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 Hurricane Q & A
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Q:
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How would a major hurricane affect the lab’s magnets?
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A:
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The resistive magnets, which use cooled water and electricity to operate, likely would not be structurally damaged, as they would not be operating during a hurricane and don’t store energy. Resistive magnets weigh between 3 and 5 tons; they aren’t going anywhere. But if the lab’s infrastructure was seriously damaged, the resistive magnets would be inoperable.
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Q:
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What do you mean by infrastructure?
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A:
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Infrastructure includes chilled water tanks and pipes, chillers, large transformers and lots of sophisticated electrical and other equipment necessary to operate the magnets. The infrastructure would have to be replaced or repaired before the magnets could be brought back into service.
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Q:
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What about the superconducting magnets – how would they be affected by a serious hurricane?
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A:
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The lab’s signature superconducting magnet, the $17-million, 900-megahertz magnet, requires a weekly supply of cryogens – specifically liquid helium and liquid nitrogen – to sustain its perpetual 21.1-tesla magnetic field. The 900 and other superconducting magnets at the lab are made of special superconducting wire that conducts electricity without resistance as long as the magnets are kept at a very cold temperature. Superconducting magnet coils are submerged in liquid helium, which is why the magnets look like overgrown Thermoses. Once the magnet is powered up, the current runs continuously through it without needing electricity as long as the operating temperature is 4.2 degrees kelvin (to put that in perspective, water freezes at 255 degrees kelvin!). Power is still critical to the magnet, however, because it’s needed to operate the cryogen pumps.
So the two biggest hurricane-related issues for the 900 are having enough cryogens to last until the roads are cleared and more can be brought in, and having enough generating capacity – and fuel – to run the pumps.
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Q:
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How long could you keep the 900 operating without refilling its liquid helium supply?
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A:
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If it was topped off before the storm, probably a week, provided the pumps are operating. In the event of a catastrophic hurricane, the lab’s leaders would have to decide whether or not to intentionally lower the current and field in the magnet to reduce its dependence on the pumps running. If the magnet is at lower field, it can remain superconducting without the pumps running, but it will still need cryogens.
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Q:
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What is a quench – and is it dangerous?
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A:
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A quench occurs when the superconducting wire goes "normal." That happens when the wire warms up enough that it loses its superconducting properties. At that point, all the tremendous stored energy is released into the rest of the coil as heat, causing the liquid helium to boil off. Sounds dynamic, and it is, but it’s not dangerous. Lab personnel are be able to see in advance the signs of a possible quench, and should the magnet quench, the boiled-off gas would travel out of the magnet and the building through one of two redundant paths to the exterior of the building. These escape hatches were built into the engineering and design of the magnet and the building for just this purpose.
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Q:
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What about the lab’s 45-tesla hybrid magnet?
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A:
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The hybrid magnet is part superconducting, part resistive. But the 14-ton superconducting outsert is not persistent; it is only energized when the magnet is operating. As such, there is no chance that it could quench and it poses no danger to personnel. Because of its enormous mass, the hybrid, even after the liquid helium boils off, takes a long time to warm. How soon it could be brought back into service depends on how long the power is out. If the power were out for only a few days, the magnet could be ready for operation in a week or two, depending on what resources are available and the extent of the damage to infrastructure. The longer the power is out, the longer it will take to bring it back into service.
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Q:
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Why would it take so long to bring the 900 and hybrid magnets back into service?
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A:
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It takes a long time to cool anything down to 4.2 Kelvin!
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