Does anyone know whether nuclear fusion energy gain numbers contain energy requirements for keeping the magnets cooled and the vacuum at high quality?
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Replying to @skdh
usually not; the Q for ignition (5) is basically about the amount of energy absorbed by alpha particles directly, the physicists handwave away the magnet cooling and vacuum maintenance energy costs as something that asymptotes out; micro reactor people sometimes factor it in
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Replying to @DanielleFong @skdh
When I left, there was some debate on desirability of ignition (Q>5 -> inf). Alpha's in the core might drive MHD/kinetic instabilities and disruptions; so accepting first orbit loses of alpha, forgoing ignition and focusing on high but not infinite Q might be more practical.
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Replying to @SebTallents @skdh
but it is going to be a vastly less expensive thing if it’s self heated rather than requiring a bunch of circulating power
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Replying to @DanielleFong @skdh
Not really, counter intuitively. If you need aux heating to get to ignition, then all you are doing is having that aux heating sitting around doing nothing, and capex and finance costs more than the electricity consumed. The whole thing is driven hugely by capex, not opex...
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Replying to @SebTallents @skdh
most aux heating operates in burst mode, to adapt it you need at minimum new cooling and probably a lot of other stuff, and you need a bunch of stuff to power it, all of which has inefficiencies. it adds up!
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Replying to @DanielleFong @skdh
Iirc the idea was keep the plasma going and pulse the heating so you get periods of fusion. Either way the point is the difference between ignition and non ignition is the cost of electricity to run heating, and depreciation of the capital invested in the aux heating kit.
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Replying to @SebTallents @skdh
yeah i guess that kind of subcritical rundown could make sense if the physics works out but you’re still trading one problem (physics of alpha heating) for another (physics of pulsed operation). still think near continuous operation is a better bet but it’s a theory really
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Replying to @DanielleFong @skdh
The trade off is less risk of catastrophic disruptions that ruin your reactor, and you don’t necessarily need so much magnetic volume / field strength to prevent first orbit losses from the region inside internal transport barrier - and magnetic volume drives the overall capex.
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But as you say, it’s all fairly theoretical. What I eventually took away from it all is “nuclear power needs to come in c. 200mw chunks of predictably long lived expensive plant, or short lived cheap plant”.
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direct conversion or non steam plant generating systems may change the equation quite a bit.
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