R. THOMAE, P. BACH, R. GOUGH, J. GREER, R. KELLER, K. LEUNG (BERKELEY LAB)
Berkeley Lab is engaged in the development of the front end of the Spallation Neutron Source (SNS) to be built in Oak Ridge, Tennessee. Parts of the front end are the ion source and the Low Energy Beam Transport (LEBT) section. The startup ion source, enabling SNS to achieve 1-MW average beam power, has to provide 35 mA of H- beam current at 6% duty factor (1 ms pulses at 60 Hz) with a normalized rms emittance of 0.15 pi-mm-mrad. The H- beam will be accelerated to 65 keV and matched into a 2.5 MeV RFQ. Ultimately an upgraded ion source is required to produce 65 mA of H- at 6% duty factor with 0.2 pi-mm-mrad emittance, consistent with the nominal SNS beam power of 2 MW. To generate the H- beam, a radio-frequency driven, magnetically-filtered multicusp ion source is being developed at Berkeley Lab. Extracted electrons are separated from the negative ion beam by a strong dipole magnet located in the outlet electrode and are then deposited on a dumping electrode inside the extraction gap. To compensate for the associated bending of the H- beam, the source is tilted by a few degrees. The design of this ion source is directed towards operation at the required high duty factor. The LEBT section incorporates two electrostatic einzel lenses and has a total length of only 10 cm. With an all-electrostatic system, space charge neutralization, is prevented. Experimental results (including emittance measurements) on the performance of the ion source and the LEBT section operated with different beam parameters will be presented.
* This work is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098
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