Your pulsing on then off, so normal error amp designs wont work, as theyll be too slow getting up and down.......so just use say a constant off time controller, and pull its reference up and down......COT because no SHO. (sub harm osc)........tweak it right with a micro say....what current has to be drawn from the pulses?
Arc detection...thats just where you detect the constant current of the arc, i think, but wont the arc be extinguished in the pulse off intervals anyway?