Conclusions

The MOT tank supply is reliably working: here are pros and cons.

Pros:

• costs nothing: just get the components from a couple of broken microwave ovens
• high current: you can easily find 500W MOTs (0.25A) or 1000W MOTs (0.5A)
• DC or AC output: run the MOTs in-phase and you'll get 4kV DC. Run them out-of-phase and you'll get 8kV AC (that is, a 11kV pulsed DC @ 50 Hz)

Cons:

• heavy: 3 MOTs weight almost as 2 microwave ovens
• small voltage: only 8kV max., without the shunt MOT
• high current: 0.25A will stress your spark gap unless you use a good design or a rotary

A higher break (repetition) rate has showed to be much more important than a higher break voltage. For a higher break rate, a shorter gap is needed and more power is dissipated in it. Thereafter the RQ static gap gets so hot that limits the highest feasible break rate: this is, of course, mostly a result of the high current the MOT tank is capable of supplying to the spark gap.

A better solutions for the spark gap has turned out to be a Rotating Spark Gap (RSG). My RSG is capable of a top break rate of 350 breaks/s, provides a higher and more reliable break/quench rate than the RQ gap and allows for longer streamers into air to be generated.

At today (2.17.2000) my TC has been hosted over one year at the Helsinki University of Technology, High Voltage Laboratory, and has been used weekly in demonstrations to students and visitors. All of it is still perfectly functional.