With all switches firing and central components cleaned, realigned, and in some cases even resurfaced, Focus Fusion-1 (FoFu-1) has pushed the frontier of DPF functioning to record pressures of fill gas. This is a prerequisite for achieving high fusion yields. The yield increases with the plasma density in the tiny plasmoid where fusion is produced, and for a given type of gas, this density is proportional to the fill gas pressure. While no other DPF has achieved fusion reactions at fill pressures above 30 Torr, and FoFu-1 had previously only done this once, on Sept. 12, LPP’s device achieved fusion reaction at these high pressures in 10 shots, including several times at 44 Torr and a single shot over 75 Torr.
The gas pressure has been increased 3 to 5 times over previous work.
FoFu-1’s fusion yield, measured in billions of neutrons produced, is tightly correlated with the height of the voltage spike (see fig. 2) in new shots performed after the tungsten pins on the cathode plate were aligned (blue line on left). Those shots were at the record gas filling pressure of 42-44 Torr and capacitor charge of 34 kV. The slope shows that fusion yield scales with spike voltage to the 2.73 power. By comparison, many shots with unaligned pins produced a correlation with much more scatter that levels off at high pinch height (green line on right).
The chart indicates that with pressures increased 3 times and with aligned pins that 30-100 times the neutron yield would be expected if the early results continue the linear relationship.
The first day’s firing showed a very tight correlation between the height of the voltage spike that occurs at the time of the pinch, when the plasma is compressed into the plasmoid, and the amount of fusion energy produced (see fig. 1 below). When this pinch and compression occur, the voltage spike is a measure of the energy being transferred from FoFu-1’s capacitors into the plasmoid.
This correlation, which continued on the second day of firing, is significant for two reasons. Its straightness on the log-log plot shows that fusion yield is increasing steadily almost with the cube of pinch height. These act like an arrow on a map, pointing to what the best yields at this current are likely to be. With the largest typical voltage spikes at 50 kV, fusion yields should be over 1 joule (about 1012 neutrons), exactly what our theory projects. The agreement of our theoretical projection with the extrapolation of the experimental curve gives us increased confidence in both. Second, this tightness of the correlation implies a more repeatable operation of FoFu-1 with its newly realigned tungsten pins (see below for details on the latest refurbishing). Of course, these preliminary results must be confirmed with more shots, but they are encouraging.
Since atmospheric pressure is around 760 Torr, this is fusion at roughly 10% of atmospheric pressure, truly putting the “dense” in dense plasma focus. For comparison, a tokamak fusion machine generally operates at just one thousandth of a single Torr. The shock wave from a blast of fusion at 75 Torr caused a glass window to break, but its quartz replacement should be able to take the pressure.
Researchers reported a number of important results at the conference and workshop. Chris Hagen reported achieving 1012 neutrons with the 1-MJ Gemini DPF in Las Vegas, but has been unable to push past this level. LPP attributes this to electrode size, as Gemini’s electrodes are twice that of FoFu-1. The large DPF at Warsaw, PF-1000, has electrodes 4 times the size of FoFu-1’s. The PF-1000 team’s lead scientist, Dr. Pavel Kubes, reported confined ions at 20-30 kiloelectron volts (keV). This is one-fifth the average energy achieved by FoFu-1, and consistent with what LPP would predict for their device. PF-1000 will be shutting down next month for 18 months of upgrades, but not before an ambitious experiment that will attempt to directly measure the magnetic field within its plasmoid. Such measurements could bolster theoretical models of the DPF