CN114828380B - Multi-magnetic loop fan-shaped magnet for improving axial focusing force - Google Patents

Abstract

The invention discloses a multi-magnetic loop fan-shaped magnet for improving axial focusing force, which is uniformly distributed in an accelerator annular vacuum chamber along an upper layer and a lower layer of an accelerator center plane, and comprises a return yoke at a large radius of a magnetic pole, a magnetic pole cover plate, and a plurality of raised fan-shaped magnetic poles, wherein one end of the return yoke is connected with the magnetic pole cover plate, and the other end of the magnetic pole cover plate extends towards the center of the accelerator; the plurality of convex sector magnetic poles comprise a main magnetic pole and more than one non-main magnetic pole, wherein the exciting coil is wound on the main magnetic pole, the exciting coil is not wound on the more than one non-magnetic poles, and the volume of the main magnetic pole is larger than that of the non-main magnetic pole; the main magnetic pole forms a magnetic field loop with the return yoke and the non-main magnetic pole respectively. The invention realizes the adjustment of the magnetic fields of the main magnetic pole and the non-main magnetic pole by adding or subtracting the magnetic yoke, thereby not only effectively saving the exciting coil, but also improving the shimming effect of the magnetic field.

Description

A multi-magnetic circuit sector magnet for improving axial focusing force

Technical Field

The invention belongs to the technical field of high-power cyclotron accelerators, and in particular designs a multi-magnetic loop sector magnet for improving axial focusing force.

Background Art

High-energy (GeV level) and high-average-current (mA level) proton beams have important applications in nuclear physics, public health, advanced energy, national defense and security, and other fields. In the field of cutting-edge basic research, high-power accelerators are one of the main tools for research on neutrino physics, proton decay observation, and muon physics at the forefront of physics intensity. In major national economic fields such as public health and advanced energy, fast neutrons produced by high-power proton target shooting are ideal for nuclear waste treatment and disposal and rare isotope production. In the defense industry and homeland security, high-energy protons have extremely important and extensive applications in many aspects, such as remote detection of special nuclear materials with shielding, prevention of nuclear proliferation and nuclear threats, and photography of dynamic processes of high-Z materials.

At present, the bottlenecks restricting the development of high energy (GeV level) and high average current (mA level) circular accelerators are:

The strong space charge effect of high-energy and high-power accelerators leads to the growth of beam halo and poor beam quality. The average flux is currently difficult to exceed 3mA. During particle movement, particles are subject to magnetic field forces on one side and repulsive forces between particles on the other side. The strong space charge effect refers to the repulsive force between particles. The repulsive force is a nonlinear force between two charges. The repulsive force causes the particles at the edge of the bunch to be loose particles and the size of the bunch to increase. The loose particles at the edge of the bunch are called beam halo. The stronger the space charge, the more obvious the beam halo. The more serious the beam halo, the worse the quality of the bunch, that is, the larger the size of the bunch and the smaller the particle density at the edge of the bunch. The increase in the size of the bunch will cause particles to be lost during the acceleration process and during the extraction process: 1) During the acceleration process, due to the poor quality of the bunch, the particles at the edge will hit the vacuum wall and be lost; 2) During the extraction process, due to the poor quality of the bunch, the particles in the beam halo will hit the deflection plate, causing the deflection plate to spark and be damaged. Therefore, the beam loss problem caused by the beam halo in high-energy and high-power accelerators is a bottleneck problem that limits the average flux.

One of the means to solve the problem of strong space charge effect is to improve the axial focusing force of the beam during acceleration and extraction. The space charge effect is the repulsive force between particles in the bunch. Enhancing the axial focusing force can overcome the repulsive force caused by the space charge effect, which is beneficial to improving the accelerator beam current.

In order to improve the axial focusing force, the prior art adopts a method of evenly distributing two forward deflection magnets and one reverse deflection magnet along the circumferential direction of the accelerator. Both the forward and reverse deflection magnets are single magnetic circuits with independent covers and yokes. As the radius increases, the absolute value of the magnetic field of the forward and reverse deflection magnets gradually increases, and the gradient of the magnetic field strength gradually increases, so that a beam with a larger energy can obtain a larger magnetic field gradient, achieving stable axial focusing at different energies. The reverse deflection magnet ensures the enhancement of the axial focusing of the cyclotron.

