Non-Maxwellian Form of the Electron Velocity Distribution in Nitrogen Plasmas

Changes in the form of the electron velocity distribution with time in the active discharge and in the afterglow of a low-energy nitrogen plasma immersed in a magnetic field, have been investigated. A gated microwave radiometer was used to monitor the radiation temperature of the plasma electrons which drops rapidly from 15 000° to 5000°K following termination of the active discharge. The radiation temperature then remains an order of magnitude higher than that of the neutral gas molecules for a time an order of magnitude greater than the calculated relaxation time of the electron temperature. The magnetic field was swept through a range around the value which produces an electron cyclotron frequency equal to the radiometer frequency. Observation of the radiation temperature as a function of magnetic field strength shows that, for certain values of the discharge parameters, the electron velocity distribution in the active discharge is Maxwellian. In the afterglow, the form of the distribution function is found to change rapidly.