Vacuum feedthrough

Got some second hand vacuum feedthrough material, a whole box full of it, here is a picture:

Got 4 with one pole, 2 with 4 poles and 3 with 8 poles. The seller told me they can handle 5kV and 150A.
The pins on the vacuum side are quite long, I wonder if I could just cut them, material might be alumel.
Does anyone recognize them, maybe even knows the manufacturer? And how do I connect something on the vacuum side?

Update:
The manufacturer is "Varian", and they can (at least?) handle 12kV.
Which is too low for fusion, but enough to start measurements on my "new magrid" idea.
About connecting something on the inside, there seems to be some kind of "vacuum side connector". The material is not alumel, it's inox.