I found the solution for switching 2000 volts - two thyristors in series should be able to handle it. I was worriying about off-state leakage current due to voltage balancing resistors in the original capacitor discharging circuit. But this problem disappears in the standard 8/20 μs impulse generator, it already has two 20 Ω resistive loads, this diverts leakage mostly to the ground instead of the load, making the series switch connection feasible again.

Capacitor size and cost are still the problem. Using non-pulse rated capacitors is perhaps an acceptable workaround if I'm willing to replace them once in a while. A lifetime of 10,000 shots is practically infinite for my purpose. #electronics