There are lots of RF based plasma sources around. Someone at LLNL has a very bright deuteron source using some permanent magnets and a fairly large RF generator.
As far as using a microwave oven, what you basically need is a cavity that you run your gas into at low pressure. There is an interesting device called the PlasmaPreen that is basically a plasma etcher made with a microwave oven and an upside down pyrex baking dish (Well.. the fit and finish is substantially better.. but that's the idea). Steve Hansen's "the Bell Jar" had a description of several microwave oven based plasma CVD devices (essentially a glass tube sticking through the side of an oven.
Ionizing low pressure gas with a magnetron is easy. The tricky parts are: 1) Making sure the microwave energy stays where it is supposed to and doesn't radiate where it shouldn't (damage threshold for eye tissue is kind of low); 2) getting good efficiency (which may not be a real issue, but does influence whether you burn up your magnetron inadvertently; and 3) controlling the process repeatedly.
If you want to ionize gas in a tube, the easiest way would be to make a cylindrical cavity resonant at 2450 MHz with the tube running down the axis, and connect up your magnetron, through a port in the side of the cylinder. Start at low power, and adjust the length of the cavity (sliding end plates is the easiest way) for best coupling to the gas. The real problem is that as the gas starts to ionize, its conductivity changes, which changes the tuning of the cavity.
Created on Sunday, February 04, 2001 12:41 PM EDT by James Lux