Lerner reported that in the same 10 shots, the variability in fusion yield from shot to shot was only about 14%, a factor of four reduction over previous results with FF-1.
These new results were possible only with the glow-discharge preionization used in the May-June experiments. This preionization, caused by a tiny, several-microampere current flowing in advance of each shot, smoothes the path for the main current, making breakdowns more symmetric and reducing or eliminating the vaporization of the anode material. “We see evidence of the reduction of vaporization from the reduction in the oscillations of the current,” Lerner explained. “This indicates that less energy is being drawn from the circuit to vaporize and then to ionize tungsten atoms.”
The more symmetric current sheath in turn leads to the elimination of the “early beam” phenomenon, when the current sheath splits in two during the compression of the plasma, robbing energy from the plasmoid. Just moving to the monolithic tungsten electrode alone considerably reduced the early beam, which LPP Fusion researchers first identified as a problem back in 2010. This is likely due to the elimination of arcing between parts of the electrodes, since there are no such parts in the single-piece tungsten electrodes. But preionization completely eliminated the early beam.
Although a record yield of 0.25 Joules was possible just with the new monolithic electrodes (as reported in the May LPPFusion report), it took preionization to get the reduced variability and the record ion energy.
Despite the progress reported, Lerner emphasized that much remains to be done. Oxides are still present in the device due to the introduction of water by a leaky valve and, unlike in the first 30 shots, are now declining very slowly, preventing further gains in yield. Impurities overall have only been reduced by about one third compared with last year’s experiments, so yield is still far below where it would be theoretically, with no impurities. In addition, there is no evidence yet of increases in the density of the plasmoids, nor of improved fusion performance with the deuterium-nitrogen mix (although 5% nitrogen is needed to stabilize the preionization discharge.)
The next step is to use an ultrafast ICCD camera to get images of the area near the insulator where erosion has occurred, to see if vaporization has been eliminated or merely reduced, and to see the details of the process. A new reassembly of the device will almost certainly be needed to really eliminate oxides. Silver plating can be used to avoid tungsten’s affinity for oxygen (oxygen is bound very weakly to silver). In addition, by September, new beryllium anodes will be delivered. While beryllium lacks tungsten’s high melting and boiling points, for a given amount of energy, 15 times less beryllium than tungsten will be evaporated and each microgram of beryllium will have 17 times less effect on the plasma, due to beryllium’s far lower atomic charge. So, one way or the other, the impurity problem will be overcome
Presentation by Eric Lerner, LPPFusion to Symposium on Plasma Physics and Technology, Prague from LPP Fusion on Vimeo.
Hydrogen-Boron Groups Announce Advances, Plan Closer Collaboration
The Prague symposium was something of a coming-out party for pB11, with several groups reporting new advances and hydrogen–boron research featured in invited presentations. The researchers present planned closer collaboration, including an international workshop and joint experiments.
Dr. Heinrich Hora, University of New South Wales, Australia, one of the invited speakers, tied together several of the advances in his review presentation to the conference. After pointing to the well-known advantages of hydrogen-boron as the route to cheap, clean, safe and unlimited energy, he turned to recent experimental results with hydrogen-boron fusion initiated by lasers. Experiments occurred in Russia in 2005, in France in 2013, and at the host city of Prague in 2015, and each time the number of fusion reactions rose a thousand-fold, now to a billion reactions at the Prague Asterix Laser System
The relatively high yield in the most recent experiment, Hora continued, is best explained by a recently published theory that shows, in some circumstances, hydrogen boron reactions can occur as avalanches, with each reaction setting off several more. In these new calculations, the three alpha particles (helium nuclei) produced by a single pB11 reaction undergo a kind of three-cushion pool shot, in which a series of collisions with protons gives the last proton just the right 600 keV energy for a fusion reaction with boron. This effect is most important at relatively low average ion energies, and thus makes hydrogen-boron reactions easier to ignite.
LPP Fusion’s report at the Symposium of mean ion energy in a series of 10 shots of over 120 keV, combined with these new results, indicates that hydrogen boron ignition is within reach of plasma focus devices, once the highest densities achieved of more than 1023 ions/cm3 can be combined with these high ion energies. At the conference, researchers discussed new collaborations involving additional plasma focus groups, as well as ideas for combining focus fusion and laser approaches. Participants plan to organize a hydrogen-boron fusion workshop back in Prague with the coming year
SOURCES - LPP Fusion