Low-energy beam transport studies supporting the spallation neutron source 1-MW beam operation

Record productions establish RF-driven sources as the standard for generating high-duty-factor, high-current H- beams for accelerators (Winner of the ICIS 2017 Brightness Award)

The Spallation Neutron Source operates reliably at 1.2 MW and will gradually ramp to 1.4 MW. This paper briefly recalls some of the struggles when the unprecedented project was started and ramped to 1 MW over a 3½ year period. This was challenging, especially for the H^- ion source and the low-energy beam transport system, which make up the H^- injector. It took several more years to push the H^- injector to the 1.4 MW requirements, and even longer to reach close to 100% injector availability. An additional breakthrough was the carefully staged, successful extension of the H^- source service cycle so that disruptive source changes became rare events. More than 7 A·h of extracted H^- ions have been demonstrated with a single source without maintenance, more than twice the single-source quantity of ions produced by any other high-current H^- accelerator facility. Achieving the 1.4 MW requirements with close to 100% availability and record-breaking source service cycles were the basis for the 2017 Brightness Award.

Simulation of H- ion source extraction systems for the Spallation Neutron Source with Ion Beam Simulator

A three-dimensional ion optical code IBSimu, which is being developed at the University of Jyväskylä, features positive and negative ion plasma extraction models and self-consistent space charge calculation. The code has been utilized for modeling the existing extraction system of the H(-) ion source of the Spallation Neutron Source. Simulation results are in good agreement with experimental data. A high-current extraction system with downstream electron dumping at intermediate energy has been designed. According to the simulations it provides lower emittance compared to the baseline system at H(-) currents exceeding 40 mA. A magnetic low energy beam transport section consisting of two solenoids has been designed to transport the beam from the alternative electrostatic extraction systems to the radio frequency quadrupole.