Ion - Gas Collisions during Beam Acceleration

The following paper is an attempt to understand the effects which residual gas in an accelerator beam tube can have on the ion beam passing through it, and on certain other aspects of the accelerator´s performance. The approach to the problem is felt to be the most fundamental. That is: all possible collision processes between injected beam and residual gas are examined (most of the cross-sections are quite well known experimentally1); a uniform axial electric field is assumed, together with a pressure gradient determined by kinetic theory equations for gas conductance assuming the source of gas to be the ion source. From this point on, it is in principle possible to calculate the resulting energy spectra of positive, neutral, and negative beam, as well as backstreaming electrons, evolved when only a positive ion beam is injected. In practice, only a numerical solution of the resulting equations can yield a solution. This solution is carried out, and the results are discussed.