Nuclear fusion is the process of squeezing two atoms together so tightly that their nuclei fuse, creating a heavier atom and releasing a blast of energy. Fusion creates the inferno inside the sun — and the hydrogen bomb — but no one has yet harnessed its enormous power for peaceful uses.

They’ve tried, however, often with skepticism. In 1989, physicists Martin Fleischmann and Stanley Pons announced they’d achieved “cold fusion” of hydrogen into helium at room temperature, only to face withering scorn when others failed to replicate their results.

Luckily, DIY nuclear engineers can achieve honest-to-goodness “hot fusion” right at home by making a Farnsworth-Hirsch fusion reactor, or fusor for short.

This mini fusor is a demonstration version — while it generates only insignificant quantities of fusion products, it does show how inertial electrostatic confinement (IEC) reactors use kinetic energy to cause fusion. It’s also a good introduction to high-voltage power supplies and vacuum systems. The skills the project imparts will help you tackle bigger fusors and other projects involving plasma and high-energy physics.

Plus, the fusor just looks totally cool. An eerie purple-blue glow emanates from the reactor, and a really well-made fusor can produce a mesmerizing phenomenon called a “star in a jar.”

Curious? Read on…


This project uses high voltages at potentially lethal currents. A high-vacuum apparatus may implode if improperly handled. This device may produce ultraviolet and x-ray radiation. Do not attempt to build or operate it unless you are capable of safely using high voltage and vacuum equipment.

How It Works

The typical Farnsworth-Hirsch fusor has two concentric electrical grids inside a vacuum chamber: an inner grid charged to a high negative potential, and an outer grid held at ground potential. Our benchtop version has a stainless steel wire inner grid, and uses the aluminum chamber walls as the outer grid.

A variac controls the AC mains voltage input to a neon sign transformer, which steps up standard 110V AC to the 10kV range. A homemade rectifier converts AC to DC power to charge the grid.

A vacuum pump evacuates the chamber to a pressure of about 0.025mm of mercury, clearing the playing field so the few remaining gas molecules can accelerate without premature low-energy collisions. A vacuum gauge indicates the pressure inside.

High voltage across the grids causes gas molecules to ionize; that is, they lose an electron and become positively charged. Electrostatic forces then accelerate the ions — mainly O2+, N2+, Ar+, and H2O+ — toward the high negative charge at the center. Some ions collide; those that miss the first time are arrested by the electric field and re-accelerated toward the center for another go.

Low-power fusors produce a beautiful purple ion plasma “glow discharge” similar to plasma globes and neon signs. In high-power fusors, the inertia of the ion collisions squeezes hydrogen atoms tight enough to fuse, hence the term inertial confinement.

High-power fusors typically fuse deuterium (D or 2H) into helium and tritium. Deuterium is a hydrogen isotope whose nucleus contains a neutron in addition to the usual single proton. It occurs naturally in very low concentrations, primarily as hydrogen deuteride (HD) but also as “heavy water” (D2O), “semiheavy water” (HDO), and deuterium gas (D2). Only 1 in 6,000 hydrogen atoms is deuterium. Tritium (a hydrogen atom with two neutrons and one proton) is even rarer.

When two deuterium atoms fuse they create a high-energy helium-4 atom, which stabilizes itself by releasing a proton, a neutron, or a gamma ray. This release leaves behind a tritium atom, helium-3 atom, or helium-4 atom, respectively.

Fusor Nation

The fusor was developed in the 1960s by Philo T. Farnsworth, who also invented television. It’s popular with DIY experi-menters because it’s easy to build and can reliably produce fusion reactions.

Fusors have yet to produce useful power, but they can be dangerous. They require high voltages and can produce harmful ultraviolet, x-ray, gamma, and free neutron radiation.

IEC reactors are currently being studied at MIT, the University of Wisconsin-Madison, University of Illinois, Los Alamos National Laboratory, and EMC Corporation, among other labs.


Step #1: Cut the chamber parts.

Learn How to Build a Nuclear FusorLearn How to Build a Nuclear FusorLearn How to Build a Nuclear Fusor

Use the hole saw to cut two 4"-diameter blanks from the aluminum bar stock. Use the slowest speed on your drill press and use WD-40 as cutting fluid. It’s still going to make a lot of horrible noise. Clean up rough edges with a file, taking care not to scratch the surface of the blanks.

Step #2: Cut the chamber parts (cont'd).

Learn How to Build a Nuclear FusorLearn How to Build a Nuclear FusorLearn How to Build a Nuclear Fusor

Print and cut out the flange templates. Stack the 2 aluminum blanks with the template on top and bolt them together concentrically with a 1-1/2"-long 1/4-20 bolt. Use masking tape on the contacting surface to prevent scratches, and to hold the template in place. Center-punch all holes and remove the template.

Step #3: Cut the chamber parts (cont'd).

