Population Inversion in a Recombining Helium Plasma Mixing with Hydrogen Molecular Gas in a TPD-I Machine

Abstract

A high potentiality of plasma cooling and its mechanism are theoretically revealed for a helium plasma which comes into contact with hydrogen molecular gas in the TPD-I machine. The stationary population inversion between the levels n=2 and 3 of the He+ ion, which is due to mixing of the stationary high-temperature helium plasma and the hydrogen molecular gas, is simulated and discussed in comparison with cooling due to the mixing of the plasma and the atomic hydrogen gas. The calculation also shows that the gain per unit length of the He II 164 nm line is ∼ 2 cm-1 for the laser oscillation under optimum initial helium plasma (T e ∼ 30 eV and n e ∼ 3.5 × 1016 cm-3) contacted with hydrogen molecular gas at a pressure of 0.1 Torr.

Pumping system with high specific energy characteristics, designed for an industrial CO2laser

“…The initial temperature of the plasma is considered to be about 1-2eV [23]. This means that gas contact cooling is accomplished on a time scale of several microseconds, which agrees with the simulation of gas contact cooling by Furukane et al[28,29].…”

“…It is considered that the plasma will be expanded more rapidly under low pressure than under high pressure. However, as will he shown in the next subsection, the electron temperature becomes lower in PI, = 6.4 Pa than in P,, = 4.0 x IO-' Pa. As was shown numerically, the plasma in the present experiments is considered to be cooled due to elastic collisions with the residual gas molecules in the expanding plasma area, which is referred to as gas contact cooling [28,29].…”

“…The axial distance from the nozzle z is (U) 8 cm, (6) 15 cm, (c) 22 cm and ( d ) 29 cm. These distances correspond to the gap positions of the coreless coils.…”

“…Although the effect of the magnetic field is not very remarkable, the pressure of the expanding plasma area affects the electron temperature drastically. When the background pressure is low, then cooling by contact with residual gas is not accomplished effectively [28, 29]. ~n e n , since the detection system was caiiiirated absolutely, we determined the electron density from figure 3.…”

An experimental study of stationary population inversion in a cold recombining expanding helium plasma jet

“…When the pressure of the plasma expanding area becomes low, the overpopulation density becomes small in the 4's-3 'P level pair (figure 5 that the plasma will be expanded more rapidly under low pressure than under high pressure. However, as will he shown in the next subsection, the electron temperature becomes lower in PI, = 6.4 Pa than in P,, = 4.0 x IO-' Pa. As was shown numerically, the plasma in the present experiments is considered to be cooled due to elastic collisions with the residual gas molecules in the expanding plasma area, which is referred to as gas contact cooling [28,29].…”