Characterization of a Hollow Cathode Plasma with Magnetic Fields

Ionization instability and turbulence in the plume of sub-ampere hollow cathodes with applied magnetic field

“…The results suggest that an applied magnetic field leads to a decrease in axial electron motion along the cathode-anode gap, despite an increase in classical transport due to larger densities at higher B. The rapid reduction in the anomalous transport and overall decrease in the ionization frequency at larger B are in agreement with previous measurements for high-current cathodes [11,25] proving that the magnetization of electrons in the plume of a cathode operating in plume mode changes not only the macroscopic plasma parameters but also affects the ionization instability and turbulence content. To better picture the dependency between the anomalous transport and plasma parameters under an applied magnetic field, the following section presents the evolution of key plasma property over the time-scale of the ionization instability.…”

“…in a more collimated plasma beam. Another study [11], however, depicted a different situation. Their magnetic field applied around the cathode and the plume seemed to induce first a drop in the anode current oscillations, followed by an increase at B > 5 mT, when the cathode was initially in plume mode operation.…”

“…In order to replicate the magnetic field topology and strength during cathode standalone testing with external anodes, magnetic field generators are employed. The magnetic field is produced by magnetic coils placed usually behind or around the anode [5,6] or around the cathode and/or the plume [7][8][9][10][11][12]. It was observed that an applied axial magnetic field did not change only the morphology of the plume, suggesting electron magnetization and changes in ionization [9,10], but also affected the discharge stability and the main oscillatory phenomena in the plume [5,10,11].…”

“…The magnetic field is produced by magnetic coils placed usually behind or around the anode [5,6] or around the cathode and/or the plume [7][8][9][10][11][12]. It was observed that an applied axial magnetic field did not change only the morphology of the plume, suggesting electron magnetization and changes in ionization [9,10], but also affected the discharge stability and the main oscillatory phenomena in the plume [5,10,11]. It was previously shown for high-current cathodes, operating in excess of 1 A [13], that the existence of an axial magnetic field led to the emergence of drift instability due to gradients in plasma density transverse to B and magnetohydrodynamic (MHD) kinks and helical modes, as the current exceeds a certain threshold.…”