For a long time, Lerner has hypothesized that the filaments in LPPFusion’s DPF devices are being disrupted before they can compress into the plasmoid, leading to much lower plasma densities in the plasmoid and much lower fusion yields than are theoretically possible. The team had images showing the filaments forming early in the pulse, and being absent at the pinch that forms the plasmoid, but had never confirmed the process of filament disruption nor detected when the filaments disappeared. During the control shots with the tungsten electrodes, at the end of July, Dr. Hassan succeeded in getting a series of images, using our ultra-fast ICCD camera with a series of shots under the same conditions, that show clearly the disruption of the filaments during the rundown.
The images below show the story. The field of view is shifting for each image so the current sheath is being followed as it moves down the anode. As can be seen, the filaments start expanding by 830 ns, are nearly gone by 1030 ns and are entirely gone by 1230. So they cease to exist somewhere around 1100 ns.
630ns, 830ns, 1030ns and 1230ns
These observations confirm Lerner’s theoretical calculations that the filaments must carry a certain critical level of current required to prevent disruption. With the tungsten electrodes and the originally-profiled beryllium cathode, too many filaments were produced, reducing the current in each filament below the critical level. Lerner expects the new profile on the cathode will cut the number of filaments in half, providing the critical current needed to prevent filament disruption. As well, when the team switches to hydrogen-boron fill gas, the greater charge on the boron ions will help to confine the filaments, as the pinch forces increase as the square of the ionic charge.
In addition, as we have reported previously, the 10-cm anode control tests seemed to be impaired by a strong asymmetry in the current sheath, which was repeated in each shot. On disassembly, part of the reason for this asymmetry became clear—the anode was off-center relative to the cathode and insulator—as shown by the asymmetric patterns of deposition seen on both the anode and insulator. Again, the asymmetric sheath also contributed to a poor compression and a too large and un-dense plasmoid. Fortunately, the team identified the error made in centering the anode in the last assembly, when the centering could not be measured from below the electrodes. This error was certainly not repeated in the new assembly, so the symmetry should be greatly improved in the upcoming tests.
The 10-cm tungsten anode shows clear signs of being off-center during assembly. The dark and bright areas mark the end of the insulator on the two sides of the anode and both the deposition below the line and the erosion above the line show that the anode was much closer to the insulator on the left-hand sector than the right. The new beryllium assembly is far better centered.
