He-Ar Mixtures: The Effect of Metastables on the Transition from Ambipolar to Free Diffusion

Temporal measurements of the electron density and ion wall currents in helium-argon mixtures in which ${\mathrm{Ar}}^{+}$ is the dominant ion show that the transition from ambipolar to free diffusion is identical to that previously measured in pure helium by Gerber and Gerardo. This establishes that helium metastables did not influence the decay of the electrons and ions, as was suggested by Gerber and Gerardo, and thus cannot account for the difference between experiment and theory. The zero-field mobility of ${\mathrm{Ar}}^{+}$ in He was found to be ${\mu }_0=22.4\mathrm{}$ ${\mathrm{cm}}^2$${\mathrm{V}}^{-1\mathrm{}}$${\sec }^{-1\mathrm{}}$.