Pushing to Higher Pressures

Despite various delays, the LPPFusion team is winding up the control shots and preparing for the next set of tests using our new beryllium electrodes. Our remaining task is to optimize the function of the device at higher fill pressures (more gas in the tank). This involves overcoming the more difficult breakdown– the transition to a plasma where electrons flow freely–at these high pressures. This week, we achieved record fusion yields for a fill pressure of more than 26 torr, but this still has not matched our best-ever fusion yield, obtained at only 18 torr. We expect to do better as we complete optimization.

To get some idea of what slows us down (other than the too-small staff!) in the past week the team fixed problems with both the pumps and the ultra-fast ICCD camera. It turned out that the scroll pump had too much moisture in it and the ICCD was not sufficiently protected against the huge electromagnetic pulse (EMP—a giant radio wave) that our device produces. These sound like easy problems, but finding them and solving them took many hours of work, limiting the number of shots we can take with the machine.

Our work has now fully confirmed the tentative observation, described in the last report, of extremely hot, thermalized electrons. Many shots have now shown the same 400-450 keV Maxwellian spectra which indicate a confined plasma. Some have even more exact fits to the theoretical curve (see Figure 1). Yes, we know it looks a bit fake—but trust us, no AI touched this graph. It’s real data! Some other shots have shown two components—an ultra-hot 400 keV one and a just plain hot 100 keV component. Since that “cooler” one is over 1 billion K it’s not exactly Antarctica. We’ll have more on this unfolding story as we observe and interpret it.

Gamma ray iter | lpp fusion
Gamma ray june 14 2024 | lpp fusion

Figure 1. top) Gamma ray spectrum from the two shots we reported on to the ITER confence. The red line is the data averaged over 100 keV and the black line is the spectrum predicted from a 420 keV(4.6 billion K) Maxwellian (random) plasma. The black line is a good fit to the data. Bottom) The gamma rays from June 14th shot 4. Again the black line is the best fit to a Maxwellian plasma. This is not just a good fit, but a great fit! The slight deviation at the low energy end on the left is entirely acounted for by a small amount of absorption as the x-rays pass through our quartz window on the vaccum chamber.

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