Although this method is feasible, it requires a large number of magnets, which are large in size and expensive.

Summary of the invention

In order to solve the problems of the prior art, the present invention proposes a multi-magnetic circuit sector magnet for improving axial focusing force, aiming to solve the problems of the prior art of large number of magnets, large magnet volume and high cost.

The present invention proposes the following technical solutions to solve the technical problems.

A multi-magnetic circuit sector magnet for improving axial focusing force is characterized in that the multi-magnetic circuit sector magnet for improving axial focusing force is evenly arranged in an annular vacuum chamber of an accelerator in two layers along the central plane of the accelerator, the multi-magnetic circuit sector magnet comprises a yoke at the maximum radius of the magnetic pole, a pole cover plate with one end connected to the yoke and the other end extending toward the center of the accelerator, and a plurality of raised sector poles on the lower surface or the upper surface of the pole cover plate; the plurality of raised sector poles comprise a main pole and more than one non-main poles, a coil is wound around the main pole, and no coil is wound around the more than one non-magnetic poles, and the volume of the main pole is greater than that of the non-main pole; the main poles respectively form a magnetic field circuit with the yoke and the non-main poles.

The multiple raised fan-shaped magnetic poles include two: a main magnetic pole and a non-main magnetic pole on one side of the main magnetic pole. The main magnetic pole is wound with a coil and the main magnetic pole has a positive deflection magnetic field, while the non-main magnetic pole is not wound with a coil and has a reverse deflection magnetic field. The main magnetic poles respectively form a magnetic field loop with the yoke and the non-main magnetic poles.

The multiple raised fan-shaped magnetic poles include three: a main magnetic pole, and non-main magnetic poles on both sides of the main magnetic pole; the main magnetic pole is wrapped with a coil and the main magnetic pole is a positive deflection magnetic field, and the non-main magnetic poles on both sides of the main magnetic pole are not wrapped with a coil and are a reverse deflection magnetic field; the main magnetic pole forms a magnetic field loop with the yoke and the non-main magnetic pole respectively.

The yoke is used for rough filling of the magnetic field, specifically: under the premise of a certain magnetic field flux, the magnetic field of the main magnetic pole and the non-main magnetic pole on one side of the main magnetic pole, and the non-main magnetic poles on both sides of the main magnetic pole are changed by increasing or reducing the volume of the yoke: if the volume of the yoke is reduced, the magnetic field of the non-main magnetic pole on one side of the main magnetic pole and the non-main magnetic poles on both sides of the main magnetic pole is enhanced; if the volume of the yoke is increased, the magnetic field of the non-main magnetic pole on one side of the main magnetic pole and the non-main magnetic poles on both sides of the main magnetic pole is weakened.

When the volume of the yoke is reduced and the magnetic fields of the non-main magnetic poles on one side of the main magnetic pole and the non-main magnetic poles on both sides of the main magnetic pole are strengthened, it is necessary to adjust the current of the excitation coil on the main magnetic pole to make the magnetic field flux equal to that before, that is, the magnetic field of the main magnetic pole is restored to the previous magnetic field; when the volume of the yoke is increased and the magnetic fields of the non-main magnetic poles on one side of the main magnetic pole and the non-main magnetic poles on both sides of the main magnetic pole are weakened, it is necessary to adjust the current of the excitation coil on the main magnetic pole to make the magnetic field flux equal to that before, that is, the magnetic field of the main magnetic pole is restored to the previous magnetic field.

Advantages and effects of the present invention

1. The present invention achieves unexpected effects by changing the shape of the elements: two adjacent magnetic poles with opposite magnetic fields are arranged under the same magnetic pole cover, wherein the main magnetic pole has an excitation coil and the non-main magnetic pole does not have an excitation coil. By increasing or reducing the volume of the return yoke and adjusting the main magnetic pole excitation coil to restore the main magnetic pole to the previous magnetic field, the magnetic field of the main magnetic pole and the non-main magnetic pole is adjusted. In addition, the reverse deflection magnet of the accelerator saves an excitation coil. Compared with the traditional method in which each magnetic pole has an independent circuit and each magnetic pole has an excitation coil, it not only achieves the same effect, but also achieves a significant saving in the cost of the excitation coil and a reduction in the volume of the magnet.

