Recent empirical tuning of the Spallation Neutron Source injection system has produced new injection kicker settings, new time-varying waveforms for each of the eight injection magnets forming a closed four-bump in each plane, for the proton accumulator ring. These new settings deliver beam parameters consistent with target requirements for beam size and peak density, and identical RMS beam sizes at upstream diagnostics. However, beam halo has been reduced from previous settings providing the same RMS size, as evidenced by a significant temperature reduction on halo-monitoring thermocouples surrounding the proton beam window that separates the accelerator vacuum from the helium-filled target environment. In this work we use PyORBIT, a PIC code developed at Oak Ridge National Laboratory, to simulate the injection process for the previous settings, and the newly identified working point to gain insight into the likely source of the halo reduction and investigate further improvements to injection tuning.

Recent empirical tuning of the Spallation Neutron Source injection system has produced new injection kicker settings, new time-varying waveforms for each of the eight injection magnets forming a closed four-bump in each plane, for the proton accumulator ring. These new settings deliver beam parameters consistent with target requirements for beam size and peak density, and identical RMS beam sizes at upstream diagnostics. However, beam halo has been reduced from previous settings providing the same RMS size, as evidenced by a significant temperature reduction on halo-monitoring thermocouples surrounding the proton beam window that separates the accelerator vacuum from the helium-filled target environment. In this work we use PyORBIT, a PIC code developed at Oak Ridge National Laboratory, to simulate the injection process for the previous settings, and the newly identified working point to gain insight into the likely source of the halo reduction and investigate further improvements to injection tuning.