Amateur Nuclear Fusion

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Oct 13, 2004
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For about 2 years I have been working on a personal project involving a device known as the Farnsworth Fusor, a type of tabletop nuclear fusion reactor. The name comes from the inventor, Philo T. Farnsworth, who is better known for inventing the modern electronic television set.

When I first heard of the concept, I did not believe it. Fusion was supposed to be done in government laboratories with billion-dollar machines. To do it on a kitchen table for "the price of a set of golf clubs" seemied impossible.

At it turns out, fusion is quite easy to achieve. You make a geodesic grid out of stainless steel or tungsten wire and place that within a larger grid, which can be either another geodesic grid or a hollow metal shell that doubles as the vacuum chamber. The vacuum chamber is then evacuated to a pressure of 10^-3 mmHg, then backfilled with Deuterium gas to a pressure of about 10^-2mmHg. The inner grid is charged to a very high negative voltage, which can be over 20,000 volts. The outer grid is placed at ground potential, making it positively charged relatively to the inner grid. The positively charge nuclei of deuterium are accelerated towards the inner grid, where they miss the grid wires and collide with each other at the center, producing fusion.

The fusion output is detectable through the emission of fast neutrons, which are detectable with various types of neutron instrumentation. The best amateur record is 10^6 neutrons per second, which is enough to turn some metals radioactive. Farnsworth used Tritium as fuel, and got 10^13 neutrons per second!

Please note that this device, nor any other fusion machine made by the hand of man has EVER managed to produce extractable and useful energy!

For those interested, you can calculate the temperature (in Kelvin) of the plasma in the fusor my taking your acceleration voltage and multiplying by 11,800. So 20,000 volts equates to about 200 million degrees. Since we are working in a vacuum, temperature is really meaningless though.

I have posted a picture of myself with my device, and will gladly answer any questions you may have. I encourge those of you with a knack for scrounging and experimenting to give a project like this a try.

For more information, please see
Here is an image of the reaction zone during operation. The fusion output is about 2.5x10^4 neutrons per second during this run.
Did anyone measure the helium or neutron flux produced by the apparatus? I did not locate any mention or original data showing the measurements of these fusion by-products. Without that proof, it looks like these things are just ionized gas light sources.

Bruce S. Levison, NAR #69055
Originally posted by teflonrocketry1
Did anyone measure the helium or neutron flux produced by the apparatus? I did not locate any mention or original data showing the measurements of these fusion by-products. Without that proof, it looks like these things are just ionized gas light sources.

Bruce S. Levison, NAR #69055

But a pretty light. Just think how excited you could get the ATF during an inspection of your magazine if you have a "fusion" device hanging around.
:D :rolleyes:
very kewl :)

Get stuff like this producing useable amounts of energy and, at the same time solve the "room tempurature superconductor" problem and we will have solved our energy problem not to mention poverty!

very kewl :)
I did a BIIIIIG double take when I saw teh words "amature" and "nuclear fusion" in teh same sentence... :D :cool:

more pics? :D ;)
Originally posted by teflonrocketry1
Did anyone measure the helium or neutron flux produced by the apparatus? I did not locate any mention or original data showing the measurements of these fusion by-products. Without that proof, it looks like these things are just ionized gas light sources.

Bruce S. Levison, NAR #69055

Neutron flux seems to be one of their main measurements. And Brian did quote some results.

I'd like to see a write up of an assembled and operating device and the time series results compared from baseline.
Like I said, neutrons are produced and detected quite easily. The amateur record is 5x10^6 neutrons per second. The University of Wisconsin, as well as other institutions, do frequent research with this device, and obtain neutron levels 2 or 3 orders of magnitude higher.

If a million neutrons are being produced every second, a million Helium 3 nuclei are being produced every second as well. The same goes for the other D-D reaction, which produces Tritium and a proton. This is really a tiny number when compared to the total gas volume in the chamber. Even then, the recoiling nuclei are buried within the chamber walls. Unless you ran the fusor for weeks on end, you wouln't be able to detect the helium with even a mass spectrometer.

Measuring neutrons is the best way to measure fusion. Once an isotropic neutron emission rate is determined, you multiply that number by 2 in order to get the total number of fusions per second (because neutrons are produced in ony 50% of the reactions.)

