Simulation of electron focusing by anode microprotrusions in gas discharges of high pressure

Abstract

Numerical simulation of the electron flux focusing by an electric field of a microprotrusion on the anode surface was carried out. A conical microprotrusion with a height of 10 μm and a base radius of 5 μm was considered. The space region near the anode was assumed to be filled with atmospheric pressure molecular nitrogen. The initial energy of the electron flux was set in the range from 0 eV up to 10 keV. The electric field near the microprotrusion was varied from 50 kV/cm up to 1 MV/cm(disregarding the electric field enhancement factor). Using numerical 2D Monte-Carlo model, the dependence of the electron flux focusing efficiency on the electron initial energy and the electric field strength near the microprotrusion was studied. The focusing efficiency was the ratio of the electron current density at the anode to the initial current density of the simulated flux. It was found that, in vacuum, the focusing efficiency did not exceed 18%. In nitrogen of atmospheric pressure, the current density could increase up to 3.5 times compared to its initial value. The optimal conditions for electron focusing were: the field strength near the microprotrusion – ~250 kV/cm, the initial electron energy – ≤250 eV.