2. The present invention uses an indirect method to adjust the magnetic fields of the main poles and non-main poles, achieving unexpected results. By adding or removing magnetic yokes, the magnetic fields of the main poles and non-main poles can be adjusted, which not only effectively saves the time for magnet shimming, but also improves the effect of magnetic field shimming. Since the pole return yoke is arranged outside the pole, it is not necessary to remove the pole or the strip when adjusting the return yoke for rough shimming, but can be operated directly outside the accelerator, saving time and effort. When it is necessary to add a return yoke, a new yoke can be attached to the original yoke, and when it is necessary to remove the yoke, the yoke can be removed from the original yoke. The magnetic field shimming strips in the prior art are attached to the periphery of the accelerator poles. When adding or removing magnetic field shimming strips, the strips or strips must be removed, which increases the time for magnetic field shimming.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1-1 is a three-dimensional first-view diagram of a multi-magnetic circuit sector magnet for improving axial focusing force;

FIG1-2 is a second perspective view of a multi-magnetic circuit sector magnet for improving axial focusing force;

FIG1-3 is a side view of a multi-magnetic circuit sector magnet for improving axial focusing force;

FIG1-4 is one of the bottom views of a multi-magnetic circuit sector magnet for improving axial focusing force;

FIG1-5 is a second bottom view of a multi-magnetic circuit sector magnet for improving axial focusing force;

FIG2 is a layout diagram of the application of multi-magnetic circuit sector magnets in an accelerator;

In the figure, 1-1: yoke; 1-2: pole cover; 1-3: main pole; 1-4: non-main pole on one side of the main pole; 1-4-1: non-main pole on both sides of the main pole; 1-4-2: non-main pole on both sides of the main pole; 1-5: excitation coil.

DETAILED DESCRIPTION

The present invention will be further explained below in conjunction with the accompanying drawings:

Design principle of the present invention

The principle of multi-magnetic circuit sector magnets saving excitation coils. Excitation coils include conventional excitation coils and superconducting excitation coils. Multi-magnetic circuit sector magnets are arranged under the same pole cover plate with more than two poles of opposite magnetic fields, one of which has an excitation coil (main pole) and the other does not have an excitation coil (non-main pole), and a yoke is arranged at the large radius of the magnet. The main pole is likened to the trunk of a parallel circuit, and the yoke and the non-main pole are likened to the two branches of a parallel circuit. In the prior art, there is only one pole under a pole cover plate and an excitation coil is wound around the pole, and the magnetic field can only form a loop through the yoke, that is, a single magnetic field loop. Compared with the prior art, the compact multi-magnetic circuit sector magnet of the present invention saves one or more superconducting excitation coils, and the superconducting excitation coil accounts for more than half of the cost of the magnet. The multi-magnetic circuit sector magnet of the present invention has a compact structure, high magnetic field utilization efficiency, and low manufacturing and operating costs.

The principle of saving a superconducting excitation coil is that the non-main magnetic pole and the return yoke simultaneously serve as the loop of the magnetic field in the main magnetic pole, that is, there are multiple magnetic field loops. The magnetic field in the non-main magnetic pole is opposite to the magnetic field of the main magnetic pole. The reverse magnetic field in the non-main magnetic pole can improve the axial focusing force of the accelerator.

The multi-magnetic circuit fan-shaped magnet structure is also conducive to the shimming of the magnetic field. The specific method of shimming the magnetic field by adjusting the size of the yoke is as follows: when the size of the yoke changes, the magnetic fields of the main magnetic pole and the non-main magnetic pole will be changed at the same time. When the magnetic field of the non-main magnetic pole needs to be adjusted, the size of the yoke can be changed to make the magnetic field of the non-main magnetic pole meet the requirements. However, when the size of the yoke is adjusted, the main magnetic pole will also change, and the superconducting excitation coil of the main magnetic pole should be adjusted at the same time to restore the magnetic field of the main magnetic pole to the original magnetic field.

Based on the above invention principle, the present invention designs a multi-magnetic circuit sector magnet for improving axial focusing force.

