Plasma Potential Control in a Magnetized Plasma Column Using a Thermionic Cathode

The ability to drive the plasma potential in a magnetized plasma column using strongly negatively biased emissive cathode is experimentally demonstrated. By analysing an extensive experimental dataset, and in particular the evolution of the radial profiles of the plasma parameters (plasma density, electron temperature, plasma potential) obtained for various background magnetic field and neutral filling pressure, we first show that current injection from a negatively biased cathode offers an additional level of control as compared to a cold cathode. The radial potential drop across the plasma column, i.e. perpendicular to the magnetic field, is observed to be proportional to the current injected at the cathode. The experimental observations are in excellent qualitative agreement with recent theoretical predictions (Trotabas and Gueroult 2022 Plasma Sources Sci. Technol. 31 025001), in particular for the scaling B2/nn of the plasma potential drop with magnetic field B and neutral filling pressure nn. However, the experimental dataset also reveals the existence of a strong electron sheath (up to a few times the electron temperature) at the outer edge of the plasma column, which is not currently included in the modelling.