All I’m saying is that the electrode forms a fairly effective counter-current heat exchanger. This makes it difficult to remove waste heat.
One way to avoid this problem would be to use decaborane as the coolant. Removing the hot decaborane (minus the minuscule portion burned) thru a hole in the base plate. This could then be cooled and sent thru again. The chamber could be maintained at any pressure.
And where the decaborane exits the electrode near its top into the chamber. The exit ports could be angled. Swirling the gas in the chamber. Angular momentum.