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: Building a Fusor as an EE Senior Project
Date: Sep 08, 09:41 am
Poster: Richard Hull
On Sep 08, 09:41 am, Richard Hull wrote:
>While this post is intended primarily for Richard Hull.......snip.......... I was wondering about how one can get deuterons up to fusion energy by accelerating them down a potential of 10^4-10^5 V.
I have answered Gerald privately, but feel that this is important enough to post openly.
The virtual cathode and other virtual electrodes are still hotly debated. Farnsworth held this virtual cathoding to be happening in his machines in the 60s. Most fusor proponents say they are indeed formed. The old tokomak crowd says they are dreaming. The problem would nomally be settled by probing the plasma, (Langmuir probe) but the perfection of the spherical concentric fields is destroyed and upset by probing, thus, another method might be found. Recently, I am told, a researcher under Miley at the University of Illinois, Urbana has published a paper in which he claims to have verified the virtual electrode field view using non intrusive techniques. I have not seen the paper yet, but it would be worth investigating.
Finally, as regards to how we get to fusion energy in the fusor......
It is known that when an electron or an ion is accelerated through a potential gradient, that the energy at the end of acceleration is that same potential difference in electron volts. Let us look at, say, 20kv potential on the two grids. Assuming zero energy at start and a deuteron ionization at the outer grid, a charged particle would have 20kev of energy at the central grid.
The tokomak folks have bamboozled the public with "new speak" in temperatures of degrees kelvin. Tom Ligon speaks to this in the fusor video.
The equivalence is 1ev = 11,400 degrees kelvin. Thus, on our kitchen table, a 20kv fusor will be producing 228 million degree deuterons at its best. As the fusor relies on collisional processes in the poissor, we can double that to nearly 1/2 billion degrees kelvin! Fusor temperatures and energies are reached and exceeded in the simple fusor. Sounds impressive as hell don't it!? You, too, can bamboozle.
In the old days (1930s) before hot fusion, nuclear physicists always used electron volts to express the energy of any particle. (they still do) As Tom Ligon notes, the tokomak folks say "we are reaching 500 million degrees kelvin!!!!", but go into their lab and ask them what their dueteron enrgies are and they will say ... "20kev".
It must be remembered that the public will laugh at 20kev, (about what a car ignition coil puts out) but not 500 million degrees kelvin. This is the logic behind the latter day kelvinization of deuteron energies. Gotta' keep that public teasure money flowing into the labs!
A small side note: A friend of mine who is a vacuum expert went on the stock tour of the Princeton facility. They were herded into a small room and shown a stock video of the facility which was to orient them as to what they would be seeing and what the machines do. (this allowed a silent walk-look-see tour). At the end of the movie the scientist or physicist asked if there were any questions. My friend raised his hand and asked when they were going to make break even fusion happen. To his amazement and to the credit and honesty of the official, the response was....... "GOODNESS!"....."NEVER,I HOPE!" ..."All this would end!" (throwing his hands upward)......"I have two children in college!".
Some might think this a joke by the official, but it is more candid than you can imagine.
Finally, we must, ourselves, realize that the idealized fusor of extremely simple design shown on the video is consuming about 1000 times more power than it produces. But it DOES DO FUSION!!!
Deuterons are produced throughout much of the volume of the fusor's inter-grid region. Many will not accelerate through the full potential drop and thus not reach fusion temperature. SOME WILL! Likewise, not all of the true fusion energy deuterons entering the poissor will hit head on or at an angle where the summed energy will produce fusion. SOME WILL! The result is that we will do fusion but not efficiently in the simple two grid fusor. We will be producing all manner of stuff in the gassey inter-grid regions such as deuterons ranging from some tens of ev to the full 20kev, slow neutrals, fast neturals, likewise a large number of free electrons over a vast range of energies.
The mean free path for deuterons (gas pressure related), the density of the poissor, the accelerating voltage and current will all impact the process such that for a given geometry, the fusion rate CAN BE MAXIMIZED, but never above unity. NOT IN THE SIMPLE FUSOR!
Increasing the voltage gradient between grids can "bullhead" the process a bit and offer more neutrons up to a point. Negatively biased dispenser cathodes just outside the outer grid will improve the simple fusor. Eight ion gun injectors around the outer grid will bump it up even higher, but the fusor is no longer simple and no longer an easy amateur project.
Everyone, keep your eyes peeled for an upcoming issue of ANALOG, the sci-fi magazine, at your news stand! Tom Ligon has an article on the fusor and its construction which will be appearing in the magazine soon! Analog has a for real science section on occasion and his article was accepted and finished for publication earlier this year.
- Re: Building a Fusor as an EE Senior Project - Jay Sicard N5PWG Dec 21, 0:51 am