Evidence For Graphite As A Room Temperature Superconductor

Magnetization M(H) hysteresis loops measured for the HOPG sample, before and after 800 K annealing to remove ferromagnetic influences. (Credit: Kopelevich et al., 2023)
Magnetization M(H) hysteresis loops measured for the HOPG sample, before and after 800 K annealing to remove ferromagnetic influences. (Credit: Kopelevich et al., 2023)

Little has to be said about why superconducting materials are so tantalizing, or what the benefits of an ambient pressure, room temperature material with superconducting properties would be. The main problem here is not so much the ‘room temperature’ part, as metallic hydrogen is already capable of this feat, if at pressures far too high for reasonable use. Now a recent research article in Advanced Quantum Technologies by Yakov Kopelevich and colleagues provides evidence that superconducting properties can be found in cleaved highly oriented pyrolytic graphite (HOPG). The fact that this feat was reported as having been measured at ambient pressure and room temperature makes this quite noteworthy.

What is claimed is that the difference from plain HOPG is the presence of parallel linear defects that result from the cleaving process, a defect line in which the authors speculate that the strain gradient fluctuations result in the formation of superconducting islands, linked by the Josephson effect into Josephson junctions. In the article, resistance and magnetization measurements on the sample are described, which provide results that provide evidence for the presence of these junctions that would link superconducting islands on the cleaved HOPG sample together.

As with any such claim, it is of course essential that it is independently reproduced, which we are likely to see the results of before long. An interesting part of the claim made is that this type of superconductivity in linear defects of stacked materials could apply more universally, beyond just graphite. Assuming this research data is reproduced successfully, the next step would likely be to find ways to turn this effect into practical applications over the coming years and decades.

Image of CFS's SPARC reactor

Commonwealth Fusion’s 20 Tesla Magnet: A Bright SPARC Towards Fusion’s Future

After decades of nuclear fusion power being always ten years away, suddenly we are looking at a handful of endeavours striving to be the first to Q > 1, the moment when a nuclear fusion reactor will produce more power than is required to drive the fusion process in the first place. At this point the Joint European Torus (JET) reactor holds the world record with a Q of 0.67.

At the same time, a large international group is busily constructing the massive ITER tokamak test reactor in France, although it won’t begin fusion experiments until the mid-2030s. The idea is that ITER will provide the data required to construct the first DEMO reactors that might see viable commercial fusion as early as the 2040s, optimistically.

And then there’s Commonwealth Fusion Systems (CFS), a fusion energy startup.  Where CFS differs is that they don’t seek to go big, but instead try to make a tokamak system that’s affordable, compact and robust. With their recent demonstration of a 20 Tesla (T) high-temperature superconducting (HTS) rare-earth barium copper oxide (ReBCO) magnet field coil, they made a big leap towards their demonstration reactor: SPARC.

A Story of Tokamaks

CFS didn’t appear out of nowhere. Their roots lie in the nuclear fusion research performed since the 1960s at MIT, when a scientist called Bruno Coppi was working on the Alcator A (Alto Campo Toro being Italian for High Field Torus) tokamak, which saw first plasma in 1972. After a brief period with a B-revision of Alcator, the Alcator C was constructed with a big power supply upgrade. Continue reading “Commonwealth Fusion’s 20 Tesla Magnet: A Bright SPARC Towards Fusion’s Future”