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MIT Inches Closer To ARC Reactor Despite Losing Federal Funding (computerworld.com)
Lucas123 writes: Experimenting with a fusion device over the past 20 years has edged MIT researchers to their final goal, creating a small and relatively inexpensive ARC reactor, three of which would produce enough energy to power a city the size of Boston. The lessons already learned from MIT's even current Alcator C-Mod fusion device — with a plasma radius of just 0.68 meters — have enabled researchers to publish a paper on a prototype ARC that would be the world's smallest fusion reactor but with the greatest magnetic force and energy output for its size. The ARC would require 50MW to run while putting out about 200MW of electricity to the grid. Key to MIT's ARC reactor would be the use of a "high-temperature" rare-earth barium copper oxide (REBCO) superconducting tape for its magnetic coils, which only need to be cooled to 100 Kelvin, which enables the use of abundant liquid nitrogen as a cooling agent. Other fusion reactors' superconducting coils must be cooled to 4 degrees Kelvin. While there remain hurdles to overcome, such as sustaining the fusion reaction long enough to achieve a net power return, building the ARC would only take 4 to 5 years and cost about $5 billion, compared to the International Thermonuclear Experimental Reactor (ITER), the world's largest tokamak fusion reactor due to go online and begin producing energy in 2027.
Completely different class of magnetic fusion device. Completely different experiments.
Tokamaks are way simpler to build, but harder to operate than stellarators. ARC is an advanced tokamak design, and this one uses brand-new, state of the art superconductors to create a much more powerful containment field for the plasma. This machine, if built, will be used to study 'burning' plasmas, that is, plasmas getting most of their heating from thermonuclear reactions (as opposed to external heating). The research is needed, because we don't yet know what kind of exotic yet-unseen instabilities might be excited in a burning plasma.
Wendelstein 7-X is a stellarator; easier to operate, but FAR more complex to build. They don't perform as well as tokamaks, although they might be optimized in ways impossible in tokamaks. The Germans have the know-how and precision to build such an insanely complicated machine. This machine has superconducting magnet, and is the biggest stellarator to date. They want to get experience running a large stellarator with fully-superconducting magnets for long periods of time (shots running for many hours). In contrast, tokamak, like electrical transfomers, are inherently pulsed machines, and the shot times on most current machines are measured in seconds.