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: Minimum fusion energy? Voltage?
Date: Aug 18, 10:47 am
Poster: Richard Hull

On Aug 18, 10:47 am, Richard Hull wrote:

>Thanks for the excellent information, Richard.
>Just a couple of quick questions that I have been wondering about for some time:
>>We make a tritium atom in 50% of all the successful fusions. This will, over time spike our reactions slightly to burn in D-T mode.
>Why is the spike from D-T only slight? As the cross section for D-T is many times higher than D-D, it would seem that all of the T that is generated should burn rather quickly - unless it excapes from the plasma permanently.
>Since the T created from the reaction would carry off about a quarter of the total energy, perhaps it is energetic enough to escape the electrostatic confinement and be be entrained in the reactor walls? If so, a reactor that has been in operation for some time should have a radiation profile due to the beta decay of T, although it would certainly be small.

Good thinking and I used to look at it much the same way.

Let us say we have a 6" diameter fusor (fusor III for example). Let us also say we are actually getting 50,000 neutrons/second. This also means 50,000 tritium atoms/second are being produced. In a reasonable 10 minute run that would mean about 30 million tritium atoms are now extant in the chamber. The chamber is ideally (never happen) loaded with pure deuterium gas to a pressure of about 3 microns. There are ~10e13 molecules/cc at this pressure. Our 6 inch chamber contains about 2000cc of gas or about
2 x 10e16 deuterium atoms. This gives a mix ratio of D to T of about 1 billion to 1!!!!!!!

The chance of a single D-T fusion after or during a really long run is virtually ZERO! The normal mix in fusors is 50:50. We are about 10 quadrillion tritium atoms short of the ideal mixture!!

Likewise the beta signature of Tritium decay is also near extinction. With a 12.3 yeaar half life we would expect 15 million of those atoms to go bye-bye during this period. That works out to about .04 betas/second or 2.4 beta's minute. With the really good insturments and carefully taken background level data, this could just be detected and be considered statistically significant. Nautrally, this could only be detected IN CHAMBER. The tritium's beta is one of the weakest known at 12kev average energy.

Nice try, but the math kills many aspects of your idea.

>What is the total accumulated time for neutron production on your fusor? I believe I remember reading that you have measured one of your fusors for radioactivity but found none- were you looking specifically for beta decay?

Yes, I did, but you can't use any known instrument to measure this beta. You must turn the chamber into its own internal reading geiger detector or proportional counter. I did this and, unfortunately, still had too low a vacuum inside to take meaningful data. Geiger systems and proportional systems work in the 5 torr or higher range.. I will work with this more in future.


>What is the highest voltage that you have ventured or planned? From the little work that I have done with my paired Tesla coils, I know that arcing becomes very significant above 50K volts. BTW, my two coils are counterwound and can give a total potential of well over 500,000 volts, but I don't see any way to safely channel that into a fusor.

Tesla coils can't provide the current needed for fusor operation and they would be horribly detuned due to the internal capacitance of the fusor.

The Farnsworth folks stuffed as much as 140kv into a 6" fusor! If you ever get to see their Mark II unit in the "pit" it looks like a dis-emboweled warp drive core. All the HV insulation and huge glass coulmns needed to allow such voltages to be introduced into such a small volume is a stunning thing to see. Many of their top insulators were huge buckets of porcelin filled with oil. One looks to be 30 inches in diameter and about 15 inches deep with a huge HV cable entering it. All this for a diminutive 6" ball perched underneath.

I plan on going up to about 80kv long term, but am a way away from that now.

Richard Hull