Design study of multi-charge low energy beams transport for BISOL post accelerator

Abstract Beijing Isotope-Separation-On-Line Neutron-Rich Beam Facility (BISOL) post accelerator is designed to accelerate RIBs extracted from Isotope Separation On-Line (ISOL) ion source and the beam energy will be upto 150 MeV/u for Stannum. The accelerated RIBs will be served as projectile to produce isotopes far from stable line. Multi-charge state beams transport is adopted to increase beam current, a low energy beam transport (LEBT) line is desired for selecting charge states, bunching beam from continuous wave (CW) ISOL beams and match the beam into a CW 81.25 MHz radio frequency quadrupole (RFQ). This paper mainly presents the design study of BISOL multi-charge LEBT line. The detailed optics design and beam dynamics simulation are presented. Due to lower beam energy (3 keV/u) and higher transverse emittance (0.2 n,r π m m ⋅ mrad ), the longitudinal nonlinear effect in the bunching system cannot be ignored compared to existing LEBT bunching systems, we have investigated two novel bunching and injection modes (180 ∘ @20.3125MHz, 270 ∘ @20.3125MHz) as well as the traditional mode (180 ∘ @40.625MHz) to optimize the output longitudinal emittance. The beam dynamics analysis indicates that the output longitudinal rms emittance can be lowered by nearly 33% with the bunching mode of 270 ∘ @20.3125MHz compared to traditional mode. The detailed results are presented in this paper.