The energy of ions bombarding the vacuum chamber walls. Elliptic beams

In high intensity positively charged beam machined the beam intensity could be limited by the ion induced pressure instability. This is a phenomenon occurs when residual gas molecules can be ionised and accelerated towards beam chamber walls causing ion stimulated gas desorption and residual gas density increase. Under certain conditions residual gas density can increase to such values when the beam loss rate becomes unacceptable. To mitigate this phenomenon, a vacuum system should be properly designed to provide sufficient pumping at correct locations, this includes an accurate gas dynamics modelling of beam vacuum chamber. This model requires a number of input parameters, among whose the energy of the ions bombarding vacuum chamber walls is the most critical one. In the previous paper the energy of ions bombarding the vacuum chamber walls was studied for round beams. This paper is reporting on how the elliptic shape of beams affects these results. •Ion induced pressure instability model requires average energy of ion hitting the walls.•The average energy of H2+, CH4+, CO+ and CO2+ was calculated for elliptic beams.•The average energy studied as a function of beam various parameters.•Model for calculating the energy of ion bombarding vacuum chamber walls is provided.•Results are compared to round beams.