Learn How to Build a Nuclear FusorLearn How to Build a Nuclear FusorLearn How to Build a Nuclear Fusor
  • Drill out the 4 bolt holes (leave the offset hole for later), first with a 1/8" bit and then again with a 1/4" bit. This is called step drilling and it makes drilling large, accurate holes much easier.
  • Make sure the blanks don’t shift when drilling. Before you separate the flanges, use a center punch or marker to make witness marks on their edges so you can line up the 2 hole patterns correctly every time you assemble the fusor chamber.

Step #4: Cut the chamber parts (cont'd).

Learn How to Build a Nuclear FusorLearn How to Build a Nuclear FusorLearn How to Build a Nuclear FusorLearn How to Build a Nuclear Fusor
  • Drill out the center bottom flange hole to 3/8" (first image) and test-fit the ceramic tubing. It should be a close fit.
  • If it’s too tight, tape a strip of sandpaper to a nail, wrap the sandpaper tightly around the nail, chuck it in a power drill, and use it to expand the hole just enough that the ceramic tube fits snugly.
  • On the top flange, drill the center hole and the offset hole to 7/16" using the step drill method (second image).
  • Clamp the flange in a vise, using tape or shims to prevent marring, and carefully tap the two 7/16" holes you just drilled to 1/4-18 NPT (third image). Note that this is a tapered thread.

Step #5: Cut the chamber parts (cont'd).

Learn How to Build a Nuclear FusorLearn How to Build a Nuclear FusorLearn How to Build a Nuclear FusorLearn How to Build a Nuclear Fusor
  • Following the templates, use a hobby knife to cut 2 gasket rings (2-1/2" ID × 3-1/8" OD) from sheet rubber (first image).
  • Use a rotary tool and diamond cutoff wheel to cut a 2" length of ceramic tubing. Sand the rough edges smooth

Step #6: Install the feed-through.

Learn How to Build a Nuclear FusorLearn How to Build a Nuclear FusorLearn How to Build a Nuclear FusorLearn How to Build a Nuclear Fusor
  • Using 24-hour epoxy, glue the aluminum standoff into the ceramic tubing, taking care not to get any glue in the threads. You may need to file or sand down the outside of the standoff to make it fit. Let the epoxy dry 24 hours. This is your high voltage feed-through.
  • Using a healthy amount of epoxy, glue the feed-through into the center hole in the bottom flange, making sure it protrudes 1/2" into the chamber. Again, keep glue out of the threads.

Step #7: Add the vacuum ports.

Learn How to Build a Nuclear FusorLearn How to Build a Nuclear FusorLearn How to Build a Nuclear FusorLearn How to Build a Nuclear Fusor

Apply Teflon tape to the threads and then thread the vacuum gauge into the center hole in the top flange and the barbed hose fitting onto the offset hole. Tighten securely with a wrench.

Step #8: Fabricate the grid.

Learn How to Build a Nuclear FusorLearn How to Build a Nuclear FusorLearn How to Build a Nuclear Fusor
  • Cut a 12" length of 1" PVC pipe and then drill a 1/16" hole in the middle.
  • Cut 48" of stainless steel wire and anchor one end securely in a vise or clamp. Thread the other end into the hole in the PVC pipe and neatly roll the wire around the pipe while applying constant firm tension.
  • Release the wire from the anchor point and clip it off the pipe, being careful to keep the wire from springing back. You’ll be left with a small coil of wire with 10–12 turns, about 1-5/8" in diameter.

Step #9: Fabricate the grid (cont'd).

Learn How to Build a Nuclear FusorLearn How to Build a Nuclear FusorLearn How to Build a Nuclear FusorLearn How to Build a Nuclear Fusor
  • Clip 3 rings off the coil. Solder one ring closed using silver solder and a MAPP gas blowtorch.
  • Link a second ring through the first, solder it closed, and carefully solder the 2 rings together so they’re at right angles.
  • Stretch the third ring over the first 2 to form a spherical cage with 8 equal openings. Trim it to size and solder it in place.
  • Finally, solder a #10-32 stainless steel machine screw to the outer ring, midway between two of the existing solder joints.

Step #10: Make the base.

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  • Cut an 8"×8" square of 1/2" plywood. Use one of the flanges as a guide to lay out the 4 bolt holes.
  • Drill 1/4" holes and hammer in the 4 T-nuts. Adhere a rubber foot in each corner, on the same side as the T-nuts.

Step #11: Assemble the fusor chamber.

Learn How to Build a Nuclear FusorLearn How to Build a Nuclear FusorLearn How to Build a Nuclear FusorLearn How to Build a Nuclear Fusor
  • Apply thread-lock to the threaded steel rods and screw them into the T-nuts until they’re flush with the T-nut flanges, as seen in the first image.
  • Slip a nylon spacer over each rod, then stack the bottom flange on top of the spacers; make sure the longer end of the high-voltage feedthrough protrudes downward.

Step #12: Assemble the fusor chamber (cont'd).

Learn How to Build a Nuclear FusorLearn How to Build a Nuclear FusorLearn How to Build a Nuclear Fusor
  • Wearing latex gloves, wipe the surface of the flange with alcohol and wait for it to dry.
  • Apply vacuum grease to both sides of a rubber gasket, carefully center the gasket on the bottom flange, and thread the spherical inner grid cage onto the end of the high-voltage feedthrough.

