A coax transmission-line transformer is easy to make and has pretty much zero leakage. I'd just be concerned about getting enough core to support your longer sweeps without saturating. Sometimes people drive the core the other way before or after each shot to demagnetize (or reverse magnetize) it and double the available volt-amps.
Hey, could you drive your electrode with a really high voltage sine wave and use the sorta linear middle region? Synchronize your particle beam shots (or whatever you're doing) with the sines. That would be a simple resonant hv oscillator, dead simple.
Or use the first swing of a damped sinewave?
John