Experimental Study of the Creation of a Fire-rod I: Temporal Development of the Electron Energy Distribution Function

Abstract

Positive voltage steps are applied to a planar electrode (collector) immersed in a magnetized discharge plasma column with its surface perpendicular to the magnetic field lines. If the voltage step and the neutral gas pressure are high enough additional ionization occurs in front of the collector and a fire-rod is created. Time resolved measurements of the plasma response are performed by a one-sided plane Langmuir probe using standard boxcar technique. The temporal development of the electron energy distribution function after the application of a positive voltage step to the collector is measured by a one-sided plane Langmuir probe. In a magnetized plasma the electron energy distribution function is proportional to the first derivative of a plane Langmuir probe characteristics. It is found that immediately (∼1 μs) after the application of a positive voltage step to the collector a short lifetime electron population is created. This electron population disappears in approximately 2 μs. It is related to the anomalously large initial electron current collected by the collector “current overshoot”. When the initial current overshoot to the collector is terminated, a high potential (anode) plasma starts to form in front of the collector if the voltage step and the pressure are high enough. The formation of the anode plasma electron population is followed experimentally.