Simulation Study Of Slow Extraction For The Shanghai Advanced Proton Therapy Facility

Because of the Bragg peak distribution,proton therapy technology has excellent characteristics such as high curative effect and low side-effect.Now,the proton therapy technology has become one of the most advanced cancer treatment in the world and it has been used in clinical treatment widely.The Chinese government also does it's best to import and develop the proton therapy technology.The Shanghai Advance Proton Therapy(SAPT)facility is the first proton therapy facility designed and constructed by China,it is the beginning of localization of proton therapy technology in China,has great significance.The accurate treatment needs the high quality spill,so there are high requirements of spill characteristic including the uniformity,stability and switching time.So the Shanghai Advanced Proton Therapy(SAPT)facility employs 3rd integer RF-KO slow extraction.The protons' trajectories in the synchrotron are relatively complicated under the effect of the RF-KO excitation,synchrotron RF cavity and resonance sextupoles;it is difficult to use simple formula to calculate,so we need do the trace simulation of the large particles trajectories.So we can know the characteristics of the spill get the appropriate control parameters and ensure to achieve satisfactory spill.In this paper,we begin with the theoretical analysis of 3rd integer RF-KO slow extraction.Then we introduce the theoretical analysis and application method of the AM amplitude modulation,frequency selection of the RF-KO frequency sweep signal and fast quadrupole iron technology needed for fast switch.Furthermore we analyze the factors that could affect the stability of extraction beam.According to the structure of proton therapy synchrotron,we build different slow extraction simulation models and simulate the trajectories of the vast particles in the synchrotron and slow extraction by using MATLAB,and compare their characteristics,advantages and disadvantages.Finally,we chose the segmented transfer matrix model witch balances speed and tracking accuracy as a particle tracking simulation model.By using the model in combination with different parameters,we do a large number of tracking simulation.So we get the influence of the spill characteristics including the uniformity,stability and switching time from the accelerator parameters changes of the resonance sextupole strength,chromaticity,horizontal tune,momentum spread,power supply ripple and RF cavity voltage.Based on these results,we give the appropriate numerical value of these parameters.Furthermore we adopt the fast quadrupole and the appendant single frequency RF-KO signal witch used for realizing quick switch.We also give the selections of the fast quadrupole strength and the frequency and intensity of the single frequency signal by simulation.In a word,my paper gives the spill characteristics influence from the changes of the main synchrotron parameters by theoretical analysis and tracking simulation and chooses the optimum values.We provide references for the debug of the synchrotron slow extraction of the Shanghai advanced proton therapy facility.