H− ion source research and development at the Oak Ridge National Laboratory

The U.S. Spallation Neutron Source (SNS) is a state-of-the-art neutron scattering facility delivering the world's most intense pulsed neutron beams to a wide array of instruments which are used to conduct investigations in many fields of science and engineering. Neutrons are produced by spallation of liquid Hg due to bombardment of short (∼1µs), intense (∼35 A) pulses of protons delivered at 60 Hz from a storage ring which is fed by a high-intensity, 1 GeV H− LINAC. This facility has operated almost continuously since 2006, with ion source performance increasing over those years, and currently providing 50-60 mA of H− ions with a duty-factor of 6% for maintenance-free runs of ∼120 days with near 100% availability. Ion source research and development at ORNL has played a key role in enabling and supporting these achievements: this report provides some historical highlights of this effort, describes our current ion source testing facilities, discusses the goals of the program and finally provides a snapshot of some of our ongoing R&D activities. In particular, we have recently simplified and improved the reliability of the plasma ignition gun for the external antenna ion source which is discussed in detail.