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Comment by paulsutter | Hacker News Reader

These are Farnswoth Fusors[1], first developed by Philo T Farnsworth, one of the inventors of television.

The devices use about 100,000x more energy than they produce FROM FUSION (edit, thanks), but some fusion does occur. An individual ion can be heated by 11,000 kelvins with a single electron volt, so 15,000ev is enough to reach fusion temperature. The statistical challenge is getting ions to collide - overcome the (repelling) coulomb force - and fuse.

There are discusson groups online for this topic [2] and there's even a high school in the Seattle area that has a fusor [3].

[1] https://en.wikipedia.org/wiki/Fusor

[2] http://www.fusor.net/board/

[3] http://www.industrytap.com/overview-polywell/31940

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I've built a fusor[1], and in its simplified form, it's just a large, negatively charged grid in a vacuum chamber with some hydrogen sitting around. Nothing to be afraid of!

You're absolutely right that these devices don't produce net energy. I built mine because I wanted to learn more about all the tech involved (high vacuum, high voltage, some nuclear physics). They're really good teaching projects for folks going into experimental physics, since there's a neat outcome without too much danger.

I assembled a coffee table book with some pretty pictures about it, PDF copy here: http://shia.wsyntax.com/stuff/fusion/fusor_book_web.pdf

[1] http://fusion.wsyntax.com/ , http://fusion.wsyntax.com/setup/

I really enjoyed reading that, thanks!

Very interesting. Thanks for that.

How much would it cost, roughly, to manufacture helium from one of these?

From what I understand, we are running out of our natural stock.

It would cost a fuck ton! Here's how I figure it:

Each fusion event makes one He atom and releases about 17 MeV of fusion energy. Since (one mole) X (one eV) = ~100,000 Joules, fusing one mole (2 grams) of He would produce about 1.7 X 10^12 Joules. That's about 472 megawatt-hours of fusion energy produced.

Another commenter says that the energy INput (to the Farnsworth fusor) is about 100,000 times the energy OUTput; so fusing that 2 grams of He would require a 2,000 megawatt power plant to run for 23,600 hours, or 2.7 years.

Readers: please correct any mistakes you find.

> fusing one mole (2 grams) of He would produce about... 472 megawatt-hours

Or, from a different angle, that energy density is why fusion is the holy grail of energy.

Since a fusor normally runs on deuterium fuel, wouldn't the output be helium-3 with a mass of 3 grams/mole?

Not that it makes a big difference - producing helium with a fusor remains extremely impractical.

Oops! I used He's atomic number (2) instead of its atomic mass (usually 4).

I believe deuterium fusion events mostly produce He4, occasionally He3 + neutron. So we'd actually produce between 3 and 4 grams.

No, deuterium-deuterium fusion reactions usually produce helium-3 and a neutron. Due to the conservation of energy, producing helium-4 requires the emission of a gamma ray. This happens rarely because, since the strong nuclear force is stronger than the electromagnetic force at small distances, fusion reactions tend to release energy as protons and neutrons rather than gamma rays.

> Philo T Farnsworth, one of the inventors of television

The (very) old game show "I've Got A Secret" had Farnsworth on as a guest, with his invention of television as the "secret".

    Player:     "Do doctors use this object?"
    Farnsworth: "Yes, it's been used in surgery."
    Player:     "Is this some kind of machine that
                 is painful when it is used?"
    Farnsworth: "Yes, sometimes it's most painful!"

https://www.youtube.com/watch?v=pKM4MNrB25o

"These are Farnswoth Fusors[1], first developed by Philo T Farnsworth, one of the inventors of television."

Wow, I've been a Futurama fan since the show first came out and just now got that reference. Well done, Matt and David.

IMO, produces energy is a poor way of describing at this. They produce ~1,000 parts light:99,001 parts heat per 100,000 units of electricity and 1 units of fusion. In other words 100,000 units of electricity liberates 1 unit of fusion power.

https://en.wikipedia.org/wiki/Fusion_energy_gain_factor is meaningful, but it's talking about inputs not outputs.

PS: Ok, heat is a poor description. 1,000 pars light, 99,000.9 units of heat, and 0.1 unit high energy particle radiation.

Isn't that like saying a lightbulb doesn't use any energy because its output of heat and light equals the energy input? Or that I didn't use any money shopping because the cash all stayed in the economy?

Sure, a light-bulb does not destroy any energy, it uses electricity and increases Entropy. If you want to say it consumes something then a light bulb consumes the potential to create Order by transforming electricity into heat and light.

It sounds like the argument is considering what the output energy might be used for. If you want a fusion device to power your heating and lighting, then the "waste" heat and light from the device may actually be useful.

It's like replacing the radiators in your house with servers or bitcoin miners; you still pay for electricity, and it's still warming up your house, but you get compute cycles or bitcoins "for free". If the waste heat/light of a fusion device is of comparable efficiency as conventional heaters/lighting, then we're "breaking even"; if the device manages to perform any fusion, that liberated energy would be a "net positive".

Of course, a fusor doesn't seem like a particularly good idea for household heating or lighting, and that argument is completely inapplicable to things like power plants.

Not many people have turned one element into another. That alone is pretty cool.

> that argument is completely inapplicable to things like power plants

Actually, it's not unheard of for waste heat from power plants to be used as residential heating.

https://en.wikipedia.org/wiki/Cogeneration

Some of the nordic countries use local power plants to create municipal steam for heating homes, I believe.

I looked at building one a couple of years ago before deciding I couldn't afford the equipment to make sure it was safe, but I always had this in the back of my mind: Don't all nuclear reactors use heat as the main output? To drive steam generators (like a conventional plant) or solid-state devices like a peltier-based battery used in satellites?

If you put a bounding box around a Farnsworth Fusor, and put in 100W of energy, would you not get a little more than 100W output from the fusion reaction?

Obviously still not viable as self-sustaining, since 100W of electric energy in would be lower entropy than the 100W+ coming out, but it would be a method of producing some energy as long as it's fed from another source.

Obviously, using a heat pump would be a much better way of turning 100W of electricity in to >100W heat, but still, a Fusor isn't net energy negative (although it is terrible with conversion of entropy).

You are ignoring the energy in the fuel. Which is arguably a reasonable thing to do as we don't have great fusion reactors yet and H Bombs are not exactly sold at Home Depot. But, it's still the kind of fuzzy thinking that leads you to assuming bad ideas will work.

As to 100W vs. > 100W. 100.001W might as well just be 100W in just about any meaningful way. However, Jet is vastly cheaper per watt of liberated fusion energy. https://en.wikipedia.org/wiki/Joint_European_Torus

It depends what the main power output is. Neutrons from D-D or D-T (deuterium-tritium) are really hard to convert into electricity, but some types of fusion like p-B11 (hydrogen/boron) generates alpha particles that can be directly converted to electricity.

> These are Farnswoth Fusors, first developed by Philo T Farnsworth, one of the inventors of television.

that sounds like something straight out of a heinlein book!

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