Fusion is measured using several techniques:

A better description of neutron counters can be found at:

1. Activation- This involves placing a thin foil of indium or silver in a block of moderator, such as wax or plastic. The 2.45 MeV fusion neutrons are slowed to thermal energies and are captured by the indium or silver nuclei (high capture cross section). The nucleus becomes radioactive, signifying a neutron flux. This has been done by an amateur, and his methodologies can be found here:

2. BF3 or He3 counter- This is the industry standard tool for detecting neutrons. However, it is only sensitive to thermal neutrons. Therefore, the detector tube is placed within a moderator in order to slow down the fast neutrons and make them detectable. This is the method I use.

3. Fast neutron scintillator- this is sensitive only to fast neutrons. The neutrons strike the detector, creating a flash of light. This is then detected with a photomultiplier tube and sent to a pulse height analyzer.

4. Fast neutron bubble chamber- this is relatively new technology involving a small, pen-sized capsule of a special fluid that is sensitive only to fast neutrons. When neutrons strike it, small bubbles are formed in the fluid. The number of bubbles produced is proportional to the total number of neutrons that have passed through the detector. Please see:

My own personal data from my first run can be found at:

Note how I did a background count before and after running the machine. The count rate during the fusion run was well over background levels. The neutron counter was calibrated to 10% tolerance in August. All instruments used were allowed to stablilize over the course of an hour, and were electrically shielded.

I first took a 15 minute background count, before turning the machine on. Then I ran the machine and neutron counter and noted the higher count rate. Finally, I did a post-run background count.

I took the count rate during the fusion run and subtracted the average background count rate from that. This is the number of counts per minute attributable to fusion alone. This number divided by 60 to get counts per second. Then, this is multiplied by 100, since the BF3 counter I used is only 1% efficient for 2.45MeV neutrons. Finally, this was multiplied by 104 to take into account the small area of the detector vs. the 4pi emission area of neutrons (it's a point source).

For those looking for more images, please see "Images du Jour "
I first discovered the idea back in May of 2003, when I stumbled across this website. I completed the machine back in April, and did my first non-fusion tests in late June and July.

Most of the equipment I purchased surplus. I got the vacuum pump for $75 on ebay, but it works as if it were new. The spherical chamber was the only thing that I paid full price for. It was $300 for all the parts, then another $300 for the high precision machining and welding. My best buy was the neutron counter, as I paid $150 for it when it would have cost me $2500 new.
If we see you running out of the room saying "oh no! oh no! oh no!..." Does that mean you left a pie in the oven? ;)

Very cool project. :). Wouldn't that be cool... imagine... next time when a lady friend comes over... she'll point over to it, and ask, whats that? Wonder what her expression wouild be when you say; Oh nothing... that's just my nuclear reactor. ;)

"who set this to overload?"

Seriously, Awesome project :) wouldnt happen to know of any cheap flux capacitors for my time traveling delorean project aye??? ::chuckle:: ::chuckle:: ::chuckle::
pretty cool project, but ... can you night-launch it!??? :)

expiring minds gotta go ...:
Actually, all my first experiments were done in total darkness. I had to get used to the properties of the plasma and the machine by observing and playing with it for over 4 hours. I had to use a flashlight to read the volt and current meters. The corner of the room would be illuminated by a dim purple glow when the lights were completely dark.

Above 15,000 volts, it is necessary to use a lead-backed video camera to peer into the viewport, since soft x-rays will start to pour out of there due to charged particle collisions with metal atoms. Above 40,000 volts, the stainless steel chamber will start to become transparent to x-rays, and lead shielding will be required. Above 45,000 volts, the neutron flux starts to become a cause for concern. This is mitigated somewhat through the use of shielding (i.e. 4 inches of water, wax, or plastic), the inverse square law, or time of exposure (<20 minutes a week).
But.... where is does the Oscillation Overthruster fit in???


Dr. Lizardo

"Laugha while you can monkeyboy."

I am still not convinced that your instrument is working in the fusion mode. You need to do the proper controls for your experiment; amoung these would be to evacuate the chamber to 10-6 torr (or lower) and turn the instrument on and record the results, another would be to introduce helium (at the same working pressure) instead of dueterium in the chamber and turn the instrument on and record the results. A friend of mine worked on a "Cold Fusion" project some years back and these were the types of controls he was compelled to do to prove his instruments did not generate any spurious results. It would also be nice to analyze the gas in the chamber before and after the fusion reaction by Mass Spectrometry to definately prove the presence of 3He.

Bruce S. Levison, NAR #69055
I think the results of 30 people, including universities around the world, speak for themselves. You can go look at all the results achieved by these various people by looking at the links I gave.

