Simulation Study On Space Charge Effects For CSNS Linac

China Spallation Neutron Source (CSNS) is a high intensity accelerator based facility. Its accelerator consists of an H-injector and a proton Rapid Cycling Synchrotron. The injector includes the front end and linac. The RFQ accelerates the beam to3MeV, and then DTL accelerates it to81MeV. The space charge effects is the most important reason to cause emittance growth and beam loss due to the low energy and the high peak current.This paper summarized the basic structure of CSNS and the basic theory of beam space charge effects, a comparation of space charge simulation code IMPACT-Z and PARMILA was given. Simulation studies were done for the new design and old design of MEBT by using the three-dimensional code IMPACT-Z, and the influence of the buncher’s radial defocusing force on beam was also studied, the simulation study verified the new design is better than the old one. The study of space charge effects for the LINAC were also performed by using the IMPACT-Z code. The emittance growth is compared and studied on the condition of no space charge effects and the condition of peak beam current of15mA and30mA. The results have shown that the emittance grew significantly with the increase of the beam intensity.The effect of mismatch is studied by simulation, and the emittance growth with different transverse and longitudinal mismatch factor are given. In addition, based on FFDD focusing structure of the DTL, the overall beam emittance growth is explained through the simulation of single particle’s phase space evolution with different mismatch factor. The results have shown the transverse mismatch effect is greater than the longitudinal, transverse match should be given the priority, and the initial beam mismatch should not be exceed1.4in the beam tuning.The error effect is the one of the most important issues in the DTL, and it is included in the simulation study. The affection of error effect on emittance growth and beam loss is studied, and beam loss with different mismatch factor are given.