Modelling Plasma Formation and Evolution from Beam Strikes on Advanced Photon Souce Upgrade Collimators

Machine protection at the Advanced Photon Source Upgrade (APS-U) storage ring (SR) will necessitate whole beam dumps capable of absorbing energy from 200 mA, 6 GeV, ultra-low emittance beams 1 . These beams will deliver acute doses of 30 MGy within 10-20 microseconds, and initial studies suggest that such rapid heating generates hydrodynamic expulsion of collimator material 2 . Subsequent emission patterns indicate the presence of plasma formation. For some bunch configurations, instantaneous magnetic fields can reach 1 T, which may constrain plasma motion within the strike region. We investigate the evolution of the irradiated material using FLASH, a publicly-available multi-physics code with robust magnetohydrodynamics solvers 3 . We first define transition conditions for vaporization and fluid release, and evaluate the resulting fluid flow for a range of beam parameters and release criteria. We then consider strategies for incorporating magnetic field source terms originating during bunch passage. Bunch patterns and strike frequency are also examined as input conditions for determining the strength of the plasma response.