Persistent Switch

2 08 2009

I’m starting to fabricate the persistent switch for the superconducting cable. Cryogenic Control Systems sells these heater cartridges for the purpose. Another option is to fabricate our own heater with the nichrome wire used for the reprap’s heater barrel. With a persistent switch we can test out the superconducting cable with a current.

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3 08 2009
theorbtwo

Note that many reprappers are starting to use low-value, high-wattage resistors, rather then using nicrome wire — it’s a lot less work that way. Also, we’re moving to using kapton tape to insulate the nicrome, for those that do still use it, rather then using cement of various sorts.
Hm. I was about to wonder if the heater element would work when you need to start it in cryogenic conditions (while your heater element won’t be superconducting, it’ll certainly be significantly more conducting then it should be). OTOH, a heater cartridge specifically designed to be able to be frozen hard, exposed to vacuum, thawed out again, and used sounds like a *very* good thing — which would mean Cryogenic Control Systems’ heater, instead of something more… home-grown.

Also, a vaugely related question for you: How would a commercial reactor that needs very nearly 100% uptime work, when your superconducting magnets will slowly discharge themselves, because there’s no way of topping them up when running in persistent mode, and your superconductors still have a (very low, but nonzero) resistance?
Does that imply that every few months, you will loose the magnetic constriction, the reactor will go offline, and you’ll have to restart?
If so, you’d need N+1 individual reactors and to do a rolling start, just to have N running full-time, *assuming nothing ever goes wrong*.

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