Picture of Build A Fusion Reactor
Yes, you can build your very own nuclear fusion reactor in your house! But first, a few warnings:

-This project includes lethal voltage levels. Make sure you know your high voltage safety or have a qualified electrical advisor.
-Potentially hazardous levels of x-rays will be produced. Lead shielding of viewports is a must!
-Deuterium, an explosive gas, will be used. Make sure to check for fuel leaks.
-All the other inherent dangers of a home engineering project of this degree (a wide gamut of potential injuries, damage to the checking account, and the loss of general sanity)

Here are the minimum required materials:

-A vacuum chamber, preferably in a spherical shape
-A roughing vacuum pump capable of reaching at least 75 microns vacuum
-A secondary high vacuum pump, either a turbo pump or oil diffusion pump
-A high voltage supply, preferably capable of at least 40kv 10ma - Must be negative polarity
-A high voltage divider probe for use with a digital multimeter
-A thermocouple or baratron (of appropriate scale) vacuum gauge
-A neutron radiation detector, either a proportional He-3 or BF3 tube with counting instrumentation, or a bubble dosimeter
-A Geiger counter, preferably a scintillator type, for x-ray detection and safety
-Deuterium gas (can be purchased as a gas or extracted from D2O through electrolysis - it is much easier and more effective to use compressed gas)
-A large ballast resistor in the range of 50-100k and at least a foot long
-A camera and TV display for viewing the inside of the reactor
-Lead to shield the camera viewport
-General engineering tools, a machine shop if at all possible (although 90% of mine was built with nothing but a dremel and cordless drill, the only thing you really can't build without a shop is scratch building the vacuum chamber)
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Step 1: Assemble The Vacuum Chamber

Picture of Assemble The Vacuum Chamber
A quality high vacuum chamber is required for the fusor to operate. Sometimes an appropriate chamber can be found on eBay, but generally it is best to make one. Parts can be scrounged for several hundred dollars, or purchased new for $500+.

Get two stainless steel hemispheres, purchase two corresponding conflat-flanges (8" flanges in my case), bore out holes for accessory flanges, and then TIG weld it all together. Flanges are typically either of the KF or the conflat style. Conflat can be seen in the image below as the flanges with bolts, and KF (kwik-flange) are seen as those with only clamps holding an o-ring on the mating surface. Only weld on the inside, never on the outside (since virtual leaks can be formed if both inside and outside are welded). If you've never TIG welded before, it would be wise to have someone with experience do it as the welds must be flawless with no pin-sized holes or porous areas to hold a vacuum.

After machining, thoroughly clean the chamber and avoid getting fingerprints in it since these will outgas, which means at vacuum pressure molecules in the oil of finger prints or machining oil will become vapor and make it hard to maintain plasma stability or reach a good ultimate vacuum level.

Step 2: Prepare The High Vacuum Pump

Picture of Prepare The High Vacuum Pump
Install the oil diffusion pump (or turbo pump if you have a bit of luck scrounging or a higher budget). Fill the pump with quality diffusion pump oil to whatever fill level the pump documentation suggests, attach the inlet to a valve which then connects to the chamber (see diagram), and attach the outlet to a mechanical backing pump capable of reaching at least around 75 microns (any higher and the diffusion pump will not operate properly or the oil will oxidize quickly).

Make sure the pump is sufficiently cooled, many oil diffusion pumps require water cooling, smaller ones such as the one pictured can get by with a decent air flow.

Once this is assembled, turn on the mechanical pump and wait for the vacuum to reach at least 75 microns. Next you can test the high vacuum pump by turning on the boiler on the diffusion pump. After it warms up (could take a while), the vacuum should rapidly drop below the single micron range.

Step 3: Build Inner Grid

Picture of Build Inner Grid
The inner grid (where the high voltage is applied) must now be built and attached to a high voltage feedthrough.

It is best to use a metal such as tungsten for the grid wires since it has a very high melting point, and the grid will get extremely hot during high power runs.

This can be built however you wish, as long as it resembles a spherical shape of roughly 1-1.5 inches in diameter (for a 6-8" chamber), it should work fine.

The grid should be internally attached to an electrical feedthrough such as the one pictured in the second image. This feedthrough needs to be rated for the cathode voltage that will be used, typically 40kv is a good target voltage.

Step 4: Assemble The Deuterium System

Picture of Assemble The Deuterium System
Deuterium gas is used as the fuel for this fusion reactor. You will need to purchase a tank of this gas (unless you wish to do electrolysis on heavy water, this process will not be documented here but nothing more than a small Hoffman Apparatus is required - higher purity gas can be gotten from a compressed tank).

