A Method for Measuring Fast Time Evolutions of the Plasma Potential by Means of a Simple Emissive Probe

A method is presented for obtaining the temporal evolution of the plasma potential, which is assumed to be given by the floating potential of a simple emissive probe. The construction of the probe is also described. The method avoids the slow time response of the usual technique where the floating potential is measured across a high resistance.

During each sweep of the probe voltage, the changing of the sign of the probe current, which is sampled at a specific time, gives rise to a negative pulse, driving the pen-lift of an X-Y recorder. Since the real floating potential is measured where the probe current is zero, the disturbance of the plasma is kept as low as possible.