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: Rudimentary attempt
Date: Feb 04, 07:18 am
Poster: Richard Hull

On Feb 04, 07:18 am, Richard Hull wrote:


There is no reason I know of why your little mini fusor should not work.

However, the control of the vacuum is critical, as you must know by now. The minimum point at which I have seen neutrons show up is about 13kv. Good, continuous, easy to detect neutron production begins usually near 20KV.

I assume you used a metered D2 leak into the chamber as the pump ran. Without some sort of vacuum gauge, you can't know much about the pressure/voltage dynamics.

At higher voltges you will require less pressure.

Fusion onset will result in a very hot inner grid. Soft solder (~500F) and even silver solder (1000F) will not be adequate for grid construction.

You have made a great start and the size of your fusor chamber will mean much tighter control over all parameters. I would be curious as to what the limit on voltage would be in so small an environment. The vacuum would have to be very good indeed, this would make the D2 gas load (density) very low and might limit nuetron production a bit.

I would say that for amateur construction, with modest materials and voltages, the best chamber size is in the 6"-10" outer grid diamter range. This allows good high voltges to be reached with little flashover problem, decent gas loads (at voltage), and good, short mean free paths for the deuterons at amateur vacuum levels.(just sub-micron).

Richard Hull

>Point: I'm a complete FF novice...I haven't even read F's patents...I just got fired up by Tom Ligon's article in Analog...and we happen to have most of the necessary equipment lying around (vacuum system, high voltage supply, etc.)
>I've whipped up the crudest pair of grids and put them in a 2.75" Conflat cross. It's relatively tiny...outer grid is 30mm dia...inner grid is 10mm dia. Today I ran it in D2 gas and got a nice-looking glow discharge but the voltage is really low...about 800 volts. Picture available at:
>The long stainless tube above the chamber is a He-3 neutron counter.
>If I apply more drive to the high voltage supply, the current goes up but the voltage stays around 800 volts...and the inner grid gets red hot.
>I tried lowering the pressure and raising the voltage together to nurse the discharge into a low-pressure high-voltage regime. That seems to work for a while. I got up to about 5,000 volts but still no sign of neutrons. At that point, either the pressure falls too low and the discharge goes out...or the inner grid gets so hot that the solder holding it to the Cu lead wire melts!
>Any suggestions?