Alcator C-Mod

Alcator C-Mod was a tokamak (a type of magnetically confined fusion device) that operated between 1991 and 2016 at the Massachusetts Institute of Technology (MIT) Plasma Science and Fusion Center (PSFC). Notable for its high toroidal magnetic field (of up to 8 Tesla), Alcator C-Mod holds the world record for volume averaged plasma pressure in a magnetically confined fusion device. Until its shutdown in 2016, it was one of the major fusion research facilities in the United States. Alcator C-Mod was a tokamak (a type of magnetically confined fusion device) that operated between 1991 and 2016 at the Massachusetts Institute of Technology (MIT) Plasma Science and Fusion Center (PSFC). Notable for its high toroidal magnetic field (of up to 8 Tesla), Alcator C-Mod holds the world record for volume averaged plasma pressure in a magnetically confined fusion device. Until its shutdown in 2016, it was one of the major fusion research facilities in the United States. Alcator C-Mod was the third of the Alcator (Alto Campo Toro, High Field Torus) tokamak series, following Alcator A (1973–1979) and Alcator B (1978–1987). It was the largest fusion reactor operated by any university and was an integral part of the larger Plasma Science and Fusion Center. In the late 1960s, magnetic-confinement fusion research at MIT was carried out on small-scale 'table-top' experiments at the Research Laboratory for Electronics and the Francis Bitter Magnet Laboratory. At this time, the Soviet Union was developing a tokamak (though this was unknown in the United States), and Princeton Plasma Physics Laboratory (PPPL) was developing the stellarator. Bruno Coppi was working at the Institute for Advanced Study at Princeton University and was interested in the basic plasma physics problem of plasma resistivity at high values of the streaming parameter, as well as the behavior of magnetically confined plasmas at very high field strengths (≥ 10 T). In 1968, Coppi attended the third IAEA International Conference on Plasma Physics and Controlled Nuclear Fusion Research at Novosibirsk. At this conference, Soviet scientists announced that they had achieved electron temperatures of over 1000 eV in a tokamak device (T-3). This same year, Coppi was named a full professor in the MIT Department of Physics. He immediately collaborated with engineers at the Francis Bitter Magnet Laboratory, led by Bruce Montgomery, to design a compact (0.54 m major radius), high-field (10 T on axis) tokamak which he titled Alcator. The name is an acronym of the Italian Alto Campo Toro, which means 'high-field torus'. With the later construction of Alcator C and then Alcator C-Mod, the original Alcator was retroactively renamed to Alcator A. Alcator was approved by the Atomic Energy Commission (AEC) in 1970 and was first operated in 1972. Performance problems (poor-quality vacuum and arcing in toroidal field magnets) led to the rebuilding of the machine in 1973–1974 with a new vacuum vessel, with scientific results beginning in 1974. Alcator A was powered by the Bitter Laboratory's 32 MW DC motor-generators and was the first tokamak in the world to use an air-core transformer for ohmic current drive and heating. The success of Alcator A led to the conceptual design, beginning in 1975, of a larger machine called Alcator B. However, the motor-generators used for Alcator A were not powerful enough to drive the new machine, necessitating the purchase and installation of new power supplies, a cost that the Energy Research and Development Administration (ERDA) was unwilling to fund. ERDA was, however, enthusiastic about building another Alcator, and a solution was found: a 225 MVA alternator was donated to MIT by Con Ed from a plant on the East River in New York City. The conceptual design was changed to accommodate the different power supply, and the project was renamed to Alcator C. Alcator C was officially authorized in 1976. This same year, the Plasma Fusion Center (now the Plasma Science and Fusion Center) was spun off from the Francis Bitter Magnet Laboratory. Construction of Alcator C proceeded rapidly and initial tests were conducted at the end of 1977. The alternator arrived from Con Ed in early 1978 (its transport was complicated by the blizzard of 1978) and was incorporated into the system in the summer of 1978. Scientific operations began in September of that year. Alcator C was a larger machine (R0 = 0.64 m) and operated at a higher field (B0 ≤ 13 T) than Alcator A. With the addition of 4 MW of lower hybrid heating in 1982, electron temperatures over 3.0 keV were reached. While Alcator C did not originally have the energy confinement time expected, due to the onset of ion temperature gradient turbulence at high values of η = d ln ⁡ T / d ln ⁡ n {displaystyle eta ={ ext{d}}ln T/{ ext{d}}ln n} , pellet fueling was used to produce peaked density profiles and values of the nτ product of over 0.8 × 1020 s·m−3 were achieved in 1983.