Description of Helium-Plasma Rate Processes by Means of Simultaneous Differential Rate Equations

A set of seven simultaneous differential rate equations which describe both the temporal and spectral characteristics of a pulsed microwave discharge in pure helium is derived. The rate equations describe the plasma characteristics, as well as the light emission, both during and after the application of the microwave power pulse to the discharge tube which is situated in a travelling wave structure rather than a cavity. A computer is used to solve the rate equations and certain of the rate constants are varied so as to obtain the best agreement between the computer solutions and the experimentally observed light emission characteristics. By doing this, two types of information become available. First, one may obtain approximate values of rate constants which are otherwise very difficult to measure and second, the time variation of variables such as electron temperature, metastable density, molecular ion density, etc. may be obtained with some degree of confidence. The role of the processes He+ + 2He ?? He2+ + He, Hem + Hem ?? He+ + He + e + KE, and Hem + Hem ?? He2+ + e + KE in producing the afterglow is examined. The computer solutions indicate that the first two processes may be ignored and that the conversion frequency for the third process is approximately 5x108cm3/ sec although the rate equations are somewhat insensitive to variations in the value of this conversion frequency.