Advanced RF-driven H- ion sources at the SNS

The US spallation neutron source* (SNS), will require substantially higher average and pulse H" beam current than can be produced from conventional H^- ion sources such as the baseline LBNL-SNS source. H^- currents of 70-100 mA with an RMS emittance of 0.20-0.35 π mm mrad and a ˜7% duty-factor will be needed for the SNS power upgrade project in 2010. We are therefore investigating several advanced ion source concepts based on RF plasma excitation. First, a generalized discussion of our source development strategy is presented as well as the performance characteristics of a large-plasma-volume, external antenna source based on an AI₂O₃ plasma chamber. The design and results of computational modeling of a high-power version of this source featuring an AlN plasma chamber is subsequently discussed as well as a high-efficiency extraction system necessary for high- current operation.

Introduction

High-brightness H^2014; ion sources are widely used in large accelerator facilities which utilize charge-exchangeFi injection into circular accelerators or storage rings [1]. One such facility, the U.S. Spallation Neutron Source (SNS)**

ORNL/SNS is managed by UT-Battelle, LLC, for the U.S. Department of Energy under contract DE-AC05–00OR22725

[2], [3], [4] employs a Radio-Frequency (RF), multicusp ion source based on a porcelain-coated Cu antenna immersed in the plasma volume [5]. To date, the source has been utilized successfully in commissioning and early operations of the SNS accelerator, delivering 10–40 mA with duty-factors of ~0.1% for periods of many weeks with availability approaching ~100% during later runs. This success can be attributed in part to advances in antenna-coating technology [6].