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: Re: 100 kV technique
Date: Feb 25, 2:56 pm
Poster: Pierce Nichols

On Feb 25, 2:56 pm, Pierce Nichols wrote:

>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.

I've actually considered this technique myself but I think the cost of vacuum-rated electronic components and plus the additional chamber size and so on would be more expensive than the larger feedthrough.

>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.

I agree with you on this -- it sounds like it would be a dandy way to do it, and much safer than mucking with it myself.

>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).

The fusor should come to steady state in that time frame, so you can do your science and get out. I don't think the duty cycle is necessarily a big deal.