Using Langmuir Probes to Measure Ion Velocities in Pyrotechnic Plasmas

摘要

The very fluctuations that often complicate measurements of plasma parameters can be used to measure ion velocities in pyrotechnic plasmas. When burned in a vacuum, many pyrotechnic devices will form exhaust plumes that are hot enough to contain small quantities of singly ionized atoms. This pyrotechnic plasma can be maintained in the laboratory for only a relatively short period of time because the chamber fills within several seconds, eliminating the desired low-pressure environment. Furthermore, the fluctuating intensity of the burning pyrotechnic causes correspondingly large fluctuations in the plasma. These fluctuations make dependable determinations of plasma parameter values extremely difficult. Under these conditions an old standby of plasma physics - the Langmuir electrical probe - can provide surprisingly reliable estimates of the average ion velocity in the pyrotechnic exhaust plume (1). The variation in the protechnic's rate of combustion creates concentrations of ions. These concentrations, or ion clumps, are tracked as they escape the reaction chamber; by measuring the time it takes one of these clumps to traverse a known distance, the ion velocity within the plume can be estimated. Keywords: Plasma parameters; Pyrotechnic devices; Langmuir electrical probe; Reprints. (jhd)