high-voltage generator decreases, the electrons again begin to reach the anode and produce ions, etc. When an electron cloud passes, ions capture electrons, compensate for their charge, and move further along a ballistic trajectory. On average, the influence of the magnetic field in the proposed diode is compensated, since the charged particles pass the lines of force of the magnetic field with a speed of V _i in different directions, Fig.3.

The electrons in the electron cloud 21 are captured by the ion beam, part of the electrons from the cloud repelled by their own space charge flows along the magnetic field lines 18, is deposited on the dielectric 13, 14 (surface 22) and flows onto the grounded screens 9, 10. During the pulse duration high voltage from the accelerator generator, the electrons in the drift cloud 21 are made up by explosive emission from the sharp edges of the cathodes 5, 6, facing the annular anode 1.

Behind the screens, which are short-circuited rings 9, 10, the magnetic field of the coils 11, 12 is practically absent. In order to fully compensate for the space charge of the ion beam, a grounded high-transparency grid 16 or metal plates are installed. Due to the loss of part of the ion beam, electrons are knocked out of the network material (approximately 15-30 electrons per one “dead” ion) and the ion beam is completely compensated for in the region free of external electric and magnetic fields, which allows ballistic focusing of the ion beam in focus F ₀ .

где j - плотность тока согласно (2), S_a - площадь эмиссионной поверхности анода, равная

с наружным радиусом R_H и внутренним R_B, S₀ - площадь пятна в фокусе. Размещая в фокусе F₀ требуемый материал, можно испарять его ионным пучком и получать абляционную плазму (Zakoutaev A.N., Remnev G.E., Ivanov Yu.F., Arteyev M.S., Matvienko V.M., and Potyomkin A.V. High-rate deposition of thin films by high-intensity pulsed ion beam evaporation. // В сб. «Film Synthesis and Growth Using Energetic Beams», edited by H.A.Atwater, J.T.Dickinson, D.H.Lowndes, and A.Polman - Mater. Res. Soc. Proc., 388, Pittsburgh, PA, 1995, p.388-392.), при осаждении которой на поверхностях, укрепленных на короткозамкпутом диске 10, образуются тонкие пленки испаряемого материала при высокой импульсной скорости осаждения. Помещая детали на большем расстоянии, чем F₂, F₃, для обеспечения меньшей, чем в фокусе, плотности ионного тока, производят модификацию поверхности изделий: упрочнение, формирование определенного рельефа, фазового и дефектного состояния поверхностного слоя материалов, очистку от загрязнений и пленок и т.д. (Ремнев Г.Е., Погребняк А.Д., Исаков И.Ф. и др. Повышение эксплуатационных характеристик сплавов под действием мощных ионных пучков. // Физика и химия обработки материалов, 1987, в.6, с.4-11; Ремнев Г.Е., Тарбоков В.А., Кузнецов П.В. Структурно-фазовые изменения в поверхностном слое твердосплавного инструмента при воздействии мощного ионного пучка // «Радиационно-термические эффекты и процессы в неорганических материалах». Труды III международной конференции. Томск, Россия, 2002. - С.369-370).In the ionic diode, (Fig. 1), to ensure the field lines run parallel to the surface of the anode 1, it is necessary that the vector magnetic potential of the coils 11 and 12 be equal to the Z axis ₁ and the emission surface of the anode 1, which is done if the number of turns W ₁ and W ₂ in the windings 11 and 12 and the centers of their ampere-turns R ₁ , R ₂ located symmetrically relative to the emission surface of the anode, are correlated as W ₁ · R ₁ = W ₂ · R ₂ . In this case, the foci F ₀ , F ₁ , F ₂ will be a continuous ion beam with a uniform current density over the beam cross section. Moreover, the current density at the focus F _{0 is} maximum and reaches a value

where j is the current density according to (2), S _a is the area of the anode emission surface equal to

with an outer radius R _H and an inner R _B , S ₀ is the spot area in focus. By placing the desired material at the F ₀ focus, it is possible to vaporize it with an ion beam and obtain an ablation plasma (Zakoutaev AN, Remnev GE, Ivanov Yu.F., Arteyev MS, Matvienko VM, and Potyomkin AV High-rate deposition of thin films by high-intensity pulsed ion beam evaporation. // In: Film Synthesis and Growth Using Energetic Beams, edited by HAAtwater, JT Dickinson, DHLowndes, and A. Polman - Mater. Res. Soc. Proc., 388, Pittsburgh, PA, 1995, p.388-392.), during the deposition of which on the surfaces mounted on the short-circuit disk 10, thin films of vaporized material are formed at a high pulse deposition rate. Placing the parts at a greater distance than F ₂ , F ₃ , to ensure a lower ion current density than the focus, the surface of the products is modified: hardening, formation of a certain relief, phase and defective state of the surface layer of materials, cleaning from contaminants and films and etc. (Remnev G.E., Pogrebnyak A.D., Isakov I.F. et al. Improving the operational characteristics of alloys under the influence of powerful ion beams. // Physics and Chemistry of Materials Processing, 1987, v.6, p. 4-11 ; Remnev G.E., Tarbokov V.A., Kuznetsov P.V. Structural-phase changes in the surface layer of a carbide tool when exposed to a powerful ion beam // "Radiation-thermal effects and processes in inorganic materials. Proceedings of the III international conference Tomsk, Russia, 2002. - S.369-370).

