Design of a Duoplasmatron Extraction Geometry and Lebt for the Lansce H

The 750-keV H + Cockcroft-Walton at LANSCE will be replaced with a 4-rod RFQ with injection energy of 35 keV. The existing duoplasmatron source extraction optics need to be modified to produce up to 35 mA of H + current with an emittance <0.02 pi-cm-mrad (rms,norm) for injection into the RFQ. In addition to source modifications we need a new LEBT for transport and matching into the RFQ. The LEBT uses 2 magnetic solenoids with enough drift space between them to accommodate diagnostics and a beam deflector. The LEBT is designed to work over a range of space-charge neutralized currents and emittances. The LEBT is optimized in the sense that it minimizes the beam size in both solenoids for a point design of a given neutralized current and emittance. Special attention has been given to estimating emittance growth due to solenoid aberrations. Examples of source-to-RFQ matching and emittance growth (due to both non-linear space charge and solenoid aberrations) are presented over a range of currents and emittances about the design point. A preliminary mechanical layout drawing will also be presented.