Beam Dynamics Simulation Study In A Dielectric Wall Proton Linac

Dielectric wall proton linac is a new concept of accelerator, which has characteristics of high acceleration gradient, miniaturization, and being capable of accelerating a variety of charged particles. Being a potential alternative to conventional proton accelerator in proton cancer treatment, this kind of accelerator has broad application prospects in the field of radioactive medical treatment. Its high voltage gradient acceleration and low cost can dramatically lower the construction and operation cost of cancer treatment equipment and significantly reduce the cost of hospital and patient treatment, which provides strong hardware and technical support for the popularization of cancer treatment. As a new concept of accelerator, the research on beam dynamics, such as particle generation, motion, acceleration and beam transport in the entire dielectric wall accelerator have not been researched intensively. The understanding of the proton beam transport is so shallow that it's very necessary to study the dynamic process of the proton beam.The thesis firstly introduces the principle of cancer treatment by using energetic charged particles, shows the effectiveness of accelerator as a cancer treatment method, analyzes the significance of emergence of the dielectric wall proton accelerator for radioactive cancer treatment.The thesis also analyzes the process of virtual traveling wave accelerating mechanism in dielectric wall accelerator, builds a quasi three-dimensional model of dielectric wall proton accelerator in the electromagnetic field simulation software-CHIPIC and demonstrates the setting and correctness of parameters of the model.Particle studio in electromagnetic field simulation software CST and CHIPIC are applied for simulation analysis for beam transport in kicher, acceleration in accelerating cavity and transport process in beam pipe after particles extraction from ECR (Electron Cyclotron Resonance) ion source. The simulation gives reasonable range of voltage setting on Kicker and analyzes the effect of space charge force generated by beam internal interaction during the long distance transport process of the proton beam on beam transport. The simulation results show that the space charge force is an important factor for energy dispersion increase of proton in free field drift. Comparing with the effect of beam internal interaction on beam transport in different particle energy, the simulation reveals that the higher the proton energy is, the smaller the influence of beam internal interaction on beam parameters. Analyzing the proton energy change in the transport process of high energy proton beam at low energy background, the simulation indicates that the interaction between high-energy proton and low-energy proton has little influence on proton energy that can be neglected, which means high energy short pulse width proton beam can achieve long distance transprot at low energy long pulse width background with little energy loss. That provides a basis for the feasibility of using a magnetic analyzer to measure the energy of proton.Establishing acceleration model of proton in variable electric field in Matlab, calculating loading timing sequence design of accelerating voltage between accelerating cavity and cavity under short pulse (the pulse width of accelerating voltage is less than the transit time of proton in accelerating cavity), and simulating the calculated timing sequence in CHIPIC model as well as comparing it with the case without timing sequence, the simulation shows that the loading timing sequence optimization of the accelerating voltage can improve energy gain and flow intensity of proton in the accelerating cavity effectively so that the charged particles can obtain high voltage gradient acceleration. The requirement of particles of different quality for accelerating voltage timing sequence setting is analyzed, acceleration status under H+ the optimal loading conditon with beam containing H2+ and H3+ is simulated and compared with the experimental results. After calculating the requirements of protons of different energy for voltage pulse timing sequence and simulating the effects of accelerating voltage pulse width increase on the acceleration of protons, the simulation manifests that when the peak duration of accelerating voltage pulse is very short, increasing voltage pulse width can prolong the duration of peak voltage and thus improve the energy gain of protons effectively while it's unhelpful for energy gain of the charged particles to continue increasing the pulse width when it reaches a certain value but to increase the number of particles accelerated.Based on derivation of electric field distribution in the process of virtual traveling wave acceleration, it is proposed to add metal reseau structure to metal round hole electrode to improve accelerating electric field and optimize the acceleration of proton in accelerating cavity. The correctness of the optimization is verified by the measurement of the energy gain of H+ before and after the improvement. The thesis simulates decelerating effect of accelerating voltage at the beginning and end of the accelerating cavity when coupling condition happens between adjacent accelerating cavity, simulates the influence of decelerating effect on accelerating voltage timing sequence setting, and puts forward with measures of suppressing decelerating electric field on particle injection. Through experiments, the existence of the decelerating field and the feasibility of suppression measures of decelerating field are verified.