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.