R&D Of An APF IH-DTL Injector

With the worldwide increase in cancer cases, cancer diagnosis and treatment tend to be more diversified. As a superior means of radiotherapy, heavy ion radiotherapy gradually draws more attention. Alternating Phase Focused(APF) Interdigital-H type(IH) Drift Tube Linac(DTL) is adopted as a backup injector of the main synchrotron of the Heavy Ion Medical Machine(HIMM).Evolution of APF put forward in 1953 has undergone the periods of positive-negative symmetric phases, positive-positive-negative-negative symmetric phases, asymmetric phases and modified phases, while the degrees of design freedom are increasing. APF IH-DTL was successfully used as an injector for a cancer therapy machine in HIMAC in the last few years.There are no such conventional focusing elements as solenoids and quadrupoles any more in APF, and instead, both the transversal and longitudinal focusing are realized by alternating synchronous phases, which contributes to small distributed capacitance, high accelerating gradient and small size of the corresponding IH cavity, thus leading to cost-efficient fabrication and reduced construction space. APF not only meets the expectations of a cancer therapy machine, but is of great significance for the miniaturization of civilian accelerators.This dissertation has made researches on APF with theoretical analysis and numerical simulation. Based on the mathematical principles of APF, theoretical inference is carried out by assuming a smooth function, and then a code is developed. This dissertation is composed of four parts: physical design of APF, numerical simulation, PSO optimizing and cavity design, aiming to reveal the universal law of APF design and propose an optimal APF IH-DTL design.Based upon the smoothness idea, a code, i MPAPF, to design and simulate APF is developed. By employing i MPAPF, hundreds of APF designs are obtained, and the design parameters are studied and analyzed to get the basic parameters in APF design.By using the standard single objective PSO in the design of APF, the Twiss parameters with Map Matrix are optimized and the smooth Beta functions are obtained transversely and longitudinally; then, the beam envelops and emittances are optimized by applying the multi-particle transmission with matrix; and finally a final optimal solution is achieved by using PIC simulation with multi-objective PSO.There are four PIC simulation plans on APF: Beampath, Leapfrogging Algorithm and two Runge-Kutta methods. The Benchmark shows that the four results of the beam dynamics simulation are completely consistent with each other but with different computing time. A series of simulation data and figures are obtained by simulating an optimal APF with the four plans.The paraxial electric field is obtained to design beam dynamics by Bessel-Fourier expansion and Finite Difference Method, and the IH cavity is designed by using MWS. The cavity parameters are adjusted and the cell structures are slightly changed, thus generating the relative flat electric field and decreased dipole components. Eventually, IH cavity is designed and the corresponding RF parameters are obtained.The innovation in the dissertation lies in the closed periodic solution of APF in the case of differential dynamics equations by applying the smoothness idea, based on which, the code i MPAPF is developed and hundreds of APF have been designed to obtain a large quantity of preliminary data and statistical regularities.