I am referring to solid state switching in my comments about cost per J stored. It seems a bit odd to use statements like $1/Joule stored when talking about a switch but the pricing goes that way. The caps I mentioned are state of the art for high current applications. Smaller caps used in everyday electronics have ~1E11 cycles. It is a complicated matter why the lifetime is so short for high current but the numbers on the GA website are realistic. I’ve found out the hard way. (see page 2 of this thread about 1/3 the way down to see my interest in this.)

FYI: Caps are mainly solid state devices but some liquid is used in almost any high voltage cap.

There are other power storage methods but none are rep rate compatible. Flux compression generators (explosively driven devices) are one shot and motor type solutions take too long to brake to allow 200 Hz operation. Out there ideas are floated about superconducting magnetic energy storage but I don’t have much faith in them.

————–

The problem is materials with caps and switches. As an example, gas switches are basically arcs internally. The cathode of an arc erodes material to support the plasma. Gas inside the switch reduces the cathode erosion but some finite amount of metal is removed every shot. This metal is vaporized and redeposits around the switch. Eventually the walls get coated. How do you stop erosion and redeposition? Stopping erosion is impossible so it must be minimized. You pick a material like tungsten or Rhenium (very expensive) but it only buys you a factor of 2-3 in erosion rate. So if you can’t stop erosion, stop it from redepositing in “bad” places. You can try baffles and other tricks but these materials get coated. Once coated, they are partial conductors. The gap between the baffles and the electrodes is reduced thus the switch hold off voltage is substantially reduced. One might ask about operating a switch that does not arc. Ahhh, welcome to the 1930’s and the thyratron. It operates in a diffuse arc mode with little erosion compared to a spark gap but it only last 50X longer than a spark gap at best. I don’t know of a gas switch option that does not operate in some kind of arc or diffuse arc mode. Caps are another story. I believe the failure is driven by magnetic forces at discharge and holding static potential for “long” periods. The switches are going to be the problem moving forward. A number of smart people are working on better switches but lifetime is not in the cards right now. The effort is put into reducing inductance, increasing voltage hold off, transferring more Coulombs and jitter. These are the most important parameters to high current folks. For those that might not know, the Z-machine at Sandia had a problem with jitter of ~3 ns with a 90 ns current rise time. To solve the problem, 6 ft by 6 ft panels of acrylic were inserted into the switches (6 ft by 6ft). To punch through the panels requires a certain amount of energy. This process reduced the jitter to less than 1ns. The PF does not have this strict a jitter (~10 ns will probably be fine), but it gives you an idea of how large current switching is handled. For reference, Z fires something like 200 shots per year. Switches with 1 shot lifetime are more than enough for the cutting edge science done at Z.

Ahhh, the cheaper than coal argument. A little history…when fission was the new thing, business models were build around the electricity being free. This was after they demonstrated an actual power generating system. I hope the day comes when fusion is cost competitive with coal. That would be a huge victory. Don’t get me wrong, I like the idea of clean fusion energy. The problem is I’ve been disappointed so many times that I try to approach fusion and other problems as a skeptic and ask questions. I think the LPP approach is as viable as any other fusion concept at this point. I hope they make the breakthrough but it will be a long road after that to a working reactor.