Broadband RF emission and electron number density measurements of an electric field dominated plasma

The authors have operated a steady-state modified Penning discharge in a magnetic mirror geometry with a 5.7:1 mirror ratio, and a maximum magnetic field on the axis up to 0.4 Tesla. This plasma is electric field dominated, with axial electric fields which trap electrons in an electrostatic potential well, and reach values up to several hundred volts per centimeter. The electron population forms two interpenetrating beams which give rise to the geometric mean and other plasma instabilities. The midplane diameter of the plasma is about 10 cm, and it draws steady-state currents up to 0.5 amps at anode potentials up to 7 kilovolts. Electron number densities were measured using a 27 GHz microwave interferometer, as well as axial and radial Langmuir probes. A factor of two or smaller discrepancy has been observed for localized number density measurements made by the Langmuir probes, when compared with the chord-averaged measurements from the microwave interferometer. Electron number densities up to 3 x 10/sup 10/ electrons per cubic centimeter have been observed