Attach a high pressure regulator directly to the tank, add an extremely fine-metering needle valve after this (or a laser drilled orifice in the range of 5 microns), then attach this to the chamber. A ball valve can also be installed between the regulator and the needle valve since needle valves are not shutoff valves.

See the attached diagram now updated with the deuterium handling system.

Step 5: High Voltage

Picture of High Voltage
If you can purchase a power supply (occasionally but not commonly found surplus) appropriate for fusion use, the high voltage becomes very simple. Simply take the output of the 40kv negative supply and attach it to the chamber with a physically large high voltage 50-100k ohm ballast resistor in series (large enough that its length will not flash-over if 40kv is applied to it in a plasma run-away or arc discharge).

The difficulty is that it is often difficult if not impossible to find an appropriate fully assembled DC supply of this voltage level that is affordable to the amateur scientist.

Pictured is my high frequency ferrite transformer pair, with a 4-stage multiplier seen behind it.

If a fully assembled power supply (typically manufactured by either Glassman or Spellman), there are a few options:
-Find an x-ray transformer, and if necessary either reverse the rectifiers for negative polarity or add rectifiers if it has none (an x-ray transformer core won't have rectifiers, it probably will if it is in its oil tank)
-Build a switching high frequency ferrite power supply. This is what I did, however it requires a bit of EE experience since several aspects must be resonant and if it is ever taken out of tune, the transistors will burn out. Probably not the best option for people with little electrical background.

Step 6: Setup Neutron Detection

Picture of Setup Neutron Detection
The proof of fusion (and a quantitative analysis of how much fusion) is obtained through detecting neutron radiation, the byproduct of a D-D fusion reaction. There are three options which will be described. They are in order of descending ease of setup.

-A Neutron Bubble Dosimeter
A bubble dosimeter is a small unit with a gel in it that forms bubbles when ionized by neutron radiation. This is the easiest form of neutron detection available since all you have to do is unscrew the top and set it next to the fusor. Some of the drawbacks are that it is an integrative detector which means all you get is a total neutron emission number over the time that it was used, rather than an instantaneous neutron rate. Additionally, they are somewhat hard to get since the only company to make them is Bubbletech in Canada, which has a minimum order of 3 with steep shipping and handling (expect to spend $700+ if ordering directly from them not in a group buy). Additionally, they tend to be fairly worn out after a year of shelf life (although I've kept mine in a refrigerated storage container at 50*F and it seems to be like new after I think more than a year). The advantage is that calibration data is provided with purchase and of course it is easy.

-Silver Activation
When silver is placed near the reactor (with a moderator [paraffin wax, water, HDPE, etc] between it and the neutron source, since only thermal neutrons will activate the material) it becomes slightly radioactive with decent neutron fluxes. It has a short half life of only a few minutes, but if you quickly put a geiger counter next to the silver, counts can be detected. In my best runs, I have gotten a piece of silver to about 250CPM over background on a CDV-700 geiger-counter. The disadvantages of this are that it requires a decent neutron flux (at least about 100,000 neutrons/s) which is above the average "beginner's first run" neutron rate. Also, it is somewhat difficult to calibrate, and the counts can't be taken until after the fusor has been shut off.

-A Proportional Tube
Tubes can be purchased which are filled with either BF3 or Helium-3 (some very old tubes are Boron-10 lined inert gas tubes). These tubes, similar to a geiger counter, can be used with a counting device to detect electrical pulses when neutrons pass through the tube. Either an all-in-one counter can be used, often made by a company called Ludlum, or a modular counting system can be made using NIM modules. The tube is surrounded by about 2 inches of moderating material such as wax or water. This is by far the most accurate and useful form of neutron detection, however the cost of a new tube is prohibitive to most people, and they are extremely rare on the surplus market. Also, counting equipment can become quite costly.

NIM Configuration: If you chose to make a NIM setup as I have, the typical layout is a charge sensitive pre-amplifier at the head of the proportional tube, which is plugged into both a high voltage power supply generating positive polarity voltage appropriate for the tube (in the range of 800V-2kV generally). The amplifier also hooks into a shaping amplifier, which is followed by a Single Channel Analyzer (for setting the detection discrimination level), followed by a pulse counter and/or rate meter.

Shown in the first picture is my NIM setup, the second picture is the pre-amplifier attached to a moderated helium-3 tube, the third picture is a bubble detector after being exposed to neutrons.

