After six months of modifying the switches, LPP finally achieved the firing of all 12 switches within 25 ns of each other in four shots on April 26. At a charging voltage of 30 kV, we achieved our first pinch at over 1 mega-amp (MA). The fill pressure of the deuterium gas was 40 torr, which is a record for a pinch in a DPF. We were deliberately using a pressure about twice what we believe is optimal for this charging voltage in order to avoid a pinch so we could test the electrical characteristics of the device. But the plasma pinched anyway, although well after the higher current had passed. The 1.03 MA current is a record for us when creating a pinch, but the 40 torr is a record for a pinch in any DPF.
During the month of May, we will be replacing the automotive spark plugs in the switches (which had been leading to the prefiring) with custom-built tungsten-rhenium rods from which we will make our own spark plugs. We expect them to have a very long life and practically eliminate prefiring in future testing.
Finally, a joint team from LPP and the Focus Fusion Society has produced a 70 ns simulation of the formation of a single plasma filament as part of the plasma sheath in the DPF. It showed a filament pinching itself down from a radius of about 300 microns to around 50 microns, a first step in compressing the plasma and its magnetic field. The simulation team consisted of John Guillory, Jeff Schoen, Henning Burdack, and Luis Angulo. FFS volunteer Burdack, who lives in Germany, provided the implementation that actually ran. Previous versions of the algorithm used had shown numerical instability where the values oscillated wildly. The new runs are the first to be stable and appear to show the filamentation process. In time, such simulations will complement our experimental observations and analytical theory, and may find applications in other fields of plasma physics as well.