Fusion Message Board

In this space, visitors are invited to post any comments, questions, or skeptical observations about Philo T. Farnsworth's contributions to the field of Nuclear Fusion research.

Subject: 100 kV technique
Date: Feb 25, 1:55 pm
Poster: Jim Lux

On Feb 25, 1:55 pm, Jim Lux wrote:

Indeed, 100 kV feedthroughs are a pain, as is working with 100 kV in air in the first place. Most of the problems will be on the air side, although you'll have to pay attention to creepage paths and ion deposition on the vacuum side.

However, why not generate your HV in the vacuum. Send in moderate HV AC through a conventional feedthrough, then either transformer it up or use a voltage multiplier, running inside the vacuum chamber.

This might (WILL) require meticulous care in choosing vacuum compatible electronic components, etc., but might save you from having to buy/build HV feedthroughs.

The other thing to consider is that you really only need 50 kV feedthroughs. You'll have to go to a multi grid system because you won't be using the vacuum enclosure as one electrode (but you'll probably be doing that anyway).

Most medical X-ray tubes run at around 110 kV across the tube, created in a bridge rectifier from a centertap grounded transformer, so that the cables and connectors only need be good to +/- 75 kV. An Xray power supply might have other advantages too, since the have provisions for measuring the current, and isolated filament supplies. In fact, as I write this, I think that the Xray supply might be the ideal source, since they regulate the 100 mA current in the xray tube by varying the filament current, and hence the number of electrons. The same would apply in a dispenser cathode approach to a fusor.

The only problem would be duty cycle. Most medical xray machines aren't designed for 100% duty cycle. For instance, mine is rated for 110 kVp at 100 mA for a 2 or 3 second exposure. I don't recall what the power limiting component is (probably the 500 Hz inverter or the NiCad batteries which have to put out 100 Amps at 120V).