Step 7: Fire It Up (and cross your fingers)

Picture of Fire It Up (and cross your fingers)
Time to turn it on (don't forget to cover any viewports/cameras with lead! Also x-rays can pour out of ceramic feedthroughs so point them away from people. It is a good idea to be monitoring for x-rays where any people are present). The basic procedure is:

-Turn on the roughing pump and wait for sufficient backing pressure, turn on the diffusion or turbo pump and wait for it to fully warm up or achieve running speed
-Throttle the chamber back (with the valve between the diffusion/turbo pump and the chamber)
-Ever so slightly open the needle valve to the deuterium tank
-Turn up the high voltage until either plasma establishes on the camera, or you've reached 40kv and nothing has happened (don't forget, you only get one chance in your life to screw up with voltages of this degree)
-If nothing has happened, keep admitting more gas and the pressure should keep going up. Plasma should form around 40kv at about 10-15 microns of deuterium.

If all goes well, you should see on your camera the image below, and you should be detecting neutrons at this point.

Operation is quite a balancing act, since the voltage is controlled by both the power supply, but also by Paschen's Curve and Ohm's Law relating to the pressure in the chamber. Great patience is required to "Get the hang of it", but after doing so it becomes quite simple to run. Operation can be aided by an ion-gun which will not be discussed in this article.
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JoshWolff71 year ago

I am really interested in this and would love to build it. Is it possible to hook this up with thorium instead of deuterium? How can I simplify this project? Is this fusion reactor hooked up to a capacitor or something of the like that it charges - how is the power harnessed?



JakeV JoshWolff711 months ago

How is the power harnessed?

The most likely way you would harness the power would be to use the heat coming off the reactor to drive a thermal process, probably with water becoming superheated steam to turn a generator turbine.

SobhanB JakeV11 months ago

Can you please explain what's the point? I don't think the efficiency of all this is 100%. So aren't we just using a lot of voltage to produce less voltage?

The points for building this sort of thing have already been described, I believe. If you would like to have a neutron source, then this could be a path to having one. Then, again, for most folk, the point would be merely to have built it and to have seen it working, and to consume extra time and money that you have. The second question you ask rather answers itself, I think.

Is it even theoretically possible to get more energy output than input? I'm not goading, I'm really asking. I would've thought that energy can be transformed into other KINDS of energy (i.e. fossil fuel into electricity) but the amount of energy would be equal at best. Assuming energy is subject to the rules of the game, where/how would energy that did not exist be produced? Where would it come from? I've always thought of energy as 'static' in the sense that x units of energy = x units of energy. The bottom line being you can't make something where there was nothing. Am I waaaay off in ignoramus territory here? I'm not as well read in physics as I should be, so constructive criticism and education is more than welcome.

Theoretically possible, but practically very difficult. Its been nearly a hundred years of well funded research and they have only just managed to do an experiment with more energy out than put in. http://www.bbc.co.uk/news/science-environment-2442... and this very far from producing a self sustaining reaction, which may take another 50 years of research.

Power generation is not the aim of this project. You would need a much more involved set up to even try.

Just to add to that answer, there is a good change we will see some fusion reactors in controlled (ie "non-commercial") settings producing a reasonable amount of power output in the next two decades. In fact, many tokamak designs already produce sustained reactions of several seconds... which may not sound like much but is long enough to use iterative techniques to squash bugs and design a long term use reactor, and long enough to have positive power out.

As for where the energy comes from, it's from mass-energy conversion. When the elements lighter than iron fuse nuclei, the product element is usually of a slightly smaller "atomic mass". If you're wondering how that works (because wait, don't we still have the same number of protons and neutrons?), you can either accept some hand waving or go take some advanced physics, but the outcome is that we loose a little mass and gain energy. Since that energy scales with the mass times the speed of light squared, that second part is really big so the first part can still be kind of small and produce energy output. That is to say, our output from fusion is common elements (and the inputs are not particularly rare), and we don't need a lot of material to get a LOT of energy.

Right now, however, we end up using a lot of energy overcoming repulsive forces between nuclei. We do that by raising the temperature to a point where the mean velocity of the (now plasmafied) atoms is high enough to keep going even against the very high forces applied by short range electric fields at the nucleus of an atom. Since energy tends to go out into a cooler space (all of earth), the current difficulty is keeping that temperature high enough, or finding another way to overcome atomic forces keeping things seperated.

lockeed martin says they'll have it done by 2026

rhercher DonJ410 days ago

And it'll fit "on the back of a truck" Is that a Semi truck or my neighbor's F150 extended cab?


Oh wait: The project estimates that it could weigh 300-1000 tons.