Step #13: Assemble the fusor chamber (cont'd).

Learn How to Build a Nuclear FusorLearn How to Build a Nuclear FusorLearn How to Build a Nuclear Fusor
  • Wearing a fresh pair of gloves, clean the glass cylinder with alcohol and carefully place it on top of the gasket. Apply vacuum grease to both sides of the second gasket and lay it on top of the glass cylinder. Try to avoid getting any grease on the sides of the glass.
  • Now clean the top flange with alcohol and stack it on top of the second gasket, making sure the flange witness marks line up. Finish it off with four 1/4-20 nuts. The nuts should be just finger-tight, only slightly deforming the rubber gasket. Overtightening them may crack the glass!

Step #14: Plumb your fusor.

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  • Cut a 2' length of 3/8" ID reinforced vinyl tubing, slide the 2 hose clamps onto it, and fit the hose over the barbs on your vacuum pump and fusor chamber. Tighten the clamps over the hose and barbs.
  • Follow the instructions provided by the manufacturer of your vacuum pump to get it operating correctly (vacuum oil, power, venting, etc.). Vacuum pumps vary, and you may have to install additional plumbing to fit a male barbed adapter sized for 3/8" ID tubing.

Step #15: Make the high-voltage rectifier.

Learn How to Build a Nuclear FusorLearn How to Build a Nuclear FusorLearn How to Build a Nuclear FusorLearn How to Build a Nuclear Fusor
  • Solder the 2 high-voltage diodes together, making sure the ends with the white bands are facing away from each other.
  • Cut three 2" lengths of 16 AWG stranded wire, strip 1/4" of insulation off the ends, and bend each wire into an S shape. Solder one wire to each free end of the diodes and the third wire to the joint between the two.
  • Crimp a ring terminal to the free end of each of the 3 wires.

Step #16: Make the high-voltage rectifier (cont'd).

Learn How to Build a Nuclear FusorLearn How to Build a Nuclear FusorLearn How to Build a Nuclear Fusor
  • Drill a #21 (or 4mm or 5/32") hole into the top center of three 1/2" PVC pipe caps and “tap” the holes with a #10-32 screw
  • Feed the diode assembly through a 1/2" PVC tee union so that the middle wire goes out the side junction and the other 2 wires go out the ends.

Step #17: Make the high-voltage rectifier (cont'd).

Learn How to Build a Nuclear FusorLearn How to Build a Nuclear FusorLearn How to Build a Nuclear FusorLearn How to Build a Nuclear Fusor
  • Cut three 1-1/2" lengths of 1/2" PVC pipe and glue them into the ends of the tee, around the wire leads.
  • Pass a #10-32 machine screw through each ring terminal and screw it into the threaded hole in each cap.
  • Glue the 2 side caps on, but not the top one yet.

Step #18: Make the high-voltage rectifier (cont'd).

Learn How to Build a Nuclear FusorLearn How to Build a Nuclear FusorLearn How to Build a Nuclear Fusor
  • Place the tee in a vise with the opening facing up, and carefully pour in mineral oil until it’s full to the bottom of the branch.
  • Loosen the vise, rock the tee gently side to side to make sure there aren’t any trapped air bubbles, and then fill it all the way up. Screw the remaining ring terminal to the inside of the top cap and glue the cap in place, sealing the tee permanently.

Step #19: Wire the transformer.

Learn How to Build a Nuclear Fusor
  • If you’re lucky, your neon sign transformer has a power cord attached. If not, open up a male plug with a ground prong and wire one end of a 3-wire AC power cord into it. The green wire goes to the ground prong. The black and white wires go to the hot and neutral prongs — it doesn’t matter which is which.
  • On your NST there should be 2 large ceramic standoffs; these are your high-voltage outputs. Ignore them for now. We’re interested in the 2 smaller input terminals and the single ground screw.
  • Separate the 3 cord wires so the black and white wires reach the input terminals and the green wire reaches the ground screw. Strip ¼" of insulation off the wire ends and crimp a spade terminal to each, then affix the wires to the corresponding terminals. Again, the orientation of the black and white wires doesn’t matter — it will work either way.

Step #20: Wire the fusor.

Learn How to Build a Nuclear FusorLearn How to Build a Nuclear FusorLearn How to Build a Nuclear Fusor
  • Cut three 12" lengths and one 24" length of high-voltage wire, strip 1/4" of insulation off the ends, and crimp a spade connector onto both sides of each one.
  • Attach a 12" wire between each of the 2 high-voltage terminals on the NST and one of the 2 side terminals on the rectifier. Connect the third 12" wire between the top of the rectifier and the fusor’s high-voltage feed-through using a 1/2"-long #10-32 screw.
  • Finally, connect the 24" wire to one of the top studs holding the fusor together, using the nut to hold it on the threaded rod. Attach the other end to the ground screw on your NST.

Step #21: Test the vacuum.

