CONSTRICTION OF THE POSITIVE COLUMN IN A DC-DRIVEN SULPHUR HEXAFLUORIDE GAS DISCHARGE

摘要

We study the constriction of the positive column in a sulphur hexafluoride gas discharge by solving the carrier rate equations and the thermal diffusion equation. The equations are solved numerically and graphs of the electron and ion numbers as a function of distance from the centre of the column are presented. It is shown that the carrier densities go smoothly to zero as we move away from the centre of the column, contrary to some previous calculations. Although the calculations presented here give exact solutions to the differential equations they are computer-time-intensive and it is difficult to explore the whole of the parameter space. To avoid this problem we contract the equations down and solve the new system approximately using a simple model. We show that the simple model reveals the generic behaviour of constrictions in the discharge. The model is compared with the numerical simulations and is used to examine experimental results. Possible modifications to the approximations are suggested. [References: 7]