Folks,
We still have to determine the intermediate electrode aperture diameter, maybe 2-3-mm? I "drilled" the molybdenum insert, but used a sharp center punch to make the hole. The metal was only 0.005" thick at the apex of the conical cavity and molybdenum is brittle. The resulting aperture is about 0.020" or close to 0.5-mm vs. 0.4-mm that we had planned. I'll end up making another insert and trying out the new 0.4-mm drill bits (that are amazingly small).
Below is a diagram of the prototype ion gun so far. I'll do some more work today and report the progress at a later date. Best of luck on all your efforts.
Regards,
TIM