Extraction System Optimization And Beam Loss Study Of HUST Superconducting Cyclotron

Proton therapy is a new technology that uses proton beams for cancer radiotherapy.Compared with traditional radiotherapy using photon beams,proton therapy can obtain more ideal therapeutic effects and cause less damage to healthy tissues near the tumor,which has attracted a lot of attention internationally.Considering that foreign countries have monopolized the core technology of proton therapy equipment,China has paid great attention to the research and development of proton therapy equipment.And the project of "proton therapy equipment research and development based on superconducting cyclotron" is included in the 13 th fiveyear key research and development plan.The superconducting cyclotron has a compact structure and high magnetic field strength.Compared with the normal temperature cyclotron,the beam radius is smaller and the turn separation is smaller in the superconducting cyclotron.There is even a phenomenon of beam staggered overlap.It is a great challenge to deflect such a high-energy single-turn beam to the periphery of the accelerator,which makes the beam extraction system of the superconducting cyclotron more complicated.A reasonable design of the extraction system can improve the efficiency of the beam extraction under the premise of ensuring the quality of the extraction beam.The extraction system is also one of the main areas where beam loss occurs.The thermal effect of beam loss will deform the structure of the extraction device,leading to further beam loss.Its radiation effect can also cause superconducting quench,which is extremely harmful to personal safety and equipment safety.For the extraction system of the HUST superconducting cyclotron,a theoretical design plan was made: the introduction of the first harmonic magnetic field to increase the turn separation,the electrostatic deflector to deflect the beam to the periphery of the accelerator,and then the passive magnetic channel to ensure beam quality while deflecting the beam.This paper makes a theoretical design scheme for the extraction system of HUST superconducting cyclotron: the introduction of the first harmonic field increases the turn separation,the electrostatic deflector is used to deflect the beam to the periphery of the accelerator,and then the passive magnetic channel is used to ensure the beam quality while deflecting the beam.It is calculated that when the amplitude of the first harmonic magnetic field is 15 Gs,the phase is135°,and the radial FWHM is 1.9 cm,the turn separation increases to 6.25 mm.At the same time,the installation space position of the electrostatic deflector is given.To minimize the fabrication difficulty and reduce the cost of the deflector,we use an arc-shaped deflector model to replace the actual beam orbit-shaped deflector model.In addition,the installation position and geometric structure of the magnetic channel are given.Multi-particle tracking is used to calculate the beam loss at the electrostatic deflector in the superconducting cyclotron extraction system.Using the numerical calculation software MATLAB and the beam tracking program CYCLONE,the radial envelope of the beam at the entrance of the electrostatic deflector is 3.28 mm,and the axial envelope is 1.79 mm.The analysis shows that under ideal conditions,the beam loss rate when the beam center passes through the deflector gap is 0.12%;In extreme cases,the beam loss rate when the beam center collides with the front of the deflector septum is 19.87%.Then,the thermal effect caused by the beam loss is analyzed by the thermal-fluid-structure coupling simulation software ANSYS.And the maximum temperature of the deflector septum is 948.9 K,the maximum deformation occurs at the V-notch of the septum,and the deformation is 0.00852 mm.Therefore,it is determined that the cooling water flow is 0.3 m/s,and the septum material is selected as tungsten.The finite element simulation software CST was used to simulate the movement trajectory of the field emission electrons on the electrode surface in the deflector when the high-voltage ignition in the electrostatic deflector occurred.The electromagnetic simulation software OPERA-3D was used to simulate the electric field distribution in the electrostatic deflector,and the electric field distribution in the deflector under different electrode structures was compared.Finally,the cross-sectional shape of the electrode of the electrostatic deflector is designed to connect two arcs tangentially.The electrode end is a chamfer with a radius of 7.3 mm.According to the simulation results,a deflector model for high-voltage experiments was optimized to test its high-voltage performance.Finally,it was determined that the high-voltage electrode material was anodized aluminum,the insulator was made of glazed aluminum oxide,and the shell and the septum material is selected as oxygen-free copper.These studies provide theoretical support for the beam loss control of the extraction system,and also provide an effective reference for the high-voltage structure design of the electrostatic deflector.