Effect of a Magnetic Field upon the Saturation Electron Current of an Electrostatic Probe

Abstract

Some experiments are performed in several kinds of discharged plasma to investigate the influence of a magnetic field upon the saturation electron current of an electrostatic probe. The apparent electron density N e ' and the positive ion density N + are calculated from the saturation electron current and the positive ion saturation current respectively and the ratio N e '/ N + is plotted against ωτ (ω: the angular cyclotron frequency of electrons, τ: the mean collision time between electrons and molecules). The curve is found to show a clear dependence on the gas pressure, and when the ratio is log -log plotted against the magnetic field, it gives a nearly straight line, showing N e '/ N + to be 0.1 at about 1,000 gauss. Since the positive ion saturation current is hardly influenced by the magnetic field of the order of several kilogauss, it is apparent that these properties are based upon the behavior of the electrons around the probe. A theory developed by Bohm and others is applied here to explain the experimental results.