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[asymmetric_implosion]

Dividing up the parts is possible, but you still have finite part lifetimes. Two months of operation is ~1E9 shots.

A common trick in rep-rate pulse power is to use 100 kV caps for a 40 kV application. The reversal (opposite polarity ring in PF) is a key factor in determining the capacitor lifetime. The reversal is usually quoted as a percentage of the maximum voltage. Typical high voltage, high current cap lifetimes with <10% reversal are 1E7-1E8 for GA Series S caps (check out the General atomics high voltage website). Larger capacitors are more like 1E5-1E6 pulse lifetime (GA Series C). This limits you to ~ 1 day operation at 200 Hz with ~1E7 shots per day. Ceramic capacitors can last longer (~1E8) but they are limited to sizes of 10 nF so you will need hundreds or thousands of units. They are also limited to 50 kV. I forgot that high current cap lifetimes were so miserable.

Switches are a bit more complicated. Switches are typically limited by erosion of the electrodes. You can operate a switch below the theoretical current (really a Coulomb limit as the eroded mass is determined by the total coulombs that pass through it) but typically you can only derate by 2-3X which buys a 2-3X increase in lifetime. A typical spark gap switch is good for 1E6-5E6 pulses. Spark gaps are the basis for most high current switches. Thyratron switches are good to 5E7 shots but they can only carry about 10 kA while the spark gap can carry 100 kA with ease. Railgap switches are the spark gaps big brother with multiple conducting channels instead of a single channel and they are limited to ~1E6 shots (Check out Perkin Elmer high voltage and L-3 communication electronic devices). New switches are underdevelopment but the incentive to go beyond 1E6 or 1E7 shots for a high current, high voltage system is very low. Cutting edge high current machines (>1MA) fire less than 1000 shots per year with very few exceptions. Fusion concepts like MAGLIF embrace the pulse power limitations by asking how they can maximize the fusion gain per shot to limit the number of shots. If it works as conceived, MAGLIF would only fire one shot every 10 s and operate at 1000 MW electric. With only ~9000 shots per day you can operate for a year before you have to work on the switches. Once a year shutdown for maintenance is comfortable to utilities that will likely supply the power. Even at 5E7 shots for a thyratron, you are limited to less than 3 days. With a spark gap, you are operating for at most 7 hrs. Pretty miserable having to replace switches 3-4 times a day.

Another problem with these switches is the realistic rep rate. Spark gap type switches are limited to ~10 Hz operation. Active cooling, flowing gas and other needs are likely required. Thyratrons operate up to 1 kHz but they need external heating at 300 W or more per switch to work. Take a 2 MA PF operating at 70 kV (reasonable thyratron limit). You need 200 switches to accommodate the current with no room to grow. That is an additional 60 kW of electrical power to operate the switch. Then you need to trigger 200 switches at low jitter (<10 ns). Each thyratron has a trigger board which needs to be timed. Once timed the switches are pretty good. It might be difficult to find a bad switch/cap module and one is enough to drag you down.

One might argue that solid state technology could be force fit into this problem with the advantage of >1E9 shot lifetime. I believe that a 2MA, 70 kV bank can be built but the actual lifetime and the cost will likely be a problem. Solid state costs something like $1-10/Joule stored at this level. Gas switch technology is more like $0.01-0.1/Joule stored without any effort. A company called SRL built an 80 Hz, 260 kA PF device. It took a true pulse power genius (Rod Petr) to design the bank to operate a 8 kV. The next immediate question is why not operate at low voltage if it is easier? In a plasma focus there is a 10-20 mOhm loss due to the moving plasma that cannot be avoided. To overcome this impedance means a minimum of 20 kV to drive 2 MA. Account for the other losses in the switches, capacitors and bus bars and you are at 40 kV to drive 2 MA. If I am correct, FoFu-1 is at ~1 MA and 40 kV. Increasing the cap bank size does not help as you still cannot get around the 10-20 mOhm impedance in the moving plasma; it simply reduces the impedance of the bank. It will take a great deal of resources to have a pulse power system that operates for 2 months at the 2 MA level without maintenance. It might not be possible with available materials.