Velocity distribution functions of Na+ ions drifting in helium, neon and argon

Abstract

Measurements are reported of the velocity distribution functions of room-temperature Na+ ions drifting in helium, neon and argon gas under the influence of an electric field at E/n in the range 16-261 Td. The distributions were found to become wider, have larger RMS velocities and become more skewed toward higher velocities as E/n was increased. They also were shifted increasingly further from the velocity space origin with increasing E/n. The ion-to-neutral-mass ratio was found to be an important parameter in determining the properties of the distributions. The experimental results were used to evaluate the accuracy of theoretical analytic expressions for the velocity distributions.