Learn How to Build a Nuclear Fusor
  • When working with glass vacuum chambers, always test the chamber from behind a safety barrier first. I used a door with a window and just ran the power cord under the door.
  • Plug in the vacuum pump and watch from safety as the needle on the vacuum gauge goes to 0. Leave the pump running for 5 minutes. If it doesn’t implode during that time, it should be OK for normal use if treated gently.
  • Turn off the vacuum pump and allow the system to return to ambient pressure before handling or storing the fusor.

Step #22: Working with high voltage.

Learn How to Build a Nuclear Fusor
  • Our fusor is a relatively low-power version, with its components grounded to minimize the danger of shock. Still, accidents happen. Here’s what you need to know to stay safe.
  • Electricians have a saying: Volts hurt, amps kill. Current is more dangerous than voltage — just 10–20 milliamps (mA) of alternating current (AC) can cause muscle contractions that prevent you letting go of the electrified object, and 70mA–100mA can cause heart fibrillation and death.
  • Household AC wall power is typically 120 volts at a lethal 15 amps of current. And it alternates at 60Hz frequency, which can also cause fibrillation. It’s very hazardous.
  • The variable transformer modulates wall power up to 140V AC at 5A current — lower, but still a real electrocution hazard.
  • Next, the neon sign transformer steps up the voltage to a high 12,000V AC and slashes the current to 30mA — unlikely to cause fibrillation but still above the “let-go threshold.”
  • Finally, the rectifier converts AC to DC — direct current — at 6,000V, 30mA. That’s half the voltage of the NST output, and falls below the let-go threshold for DC current (about 75mA). But it can still be deadly, as DC causes worse contractions and tissue burns than AC.
  • So be sure to wire your fusor correctly, and avoid touching any part of it during operation except the variable transformer knob. And when in doubt, ask an expert before proceeding.


Running Your Fusor

Plug the transformer’s power cord into the outlet on your variac, then plug the variac into the wall outlet. Don’t switch the variac on yet.

Turn on the vacuum pump, wait for the gauge to reach 0, then wait another 2–5 minutes to reach deeper vacuum. Leave the pump running. Now switch on the power for the variac and slowly turn the knob, increasing the voltage fed through the transformer.

If everything works, you should see a bright purple discharge inside the chamber, and as you turn up the voltage a defined plasma ball will form inside the grid, with the occasional plasma beam leaching out through one of the grid openings. If you’ve built carefully, you may achieve the coveted “star in a jar”: a glowing plasma ball with fine plasma lines radiating out in all directions through the grid openings.

Congratulations, you have successfully built a demonstration fusion reactor based on the principle of inertial electrostatic confinement!

Never run your fusor for extended periods of time. A minute or two is plenty. Plasma beams escaping from the core may spot-heat the glass and cause it to implode. Make sure that you and everyone nearby wears ANSI-approved safety goggles whenever the cylinder is under vacuum.


Glass vacuum chambers can implode. Do not operate the vacuum system without safety goggles. Reminder: High voltage and current can injure or kill. Fusors may generate harmful radiation. Do not attempt to build or operate this fusor unless you understand the risks and are capable of safely using high voltage and vacuum equipment. Do not run this device at more than 12kV rectifier input.


When you first ignite your reactor, you may see sparks and arcs on the inner grid. As long as these don’t persist in one spot, it’s fine — just bits of dust and debris burning off, and after a while the sparks will stop. But if arcing persists, you’ve probably got carbon deposits, which will continue to arc. This can be dangerous, so stop and clean the chamber thoroughly before proceeding.

If the glow discharge is deep purple, the seals are probably leaky; check the gaskets and reapply vacuum grease. With a good vacuum, you should see a bright, almost-blue purple glow.

This project first appeared in MAKE Volume 36, page 90.

Dan Spangler

Dan Spangler

Dan Spangler is a freelance maker with a passion for fabricating speed, high voltage, and the things that go boom.


  • OK. “who also invented television.”

    Better. “who also invented the world’s first working all-electronic television system”


  • This looks scary as hell.

  • Adans

    Nice weekend-project!
    This is slightly bigger and self-sustained fusion reactor:

  • Ian Lee

    Wow! Super cool project, Daniel. I’m adding this one to my to-do list!

  • While not yet useful as a net energy source, it makes a handy vacuum cleaner size neutron source for hospital isotopes or airport bomb detection.

  • bcook65

    So, how would one theoretically harness the energy from a device such as this provided it actually was able to produce it on a usable scale? (as heat to generate steam?) (induced electrical?) ??????

    • Unfortunately, this system would fail to produce more energy than it takes to initiate and maintain the reaction. I believe that doing so requires much higher energy levels and much trickier containment.

      • Nick Marshall

        Currently the best reactor that I am aware of is called the Tokamak reactor. IIRC it has only just broken even with energy output. http://en.wikipedia.org/wiki/Tokamak

      • cthorm

        IEC fusion devices have very different problems from magnetic confinement fusion devices like ITER and tokamaks.

        Magnetic confinement fusion devices have problems of scale; these devices create a magnetic ‘bottle’ to trap and condense a hot plasma, but hot plasmas have poorly understood scaling properties.

