Personally I'd get some 2-conductor wire to take care of the current, then marry it to something load bearing, taking care that there's enough slack in the conductors that they're never strained. There's a rich selection of load-bearing steel cable and braided plastic line in that load range thanks to people who fish.

Alternatively, copper wire made for continuous flex, married to insulation that's abrasion resistant may do the trick, but it'll take some shopping.

@TimWescott I would need a way to marry them so they could be spooled but I couldn't think of anything satisfactory that would maintain flexibility without being being vulnerable to being split up. I guess I would also need to ensure the structural cable doesn't abrade through the electricasl insulator either if it is metal.

I suspect that anything with enough ampacity for the job (the wire will get MUCH hotter in vacuum!) will handle the tension. Preference would be stranded copper with full-hard temper, with insulation firm enough to handle the abrasion and suitable for vacuum use (probably not PVC?). Steel cores are available in some kinds (CATV laterals for example) but I'm guessing you need a stranded (steel cable not solid steel wire) element for this. I agree, I would be much more comfortable with something explicitly structural in there though.

You could consider flat flex. Terminate for load, then for 'lectricity. This assumes that you can make it fairly wide. Too bad none of it's black...

@TimWescott Yeah, flat won't work. It'd be great for spooling but it won't work on the electromagnet end.

@TimWilliams That's a good point. I will need to run tests to see how hot it different AWG actually heat up. I had in my mind to go with 22AWG or 24AWG two conductor with reinforcement but if that heats up too much then the reinforcement might not be needed.

So a cable for the load, two for the current and then two pipes to run coolant !

@SolarMike Aha, if I were to go that elaborate I would first go with a tandem pulley system with one pulley for the structurable cable and the second for the electrical conductor so they wind up properly. Or use a worm screw pin and slot crane mechanism that doesn't need continuous power to hold onto the mass.

Dual pulleys came to mind as well, maybe could even use an off-the-shelf self-retracting cable -- maybe not a bad idea anyway just out of convenience, hm. (Also, you need slip rings for the electrified spool, but I'm guessing that's not a problem under the conditions.) Other version is an accordion or coil, free hanging between the jib and magnet, and independent of the support cable; could be a little better thermally I guess, more radiation surface?

@TimWilliams Yeah, slip rings are the easy part here. I had not considered a coil that would would be easier on making the spool. The issue with a coil is that this is a tall vertical vacuum chamber and we only have a couple of feet at the top at 15 feet at the bottom so any coil would need to be extendible to 15 feet but retract to 2 feet. But it's worth a looksey.

@DKNguyen The stranded cable idea from Tim W. makes sense to me, as well. I might use 19 strand silver-plated high strength copper with an extended ETFE jacket. All of that is available on the market. There are milspecs for such, as well.

@periblepsis What type of keyword am I looking for to know that the copper is high strength copper? I don't think I've ever seen full hard tempered specified unless it something I have to check each datasheet one-by-one to find.

@DKNguyen Don't know, off-hand. It's been years. But I definitely remember spending hours reading through milspecs. In my case, I was looking for something that needed to be very highly flexible and wear for a very long time of continual abuse. What I got wasn't able to carry 2 kg, though. ... though looking at it right now? Maybe. If I get a moment, I'll see if I can recall/track down some info.

@DKNguyen What I have is based on milspec Mil-W-22759. The wire is M22759/19-26-9. Just looking at the spool here. McCaffrey Associates in Burlington NJ.

@periblepsis Okay thanks I'll check it out. I guess one other advantage of a coil cable is I can actually run the structural cable down the center and that could alleviate much tangle issues.

@DKNguyen Good luck. I can definitely say that I've been satisfied with the stuff I finally bought!

@periblepsis Naturally the gauges I am most interested in are out of stock there so no price is available. I can always go 4 conductor though. Those are in stock,.

Other metals do conduct electricity. If electricity wasn't involved you'd have some sort of steel wire rope to carry the weight. Use that as your negative, bada-bing.

@Harper-ReinstateMonica If I knew of steel cable where there were two separate cables in a single assembly that were insulated from each other for some mysterious reason, I would.

@DKNguyen Run the other wire as a wire. It seems like you are looking for magic. Otherwise you'll need to invent the thing you want. Just remember copper has no fatigue limit.

@Harper-ReinstateMonica My main goal is to try and avoid running two independent lines to begin with since that introduces complications in the spooling. If I ran two lines then it's just as easy to run a non-conducting steel and copper cable where both conduct, or a non-conducting steel cable two-conductor copper cable.