REDUCING EMITTANCE OF A H − BEAM IN A SOLENOID-BASED LOW-ENERGY BEAM TRANSPORT THROUGH NUMERICAL MODELING ∗

A solenoid-based low-energy beam transport (LEBT) subsystem is under development for the H – linac front end of the Spallation Neutron Source. The LEBT design includes MHz-frequency chopping of a partially neutralized H – beam that can potentially lead to beam instabilities. We report results of numerical modeling using the parallel VSim [1] framework for 3D electrostatic particle-in-cell (PIC) to simulate H – beam dynamics in the LEBT, over multiple chopping events. We detail how the addition of a positively biased potential barrier near the entrance of the chopper can improve LEBT performance by eliminating chopper-induced emittance increases over many chopping events.