        IEC devices do not have problems of scale, they have problems of optimization. An IEC uses static electro-magnetic fields to collide a beam of high-energy particles. The geometry of the fields and precision of the beams are the current (and long-standing) hurdles to net energy from IEC fusion. If these problems can be adequately solved, then almost certainly Deuterium-Deuterium and Deuterium-Tritium will NOT be the fuels used, because those reactions produce a very high neutron flux (which will damage the device over time); instead the device would use proton-Boron or He3-He3 reactions, which only produce charged particles and are directly converted to electricity (much like PV solar).

  • John

    Marty McFly: [looks through a camcorder] This is heavy-duty, Doc. This is great. Uh, does it run, like, on regular unleaded gasoline?
    Dr. Emmett Brown: Unfortunately, no. It requires something with a little more kick. Plutonium.
    Marty McFly: Um, plutonium. Wait a minute. Are…
    [lowers the camcorder]
    Marty McFly: Are you telling me that this sucker is NUCLEAR?
    Dr. Emmett Brown: Hey, hey, hey! Keep rolling. Keep rolling there.
    [Marty raises the camcorder]
    Dr. Emmett Brown: No, no, no, no, no, this sucker’s electrical, but I need a nuclear reaction to generate the 1.21 gigawatts of electricity I need.
    Marty McFly: Doc, you don’t just walk into a store and-and buy plutonium!

    • Mark Harder

      Actually, it’s uncomfortably feasible to walk in a store and buy some Pu. In Russia, and I hope this has changed, employees of factories and institutions that used Pu could easily break a lock on a wood shack and walk away with some. In one case, this guy simply asked a friend if he knew anyone who would pay for some Pu. His friend contacted a friend of his who recycled car batteries and did some miscellaneous business on the side, as it were. Sure, the friend-of-a-friend said he could unload some. So the guy and his friend walked into the battery guy’s office with the goods. While negotiating the transaction, the place was raided by the cops and they were caught with the goods. Were the cops tipped off about the Pu? Heavens, no! They were there making a bust of one of the battery guy’s side businesses. The stolen Plutonium was just a lucky break for them. A study of the cases where Pu theft was discovered shows that all but a few of these were accidental. In other words, like the battery guy, the perps were discovered not by police detectives who were pursuing reported Pu thefts, but by border guards and others who were inspecting for contraband in general or related black-market crimes. It’s safe to say that we know there is a significant quantity of Pu floating around the world’s black markets, and that we have no idea how much or in whose hands.

      BTW. Just to show where the world’s priorities lie, in the entire history of Fort Knox no gold in any quantity has ever gone missing…

  • Joey

    What kind of transformer do I need and where can I get he transformer at.

    • Its called a Neon Sign Transformer or NST. I used a 12,000v or 12Kv transformer it can either be 30mA or 60mA both will work. I purchased the transformer from ebay, but you should also look for local sign shops that do neon signs they sometimes have some old transformers lying around. You need to choose carefully, modern NST wont work. You need to find a transformer that dose NOT have a Ground Fault Interrupter Circuit or GFI.

  • Jordan Page

    Where might one be able to find the variac you speak of I have already checked variac.com and amazon to no avail. How much can the specs of the variac very?
    Thank You

    • Chris

      Really? I just typed Variac into Ebay and had 547 results… you know the adage “if you don’t know what something is, you probably shouldn’t play with it…”

  • Bob Spline

    Despite decades of research, fusion has yet to be demonstrated in a continuous process. It’s all based on theories about how our sun works, which are being modified as we speak… so the underlying basis for the idea may not be kosher (yes, I am oversimplifying hundreds of academic papers in one sentence ;) ) We would probably be better off thinking about other ways of doing fusion that are based on things which we know can work, such as plasma focus fusion, but unfortunately the pipe dream is still alive. Hopefully, we’ll get more money into PFF and other experimental methods and move forward soon.

    Beautiful toy though :)

    • Dax

      The F-H fusor is a continuous process. It’s just not self-sustaining.

  • Joey

    Someone make a video on how to make it. I bet the video would get a lot of view and it would be really helpful.

  • Re. transformers, an alternative to NSTs is old bug zappers.
    I’ve got just such a beast here and the transformer outputs 7KVAC.
    A worthwhile check is to measure its output inductance and this will show if the problem is a shorted secondary (junk) or just an open primary thermal protector.

    I’ve also experimented with connecting multiple B/W TV flybacks in parallel via diodes, this can increase output current but is very dangerous so please be careful!

    • Dan Spangler

      Other good alternatives are Microwave Oven Transformers. You can daisy chain them together to get high voltages but they are not current limited so they can be more dangerous to handle. you could also try oil burning furnace’s ignition transformers.

  • Paco

    Your build is pretty neat and the result impressive, but have you tested that the system is producing neutrons. I will try to prove this statement later but from memory I think 12kv is not enough (not even near) to achieve fusion.


