Evaluation of beam-loss suppression method by nonlinear space charge force in a high intensity linac

The increase of space charge effect in high intensity beam causes the increase of the beam-loss. Beam-loss limits beam intensity depending on the amount of accelerator equipment activation. Therefore, it is important to suppress the emittance growth due to the space charge effect. I focused on the low energy region in the linac where the space charge effect becomes remarkable. In order to identify the origin of the emittance growth due to the space charge effect, a simulation was performed with IMPACT, a 3-D particle-in-cell simulation code, and evaluated the influence of space charge effects in the J-PARC medium energy beam transport line (MEBT1) entrance to DTL exit. As a result, it was confirmed that distortion of phase space distribution occurred due to nonlinear space charge force and that leading to emittance growth. I proposed to suppress the emittance growth by using an octupole magnet that gives nonlinear force to the beam. The simulation in the MEBT1 entrance to DTL exit in the case of three octupole magnets were installed to MEBT1 was shown that the emittance growth ratio that the emittance growth ratio ∊_f/∊_i was suppressed from ∊_f,x/∊_i,x, ∊_f,y/∊_i,y) = (2.32,1.81) to ∊_f,x/∊_i,x, ∊_f,y/∊_i,y) = (1.42,1.32). (author)