Reply To: Great News!

[asymmetric_implosion]

The switch problem is not that the electrodes erode away. That is a problem for the anode in the PF. The switch problem is the materials erode leading to a plasma/vapor of that metal. When the current turns off, the plasma/vapor expand and coat all surfaces. After some number of shots, a thin metal film builds up on the insulating ceramics or plastics that normally hold off the high voltage. The finite conductivity can lead to problems with voltage hold off, excessive leakage current in the switch. These conditions can lead to pre-fire and large jitter. Pre-fire and large jitter were the reason LPP is changing switches. The switches by R.E. Beverly had a poor materials choice internally. Scroll back through the photos on the switches.

I think LPP is on the right track with a physics demo but to do a complicated physics demo you need the correct equipment. FoFu-1 has been hampered by switch problems since its inception. The Raytheon switches, if they are the one I know of, will improve reliability dramatically. They are used on a 1 MA pulse power system that fires at 1 Hz and holds off 200 kV. Look up the linear transformer driver if you want to know more. I’m guessing these are the little brothers but they are good switches. They are talked about at many conferences. A few folks I know use them and they frequently comment on the high quality of the switches.

To my knowledge only a few groups operate their PF device at more than 1 Hz. The SRL group operated a PF using solid state up to 80 Hz at 260 kA. The NTU/NIE group in Singapore can operate two devices at up to 10 Hz. A few others operate at 1 Hz and above (~80 kA and ~300 kA) but they are rare. I’ve heard rumors of an Italian PF at 1 MA and 1 Hz but I haven’t come across any data. They were interested in radioisotope production so they would publish in journals I don’t frequent. I haven’t run across any talks at meetings I usually attend. The group I work in is using thyratron switches for 10 Hz, 60 kA and a type of spark gap for 0.25 MA, 1 Hz. Very few people have interests above ~10 Hz. The beauty of the PF and Z-pinches for most folks is the strong non-linear scaling in yield with current.

Many problems in fission can be mitigated. After fuel is burned it can be reprocessed extracting the useful components and burning the other products in an accelerator. Proliferation is a concern but thorium cycles can by-pass many of those concerns. Ask the Indians about whether they are investing in fusion or thorium fission. The Chinese have a more diverse picture but they are investing in tokameks for their fusion program.