On February 28 Lawrenceville Plasma Physics’ (LPP) experimental plasma focus device was fired and the team observed a record 380 Gigawatts (GW) of peak power in the ejected ion beam. The most powerful beam previously observed had a peak power of 93 GW making the newest beam measurement a four-fold improvement.
To provide context for this large power output, the peak input power to the Focus Fusion-1 (FF-1) device from its capacitor bank is currently around 53 GW. In comparison, the total average electric power used in the United States is 440 GW.
The beam was probably considerably more powerful than the figure measured, as LPP Chief Scientist Eric Lerner calculated that about half the beam spread out beyond the 1-cm wide entrance hole to the drift tube. We believe this is the most powerful beam ever measured from a plasma focus device, although LPP will have to search the literature more thoroughly to make that claim with certainty.
From a power standpoint the beam only lasted 5 nanoseconds, so it and the equally powerful electron beam emitted in the opposite direction carried only about 4 kJ of energy, about 1/15th of the total energy fed into the electrodes during the much longer 2 microsecond rise-time of the current from the capacitors driving the experiment.
To get more energy out of the beam than is put in will require much higher fusion yield than is presently obtained in FF-1. However, the gain needed is only about a multiplying factor of 6.6, making the progress impressive new.
The LPP team measured the ion beam with two Rogowski coils near the top and bottom of the drift tube. When a beam of ions or electrons passes through these coils, a current is induced in them, creating a signal that is stored on an oscilloscope. Figure 1 shows the signal from the Upper Rogowski coil, close to the plasmoid, with the large beam to the left and a smaller subsequent beam on the right some 35 nano seconds later. The dips following the beams show a reverse current of electrons drawn along behind the ions.
The height of the integrated Rogowski signal gives the peak current in the beam. The difference in timing between the two Rogowski signals gives the velocity of the beam and thus the energy of its ions – in this case 3 MeV (million electron volts), which is a new record for the FF-1. LPP checks this energy by comparing the timing of the Rogowski coils with the timing for the signal from an x-ray detector, or photomultiplier tube, that detects when the electron beam hits the anode. Again the result is the exact same energy of 3 MeV. Calculation by multiplying the average energy by the peak current of 127 kilo amps shows the peak beam power of 380 GW.
LPP’s experimental team has been trying to improve the symmetry of the compression that creates the plasmoid, so that the plasmoid will become smaller and denser. Higher density will make the fusion fuel burn faster and produce more energy output. Up until now, the plasmoid cores, which are shaped like the sugar glaze on a doughnut, were no smaller than 300 microns in radius. Although this sounds pretty tiny, the goal is to get it down to a 50 microns radius, with much higher density. The folks at LPP know that this is possible, as other researchers using similar plasma focus devices have observed and measured plasmoids this small. LPP also knows that other researchers have achieved ion densities up to a few thousand times higher than LPP has achieved, (hundreds of milligrams/cc vs. LPP’s 0.1 milligram/cc) showing that this too is possible.
February 28 imaged the smallest LPP plasmoid yet, shown in Figure 2, with a core radius of only 200 microns. The plasmoid core is seen forming at the narrowest “waist” of the pinch column, before the current has twisted itself up into the fully formed plasmoid.
LPP interprets this smaller plasmoid as the result of improved symmetry in plasma compression, due the progress with the vacuum system.
It’s been the vacuum system that has posed the difficulty. The FF-1 has had persistent leaks since the beginning of 2013. These leaks were allowing oxygen to be present during the test shots, such that the copper on the anode was rapidly oxidized in uneven patterns. The oxidized copper is an insulator forcing the current filaments to cut through the oxide layer to reach the copper below. In the process the filaments would wander around, getting closer to each other in some places and farther in others as determined by the oxide insulation effect. This in turn led to non-symmetric compression and the “early beam” phenomenon, where energy would be released in filament collisions before compression was complete.
By early March, with the help of consultants and investors, LPP’s Chief Scientist Lerner and Lab Coordinator Derek Shannon had cut the leaks down from 30 milliTorr per minute at the beginning of January to only 0.3 milliTorr/min, by the beginning of March.
First LPP received help from a new consultant, Brian Bures, who has had years of experience with small plasma focus devices. Then, LPP used an idea suggested earlier by LPP investor Rudy Frisch, who is a mechanical engineer. Frisch suggested putting a Teflon restraining ring around the rubber O-ring that seals to the anode, forcing it to have a good seal when it is compressed. That formed a good seal before firing, but a large ‘leak’ reopened after the first shot.
Investor Walter Rowntree contributed by acquiring on LPP’s behalf a Residual Gas Analyzer (RGA), a sensitive instrument that analyses and identifies the gas in the chamber. Using the new RGA, Shannon rapidly identified the main leak gas as isopropyl alcohol. Procedures had been using the alcohol to check for leaks and it had gotten trapped in a cavity in the anode, bursting out in rapid evaporation when heated by the current in the anode. Draining the cavity solved the problem.
Now very small leaks remain, but LPP expects that a growing understanding of the issues will enable them to solve the remaining leaks soon.
LPP deserves a grand missive of appreciation for the wonderful updates and insights into the effort to build the first net power fusion device. The personal attention given through the Focus Fusion Society has attracted thousands of followers who can see what looks like a coming revolution in energy creation. It’s a story headed for history we can follow in real time. There are about 200 photos for public viewing at this link.
This discipline, care and concern on the part of the LPP staff cannot be overlooked. This team is setting a precedent of personal and professional conduct to be admired, and hopefully emulated. This quality of character deserves support and it looks like they very well may earn the success that Eric Lerner’s theory says is out there for humanity’s benefit.
Thank you guys.