Should have read the article. Sorry.

DonJ4 rhercher9 days ago

I don't know, it can't be the same one here on 'Instructables.' If so, I think they made a mistake; I think it should say 300-1000 lbs, not tons, but you can make one under 300lbs. It will easily fit in the bed of an f-150, especially if you keep that in mind while you're making it, but what's the point? OK, I just saw the link and your other comment; you meant the one Lockheed is making that will have a net positive output power ratio. Yea, not fitting on a truck any time soon. I don't think that one has even started to be developed yet, first they need to get the fusion right before they can make a compact model. Here's the Lockheed website for their compact fusion version:


And here's a little known company that says they'll have it done before Lockheed-Martin; may be a company worth investing in:


Of course you probably know the articles people are posting here, that say, "nobody has yet produced more energy from fusion reaction experiments
than was required to conduct the experiments in the first place," are wrong. That turned out to be false shortly after the articles were published last year; it has been done since then, pick a link, choose one:



That reminds me- Why don't you have anything to drink? Choose one, making you better feeling:

No, no you're making good observations, and moreover you're correct! While energy is not "static" in the sense that energy can become mass (e.g. the big bang) and mass can become energy (e.g. solar fusion or black holes) by the equation we know as E = mc^2 + [other things nobody cares about], it IS in fact conserved in a fusion reaction. "eV" is a unit of energy, but it's also a unit of mass for small particles, so let's just equate mass and energy for this oversimplified explanation: particles like protons and neutrons have specific "resting" energies (i.e. when they have not been excited). However, when they combine to form a nucleus, there is a binding energy that means that the final nucleus has LESS energy than the individual particles did before! Mathematically, you still have x = x, but it looks more like (y+z) + (y+z) + energy => 2y + 2z where 2y is the final energy of the new nucleus, and 2z is radiated energy--much greater than the initial activation energy. Thus it would appear that more energy is created than applied, when in reality, you're just helping the system reach a lower energy level, thus giving off more external radiation. (Think of it like pushing a box up a hill 10 feet then letting it slide down the other side 20 feet. It takes x amount of energy to push it up, but y > x energy comes out because gravitational potential energy is converted into mechanical energy (then friction and heat). There is an activation energy for fusion, but because the free particles move to a lower energy state, like the box, they will give off more energy and make it worthwhile.)










as far as energy forming more than its original amount it is very likely. Imagine multiple explosions timed at the right time one building off of the other to form a new KIND of energy not amount. This is probably how the concept of the atom bomb was theorized. See what we are missing is not all energy is the same type of energy therefore all energy cant be lumped into one category.

As far as I know the conservation of energy law still holds, so, no you can't get more energy out of a process than is put in. As I'm sure you know, though, there's an awful lot (E=MC^2) of energy to be had from a small amount of matter. Difficulty is damping a fission reaction or sustaining (and containing) a fusion reaction.

Conservation of energy- that's the one I had in mind, thank you. Yes, I understand that the challenge is to efficiently unlock the energy in one thing to use in whichever way... They say one mega-thunderstorm can power the U.S. for however many days, but how to harness it? I suppose for that matter that a mountain has a vast amount of potential energy, but good luck trying to get a mountain to power your toaster. NOW, confusingly, someone else replied that YES, it is theoretically possible to get more energy out than you put in... But as you say, and I'm inclined to agree, that seems to violate the laws of physics. The energy cannot just 'appear' where it previously didn't exist, no? It would be amazing to harness the energy in a grain of sand and use it to run a car, no question. But to my thinking, (which may be flawed,I'm open to that) the very best result you can hope for is that you convert every last drop of energy in the grain of sand to an exactly equal amount of energy in the form of electricity let's say. If each grain of sand has a calculable amount of energy, and I convert that energy into another form of energy- where would 'more' energy come from? It cannot physically be.
I just had a thought: I'm thinking maybe what people mean when they say "more than you put in" they mean getting more electrical power output than input... That completely ignores the source of energy that you're using the electrical input to unleash. If I use 100 tons of coal to produce enough electricity to power a machine that unlocks the energy in hydrogen atoms, and I do it effectively enough to get back the equivalent of 200 tons of coal's worth of electricity, I did NOT get back more energy than I put in. I tapped into the energy of the hydrogen atoms to get that output. I'd much rather use hydrogen than coal, so that's a win- but I only changed the form of the energy, I didn't get more out than I put in.

