Magnetohydrodynamic velocimetry of a low-pressure plasma jet

Abstract

The velocity of a steady, low-pressure (~0.1 Torr) plasma jet is measured by analyzing the local response of the medium to the action of an external magnetic field set up by two Helmholtz coils placed at the edge of the jet, yielding a field of 0.92 G/A. The induced electric field is measured by two floating-potential electrostatic probes. The mean velocity of the electrons (between 1000 and 5000 m/ s) is found from the generalized Ohm's law. *  10 18 s-1). The last term of the equation represents the ion slip effect, it can be neglected if the Hall parameter: ϖ e ϖ i ν e ν in * is much less than unity, where ϖ e , and ϖ i are the cyclotron frequencies of the electrons and ions, respectively. In our experimental conditions, this quantity ranges between 10-3 for argon and 10-2 for hydrogen. With these orders of magnitude, Ohm's law takes a simple form that will be used to determine the electron flow velocity:

Optical spectroscopy investigation of N2–CH4plasma jets simulating Titan atmospheric entry conditions

“…The strong relaxation of the gas in the diverging region between the throat and the nozzle exit induces a supersonic speed to the gas. The speed of the plasma flow has been measured by Tardy and Dudeck [36] in an earlier work. In pure nitrogen plasma flow, the measured velocity at the nozzle exit is around 5000 m s −1 .…”