LPP Fusion has resumed dense plasma fusion test firing now using the new tungsten electrode

Next Big Future

The Tungsten electrode has been attached and tests shots are being made with the LPP Fusion dense plasma fusion experiments.

The connection of the Tungsten electrode show extremely low electrical resistance, no more at any point than 18 micro-ohms, and good mechanical strength. This ensures that the cathode can safely take up to 1.6 MA of current, enough for the planned experiments.

With just a dozen shots performed so far, they can draw only very preliminary conclusions from our results. The first is that impurities do indeed seem to have dropped significantly with the new electrodes—the first main goal of the new experiments. Impurities appear to be the basic obstacle to high fusion yields, as they disrupt the filaments that are the first stage of compression of the plasma. The optical spectra obtained in the new experiments show peaks at wavelengths characteristic of tungsten, but at roughly ten times less abundance than the copper and silver impurities seen in shots with the old electrodes.

While a tenfold reduction in impurities—to about one impurity ion for 500 deuterium ions—is a good start, it is not what Lerner calculated would be needed to preserve the filaments, nor what theory and previous experiments indicate can be achieved. For that, a 50-100 fold reduction in impurities is required, or 5-10 times less impurity than that has been achieved so far. Indeed, the initial results show the same symptoms of impurity—an “early beam” before the main pinch, and a slower motion of the current sheath, as had been observed with the old electrodes, although the early beam seems much smaller in the new shots. Given continued impurities, it is no surprise that fusion yields of about 1/8 of joule of energy are no higher than the best results observed with copper electrodes.

A possible source of inpurities might be a very thin layer of tungsten oxide—too thin to be seen or removed during the electrodes’ cleaning. Tungsten oxide dissociates at 1970 C, far below tungsten’s vaporization point of 5500 C, so an oxide layer will be far more fragile. The oxide layer might well give rise to the tungsten in the plasma as well. If this is the case, repeated firing will burn the oxide layer off and impurities will fall.

There are some hints that this may be happening, as x-ray emission and the pressure “pop” are falling as fusion yields are rising over the course of the first shots. But only more firing will confirm or refute this idea. The research team expects that as kinks are worked out of the system, firing will proceed more quickly, eventually reaching a goal of about 30 shots per week.

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