You're switching less than a joule of energy, but peak current may be
10's of kA. Although a number of gas tube devices (krytrons, thyratrons,
or similar) could do the job, they're expensive and require triggering
circuitry. They're overkill unless you need to precisely switch
(time-wise). Triggerable spark gap switches and ignitrons are simple but
expensive, and they also require HV triggering circuitry. IGBT's are
available with 4 kV ratings, but these also tend to be expensive.
If your timing needs are not critical, an inexpensive HV relay switch
should do the job. For example, to generate ultrastrong pulsed magnetic
fields, I use a simple solenoid-driven high voltage switch with 2"
diameter brass contacts. It has reliably switched up to 8500 joules at
9.5 kV, with peak currents up to 100 kA for thousands of
maintenance-free operations.
http://www.capturedlightning.com/frames/gallery/newgap5a.jpg
http://www.capturedlightning.com/frames/Newgap2a.jpg
The above switch replaced a triggered spark gap switch that required
disassembly and maintenance after every 50 - 100 shots. A much smaller
home-brew HV relay should do the job for your application, using
repurposed 1/4" - 3/8" diameter power relay contacts. At 4 kV, you only
need to bring the contacts close enough to arc over, thus avoiding
potential problems with contact welding.
Bert