    • Hey Paco, you are actually correct, 12kv is not enough to achieve fusion. this is only a “Demo Fusor” a working reactor giving off detectable neutrons would be much more involved, and prohibitively expensive.

      • Paco

        “Demo Fusor” as is clearly stated, my fault, went directly to the project steps section.

  • Tom Mc

    So is this thing safe to use, or to have around children? UV is one thing..gamma radiation and x-rays are another. I think this would look absolutely cool as a conversation piece on a coffee table.

    • Dan Spangler

      yup its safe to use. It wont generate any more radiation then the normal background reading. although I would recommend only running it for a few minutes at a time, ion beams generated by the plasma can spot heat the glass and increase the risk of implosion. Other then that it would totally make an awesome conversation piece to have on your coffee table.

    • Safe? Not even remotely.
      Did you read the disclaimers? Dangerous high voltages, possible implosion of a glass cylinder, run only for short periods with adequate safety gear, possibility of x-rays…

  • tapsa

    did you measure also how much this produce UV B and C?

  • ops

    The rectifier construction had me stumped for a second. At first it appeared as though the diodes were backwards and I was like: “Ewww, your anodes are touching!”

    Then I realized, you’re probably shooting for a negative full wave rectifier. Correct me if I’m wrong; I’ve been known to be wrong on occasion. Of course, I think this would only work with a center-tapped transformer.

    This makes oodles more sense than the other way round. In this configuration the more positively charged ions from the relatively high-voltage ground would fall across the voltage drop to the negative voltage ring at the core and *hopefully* collide.

    Though, as others have stated previously, there’s probably not a high enough potential for this to occur at any meaningful or measurable level.

    Fun though! Perhaps I’ll give it a go and start making tweaks until I get delicious neutrons. Mmmm….

    • Richard Hull

      No deuterium gas in this system means not one single fusion will take place. It is a demo system only. In the Intro the comment related to saying there would only be limited fusion is wrong. Zero fusion is correct. With deuterium in the system, fusion is possible but not detectable until you supply -30kv or more…. Far beyond this small system’s capability.

      Real amateur fusors that do real fusion are commonly made with spherical stainless steel chambers. More info on real fusion at Fusor.net. No fusor will ever break even, but will do a decent and usable amount of fusion for amateur research.


  • Matt Wachter

    I don’t understand where the fuel for the reaction is coming from. There’s essentially no hydrogen or duterium in the atmosphere. It seems like the glow could be due to the ionization of the oxygen and nitrogen not removed by the vacuum instead of being due to a fusion reaction.

  • Max Nager

    Could you use a high voltage power supply, such as an induction coil, instead of a neon sign transformer and rectifier?

  • Take Richard’s advice before attempting to build a Fusor, demo or real. There are several ways of hurting/killing yourself and/or your spectators with this equipment. Fusor.net is the best source of information.

  • Wow! It is amazing. The way that you explained about the process of doing this project is very interesting. Keep updating these kind of projects.

  • Anthony Robbins

    Hi, and thank you for posting this build! I’m adding it to my ‘must do’ list.

    I’m a little worried, though about your advise regarding high voltage. Unfortunately, the adage, “Volts hurt, amps kill” is dangerously misleading. Without getting into deeper technical details, the most important thing to keep in mind is that the voltage that shocks you depends on the source, but the current (current=amperage) _depends_ _on_ _the_ _Voltage!_ So a 240v shock delivers twice as much shock current as a 120v shock. The current rating on a supply is the _max_ _continuous_ current it can provide, not the current you will be shocked with.

    So, if you are shocked with 120v, and your body’s resistance is 500000ohms (typical) you will receive 120/500000=0.00024 amps or 0.24mA. If you are shocked with 150000v you will receive 15000/500000=30mA in the deadly range. As the voltage goes up, so does the danger!

    Also, the power supply current rating does not imply a current _limit_ so if you create a low resistance path, your 30mA NST can deliver a brief pulse of much more current, until its internal resistance builds up. If an arc pierces your skin, it will produce just such a low resistance path!

    Please, everyone, keep a healthy respect for these high voltages. These projects are fun and enlightening, but the danger is usually invisible, and misunderstanding can kill.

    Happy star building!

  • art

    Hi guys just wondering does anyone have a list of everything that is needed for this fusor, including tools?

    • art

      Hi guys just wondering does anyone have a list of everything that is needed to make this fusor, including tools?

    • Dan Spangler

      the parts and tool lists are at the top of this page to the right of the picture

  • Don

    Just a note that McMaster-Carr are not able to ship outside of the US, any ideas on other suppliers who can help?

  • James

    Does anyone know where to find a vacuum pump that meets the requirements for this? I have been looking for a 25 micron one to no avail and just realized it says minimum, so does that mean a 75 micron one could work, or as long as its 25 or lower you are good. In desperate need of an answer soon, Christmas is coming.

