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 (0.2n,rπmmmrad), 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∘@20.3125 MHz, 270∘@20.3125 MHz) as well as the traditional mode (180∘@40.625 MHz) 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∘@20.3125 MHz compared to traditional mode. The detailed results are presented in this paper.