If plasma effects cause the capacitor to pump itself down, and if the (glass?) dielectric doesn't release too much gas under plasma bombardment, then the pressure within the capacitor might drop quite low.
Here's a 2005 paper where a small crude x-ray generator is made from a
2cm diameter PP plastic syringe pumped down to only 3e-2 Torr, with 2 to 3 KVDC applied. The photos show that it glows brightly. Apparently with close electrode spacing you can get significant x-ray output, even while the pressure is still high enough to give a bright visible discharge. But they did use a 150um Be window to let the soft x-rays get out. (Maybe even a neon sign produces x-rays, but they can't penetrate the glass?)The paper shows a spectrum with a big peak around 2KeV or so, and a tail going up above 4KeV. I wonder if 2KeV x-rays would get through the metal foils and dielectric layers of a stacked-plate capacitor? If they do, then a large stack of layers would obviously contribute to x-ray intensity. But unless hydrogen ions would rapidly get ion-pumped deep into the metal foil layers, this whole plasma pump-down trick might not work with plastic or waxpaper dielectrics.
Simple X-ray Emitter, Murakami et. al.
((((((((((((((((((((((( ( ( (o) ) ) ))))))))))))))))))))))) William J. Beaty Research Engineer beaty chem.washington.edu UW Chem Dept, Bagley Hall RM74 billb eskimo.com Box 351700, Seattle, WA 98195-1700 ph425-222-5066