Investigation of gas breakdown in cylindrical inertial electrostatic confinement device with inner cage anode

The gas breakdown in the Inertial Electrostatic Confinement (IEC) device has been studied by DC discharge of Nitrogen gas in the pressure range between 0.03 Torr and 0.7 Torr. Paschen curves and Townsend coefficients are obtained in a cylindrical system with inner anode in shape of rods and the outer grid cathode. The breakdown occurs and the plasma is formed at the center of the electrodes. Townsend coefficients are calculated for anode transparencies of 84%, 92%, and 96% (24, 12, and 6 rods respectively). On the left hand side of Paschen curves, the high transparency has a higher breakdown voltage. More electrons are allowed to pass the anode. So, the collisions increase, leading to a slight increment of the first Townsend coefficient (alpha) decreasing of the second Townsend coefficient (gamma) while the ionization efficiency (eta) is not affected. For high reduced electric field E/P, i.e. a high electric field with low pressure, the probability of ionizing collision events decreases. This causes a decrement of alpha while gamma is raised because the ions' energy is not exhausted in collisions at the center. The coefficients alpha and gamma are working in harmony to balance the rates of electrons generated in gas ionization so that the relation between the two coefficients is satisfied. (C) 2017 Elsevier Ltd. All rights reserved.