You are seeing what every real doer in this club sees and will learn by the doing anyway, but here goes some answers.
Yes, increasing the voltage at any given pressure will resume glow discharge. Yes, 20kv will make a real difference in how low in pressure you can go. 30KV will allow even more range, etc. Glow discharge is a function of voltage, pressure and ultimately electrode geometry.
One doesn't need glow discharge to do fusion. However, at our level of refinement, in these simple devices, it is demanded. With no dispenser cathode scheme to ionize the gas or ion guns to beam them directly, we must rely on a crude field emission regime and glow discharge to create the deuteron currents needed to do fusion.
At reduced pressures in our devices, this translates into the requirement for very high voltages which thankfully also means more collisional energy and a better position for fusion opportunity on the cross sectional curve of deuterium.
A larger supply can be made up with a voltage multiplier using moderately HV diodes. The current available from such a supply run off 60hz is a function of capacitor size for the most part.
Only an X-ray transformer or a special potential or pole transformer would normally have enough output voltage to do a simple, single rectifier, HV circuit. Here we are back to the question about single, very high voltage standoff rectifiers. Rectifiers can, indeed, be series connected with care, but it is always a crap shoot. In general, the reverese voltage should be on the order of 3 times that of the supply voltage for safety. (i.e. 20kv supply - 60kv of diodes)
I personally prefer that over 20kv, a voltage doubler be considered.
A 15kv transformer will supply about 21kv peak. with a good full wave doubler this could translate to a no load supply of 42kv! Again, the load current and capacitor values will determine the actual output voltage. Four 12kv microwave oven diodes in series for each of the two required rectifiers in such a circuit should be adequate.
Most of the internal wiring can be done with good new and clean neon sign wire. The actual HV lead flying through air to the fusor above 20 kv should be of silicone wire only and 40kv silicone wire can be had for ultra high performance automobile use (racing). I believe J.C. Whitney carries it on spools at about $1.50/foot.
The key to a good supply is to hopefully find a transformer whose center tap (if it has one) doesn't have to be grounded like that in a neon sign transformer.
Good hunting at your hamfest.
Richard Hull
Created on Friday, June 01, 2001 9:52 AM EDT by Richard Hull