High voltage coax cable

[LukeW]

What type of coax is the "right" cable type, for use at about 3-5 kV DC, with 5kV SHV connectors?

It needs to be a patch lead (somewhat flexible and movable) and the cable needs to be the right thickness (no thicker than RG-59, basically) or it won't fit in the connector.

RG-59 with solid polyethylene dielectric (not foam) is the best candidate I've found.
It also has the right outer diameter for the SHV connectors, and I've seen commercially sold SHV cables that use this type of cable.

Belden 8241 is a good example - it is specified in the datasheet at 1700V RMS, but I'm intending to operate it at (DC) voltages a bit higher than that.

RG217 is specified for these kinds of voltages, but it's too thick to fit in the connectors.

[MarkF]

Far outside my knowledge...
Here are two pre-made cable assemblies with SHV connectors:

https://www.pasternack.com/shv-plug-shv-plug-rg225u-cable-assembly-pe34421-p.aspx

https://www.pasternack.com/shv-plug-shv-plug-rg393u-cable-assembly-pe3338-p.aspx

The RG393 is rated for AC Operating Voltage 3500 Vrms

[TimFox]

In grad school, we always used solid polyethylene RG-59/U cable with MHV and SHV connectors, but my experience only went to 3 kV, from -hp- 6516A power supplies.  I once made the big mistake of using “better” polyethylene-foam cable (lower RF loss and faster velocity), which failed catastrophically.

[MagicSmoker]

Yeah, foam anything is absolutely verboten if you need high dielectric strength.

More than likely, good quality solid PE (good) or PTFE (better) dielectric cable will have more than adequate dielectric strength here, but note that breakdown is almost entirely the result of voids, moisture ingress, cracks or other defects in the insulation, and not the thickness of the insulation itself (PE has a dielectric strength of ~20kV per mm while PTFE is around 60kV/mm).

Usually the dielectric strength for coax assumes RF rather than DC and so some allowance is made for dielectric heating, in which case PE is far inferior to PTFE. Of course, it never hurts to actually test samples of cable for breakdown using a current-limited HV power supply; that's what I would do if I planned on exceeding the datasheet ratings here.