Modelling the evolution of an ion beam through a 3 MV Pelletron accelerator

Abstract: In this work simulations of the LIBAF Pelletron were performed to gain insight into the parameters that govern the machine operation and control. Three simulation packages: COMSOL, WARP and TURTLE/TRANSPORT were employed, and cross-validation of these software packages was performed by test-case simulations. The major components of the Pelletron were simulated on a individual basis to ensure their behaviour was well understood. These components were finally incorporated into a full source-to-exit simulation in COMSOL. Disagreement by a factor of two was found between the beam divergences predicted by TURTLE and the other two packages at an initial energy of 30 keV, for test-case simulations. Good agreement was seen in test-case simulations of the Einzel lens, for the envelopes and focal points, predicted by WARP and COMSOL. A focal point at infinity was obtained for Einzel potentials of between 12.7 and 12.8 kV, for both packages. For the full LIBAF Pelletron simulation in COMSOL, the emittance of the beam exiting the machine was found to be proportional to the beam current. This proportionality indicating that simulations of this type could potentially be used to optimise the accelerator settings for specific user needs. As beam losses were also quantified in the full Pelletron simulations, it is possible to estimate the maximum attainable beam current from the machine, for a given set of user setting, if the current produced by the ion source is known.