    • here ya go James, Harbor Freight Special http://www.harborfreight.com/3-cfm-two-stage-vacuum-pump-60805.html . Also the maximum vacuum rating listed on vacuum pumps is a “best case scenario” kind of thing, due to outgassing and micro leaks your chamber will probably not reach the low of a vacuum. So while i know we recommend 25 micron, I’m pretty confident you can make it work with a 75 micron pump. hope this helps

  • Zach Cloud

    Alright. This looks cool and all, but my one question is this: Where does the fuel needed to supply the reaction come from?

  • Max Nager

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  • jake

    Before I build this I want to know if it will release any harmful amounts of radiation. I don’t see where the uv, x-rays, and gamma rays would come from as there is really nothing to be fused. I read all of the comments and I understand this is a demo, but comments on the youtube video and some here make me feel like I need a lead lined body suit and something to put this in to stop damage from radiation. I’m not worried about the electric components because I’ve worked on other high voltage projects like Tesla coils. Could I please have a solid reply? thanks

    • Hey Jake, so we put a Geiger counter right next to the chamber when it was on and we didn’t get a single click out of it. that being said it does produce soft x-rays from bremsstrahlung collisions. But these soft x rays wouldn’t expose you to anything more then standing in front of a CRT monitor. so no you don’t need a lead lined suit, and the only shielding I might consider around the chamber would be some polycarbonate sheets to capture derbies in case of implosion. hope this helps, we would love to see pictures of your finished reactor.

      • jake

        Thanks :)

  • Felix K

    You just made a big neon bulb with air instead of neon.
    I can do same with a microwave oven and a glass chamber under vacuum. It is called Pashen discharge. I suppose someone could build this to graduate to one at 35kV. Tesla anyone?

  • Max Nager

    I would still like to no if you can use a high-voltage power supply, like an induction coil, instead of a rectifier.

  • Matt Forquer

    Where can I find a glass cylinder?
    I’ve been looking at a lot of industrial and scientific supply websites, yet I can not seem to find someone who sells glass tubing of that diameter.

    • Jimmy Tsang

      It’s actually on the parts list on the top right part of the screen, just right of the first picture. There it gives a website and the part number for the glass cylinder. hope that helps

  • karston P.

    what kind of radiation does this give off? and would it be anything to worry about?

    • M_Wilson271

      UV radiation may be an issue. It is unlikely that you will produce neutrons out of this device so long as you keep the voltage below 8KV and only use air in the chamber.

      • Isaac Metcalf

        X-rays will be produced. Use an old TV screen to block them, or any leaded glass.

        • Adi

          Actually since all you are doing is ionizing common elements in the air like oxygen and nitrogen, all this is doing is creating a plasma, no actual fusion reactions are happening here, the elements aren’t capable of it, however if you were using deuterium that would be a different story. With no fusion reactions, there is no production of x-rays, just visual light given off by the plasma. No shielding will be necessary for this type of fusor.

          • Cheezey

            X-rays can be produced without fusion by high-voltage discharge. Fusion creates neutron or gamma radiation.

  • Jason Grote

    like whoa

  • Can you use a ball valve to sustain the vacuum, or does the pump need to constantly run?

    • Nuc101

      Unless you’re able to create a perfect seal around all aspects of the device, you have to keep the pump running at all times. Even then, I would use one-way check valves.

  • Codey Bond Tynan

    wish this had a parts list.

  • Guest

    I’m trying to do this project in Britain. What changes will i have to make to the electronics in my fusor?

  • Aiden

    I am building this project, and am struggling with step 9. I have tried 3 types of solder and 2 types of flux, but none of them will flow into the joint. The solder beads up and/or falls off. The latest solder I tried is a hard silver solder, melting at 1400 degrees. Any ideas on what could be going wrong?

    • TheOtherGuy

      I’m having the same problem. I’m wondering if the stainless wire in the parts list is too thin, It looks a lot thinner than the picture. I wonder if a jeweler might have the ability to do this. If thicker wire won’t work I’ll go check with one and see what they say or have them fabricate the grid.

      • Jay Jacobs

        We had this same problem, but we ended up getting both hard silver solder (high melting point) AND flux rated for the same high temperatures. When we tried “regular” flux with the hard silver solder the flux burned away quick and the solder would never stick and just beaded up. However, with the high-temp flux applied it didn’t burn away and was able to suck the solder into the joint.

        • TheOtherGuy

          I will try that.

    • Ben Moss

      We are also struggling with this step. I’ve tried using gas torch, sanding to clean, using the high temp solder and flux and nothing I have tried comes close to being able to get the solder to stick to the wire. The wire that we ordered, as mentioned in another post here, is much thinner than it looks in the photos of the build. Is there an alternative to SS? Copper? Did you ever solve this problem? What did you do?

      • I know two ways to join stainless steel – both work very well.

        a) Use gel-phosphoric acid (sold as Naval Jelly) and lead-tin solder. Wets wonderfully. But it’s soft-solder so won’t take high temperatures.

        b) Use a propane flame and silver-loaded pre-fluxed spelter. Heat to dim red, and dab on the spelter. But, you’ll need to grind off the oxide layer to retain the passivation.

  • TheOtherGuy

    The wires used to make your grid look a lot thicker than the .032″ wire in the parts list. Is the parts list correct?