A multi-magnetic circuit sector magnet for improving axial focusing force is shown in Figures 1-1, 1-2, 1-3, 1-4, 1-5 and 2, and is characterized in that the multi-magnetic circuit sector magnet for improving axial focusing force is evenly arranged in two layers along the upper and lower central plane of the accelerator in the annular vacuum chamber of the accelerator, and the multi-magnetic circuit sector magnet includes a yoke 1-1 at the inner radius of the magnetic pole, a pole cover 1-2 with one end connected to the yoke 1-1 and the other end extending toward the center of the accelerator, and a plurality of raised sector poles on the lower surface or the upper surface of the pole cover 1-2; the plurality of raised sector poles include a main magnetic pole 1-3 and one or more non-main magnetic poles, a superconducting excitation coil 1-5 is wound around the main magnetic pole 1-3, and no superconducting excitation coil is wound around the one or more non-magnetic poles, and the volume of the main magnetic pole is greater than that of the non-main magnetic pole; the main magnetic pole 1-3 respectively forms a magnetic field circuit with the yoke 1-1 and the non-main magnetic pole.

The multiple raised fan-shaped magnetic poles include two: a main magnetic pole 1-3 and a non-main magnetic pole 1-4 on one side of the main magnetic pole. The main magnetic pole 1-3 is wound with a superconducting excitation coil 1-5 and the main magnetic pole 1-3 is a positive deflection magnetic field, and the non-main magnetic pole 1-4 is not wound with a superconducting excitation coil and the non-main magnetic pole is a reverse deflection magnetic field; the main magnetic poles respectively form a magnetic field loop with the yoke and the non-main magnetic poles.

The multiple raised fan-shaped magnetic poles include three: a main magnetic pole 1-3, and non-main magnetic poles 1-4-1 and 1-4-2 on both sides of the main magnetic pole; the main magnetic pole 1-3 is wound with a superconducting excitation coil 1-5 and the main magnetic pole 1-3 is a forward deflection magnetic field, and the non-main magnetic poles 1-4-1 and 1-4-2 on both sides of the main magnetic pole are not wound with the excitation coil and are a reverse deflection magnetic field; the main magnetic poles respectively form a magnetic field loop with the yoke and the non-main magnetic poles.

The return yoke 1-1 is used for rough padding of the magnetic field, specifically: under the premise of a certain magnetic field flux, the magnetic fields of the main magnetic pole 1-3 and the non-main magnetic pole 1-4 on one side of the main magnetic pole, and the non-main magnetic poles 1-4-1 and 1-4-2 on both sides of the main magnetic pole are changed by increasing or reducing the volume of the return yoke 1-1: if the volume of the return yoke 1-1 is reduced, the magnetic fields of the non-main magnetic pole 1-4 on one side of the main magnetic pole, and the non-main magnetic poles 1-4-1 and 1-4-2 on both sides of the main magnetic pole are enhanced; if the volume of the return yoke 1-1 is increased, the magnetic fields of the non-main magnetic pole 1-4 on one side of the main magnetic pole, and the non-main magnetic poles 1-4-1 and 1-4-2 on both sides of the main magnetic pole are weakened.

When the volume of the yoke 1-1 is reduced and the magnetic fields of the non-main magnetic pole 1-4 on one side of the main magnetic pole and the non-main magnetic poles 1-4-1 and 1-4-2 on both sides of the main magnetic pole are strengthened, it is necessary to adjust the current of the excitation coil 1-5 on the main magnetic pole 1-3 so that the magnetic field flux is equal to that before, that is, the magnetic field of the main magnetic pole 1-3 is restored to the previous magnetic field; when the volume of the yoke is increased and the magnetic fields of the non-main magnetic pole 1-4 on one side of the main magnetic pole and the non-main magnetic poles 1-4-1 and 1-4-2 on both sides of the main magnetic pole are weakened, it is necessary to adjust the current of the excitation coil 1-5 on the main magnetic pole 1-3 so that the magnetic field flux is equal to that before, that is, the magnetic field of the main magnetic pole 1-3 is restored to the previous magnetic field.

