Magnetically-Insulated Baffled Probe

Baffled probes are 'magnetically-insulated' probes used to measure plasma potential and utilize baffles to block the collector on two or three sides. By utilizing the large separation between the electron and ion gyroradii, the baffles are positioned so that the majority of electrons from the plasma are blocked from reaching the collector while the majority of ions are unimpeded. This restriction of the electron flux allows the probe to float closer to the plasma potential since it no longer needs to electrostatically reject electrons. By rotating the probe so that the collector is either directly exposed to a magnetic field line or so that the baffles are able to block incident electrons, the floating point of the probe should change between the regular floating potential to one that is much closer to the plasma potential. Baffle probe studies include the designing of new baffled probes to reduce anomalous electron current that is often seen further behind the baffles than expected.

Schematic of a baffled probe.

This current into the tip of the probe reduces the electron shielding measured on the baffled probe's I-V and new probes with a top cover could greatly improve their performance. At low pressures of neutral gas, the so-called spoke oscillation is observed. This oscillation is shown to drive anomalous current in Hall thrusters and applying a baffled probe to this unstable system could be a way passively measure the plasma potential on time scales that are unavailable to standard Langmuir probes.

Spoke Instability shown with visible light intensity images.