The switch must deliver the energy stored in 50kV capacitors. I would place some of them in parallel to obtain 0.5-2 Megaamps.
We could use a trigatron but I do not know if it would work well with AC current.
I could not use power mosfet or SCRs unless place them serially.
Other option is using a mechanical switch, but it would be almost impossible to switch in so short time.
We need also a trigger generator with more than 12 outputs that generates independent triggers within 1ns accuracy.
Plasma physicists in Dense Plasma Focus research cope with a similar problem: capacitor banks (ranges are 20 - 45 kV, 1 kJ - 1 MJ) should feed a plasma (100 kA - 1 MA) in less than 2 - 3 microseconds. Usually, they use no trigatron. Rather, they connect the capacitor bsank and the electrodes with a spark gap and a series of low-inductiance conductors. Total inductance should never exceed 10 nH: this is a severe requirement indeed, and suitably sphaped conductors are to be used. See Heinz Knoepfel's comprehensive treatise, "Pulsed high magnetic fields: physical effects and generation".
That is the same approach used in Pulsotron, it delivers most of the energy in less than 100ns. Now I am asking for more accuracy but a lot less current for one of the Z pinches used in the Pulsotron-3
For excimer/metal vapor lasers for same kind of voltages but only hundreds of amps at best, you may use thyratrons for high repetition rates in the 1-5 kHz range. Otherwise, as has been said, a pressurized (under dry nitrogen continuous flow) spark gap is probably the only choice I know of.
I read it is used sometimes SF6.
Did you used an electrode to ionize the gas in the cathode before triggering?
That is usually part of the spark gap: the cathode has a center hole (about 3-4 mm I think) and there is a "trigger" electrode in the middle of that hole that will trigger the switch (usually at a much lower (2-3 kv ?) voltage than the main switched voltage. And yes,you are correct, some of them use SF6 as a working gas, but if I remmeber correctly those are self contained, the gas does not continually flow through the spark gap.
As far as I know, utiliization of SF6 is restricted under severe regulation across the EU. Even if non-toxic, it is heavier than air, and can lead to asphyxia in closed environments if not properly treated. Usually SF6 is utilised in high voltage circuit breakers due to its huge electric rigidity. However, due care is given even in open air applications, as it is one of the worst greenhouse-related gases.
As I mentioned, if I remember correctly (it's been some 20 yrs since) theSF6 is used in a sealed in type of switch. You are right on both counts - it is used due to its high breakdown voltage, and it is toxic; not to mention if it dissociates, you have to deal with sulphur and fluorine.
Water disassociates in H2 and O2 that goes out. Oil generates carbon that contaminates the oil and make it conductive.
Another issue is the switch speed. With high pressure SF6 it would be reached
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