Experiments on the Energy Distribution Function in Hydrogen Plasmas

The electron energy distribution function has been measured in typical hydrogen plasmas in a multipole plasma device by an improved alternating-current probe method. The function is found to be non-Maxwellian, containing primary electrons, thermal electrons and groups due to inelastic scattering of the primaries. A characteristic peak due to negative ions in the distribution has been detected and is used to determine the density of negative hydrogen ions. The variations of their density with the densities of thermal electrons and primary electrons have been studied and interpreted. The dependence of the relative intensity of the negative ion peak on the probe material, probe shape, and frequency of the superimposed ac signal has been investigated. The optimum conditions have been determined for using the probe method to measure the negative ion density in plasmas.