Homepage Forums Dense Plasma Focus (DPF) Science and Applications Why 5MW? (question from Indiegogo campaign)

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    Hey, I eventually found my way here after contributing to the Indiegogo campaign. (Is this the right forum?)

    I’m excited for you all, but I thought of a few questions, mostly around scaling, that the Indiegogo 500 character length made difficult to ask and answer:

    * Is 5 megawatts the optimum size, or the minimum-viable-prototype size?
    It just seems small when “typical” power plants are in the hundreds or thousands of megawatts range.

    * What metric are you trying to optimize in this 5MW size?
    (cost per reactor, time to prototype, “best” fusion results, convenience, etc.)

    * What limitations are there to going bigger or smaller?

    * If this is the minimum-viable-prototype size, what are the cost-per-reactor or the cost-per-watt optimal sizes?

    * What parameters can you tweak on this design?
    (size of chamber, pulses (in Hz), current, voltage, number of spokes on cathode,etc)

    * Broadly, how do changes in these parameters affect performance?

    * Does it run only p-B11, or can I run other fuel if I don’t care about radiation?

    Again, I’m really excited to see that this team (or any team) feels they are just one step away from net energy. I’m happy to help humanity along by contributing!

    AvatarIvy Matt

    The DPF is unusual among nuclear fusion devices in that it is not expected to work better as a fusion reactor at larger scales. The Focus Fusion-1 device is already at the optimum* size for net fusion gain according to Eric’s theory, except that the electrodes will need to be shorter for the final experiments. (*Actually, i believe the DPF could be smaller, but then you’d have the electrodes too close to the plasmoid for comfort.) My understanding is that the major difference between FF-1 and other DPFs is that FF-1 has a greater amperage-to-size ratio than other DPFs.

    With regard to the energy output, that’s determined by the frequency of the pulses. Too few pulses and the boron precipitates onto the electrodes. Too many pulses and cooling becomes difficult. I believe 5MW is the minimum viable output, and the maximum viable output is something like 20MW. Of course, if you want greater output, you can always use several devices in one power station.

    You can use anything you want as the fill gas. LPP has been using deuterium to achieve the neutron yields they’ve reported. However, as I understand it, using heavier elements is an important factor in achieving higher density. For this reason they don’t expect to achieve net fusion gain until after they switch to using boron with hydrogen.


    Hello, NortySpock, and you’ve come to the right place. Welcome to the forums!

    The 5 MW per Focus Fusion (FF) unit seems pretty firm at this time. But that’s perfectly suitable for a distributed, modern, disaster-resistant power grid.

    The current gigawatt-class power plants are a convenience for those that own the plant and/or the fuel supplies… for the rest of us, not so much. Especially when one plant going down puts the whole system under critical stress.

    But if a location such as a large factory needs more than 5 MW on hand? The units will stack easily… and cheaply 🙂

    As for why 5 MW? The power output is primarily determined by the repetition rate, 200 hz for 5 MW, and is bounded by two limits: cooling and heating.

    A. Too much slower than 200 hz and the vaporized boron in the fuel will plate out and coat the interior of the vacuum chamber. Not good as things grind to a halt.

    B. Too much faster than 200 hz and the anode, the central electrode, begins to melt. It will be cooled by helium under pressure and while that should be doable for 200 hz it probably couldn’t be pushed too much further.

    As for using D-T and other neutronic fuels? While technically it’ll be possible to use such in an FF unit but you’d run into three immediate problems:

    1. Fuels such as D-T release their energy primarily as neutrons, which will have to be used heat water to make steam to tutn (very expensive) turbines in order to generate power.

    2. The FF unit can only run at a few hundred degrees Celsius, and that’s with the helum cooling. That’s well below what’s needed to run those expensive turbines efficiently… but trying to crank up the power will just melt your electrodes into slag.

    3. … and the slag, the vacuum chamber and all the surrounding gear will be highly radioactive for a long time.

    The direct conversion made possible by aneutronic fuels skips all that, even if the bar for breakeven is set much higher.


    Thanks for the explanations, Ivy Matt and zapkitty. You answered all my questions! Interesting to hear that the power output is basically all in the pulse rate.

    AvatarAlex Pollard

    zapkitty wrote:

    As for using D-T and other neutronic fuels?

    Also tritium is much more costly than the common isotopes of boron and hydrogen:


    “225 kg (496 lb) of tritium has been produced in the United States since 1955. Since it continually decays into helium-3, the total amount remaining was about 75 kg (165 lb) at the time of the report.”

    This is a key advantage of FF over almost all other concepts. There is no need to “breed” the fuel. Quite frankly ITER is pie in the sky on this count alone.

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