Yes, you're right. Pretty much uniquely to fusion discussions, when people talk of "getting more energy out than put in" they are discounting the energy in the actual fuel ... If they're not the refer them to Scottie: http://youtu.be/nfZ12UGiisM

were it possible to produce more energy output than input series of the devices would be installed on every power grid in the world. They are not. That should logically answer your question

Energy is produced when atoms fuse together, it's the reason our sun produces energy.

You could argue that the point is neutrons out. You could also argue that the point is "because I can".

JakeV SobhanB11 months ago

Ultimately the idea would eventually be to use a fusion reactor to produce more power than it requires to run, but that's not what it's capable of right now.

Why bother doing this at all?

Even if it's not producing more power than it takes in, it still has its uses. I don't know about how useful it would be for home projects, but it does make a powerful neutron source for various kinds of analysis.

For examples of neutron spectroscopy, see http://www.isis.stfc.ac.uk/instruments/neutron-spe...

"Produce more power than it takes to run". That's a perfect, succinct way to say it. That is critically different than 'more energy out than in'.
cbosse1 JakeV3 days ago

In this design power isn't harnessed. Even if you could capture 100% of the expelled radiation, the unstable nature of the fusion reaction in this environment (the high voltage is essentially restarting the reaction over and over) makes it so this is a net loss system.


Thorium is unstable and decays, while deuterium is fusionable with energy output, which are essentially opposite processes. What you could do (though I don't recommend it unless you darn well know what you're doing and also have a ton of licences and a record with radiation safety) is use the fission reactor as a "breeder" for thorium, to turn it into the less common, more fissile, isotope, and then essentially substitute it in for uranium. While I don't think actually building one is a good idea, if the topic interests you then you should look up thorium reactor designs - many interesting ones are basically publicly available, and I would argue that this is a cheap and relatively easy power source to replace fossil fuel power generation.

By the way, another interesting thing: fission reactors easily produce large positive power output, while fusion (what's happening here) really only has a long term positive energy out in the sun, so far. That will probably change in the next few decades, but for now thorium is an abundant and relatively (compared to uranium or even coal) safe energy source.

CaiE JoshWolff710 days ago

Thorium requires a particle beam to promote it up to an unstable isotope so sticking thorium in thing would do nothing, this also has the potential to be weaponised.

You can't use Thorium in a Fusion Reactor because Thorium is a Fission fuel. Also Thorium is usable for Fission because it converts to Uranium 233 during Neutron bombardment, but to start the reaction you need a supply of pure U233. After the reaction is underway the Thorium conversion is self-sustaining.

Thorium is a fuel used in a fission reactor. It is essentially a replacement fuel for Uranium 232. Thorium is transformed into Uranium 232 after being bombarded by neutrons traveling close to the speed of light so you need a small cyclonic particle accelerator (think tiny CERN) to make it work.
So no Thorium will not work.

If you did turn thorium into uranium 232 youd be closer to makeing an atomic bomb if you wanted

Then you would need to filter out the U-235 and purify it to 90 percent weapon grade.

christensent (author)  JoshWolff71 year ago

No thorium, can't really be simplified much, no capacitor, and no power harnessing

can we set it up to use ( I hope I spell it right ) helium ( my spelling sucks )?

what there are resticshens ??? wich counchery is that ? ( sorry for spelling ) and can we use magnets to control it so make a ( by way of trikel filling and emtiying ) a sustand fusion reactor?

Magnets are used in a pollywell reactor which forces tje atoms to hit each other in the middle using the velocity gained by the magnetic force
christensent (author)  ElectricBlue1231 year ago

No, deuterium and tritium are the only gasses that will produce fusion in a DIY fusor. Deuterium is the only one that is legal to use.

Can the valve be manual ones? I prefer to use manual (for simplicity) but can high voltage be dangerous that I shouldn't use a manual valve? I'm not familiar with pneumatic valves or other type of valves.Thanks in advance.

ty by the way

Thank you!

Thorium is much more stable so it is harder to fuse. At this scale probably not.

Would would also need to pump in even more power than the deuterium would need in order to get a reaction if it were even possible.

JakeV JoshWolff711 months ago

You're talking about a very different nuclear reaction. Deuterium is hydrogen with an extra neutron attached to it, and you get two Deuterium atoms colliding with each other to create heavier Helium atoms, releasing lots of energy in the process. This process is called nuclear fusion.

For Thorium, the reaction is nuclear fission. Take Thorium, bombard it with neutrons to turn it into radioactive Uranium, and the Uranium undergoes a chain reaction dropping off Helium nuclei and eventually leaving you with lighter lead.

Fusion creates heavier elements, fission destroys them.

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