There are a lot of options for vacuum tubes.
Currently, using relays we are limited to the switching time of the relay. In fact in my testing so far the turn off and turn on time change. as the spring tension versus the magnet field pulling the contact over is different.
Now, some of you may be asking, "But Cycle, those MOSFETs are going to blow with the voltages this thing is making! It's spiking up into the megavolt range when the MOSFETs open!"
True... and I've thought of a solution. A solenoid-driven variable-spacing spark gap.
Envision a quartz tube with spark gap electrodes on each end. The tube is evacuated to a high vacuum. One of the electrodes can slide upon a polished metal rod. Outside the tube is a ring magnet connected via connecting rod to a solenoid.
When the solenoid is energized, it slides the magnet back. The magnetic attraction to the sliding electrode causes the electrode to slide back, increasing the gap between the two electrodes. And as we know, a strong magnetic field in the vicinity of the spark gap will tend to quench the spark quickly, so the ring magnet serves a dual purpose.
When the solenoid is deenergized, a spring pushes the whole assembly forward, closing the spark gap distance.
The solenoid on and off times can be controlled by the same 555 timer circuit as is used now, through the same MOSFETs that are used now.
The way I envision it working is that the sliding electrode will be touching the other electrode most of the time, and will slide back to open the circuit momentarily, just as the MOSFETs are closed most of the time, and only open momentarily to create the pulse needed to make this system operate. Thus there shouldn't be much heat buildup.
It's the caveman version of a MOSFET. :D