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I’d like to know the current carrying capacity of copper wires in vacuum.
The current plan (NPI) calls for sending ~3 amps through the vacuum space of a cryostat.
Has anyone done this? Have any references, links, or sage words of advice.
I found this,

http://snebulos.mit.edu/projects/reference/International-Space-Station/TM102179.pdf

and a few other references. (Kurt J. Lesker gives single numbers.) The slope of those curves in vacuum is about 2. Which at least makes some physics sense. Heat generated goes as I^2 and heat dissipated goes as T^4 (Assuming all the heat dissipation is by radiation… Stefan- Boltzmann law.)

Oh one kinda crazy idea would be to put a thick layer of heat shrink tubing over the wire. Better emmisivity and a larger area. (Perhaps something other than heat shrink.)

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  • \$\begingroup\$ We do it for short bursts. I think much heat loss is via conduction. We don't let the wires get hot enough to damage the insulation. Are the temperatures sensible to start with? Things get strange as you approach 0K. \$\endgroup\$ – Spehro Pefhany Jul 21 '14 at 14:25
  • \$\begingroup\$ Oh yeah, Temperature range from ~80 to 400K. This is for some B-field coils. Originally they were going to be outside the vacuum chamber, now they've moved inside. I think it's a bad idea, but I'll design what's put before me. \$\endgroup\$ – George Herold Jul 21 '14 at 14:30
  • \$\begingroup\$ Can you handle copper atoms subliming into the vacuum? \$\endgroup\$ – Ignacio Vazquez-Abrams Jul 21 '14 at 14:52
  • \$\begingroup\$ Hi @IgnacioVazquez-Abrams, I think that will be at a very high temperatures. (No?) I'm more worried about the insulation around the wires. Maybe a max. temperature of ~150C. \$\endgroup\$ – George Herold Jul 21 '14 at 15:17
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    \$\begingroup\$ Do you know how hard the vacuum will be? Heat shrink tubing is a bad idea because of the plastizers in it will out gas in the millitorr range (but do check that out - don't take my word for it as it is brand dependant). You can probably get some PTFE tubing (Teflon) to cover your copper. \$\endgroup\$ – placeholder Jul 21 '14 at 16:05
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Since the current capacity of a wire increases in vacuum (about 20%, per your citation), you can use the design parameters allowed at 14.7 psi, and know that it will work safely in vacuum.

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  • \$\begingroup\$ The citation shows the current capability decreases with vacuum. It kind of makes sense since the current capability is related to temperature and with a decreasing vacuum the ability to remove heat via convection decreases (while the radiated capability should remain constant) \$\endgroup\$ – JonRB Dec 1 '14 at 10:58

protected by Community Jul 21 '14 at 20:28

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