Effect of Self-Magnetic Forces on the Anode Mechanism of a High Current Discharge

When a dc discharge is operated between a central cathode and a ring-shaped anode at currents up to 6 × 103 A and pressures on the order of a few torrs, the stable discharge regime is found to be limited. The anode fail voltage is determined experimentally from calorimetric and potential measurements. In a wide range of operating conditions its variation correlates well with the parameter J
₂
/&xle41; where J = current, &xle41; = mass flow rate through the discharge. With increasing values of J
₂
/&xle41;, the anode fall increases continuously from small negative values, through zero, and up to moderate positive values. Then, within a small increment of J
₂
/&xle41;, it jumps to values on the order of the ionization potential of the gas. A theoretical two-dimensional description of the flow field indicates that the self-magnetic forces, which are proportional to J
₂
, pinch the gas towards the discharge axis, thereby leading to particle starvation in the vicinity of the anode. Based upon the results of this study it is shown that, as a consequence of the altering boundary conditions, which are characterized by the parameter J
₂
/&xle41; the anode responds by adopting different operating modes. Existing theories yield values for the anode fall which are in good agreement with experimental data.