  • Taegan Hallahan

    Where can i get the nptf pipe male threads?

  • Vincent Castilow

    If the ions are accelerating toward the charge on the wire frame, why not substitute the core with Boron wire to see if Aneutronic fusion would occur between the boron and hydrogen, instead of Deuterium-Deuterium Fusion?

  • Farasat Ahmed

    Can I use a single stage vacuum pump for this?

  • Aiden

    What type of vacuum pump did you use?

  • Farasat Ahmed

    How can we measure the energy output of the fusor?
    How can we prove that the fusor is working?

    Thanks in advance!

    • Atabey Önür

      Actually this one is not working, it is just demonstrating the principle of the fusor.

  • Cameron

    Does anyone know if the method of constructing a vacuum chamber described can handle a vacuum of 0.1 microns?

  • Guest

    What is the ideal thickness of the aluminum discs, I may be buying pre-cut discs for a lack of equipment and money.

    • Guest

      Would 1/4 inch be sufficient?

  • Caedon Bates

    Will this work with acrylic tubing instead of glass for the main chamber?

  • Apply raw wood putty, following the instructions on the box, to the prop holes in addition to sand soft. Add stain or color as needed.

  • Laura Benzing

    Does this produce detectable radiation? It uses air and not deuterium gas.

    • Dane Cross

      From what I know, the only radiation this releases is medium-energy neutrons and very few X-Rays. I would stare at it for too long, but otherwise it is safe.

  • Otis Bagshots

    Where’s the link to the flange template?

    • Dane Cross

      Just in case you didn’t find it; it’s in step #2.

  • Dane Cross

    Do things such as the ring and spade terminals need to be rated at high voltage? Or can I just use ordinary ones. Also, a link to the flange template would be fantastic. Otherwise, great tutorial.

  • Guest

    can I also build a mini nuclear bomb at my home? If the ans is yes, how can I do it?

    • Wojak

      Nuclear bombs work with fission, not fusion. Wrong type of nuclear reactor.

    • Mr. Cat

      This would be for a hydrogen bomb.

      • Nyzen

        First the A-bomb, then the H-bomb, now it’s time for america to drop the F-Bomb

  • Juan Martinez

    I am not sure if I missed it but what’s the OD and length of the large glass/pyrex cylinder thats responsible for actually containing the grid?

  • Sam Reid

    Does this thing use the usual components of air or does it use deuterium? If it uses air, does it create actual fusion or just glowing plasma?

    • The build directions show you how to make a Mk-1 Farnsworth Fusor which just uses air and by utilizing IEC, the particles will be ionized and will fall into a voltage drop (generally the center) while being repelled by the inside walls. Henceforth an outside force vector will accelerate the particles toward the center where they will collide/bounce/miss eachother.

      This is just a demo fusor so actual fusion will not be happening; however, by improving the design from this page, you can achieve true fusion. The diagram shows a deuterium fuel injection; by following the same procedures, using a higher CFM vacuum pump will clear almost all the obstructing air, then augmenting a lever pipe somewhere on either of the metal blanks and attaching it to a deuterium tank.

      Run the fusor including the vacuum, after “very” brief moment start injecting deuterium and you will get fusion.

      And of course go through the same safety tests before experimenting, High Voltage, Implosion, and UV/X-Ray Radiation are the biggest concerns I can think of on the top of my head. A lead plate should block the irradiation.

  • Sam Reid

    Also, the diagram at the top shows deuterium fusion. How would one go about adding deuterium to the vacuum using the mechanism of this particular design? How much deuterium should be added?

  • Isaac Pooop

    I was just wondering what vacuum pump you have and if you can tell me any pump that would work

  • Isaac Pooop

    Can anyone tell me a fairly cheap (around $130) vacuum pump that would work for this and where it is found, THANKS!!!!

  • Otis Bagshots

    On the parts list the spade terminals are for 14-16 AWG but shouldn’t they be for 20 AWG (as thats the high voltage wire they are connected to)?

  • Oliver Murfett

    does this actually use deuterium or any other type of fuel. if not can someone please explain how this can be called a fusor

  • Amber

    What is the approximate time of completion?

  • Amber

    Is there any where I could directly buy these parts?

  • ahmad

    i am building this project, and i am wondering about the parts list, somethings look unnecessary, such as 20 High-voltage wire, 302°F, 20 AWG, 0.138″ OD, 20,000VDC. doesnt it have to be only 6KVDC?

  • John

    Could I pump deuterium gas into this fusor and get real fusion reactions or is this demo fusor to fragile to handle it?

  • John

    I have been looking for an NST without ground fault protection for a bit now but I cannot find one for the life of me. If someone could point me in the right direction or tell me where they bought their NST that would be much appreciated.

  • Blake Sturges

    I’m finishing up buying the parts in preparation to build this, but the wiring confuses me a bit. Why would you bother getting an NST with an output of 12kV if you’re just going to step it down to 6kV before doing anything with it?

    Also, when you say “110-140V Variac,” does that mean I could buy a 110V variac or that it should be capable of handling a range of voltages?