Gas pressure effect on plasma transport in a magnetic-filtered radio-frequency plasma source

Volume negative ion production relies on a magnetic filter (MF), where the plasma downstream of the MF is characterized by a strip-like pattern that consists of a bright and dense plasma region. In this work, we study, in a radio-frequency plasma source, the effects of operating pressure on this strip. This investigation, conducted using a Langmuir probe, shows that the plasma uniformity might be controlled through the gas pressure. Moreover, the operating pressure determines on which hemi-cylinder (side of magnetic field lines) the strip forms. This side inversion of the high-density plasma hemi-cylinder is due to an inversion of an ambipolar electric field that changes the E × B drift direction.