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Fusion energy gain factor

  1. Nov 21, 2007 #1
    I have a general interest in fusion energy and I'm currently looking at the 'fusion energy gain factor' (Q) of fusion reactors (the energy produced divided by the energy used to induce ignition). I'm aware that the JET recorded a Q factor of 0.7 in 1997, the ITER is anticipated to have a Q factor of 10 and the DEMO a Q factor of 25. The Q factor doesn't include the energy used to power the toroidal magnets and I would be interested to know what power these would require and by how much superconducting electromagnets would reduce energy use (power consumption being negligible in the steady field state for SC electromagnets). I've read that for a fusion power station to break even, the Q factor would have to be over 20 due to the power required for current drive, refuelling, profile control and burn control, I'd be interested to know how the factor of 20 'breaks down' regarding these different aspects of energy use (specifically the powering ot the toroidal magnets).

    Last edited: Nov 21, 2007
  2. jcsd
  3. Nov 26, 2007 #2


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    One has to properly define Q for it to be useful. I've learned scientific Q vs engineering Q-values.

    Here is a reasonable discussion. Technically the energy input must includes all energy inputs including that used to establish and maintain confinement.


    It doesn't address all the details and nuances, but it is one I can readily get my hands on. :rolleyes:
  4. Dec 5, 2007 #3
    Thanks for the reply Astronuc. I sent an email to EURATOM/UKAEA Fusion Association at Culhum Science Centre asking the same question but I'm yet to get a reply.

    One thing I did find on the web was an interactive simulator for ITER (you can choose between ITER 85 and 05) where you decide the strength of the magnetic confinement, the power input and amount of fuel used (a dial tells you underneath how much power you are using). You can also configure the cross section of the plasma to obtain optimum output. Dials to the left tell you how much energy you're producing (taking into account the energy used). Apparently, you should get an output of 1000 MW. Though obviously this isn't hard evidence of the energy used by the magnetic confinement, it's still an interesting simulation.

    Link- http://fusion.gat.com/diii-d_global/simulation/jstar/ [Broken]
    Last edited by a moderator: May 3, 2017
  5. Dec 5, 2007 #4
    Hey, that's fun! I had found something similar a while back, it looks about the same here.

    I got 1405 MW of electrical output. I suppose the introductory fusion class helped. :rofl:
    Last edited by a moderator: May 3, 2017
  6. Aug 21, 2008 #5

    Q simply refers to the energy quotient as you describe above, and by rights all energy should be taken into consideration. There are always suspicions that the big labs fiddle the numbers and leave out some important information to make the numbers look better. After all they depend on getting more funding next year.

    I atttach a pdf file that gives some information about Q from the JET reactor in Culham.

    As you may be aware, I belong to a group of amateur fusioneers at www.fusor.net and we have a simple method of calculating Q, where we include all energy in (except the energy required to drive vacuum pumps).

    I have set up a permanent Q calculator at

    http://www.beejewel.com.au/research/fusion_calculator.htm" [Broken]

    ,that anyone with a bubble detector can use, even the big guys if they dare :)

    The reason we trust the BTI bubble detector is that all electronic detectors are subject to interference by EMF and we have found that neutron readings are often overstated.

    In world of amateur fusion we are still aiming to break the Q 1e-8 barrier http://www.fusor.net/board/view.php?bn=fusor_construction&key=1212188288" [Broken]

    Have fun..


    Attached Files:

    Last edited by a moderator: May 3, 2017
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