Non-hydrodynamic Contributions to the End Effects in Time of Flight Swarm Experiments

Abstract

The hydrodynamic part of the distribution function of a swarm is separated from its nonhydrodynamic part using a projection operator, leading to an explicit expression for the timedependent transport coefficients. These are then related to a time of flight experiment. The contribution from non-hydrodynamic effects to the measured drift velocity is shown to be a power series in 11 d, where d is the drift length. A calculation based on an exactly soluble Fokker-Planck model shows that the correction to mobility measurements of lithium ions in helium due to non-hydrodynamic effects is of the same order of magnitude as those observed experimentally.