This is not cold fusion! It is hotter than a Tokamak or ICF device! It is a spherically-focused ion collider, much like a more typical particle accelerator. It operates on well known principles.

Nobody is claiming breakeven. 10^6 neutrons is about a microwatt of excess energy. If I put in 1000 watts and get that many neutrons, than I am getting 1000.000001 watts out mostly in the form of waste heat, x-rays, and recoiling charged particles. Fusion is almost an afterthought.

I don't want to hear nonsense about "stripping" the neutrons off the deuterons. This is known as the Oppenheimer-Phillips reaction, and its THRESHOLD energy is 4.45 MEV! My input energies are more like 25Kev. Because of the collisional nature of the device, you can double that input figure to arrive at a grand total of 50Kev. Furthermore, the stripping reaction produces an entire spectrum of neutrons, rather than the monoenergetic 2.45Mev neutrons. If my fusor was doing this reaction, I could simply pull the BF3 tube out of its moderator and still get a neutron count. I have tried this and it is simply not the case.

I have attached a cross section curve for the 2H(d,n)3He reaction. Note the 10-200KeV region most typically operated by amateurs. It is fairly low on the curve, but it is still significant. Sensitive 3He neutron counters can detect fusion processes at input energies as low as 7KeV.

If it is my personal work you are doubting, let me give you a few more facts. I have done "dry runs" as you have stated, with Helium, Nitrogen, and Argon. All were done at a variety of different pressures, and there was no significant increase above the background count rate. It will take me a while to transcribe them from my notebook, but I can post them if you like.

What justifies running at such a low pressure? The gas atoms would be so few and far between that fewer reactions would occur per unit of volume.

This machine works in glow discharge mode. It WILL NOT OPERATE at 10^-6 Torr due to the very nature of its design. All ionization is done through field eimission, but at that low pressure, there just arent enough gas atoms for a breakdown and discharge to occur. Ions need to be injected directly, adding complexity and expense. Philo T. Farnsworth used ion guns instead of field emission and operated at 10^-3 to 10^-4 Torr. I have gone down as far as the latter figure, as this is th limit of my pumping system. If I pump down to 10^-4 Torr, then backfill to 10^-2, 99.99% of the gas in the chamber is Deuterium.

If a million neutrons are being produced every second, a million Helium 3 nuclei are being produced every second as well. The same goes for the other D-D reaction, which produces Tritium and a proton. This is really a tiny number when compared to the total gas volume in the chamber. Even then, the recoiling nuclei are buried within the chamber walls. Unless you ran the fusor for weeks on end, you wouln't be able to detect the helium with even a mass spectrometer.

What has been tried is the use of a silicon-based PIPS detector for measuring the fast protons produced in the 2H(d, p)3H reaction. The university of Wisconsin has published results on this.
All this discussion of nuclear physics (which is a bit over my head anyway) makes me think of an episode of Sponge Bob Squarepants that I've had stuck in my head lately.


You see, the episode is "F.U.N." SpongeBob and Patrick are trying to convert Plankton (the evil little maniac in the show) into a "good guy" by teaching him a song based on the word "fun."

So they start dancing around and singing, "F is for fun you have with your friends, U is for you and me...." and so on. Then they get Plankton to give it a try: "F is for *fire* that burns down the whole town; U is for Uranium.... *BOMBS!!*; N is for No Survivors....."

It cracks me up!!!!

Ok, now back to your real topic.

(Geophysics? I'm all over it. Astrophysics? Fascinated, and I get it. Nuclear Physics? Better you than me. ;) )

Are the proper controls are being done? I am not questioning that fusion could be possible under these circumstances, and I understand that this is not a "cold fusion" device.

When you are working with very low levels of signal you need to establish your detection limits. From your data background is about 1.6 cpm (fusor off) and signal (fusor on) is about 15.8 cpm. That's barely 10:1 signal to noise; how do you know you can accurately detect neutrons at that low level? Did you calibrate your detector from a known neutron emitter at 10 cpm?

Do the background counts (noise) go up with no gas in the chamber (fusor on at 10-6 torr); and does the noise increase with helium in the chamber (fusor on mode)? If so, that makes your signal to noise less than 10:1. Note that both controls I mention are done in the fusor on mode where no fusion would be expected. These would be better indications of background since the effects of the fusors electronics on the neutron detector can be determined. What are the detection limits that you are certain you can really see fusion occurring?

