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: Gas densities, tritium production
Date: Apr 08, 5:01 pm
Poster: Richard Hull

On Apr 08, 5:01 pm, Richard Hull wrote:


Scott Little and I were talking over the phone the other day about his RGA (residual gas analyzer) sniffing out tritium produced in our simple fusors. He seemed to think it might not sniff that deeply. I got to crunchin' some numbers and thought you folks might like some info.

We'll make a lot of assumptions here which are idealized and probably not all are realizable in anything but a perfect world.

Assumption 1.

we have a 6" spherical fusor chamber.

Assumption 2.

It is filled with 100% deuterium gas at a pressure of 10-3 torr (1 micron).

Assumption 3.

We have run the system totally valved off for 20 minutes at 25kv @ 10 ma and recorded an average neutron count of 5X10e4 neutrons per second.


Now for some statistics.

1. a 6" sphere has a volume of about 1850 cubic centimeters. Even at a vacuum of 1 micron (nearly one millionth of an atmosphere), there are still ~10e13 deuterium gas atoms per cc. That means about 2X10e16 deuterium atoms are in the chamber

2. The current of 10ma means that we have created about 10e17 deuterons/second and sent them hurtling in towards the central grid region.

3. From the above, it appears we are ionizing each second, more gas atoms than are in the chamber! Not to worry, at these pressures, ion life times are still under 1 second, but more important, most of those deuterons never see the inner grid!!!

4. The mean free path at 1 micron is on the order of 100mm or 4". That barely makes deuterons created out at the chamber walls (ideal spot for max energy deuterons) able to make the inner grid without colliding with other atoms in the chamber. Many of them do. This is both the horror and the glory of high pressure (1micron) fusors. We are reionizing many more gas atoms per unit time than at lower pressures, but we are also having more losers in the bunch who just crash and burn.

5. Based on all the above, we can see we are utilizing more than 100% of the gas load to make deuterons, but for all that, the bulk of them just wind up as heated slow and fast neutrals, slow deuterons, etc due to inelastic collisions.

6. Since we are seeing 50,000 neutrons/second that means at least 100,000 deuterons did useful work each second. That is, 10e5 deuterons out of 10e17 worked for us. The actual figures on efficiency of deuteron production vs. neutron production are 1 neutron per trillion deuterons, or about .00000000001% efficiency.

7. As we can expect 50% of the fusion reactions to yield tritium, we could realize little more than 25,000 tritium atoms/second. Over a 20 minute or 1200 second run time that would mean the total tritium production would be about 3X10e7 tritium atoms. These will be mixed in with the total chamber gas load of 2X10e16 gas atoms or making 1 tritium atom for every billion other gas atoms at the end of the run. So tritium should be about a billionth part of the gas load under the above ideal stated conditions. This should be within the range of detection of a good RGA. I would be prepared however for a realized .1 parts/billion of tritium in a real world situation.

So my fellow fusorite buddies, you see the numbers bear out low efficiency, real easy neutron production at low voltages with simple gear, real tritium production and lots of room for improvement.

I pray that I have made no more than a small order of magnitude error in the above calcs.

Richard Hull