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Yup. One thing I'm wondering: superconductors are supposed to be more efficient because they waste no power as heat. But doesn't it take power to maintain suc

Yup. One thing I'm wondering: superconductors are supposed to be more efficient because they waste no power as heat. But doesn't it take power to maintain such cold temperatures, even for "high temperature" liquid nitrogen temperatures? How does this compare to the energy we save from the lack of resistance in the superconductor?

AussieWog93 4y ago
>But doesn't it take power to maintain such cold temperatures, even for "high temperature" liquid nitrogen temperatures? How does this compare to the energy we save from the lack of resistance in the superconductor? Not a thermals guy, but bog-standard, consumer air conditioners tend to have efficiencies of 300% or so. Ie, for every joule of electrical energy consumed, they'll reduce the thermal energy in the room by 3 joules. Regardless of this, having zero heat output in the wafer itself could be far more interesting than just increased power efficiency. For example, without the issue of thermals one could imagine silicon wafers with thousands of layers and 3-D interconnects.
willis936 4y ago
It depends on how much current you want. I worked on a 1.2 m major radius 1 T copper stellarator that used 10 MW of power for the confinement coils. The coils are water cooled but even then the shots are only 1-second to avoid overheating (and to save on the engineering cost of the power system). Any real fusion reactor would need 5+ T confinement fields and be 2+ times the radius of this machine. You would be using many GW in ohmic losses in copper confinement coils for hundreds of MW of fusion power: it simply could never work. A cryoplant for an LTS fusion reactor would use on the order of 50 MW, a bit less for HTS. So for the big magnet application superconductors are an incredible win.
XorNot 4y ago
It's a question of what you're spending power on. When you cool something there's the action of pumping heat away from it, and then the issue of how easily heat can migrate back in. So you're only really fighting the inefficiency of your insulation, and insulation can be very, very good (at the extreme end you could magnetically balance something in a vacuum chamber and then chill it - it'll take a very long time to heat up by radiative emission from the walls (double wall insulated cups use this property though my take is they're just gas filled - same idea though). Essentially the ongoing cost of keeping something cool is purely a function of heat load making it through insulation, and in all cases that's going to be much lower then generating heat in the system - the problem is that engineering and complexity wise, it's non-trivial and failure scenarios can be bad - i.e. an SC magnet quench can be very bad since you amongst other things might immediately boil your coolant. This happened at the LHC during commissioning.

AussieWog93 4y ago

>But doesn't it take power to maintain such cold temperatures, even for "high temperature" liquid nitrogen temperatures? How does this compare to the energy we save from the lack of resistance in the superconductor? Not a thermals guy, but bog-standard, consumer air conditioners tend to have efficiencies of 300% or so. Ie, for every joule of electrical energy consumed, they'll reduce the thermal energy in the room by 3 joules. Regardless of this, having zero heat output in the wafer itself could be far more interesting than just increased power efficiency. For example, without the issue of thermals one could imagine silicon wafers with thousands of layers and 3-D interconnects.

willis936 4y ago

It depends on how much current you want. I worked on a 1.2 m major radius 1 T copper stellarator that used 10 MW of power for the confinement coils. The coils are water cooled but even then the shots are only 1-second to avoid overheating (and to save on the engineering cost of the power system). Any real fusion reactor would need 5+ T confinement fields and be 2+ times the radius of this machine. You would be using many GW in ohmic losses in copper confinement coils for hundreds of MW of fusion power: it simply could never work. A cryoplant for an LTS fusion reactor would use on the order of 50 MW, a bit less for HTS. So for the big magnet application superconductors are an incredible win.

XorNot 4y ago

It's a question of what you're spending power on. When you cool something there's the action of pumping heat away from it, and then the issue of how easily heat can migrate back in. So you're only really fighting the inefficiency of your insulation, and insulation can be very, very good (at the extreme end you could magnetically balance something in a vacuum chamber and then chill it - it'll take a very long time to heat up by radiative emission from the walls (double wall insulated cups use this property though my take is they're just gas filled - same idea though). Essentially the ongoing cost of keeping something cool is purely a function of heat load making it through insulation, and in all cases that's going to be much lower then generating heat in the system - the problem is that engineering and complexity wise, it's non-trivial and failure scenarios can be bad - i.e. an SC magnet quench can be very bad since you amongst other things might immediately boil your coolant. This happened at the LHC during commissioning.