A helium plasma simulator

The results of an investigation of the plasma parameters generated by a large V-groove cathode discharge are presented. Stable plasmas with electron densities up to 2×10¹²cm^-3have been obtained in a 30-cm diameter chamber. The electron temperature is about 1200°K and is independent of discharge current and gas pressure over the range, 0.3 to 0.9 torr. The discharge operates in much the same fashion as a conventional brush cathode discharge but with lower operating voltage for equal current densities. It is shown that the plasma is beam generated and the dominant electron loss mechanism in the steady state is electron-ion recombination. However, although most electrons are lost by recombination, diffusion losses still play a strong role in determining the electron density profile. Some measurements of primary electrons in a helium negative glow are presented. The measured flux of the high energy electrons is an exponential function of pd/V²where p is the helium pressure, d is the distance from the edge of the cathode fall and V is the discharge voltage. Some data on microwave noise radiation near the plasma frequency are also presented. In particular, the noise radiation near the cathode is shown to be proportional to the flux of high energy electrons near this electrode. Data are shown which correlate the high energy flux and the peak noise radiation.