While LPPFusion’s research team expects to eliminate the major sources of electrode erosion, enough to get rid of significant impurities in the plasma, some erosion will still exist. It won’t be enough to bother us during the current experimental phase, but once they are engineering a generator that fires 200 times second, remaining erosion will limit the lifetime of the electrodes. But there may be a way to protect the electrodes better—with a coating of carbon nanotubes.
Neil Farbstein of Vulvox Nanobiotechnology Corporation suggested to LPPFusion joint development of a coating of CNT to protect the future beryllium electrodes in the Focus Fusion generator. While more research is needed, the extraordinary qualities of CNTs may help to reduce two sources of erosion. The first is sputtering. In this process, high energy ions from the plasma hit against atoms in the electrode, knocking them out of the material one by one. Beryllium is only slowly eroded by sputtering, but CNTs may be still better. Due to their structure, with sheets of atoms surrounding tiny voids, CNTs can allow high energy ions to slow down gradually, dissipating their energy without knocking off so many atoms.
Second, between shots, a layer of boron may form on the electrodes after the molecules of the decaborane feed gas break apart. If the boron condenses fast enough to form a continuous layer, the current from the next shot will have to vaporize it off. (Boron does not conduct electricity at all well.) Since the vaporization temperature of boron is much higher than that of beryllium, some of the beryllium electrode will also vaporize, causing erosion.
CNTs could help this problem as they have high thermal stability. They don’t melt even at the melting point of tungsten, 3400 C. Whether they remain stable as high as boron’s boiling point of 3927 C not yet known. But if that is true, boron could evaporate from CNTs without damaging them.
LPPFusion and Vulvox Nanobiotechnology Corporation will be seeking government funding to investigate further CNT coatings of beryllium electrodes.
Tungsten electrode delayed
The time needed to machine the interior surface of the Tungsten electrode by electro discharge marching, a process in which electric current melts away the material to be removed was greatly underestimated. Tungsten is a notoriously difficult metal to machine because its brittleness makes it vulnerable to cracking if there is vibration during the marching process. Give the large size of the cathode, only a few shops in the US can safely machine such a piece.
These delays are expected to push back the start of our new set of experiments into September, approximately. They also serve to highlight that a monolithic tungsten cathode of this size reaches the limits of the technical capabilities of the global tungsten industry. This is one reason why this approach, which LPPFusion’s team believes is vital to solve the impurity problems, has not been tried on other powerful plasma focus devices. Since all the other devices that exceed 1 MA peak current are physically much larger that our FF-1, a monolithic tungsten cathode would not be technically feasible for them.
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Brian Wang is a Futurist Thought Leader and a popular Science blogger with 1 million readers per month. His blog Nextbigfuture.com is ranked #1 Science News Blog. It covers many disruptive technology and trends including Space, Robotics, Artificial Intelligence, Medicine, Anti-aging Biotechnology, and Nanotechnology.
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