Significance of first shots and pinch, and note on process
Eric Lerner summarizes the significance of first shots and pinch as follows:
The achievement of a pinch, and on the second shot, means that we have accomplished one of the eight technical goals of the current experimental program. The machine is doing what we designed it to do, which is to transfer energy into a tiny plasmoid. It is quite unusual for a DPF to pinch right way. Normally fine-tuning of the electrodes and insulator and “conditioning” of the electrodes by several shots is required. That this was not needed is confirmation that our electrode and insulator dimensions, derived from LPP’s quantitative theory of DPF functioning, are accurate.
This summary helped to clarify something for me. It appears that going through the “fire” sequence is only counted as a “shot” when everything works and the machine doesn’t misfire.
The “down time” the crew has been experiencing stems from various components in the machine which prevent the “shot” from going off as it should. The whole machine, in a sense, has to be fine tuned to eliminate leaks and losses and bring the charge to bear along the electrodes with the correct timing, and keep the gas in the vacuum.
Various components such as the vacuum, switches, triggers and so forth have been assembled, disassembled, tweaked, re-assembled.
Consider the vacuum chamber. It has many vulnerable points - there are “windows” for observation and connecting diagnostic instruments. Each connection point represents some vulnerability. Every time they change something, they have to test the vacuum again. There’s a big table in the room with FoFu, covered with tools. I visit the lab, and the guys are in there, switching out a rogowski coil from the drift tube, for example. Re-connecting it. Testing the vacuum again. This is why the machine was designed as it is, with access to walk in under the machine and constantly take things off and add things on.
The clarification for me from Eric’s statement above is that the concept of “conditioning” pertains to the electrodes, not to getting the whole machine running consistently, as I had thought. And the good news is, the electrodes are conditioned.
The other clarification is that the “down time” is a regular part of the process of these experiments as each sequence of shots will require fitting something new to the machine for diagnostics, and also as each shot runs enormous energy through the components - with the possibility of damaging or loosening something in the process. Perhaps, rather than “conditioning” we can talk of “tuning” the machine, and how it falls out of tune as changes are made when you play it. So, there will be constant tuning.
It’s a time consuming process, very detail oriented.