Alright, so it sounds like my path forward with an arduino to run in closed loop is:

1) The arduino knows the voltage between the work and the electrode.

2) The arduino opens the mosfet, behind which we have our capacitors. Voltage builds in the spark gap.

3) The arc initiates at about 9.5v. Then, the arduino holds the gate open for the specified time - for example, 10us.

4) Then it allows the gate to close, and it waits for the specified time - for example, 30us.

5) The process repeats.

The way I'd link this in with LinuxCNC is:

1) LinuxCNC moves the electrode closer to the work.

2) The arduino tells it to stop once the arc initiates.

3) The arduino tells it when it's okay to move again.

4) LinuxCNC runs the feed in reverse, backing the electrode away in the direction it came.

5) The process repeats.