Model of a SNS Electrostatic LEBT with a Near-Ground Beam Chopper.

The low energy beam transport (LEBT) of the Spallation Neutron Source (SNS) accelerator consists of two electrostatic lenses, of which the second is split into four electrically-isolated segments. Adding fast pulsed voltages to the lens high voltage creates the transverse fields required for beam chopping. Electric sparks, however, create transients that enter the fast high-voltage switches, which are occasionally damaged and cause machine downtime. This work models a new configuration of the electrostatic LEBT, which chops the beam with four shielded, near-ground electrodes between the two lenses. The model shows that the new configuration can match the RFQ injection requirements and sufficiently deflect the beam in the phase-space using the same chopping voltages as in the baseline LEBT. [ABSTRACT FROM AUTHOR]