I commend you for assembling and testing out such an apparatus; but anyone claiming fusion should be able to answer the questions above.

Would there be a real problem with running a fusor device for a few weeks (or even months) to get and enriched 3He sample for mass spectrometry analysis?

Bruce S. Levison, NAR #69055
The counter was calibrated by a NIST laboratory in August. They did a full meter range calibration on every single scale resolution the meter had. From the data sheet they gave me after they did the cal work, anything 10% above the background count could be considered "out of the noise." I allowed for some more error in counting and demand at least a 50% increase over the background before I consider the data to be real. I have done runs using only the residual gases in the chamber, as well as different inert fill gases, and none of them have had an effect on the background count.

Also bear in mind that the data I posted was from my first run ever, which was done at a really low power level (50 watts input). In most of the runs I do now, the count rate is up at 130 cpm (35,000 neutrons per second), which is readable on both the neutron counter's built in meter, as well as the digital counter I have attached to it. The total isotrpic output is a typically a full order of magnitude greater than cited in that first data I gave here. I also have been able to try out one of those bubble dosimeters, which are sensitive to nothing but fast neutrons. It is right to not trust an electronic counter, but the bubble dosimeter is really the best way to prove fusion is occuring.

Congrat's, based on the controls you just mentioned, I believe you got fusion!

How long can you run the fusor? Do you think it would be possible to get an 3He enriched sample for an independent Mass Spec. confirmation?

Bruce S. Levison, NAR #69055
Hey Brian,

I would really like to see this for sale on E-bay.
A fusor can be run almost indefinately, but you are limited by the amount of heating your inner cathode can withstand. Also, metal particles get sputtered off the cathode, and need to be cleaned off after a few weeks of even intermittent operation.

I couldn't build up appreciable amounts of helium-3 and tritium at my current output levels. However, I do know of one man who is getting two orders of magnitude better in his results due to a higher input voltage, and he has used an RGA (residual gas analyzer-a mini mass spec. for measuring partial pressures of gases) to detect the build up of these fusion ashes. He says that it is quite obvious after about 30 minutes of run time, and he is going to post results and a write up in a few weeks to
Coincidentally, a full working fusor system DID show up on ebay a while back. It was made by a college student who later sold it when he was looking for some extra money. It was sad to see this device go, because it was quite beautiful and was a good performer. The fusor system itself never sold (was over $9000 on ebay), so he had to sell all the parts separately, including a $5000 turbomolecular vacuum pump.
In researching the use of liquid ozone as an oxidizer I happened across this:


Advanced Energetics for Aeronautical Applications

In it is section 3.1.4 Intertial Electrostatic Confinement Fusion as a Potential Power/Propulsion Source

It is a discussion of using the Farnsworth fusor as a propulsion device. The concept was seriously extended by someone known to anyone who's surfed the edge between science and science fiction, Bussard. It is the central power unit of his famed interstellar ramjet.

What Bussard also proposed was H+B -> He fusion. This produces no gamma rays no neutrons.

Neutron production is NOT the mark of fusion, it is the mark of the sort of fusion that the US wants to see done. Same with fission. If the US wanted clean fission, it could run thorium reactors, which can be run so as not to produce excess neutrons (it does run them but in such a way as to produce excess neutrons). The US recently turned pulled out of development of a European fusion generator that produced fewer neutrons (and the consortium had spoken against using it for weapons research) in favor of a Japanese one which produced more (and who didn't say no to weapons research).

The primary reason to produce more neutrons is to produce weapons grade material. For sheer energy purposes, neutrons are a PITA and a waste of output.

Keep it up, bjmcder. You're helping to keep more than one hope alive.
A while back, Bussard sent one of his consultants to an amateur Tesla Coil meeting to demonstrate a non-fusion fusor. One man by the name of Richard Hull picked up on the idea, and a fan and historian of Philo T. Farnsworth created a discussion forum to attract more people. So Bussard is at least partly responsible for the amateur fusion movement.

The H+B11-->3 He4 is a very good fusion reaction. The three alpha particles it produces can be collected directly and converted to electricity with better than 95% efficiency. The downside? The fusion fuel usually comes in the form of diborane, a highly toxic gas. Furthermore, the minimum energy for this form of fusion is ten times higher than for the D-D reaction.

Right now, the neutron count is the best way to quantify how well a fusion reactor is doing. All the labs use it in one form or another. But they are a real pain in the energy generation regime, since they will activate everything and can damage the crystal structures of metals, thus weakening them.