Physical Design And Research On The Central Region Of The Superconducting Cyclotron SCC250 For Proton Therapy

At present,the number of cancer cases and deaths in China is the highest in the world,and the number is constantly rising.The demand for cancer treatment facilities has increased dramatically,which has become a rigid demand for our country's medical system.Radiotherapy is one of the three main methods for treating cancer.The dose distribution of proton therapy has the characteristic of Bragg peak.Compared with photon radiotherapy,proton therapy can kill cancer cells more accurately.Under the support of the Ministry of Science and Technology and the government,Huazhong University of Science and Technology and several agencies,have jointly undertaken the project "Research and Development of Proton Radiation Equipment based on Superconducting Cyclotron" to develop a proton radiotherapy system for cancer treatment.In this system,the cyclotron uses superconducting coil for excitation and a cold cathode PIG internal ion source is used,thus reducing the size to achieve a compact design.Finally,the proton beam of 250 MeV/500 nA is extracted.However,the compactness of superconducting cyclotron imposes a challenge to the central region design.This thesis focuses on the physical design of the central region and the related issues of beam dynamics.In this thesis,the beam dynamics in the superconducting cyclotron SCC250 is briefly introduced and discussed firstly.The stability of radial and axial motion in cyclotron is introduced.The isochronicity of magnetic field is studied.The influence of first harmonic magnetic field on the center of static equilibrium orbit is shown.In order to compare and verify the reliability of beam tracking codes and to provide a reference for the subsequent design of the central region,a MATLAB program is written to calculate the beam trajectories under the joint effects of the static magnetic field and the high frequency electric field.Then the different beam tracking programs are compared and it is found that the calculated results are consistent.Then the effect of different initial conditions on beam motion is studied.This thesis mainly focuses on the design and research of the central region of the superconducting cyclotron SCC250.In the design process,the beam centering,radial and axial focusing are considered.For the preliminarily designed structure of the central region,the electromagnetic field distribution is calculated using the finite element analysis software OPERA/TOSCA and then beam dynamics calculation is performed using Z3 CYCLONE.Based on the beam tracking results,the electrode and magnetic pole structure in the central region are optimized iteratively,and the finally optimized central region structure is obtained.The beam centering,radial oscillation,axial oscillation and radial-longitudinal coupling are studied.The preliminary design and optimization of the central region of the superconducting cyclotron SCC250 have been completed.