On the calculation of ion swarm properties by velocity moment methods

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Abstract
The convergence problems sometimes occurring with Gaussian weight polynomial expansions have been investigated, and found to be connected with the weight function only and not with the velocity moment methods per se. A modified isotropic weight expansion method with better convergence properties has been developed and successfully tested for simple cold-gas models and for a 300K Li+-Ar model. For very soft interactions and finite electrostatic fields all moment methods will however apparently fail, and moment methods are therefore useless e.g. in the study of runaway phenomena.