In a spherical ion diode with external magnetic insulation, Fig. 2, along with ballistic focusing, electrostatic focusing is used directly in the accelerating gap, and in the focus F _0, the ion current density can be increased 10 ² -10 ³ times compared with (2). In the focus of F ₁ , Fig. 2, it is possible to modify the surface of cylindrical parts, for example, to process the cutting edges of mills, threaded pipe joints, or to remove the spent various functional coatings, including especially resistant and heat-resistant (Shulov V.A., Nochevnaya N .A., Remnev G.E., et al. Ion-beam technology for repairing gas turbine compressor blades using powerful nanosecond ion beams. // Aviation Industry, 1993, No. 2, p. 14-22).

, а помещая в фокусе F₀ дейтерий-тритивые мишени, иметь нейтроны термоядерного синтеза.If we use polyethylene as the dielectric 2, in which hydrogen is replaced by deuterium, then an ion beam of deuterium will be produced, which can be used to generate neutron bursts on targets from transuranium elements or nuclei oversaturated with neutrons, for example beryllium

, and placing deuterium targets at the focus F ₀ , have neutrons of thermonuclear fusion.

The above-considered ion diode with external magnetic isolation according to the scheme of Fig. 1, with a potential at the anode of 400 kV, with an output impedance of an accelerator voltage source of 40 Ohms, a pulse duration of 60 ns, ensured the efficiency of ion beam formation of more than 60% of the energy stored in the forming line accelerator (nanosecond generator). With an anode area of 80 cm ² (R _H = 80 mm, R _B -55 mm) in the focus F ₀ at an angle α = 60 ° and a beam diameter at the focus of 4 cm, an ion current density of 600 A / cm ^{2 was} obtained. An external magnetic field required an energy of 300 J, which provided a capacitive storage with a capacity of 20 · 10 ^-6 F at a voltage of 6 kV. Moreover, in the free from the conductive surfaces of the anode 1, the induction of the magnetic field 17, Fig.3, was more than two times lower than in the presence of the anode 1, and the lines of force of the magnetic field 18 were parallel to the emission surface of the anode.

Figure 5 shows a photograph of the cathode assembly from the anode side after more than 10 ³ operations with the parameters indicated above. The trace 22 from the pushed electrons from the cloud 21 on the surface of the dielectric 13 is clearly visible. The second trace 22 from the edge of the cathode 5 passes the dielectric 14 and enters the supporting disk 7 according to the course of the magnetic field lines.

Thus, an increase in the stability of the current of the generated pulses and the efficiency of converting electric energy into kinetic energy of the ion beam over 60% is achieved by increasing the uniformity of plasma formation and the rigid feedback between the value of the electronic component of the total current in the ion diode during plasma production symmetrically across the entire emission surface of the anode and suppressing the electronic component of the total diode current in the accelerating gap during ion acceleration. This allows you to exclude additional circuits and devices for preliminary production of plasma and provide the most favorable conditions for the implementation of the "law 3/2" (1) - i.e. for a given potential U, to have the smallest value of the accelerating gap d by controlling it by the magnitude and rate of increase of the magnetic field from one source, using induced currents in the anode body and short-circuited screens.

Claims (3)

1. An ionic diode with external magnetic insulation, containing a ring anode and cylindrical cathodes, two concentric coils according to included, placed behind the outer and inner radii of the cylindrical cathodes, and switching power supplies, characterized in that the emission surface of the anode is provided with annular grooves with a dielectric coating or dielectric inserts, the anode is made of highly conductive material, and the number of turns in the windings W ₁ and W ₂ and the centers of the radii of their ampere turns R ₁ and R ₂ are located symmetrically with respect to the emission surface of the anode, and are correlated as W ₁ · R ₁ = W ₂ · R ₂ . 2. The ion diode according to claim 1, characterized in that the surface of the anode with a dielectric coating forms a spherical surface centered on the axis of symmetry of the ion diode and contains more than two concentric coils uniformly distributed along the emission surface of the anode. 3. The ion diode according to claim 1 or 2, characterized in that the cylindrical cathodes are equipped with short-circuited turns of a material with high electrical conductivity, and behind the short-circuited turns there is a grid or radially standing plates along the cross section of the ion beam.

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