The Study Of Some Key Beam Dynamic Problems In The Room Temperature Front-end Transport Line For High Power Superconducting Linac

The high-power superconducting linear accelerator is a research platform for highenergy material density research,spent fuel proliferation and transmutation,isotope production,and high-throughput neutron plants.For high-intensity superconducting linac,beam loss will cause component activation and damage,which is a key factor restricting the stability and maintainability of the accelerator.And for the uncontrollable beam loss and its suppression,theoretical and experimental research is a popular direction in the accelerator subject.The room temperature front-end includes medium and low energy transport lines and a radio frequency quadrupole accelerator.It is the section where the beam experiences the most serious space charge effects and highfrequency nonlinear effects.The optimization of beam quality at the front end has important scientific value and engineering significance for the stable operation of highpower superconducting linac.Halo is a key characterization of beam loss.This dissertation is mainly oriented towards the mechanism of halo generation and suppression to ensure high-quality beam transmission into the downstream accelerator at the room temperature front end.As the beam space charge effect is strong and related to the distribution type,halos may be caused due to the inconsistent of the interaction with the external focusing force and space charge force.Numerical simulation analysis is carried out on the low-energy transport line to quantify the boundary where the beam ions feel the linear action of the solenoid field to avoid the generation of halo ions.An optimized iterative design is adopted in the medium-energy transport line to judge the balance of internal and external focusing forces,which is considered of tune depression factor and beam phase advance transition.This method can effectively reduce the increase of normalized emittance and total emittance.Phase space scraping to achieve the restriction of halo ions is an effective method to reduce the probability of beam loss in the downstream acceleration section.Multiparticle simulation and particle marker tracking method are used for tomographic analysis of beam halo particles in LEBT for the mechanism of "point scraping" study.Based on the conventional phase space scraping scheme,the multi-focus MEBT is designed with smooth envelope to achive a feasibility scheme of full-phase space scraping.Iterating with the effective acceptance of the downstream accelerator,the purpose of restraining the halo ions entering the downstream accelerator can be achieved.Based on the study of key physical problems,the dynamic design of the room temperature front-end beam line of the Ci ADS accelerator was completed.The bending LEBT can effectively realize the purification of the mixed beam.With the highprecision of main accelerated ion measurement,the beam dynamic is good matched with the downstream accelerator.The MEBT is adopted with a multi-foucs structure.Combined with redundant error analysis and optimized with the maximum acceptance of the front end,by optimizing the beam aperture,the high-quality beam is guaranteed before entering the downstream accelerator.