New results from LPPFusion FF-2B experimental fusion device have dramatically confirmed important theoretical predictions. The research team has been working again with deuterium fuel to better understand the cleaning process of the electrodes and insulator that are at the heart of the device. This is preparing for new experiments with our hydrogen-boron fuel, decaborane, when cleaning will become more complicated. The deuterium experiments have not only provided important new insights into the cleaning process. They’ve also confirmed the calculations that indicate we can reach net energy production (more energy out of the device than in) with decaborane.
At the end of June, we had already observed that cleaning the anode of deposits of decaborane that condensed before the shot was crucial to our goal of getting fusion with pB11 fuel. We made a lot of progress on improving this cleaning. But when we changed out a small window that had become too coated with debris, we saw that pink deposits were forming on the tip of the anode. (Fig.1) These were clearly chemical compounds of the beryllium in the anode and boron from the fuel, compounds that are pink or copper-red in color.
Figure 1. Pink deposits on the tip of the FF-2B anode are generated when boron ions react with the beryllium of the anode to form beryllium-boron compounds, which are mostly pink or red. The vertical lines result from the combination of the tiny mini vortices depositing the material and the large electrical current cutting through the deposits to reach the beryllium below.
With repeated cleaning shots, the pink color faded slightly but remained fairly intense. We saw that an array of tiny vertical corrugations were imposed on the pink coating, exposing the gray beryllium below. But continued cleaning seemed very slow. We also had not succeed in getting shots with the conditions to produce boron fusion. So, to study the cleaning process without adding more boron to the anode, we stopped the boron shots and proceeded with just deuterium.
In the course of these shots, we found that through our new, small window, we could use the ultrahigh resolution of new iPhone cameras to take excellent images, thanks to the skill of our summer intern Matt Mglej and our IT Assistant Sam Grund. These images showed that the pink deposits were only the lowest of a series of distinct zones on the anode. There is an intermediate gray zone (Fig 2a) with much thinner deposits that formed characteristic rainbow colors from interference (bottom, Fig. 2b), like oil creates when spreading on water. Then there was a top-most layer that was mirror-smooth but marked by ripples like those on a small pond (top, Fig. 2b).
Figure 2. (a, left) The pink color fades to the gray beryllium color as we look higher on the anode. This is probably due to more deposition lower, rather than better cleaning higher. Near the top of the anode (b, right) the coating thins to the point that interference rainbow colors are generated, with blue being the thinnest and red the thickest layers. The shiny reflectiveness may come from crystals of the beryllium boride coating. At the very top, a mirror -smooth layer of beryllium is generated, with ripples imposed on it by the sudden onset of the current at breakdown. These ripples are seen more clearly with different lighting (c, bottom)
Initially, we decided to concentrate on cleaning the top zone, which we knew affected the critical breakdown process and the launch of the filaments. The pink zone we would leave later. We also learned that beryllium-boron compounds are being studied for use as military armor, indicating that cleaning them off might be tough. If we are lucky, the deposits may even protect the beryllium without negatively affecting the pinch—we still need to find out.
As we worked to optimize the cleaning process of the top breakdown zone, we saw a pattern emerging that confirmed a critical part of our theory. Back in the 1980’s when Eric Lerner, now LPPFusion’s Chief Scientist, published his first theoretical study of the dense plasma focus, he derived a simple formula for the optimal velocity for the plasma to move down the anode in order to form and preserve plasma filaments. These filaments are the crucial first stage in compressing the plasma, and high plasma density in turn is essential for high fusion yields. The formula depends only on the mass and electrical charge of the ions in the gas. Knowing the formula and the length of the electrode, we can easily calculate the ideal “rundown time”—the time between the start of the pulse and the “pinch,” when the fusion-producing plasmoid is formed.
While there is still some variability in the data, as Fig. 3 shows, the maximum fusion yield is peaked exactly at the predicted run-down time. Sub-optimal cleaning covered up evidence of this relationship in the past, and the variability shows we can still optimize conditions better. But this is a big confirmation of the theory that we use to run FF-2B. Most importantly, this is the theory we have used to predict that our machine can produce net energy with pB11 fuel.
In addition, the data shows that the fall-off in deuterium fusion yield occurs due to exceeding the optimal run-down time, not to the difficulty of high-pressure breakdown, as we had previously suspected. We can measure how difficult it is to break down the gas—covert it to current-carrying plasma. This increase in breakdown difficulty occurs at still longer rundown times (lower velocities and higher pressures) than the drop-off we observed. This is more good news. We may still have to deal with the breakdown problem with decaborane as we increase the current in the device later in the year, but for now it looks like it is easier to solve.
With the new cleaning techniques, new confirmation of our theories and new data, we are ready to go back to burning boron in August. We hope to make it a hot August—billions of degrees hot!
Figure 3. When fusion yield is plotted against rundown time (the time to reach the pinch area at the end of the anode) for the shots with the best cleaning conditions, a clear peak is seen around 1620 ns. This is exactly the time predicted as optimum (vertical red line) by the theory LPPFusion’s Lerner first published in the 1980’s.