2D simulation and optimization of the volume H− ion source extraction system for the spallation neutron source accelerator

The low-energy beam transport system (LEBT) for the Spallation Neutron Source (SNS) is required to transport 35 mA of a 65 keV H− ion beam from the ion source to the RFQ accelerator entrance with a normalized rms emittance of less than 0.15 π mm mrad. A radio frequency driven, magnetically filtered multicusp ion source is under development at LBNL. The H− beam extraction from this ion source is being simulated utilizing the 2D-computer code IGUN [Rev. Sci. Instr. 63 (1992) 2756]. An H− ion extraction model is discussed. Computational results are presented for the H− ion beam emittance of a single aperture two electrode extraction system and for the tuning range of the low-energy beam transport system.