Emission Coefficients in Helium

Željka Nikitović, Aleksandra Strinić, Vladimir Šamara, Gordana Malović, and Zoran Petrović
Institute of Physics, Pregrevica 118, 11080 Belgrade, Serbia and Montenegro. E-mail: zeljka@phy.bg.ac.yu

Abstract
We have presented measurements of emission coefficients for two levels of helium at high E/N values. Measurements were performed in a drift tube which consists of a pair of plane electrodes, with a diameter of 79 mm at a distance of 14.7 mm, placed inside a close fitting quartz tube. The cathode was made of stainless steel and the anode of graphite so that backscattering of electrons from the anode is minimized. The self-sustained Townsend discharge between 1 10^–19Vm² and 3.3 10^–18Vm² was maintained by running low current discharges at pressures between 5 10² Pa and 1 10² Pa, respectively. The absolute emission coefficients were determined from the measurements of the optical signal at the anode.

Key words: helium, spatial profiles, ionization and emission coefficients