Supplementary explanation: The magnetic pole return yoke of the present invention is arranged outside the accelerator vacuum chamber, which is convenient for adding or reducing the magnetic yoke. When a magnetic yoke needs to be added, a new magnetic yoke can be attached to the original magnetic yoke, and when a magnetic yoke needs to be reduced, the magnetic yoke can be reduced from the original magnetic yoke. However, the magnetic field shimming strips of the prior art are attached around the accelerator magnets. When adding or reducing the magnetic field shimming strips, the vacuum chamber must be disassembled, which increases the number of times the on-site personnel are exposed to radiation.

It should be emphasized that the above specific embodiments are merely explanations of the present invention, and they are not limitations of the present invention. After reading this specification, those skilled in the art can make non-creative modifications to the above embodiments as needed, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims (5)

1. A multi-magnetic circuit sector magnet for improving axial focusing force, characterized in that the multi-magnetic circuit sector magnet for improving axial focusing force is evenly arranged in the annular vacuum chamber of the accelerator in two layers along the central plane of the accelerator, the multi-magnetic circuit sector magnet comprises a yoke at the maximum radius of the magnetic pole, a pole cover plate with one end connected to the yoke and the other end extending toward the center of the accelerator, and a plurality of raised sector poles on the lower surface or the upper surface of the pole cover plate; the plurality of raised sector poles comprise a main pole and one or more non-main poles, an excitation coil is wound around the main pole, and no excitation coil is wound around the one or more non-magnetic poles, and the volume of the main pole is greater than that of the non-main pole; the main poles respectively form a magnetic field circuit with the yoke and the non-main poles; The yoke is used for rough filling of the magnetic field, specifically: under the premise of a certain magnetic field flux, the magnetic field of the main magnetic pole and the non-main magnetic pole on one side of the main magnetic pole, and the non-main magnetic poles on both sides of the main magnetic pole are changed by increasing or reducing the volume of the yoke: if the volume of the yoke is reduced, the magnetic field of the non-main magnetic pole on one side of the main magnetic pole and the non-main magnetic poles on both sides of the main magnetic pole is enhanced; if the volume of the yoke is increased, the magnetic field of the non-main magnetic pole on one side of the main magnetic pole and the non-main magnetic poles on both sides of the main magnetic pole is weakened. 2. According to claim 1, a multi-magnetic circuit sector magnet for improving axial focusing force is characterized in that: the multiple raised sector-shaped magnetic poles include 2: a main magnetic pole and a non-main magnetic pole on one side of the main magnetic pole, the main magnetic pole is wound with an excitation coil and the main magnetic pole is a positive deflection magnetic field, the non-main magnetic pole is not wound with an excitation coil and the non-main magnetic pole is a reverse deflection magnetic field; the main magnetic poles respectively form a magnetic field circuit with the return yoke and the non-main magnetic poles. 3. According to claim 1, a multi-magnetic circuit sector magnet for improving axial focusing force is characterized in that: the multiple raised sector-shaped magnetic poles include three: a main magnetic pole, and non-main magnetic poles on both sides of the main magnetic pole; the main magnetic pole is wrapped with an excitation coil and the main magnetic pole is a positive deflection magnetic field, and the non-main magnetic poles on both sides of the main magnetic pole are not wrapped with an excitation coil and are a reverse deflection magnetic field; the main magnetic poles respectively form a magnetic field circuit with the yoke and the non-main magnetic poles. 4. A multi-magnetic circuit sector magnet for improving axial focusing force according to claim 1, characterized in that: when the volume of the yoke is reduced and the magnetic field of the non-main magnetic pole on one side of the main magnetic pole and the non-main magnetic pole on both sides of the main magnetic pole is enhanced, it is necessary to adjust the current of the excitation coil on the main magnetic pole so that the magnetic field flux is equal to that before, that is, the main magnetic pole magnetic field is restored to the previous magnetic field; when the volume of the yoke is increased and the magnetic field of the non-main magnetic pole on one side of the main magnetic pole and the non-main magnetic pole on both sides of the main magnetic pole is weakened, it is necessary to adjust the current of the excitation coil on the main magnetic pole so that the magnetic field flux is equal to that before, that is, the main magnetic pole magnetic field is restored to the previous magnetic field. 5. A multi-magnetic circuit sector magnet for improving axial focusing force according to claim 1, characterized in that the excitation coil comprises a superconducting excitation coil and a non-superconducting excitation coil.