Ion Sampling from the Positive Column of dc Discharges in He–Ar Mixtures

Abstract

Measurements have been made of the ion species present in the positive column of dc discharges of 0.05% and 0.5% argon in helium, by sampling through a 35-Il-diam orifice in the wall of the discharge tube. Data for 0.05% argon has been obtained over a current range of 15-90 rnA and for pressures from 3 to 30 Torr. The main ion species observed were Ar+, He+, and He3+' Theoretical analysis combined with measurements of the variation of Ar+ with distance from the cathode, enable estimates to be made of the degree of ionization of Ar, and also an upper limit for the helium metastable particle densities present in the discharge. Metastable density values are, in general, an order-of-magnitude larger than the electron densities.

Cathaphoretic confinement of Zn evaporated into helium and neon discharges

“…However, at a certain distance from the metal source the metal density drops below a critical value, N crit , and its decrease changes from linear to exponential. This behaviour was theoretically predicted in [7] and to some extent experimentally proved for many other gas mixtures [8,9,10]. As can be expected, the characteristics of the Zn confinement are very similar to those of Cd because of the similar properties of these metals [11].…”

“…Here is the flux of Zn + , K 1 and K 2 are the rate coefficients for reactions (7) and (8), v e and n e are the velocity and density of electrons, respectively. σ e v e is averaged over the electron energy distribution function (EEDF) and represents the rate of reaction (9).…”