How to make an automatic supply of electrodes?

Question

Do it yourself

There are 2 electrodes in the vacuum chamber. There is a 1mm gap between them. The gap is visible through the window. Between them I get nanotubes and fullerenes.
When the arc is working, the “-” electrode, for obvious reasons, grows, and the “+” shortens and they also burn out. Thus, the interelectrode gap escapes from the field of view and increases.
We need a solution for a constant supply of electrodes (there are handles on the camera). Control - through the window.

Answer 1

turn the knobs with a stepper motor

Answer 2

The distance between the electrodes can be (at a given arc current - is it stabilized?) Determined by the voltage drop across the interelectrode gap. Determining the location of the arc is more difficult. I would put a screen and two photodetectors - when the arc is displaced from its correct location, one photodetector will be illuminated more strongly, and the other will be obscured by the screen. And as an actuator - two motors (stepping or DPM-20 - the latter are good because they can work in a vacuum) with suitable gearboxes to ensure the required accuracy. The controller itself is easy to implement on a microcontroller that has an ADC on board (yes, even on an arduino).