Emissive probes for plasma potential measurements on the SERT II spacecraft

Two emissive probe (hot wire) systems having different measurement requirements have been designed, fabricated, tested, and delivered for use on the SERT II spacecraft. With emissive probes, emitted electrons are drawn back to the probe when the probe is positive (with respect to space potential at the probe location) and the collected electron current from the plasma should be unaffected by the emission. When the probe is negative, electrons are emitted from the probe, and by measuring the space-chargelimited current flow, the value of space potential can be determined.