Electron temperature characterization and power balance in a low magnetic field helicon mode

Abstract

The electron temperature in a low-field helicon mode has been characterized in the presence of a diverging magnetic field (B0 < 5 mT), using a number of electrostatic probes. At the low pressures investigated (<0.3 Pa) the electron energy probability function (measured with an rf compensated Langmuir probe) shows a depleted tail in both the upstream and downstream regions, with the tail temperature being about half that of the bulk electron temperature. Independent measurements of the tail temperature have been made with a retarding field energy analyser (operated in electron collection mode), which closely match those from the rf compensated probe. A global model is developed to predict the electron temperature, plasma potential and plasma density during the low-field mode, and is found to be in very good agreement with the experimental measurements.