Simulation of the ion source extraction and low energy beam transport systems for the Spallation Neutron Source

Abstract

The ion source for the Spallation Neutron Source is a radio-frequency (rf) multi-cusp, volume-type H− source that is coupled to a rf quadrupole accelerator through a low energy beam transport (LEBT) system consisting of five electrostatic elements. To gain a deeper understanding of the operation of this system and to continue to refine the design, we have performed ion extraction and transport simulations using the computer code PBGUNS. A comparison is presented between simulation and the measured phase space of the beam for various values of LEBT electrode potentials. Both the emittance magnitude and orientation in phase space were found to be in reasonable agreement with measurement. A design study is also presented where the angle of the source outlet electrode has been optimized with the aid of PBGUNS simulations, resulting in a substantial reduction of the emittance.