Direct indication technique of plasma potential with differential emissive probe

We present a new method of plasma potential measurement with a differential emissive probe. The dc heated probes are combined with a feedback loop control circuit to measure plasma potential automatically. In addition, it is shown that connecting to the central point of the filaments reduces the effect on the emissive currents of voltage drops across the filaments. The decay time constant of half-cycle heated emissive probe current during the off heating cycle is shown to depend on the initial emission current and on the bias voltage.