I’ve been doing some brainstorming on the standoff for the superconducting magrid. This is a messy problem! You need a cryogenic feedthrough that is also a high voltage standoff. Then you need to pass in the YBCO superconducting cables, and wiring for the persistent switch.
Yesterday I realized that we can get most of the way there by welding together two off the shelf components:
This diagram refrences parts 9812107 and 9611005 from insulatorseal which is a subsidiary of MDC Vacuum. I’ve sent this drawing to insulatorseal for a quote. One problem is that part 9611005 is only rated up to 6kV so we will need a custom variant to get to the 10kV to 40kV range.
The idea with this setup is that the high voltage could come through a standard HV feedthrough and connect to the insulated tip of this feedthrough via a connecting wire:
Prometheus Fusion Perfection 
Got a quote from insulatorseal: $400 using off the shelf parts. Jim says:
the 9611005 break is rated at only 6KV but may handle a bit more because the parts are a bit “over engineered” to give a safety factor. 10KV may be a bit much however – I simply don’t know what the “true” capacity is.
It is my understanding that the larger breaks rated at 10KV+ that use Kovar sleeves and larger ceramics will not hold up under cryogenic applications. I have also heard that using the nickel iron alloys (used in the small cryo breaks) in larger breaks results in a part that will not hold up structually compared to ones made of Kovar.
I don’t have a solution to offer you using our standard parts at this time.