Hydrodynamics of ISOLDE liquid metal targets

At ISOLDE, target units are exposed to a driver beam from the CERN proton-synchrotron booster (PSB) with a highly pulsed structure. The instantaneous power during a bunch from the PSB is 12 GW, more than six orders of magnitude higher than the average power on target of 3 kW during a typical physics run in standard beam mode. Observable effects on early liquid metal target units exposed to the PSB pulsed beam included flow of liquid metal into the ion source, broken welds and corroded proton beam windows. To reduce the energy densities for liquid metal target units, the current practice is to spatially defocus the beam and apply a time-staggered extraction mode to the four PSB bunches. Hydrodynamic simulations to qualitatively assess proton-induced transient thermo-mechanical effects such as splashing were carried out with the aim to further improve ISOLDE liquid metal target release properties and lifetimes and to benchmark EURISOL.