Electrical characteristics of breakdown phase of a wire ion plasma source

Summary form only given, as follows. The wire ion plasma source (WIPS) has the potential as a high-density-plasma source and a large-cross sectional ion source that can be used for the secondary emission electron gun. The WIPS is a cold-cathode gaseous discharge device based on the low-pressure wire discharge. The anode is a thin tungsten wire (/spl phi/0.2 mm). The cathode consists of a stainless steel cylinder (40 mm i.d., 100 mm long) which is set coaxially to the wire anode and the plates having central apertures (/spl phi/20 mm) at both ends. This configuration produces not only a radial logarithmic trapping potential but also an axial one for electrons, and permits low-pressure (/spl sim/10/sup -2/ Torr) gaseous discharge to occur with very low applied voltage (/spl sim/1 kV). The Townsend theory gives a good description of the avalanche mechanism of breakdown with the first Townsend coefficient. However, for the case of low-pressure WIPS where the mean free path of electrons is comparable to the distance between the electrodes, a steady flux of electrons can not be established and the first Townsend coefficient obtained for the uniform electric field is not adequate. Therefore the characteristic of dc breakdown voltage of the low-pressure wire discharge in helium was calculated numerically using a Monte Carlo technique. The calculated breakdown voltage is about 800 V at the gas pressure of 20 mTorr, which is close to the measured value of 700 V, and is inversely proportional to the gas pressure.