I know that USA it is produced in small quantities, but I have badly lost the USA factory name what I collected in one German exhibition.
That is special pulse transformer of 1 nsec 60 kV peaks of about 4 kW, wound on the special toro-core, so that in four places the braid is cut but inner wire is still insulated. It is actually the power source for some high laser, costing rather much. And I have two of such with the same defect - burned this coaxial winding.

Originally there stays silicon rubber insulation d=9mm and inner wire d=1,0mm consisting of silver-coated 7-wire litcendrath. The outhern d over braiding is 13mm. Need for such coaxial cable is 2 pieces of 3 meters long.

I have tried to use the normal antenna coaxial cable instead (like RG8u), all the 10 mm cables was burned in the first second, but the 18 mm I had no enough free place, and them are heavily too hard to make a winding of rather small diameter of 60 mm. Thus, the silicon rubber and litcendrath both are must-to-be, but insulator diameter is willed even to be 10 or 11mm to avoid the burn.

So, may someone be able to give a hint who are producing such coaxial cable of very high voltage?
The impedance, seems, have no a large meaning, however geometric relations makes me think that is 75 Ohm.
Foam filled cables are hardly improper.
Copper-pipe in the middle is even more improper.

I found one Rowe Industries R1006-1 High Voltage Coaxial Cable 50 KVDC but it have a 50 Ohm.... I am not much sure is it so innocent or not, when high power tyrathron is pushing the 10 kV pulse over him and he is four-folding the pulse voltage, but resulting unipolar peak is going by transmission cable to gas-discharge lasing tube.

 

It's difficult for you when most manufacturers are U.S. based and your native language is Lettish (Latvian). The best I can offer is this English search term: "coaxial+cable+assemblies" which had good results; it produced all of the makers I'm familiar with.

 

I can't really help you with what you are looking for, but can you tell me how you can achieve 1ns pulses at 60kV? The risetime sound like outside this world, 60MV/us, is that some sort of krytron, or how do you make such a risteime?

 

That amount of laser power does rather sound like some military type of system, the only other systems that I am aware of that use such high powers and rapid rise times are for detonating nuclear devices. So I too and wondering about what the whole process is for. There are a number of laser technology publications and they all have websites with lots of advertising by the makers of everything associated with lasers and laser systems. So searching those may yield what you seek.