High-speed transverse flow of atoms in a high-current, low-pressure discharge

Abstract

The influence of the supersonic transverse flow of atoms on properties of a high-current, low-pressure discharge is investigated for the first time. Such a discharge is used in particular, in powerful CW ion lasers. The theory of the discharge of this type is suggested. The equations for the electric field and the density profiles of atoms and ions in plasma were obtained and solved analytically. The flow velocity, temperatures and radial intensity distributions of the spontaneous emission of ArI and ArII were measured. It was shown both theoretically and experimentally that, unlike the discharge in a motionless gas, the distributions became asymmetric. Moreover, the ion density maximum was displaced with respect to the discharge axis opposite the flow, while in a high-pressure discharge the charged particles are carried away with the flow.

High-power CW UV Ar++laser with a transverse gas flow

“…In this case expression ( 2 ) is invalid because the electron and ion pressures must be taken into account. On the other hand equation (2) may he used with V, changing to V i at the discharge axis only where the directed flow of ions is zero and the total flow of heavy particles is equal to the atomic flow [7]. Hence, measuring V i one obtains an estimation of the neutral atom density N i near the discharge axis.…”

“…Under the strong ionization condition it is necessary to take the depletion of atoms at the discharge axis [9] into account. The transverse flow of atoms may lead to the asymmetry of the discharge [5,7]. DTF theory [lo] gives a connection between mass How rate Q , asymmetry of the discharge AF and flow-ionization parameter y (2y is the ratio between the How of ions from the plasma and the flow of atoms to the plasma)…”

“…For example, the gas heating near discharge decreases the asymmetry. Furthermore, the onedimensional model [7,10] does not take into account a momentum loss on discharge tube walls, which may be significant in the free fall regime. Thus the further theoretical and experimental study of a pressure balance in an argon laser is necessary.…”