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{{Short description|Nuclear fusion research device at MIT, United States (1991–2016)}}
{{Fusion devices▼
{{Use mdy dates|date=September 2022}}
|name = Alcator C-Mod▼
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|fullname =
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|city = [[Cambridge, Massachusetts|Cambridge]]
|current = 0.4–2.0 [[Ampere|MA]] (typical)▼
|state = [[Massachusetts]]
|country = [[United States|US]]
|affiliation = [[MIT Plasma Science and Fusion Center]]
|major_radius = {{cvt|0.68|m}}
|minor_radius = {{cvt|0.22|m}}
|volume = {{val|1|ul=m3}}
|field = {{cvt|3|-|8|T}} (toroidal)
|heating = <!-- {{val|00|ul=MW}} -->
|power = <!-- {{val|00|ul=MW}} -->
|time = <!-- {{val|00|ul=s}} -->
|temperature = <!-- {{val|00|e=6|ul=K}} -->
|construction_date =
|operation_start_year = 1991
|operation_end_year = 2016
|ongoing = <!-- set to any non-blank value -->
|next =
|related =
|website = <!-- {{url|insert here}} -->
|other_links =
}}
'''Alcator C-Mod''' was a [[tokamak]]
▲[[File:Alcator C-Mod.jpg|thumb|The Alcator C-Mod tokamak experiment at the MIT Plasma Science and Fusion Center. Overview showing the device itself (under concrete shielding) and diagnostics in surrounding bay.]]
{{toclimit|3}}
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=== Alcator A ===
In the late 1960s, magnetic-confinement fusion research at MIT was carried out on small-scale "table-top" experiments at the
[[Bruno Coppi]] was working at the [[Institute for Advanced Study]]
This same year, Coppi was named a full professor in the [[MIT Physics Department|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 and initialism|acronym]] of the Italian '''''Al'''to '''Ca'''mpo '''Tor'''o'', which means "high-field torus". With the later construction of Alcator C and then Alcator C-Mod, the original Alcator was [[retronym|retroactively renamed]] to Alcator A.
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=== Alcator B and C ===
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 [[Consolidated Edison|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 [[MIT Plasma Science and Fusion Center|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 [[Northeastern United States blizzard of 1978|blizzard of 1978]]) and was incorporated into the system in the summer of 1978. Scientific operations began in September of that year.
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=== Unfunded ideas and the C-Mod proposal ===
Several ideas for new devices and upgrades at the PSFC were never funded. From 1978 to 1980, a design activity was carried out for Alcator D, a larger version of Alcator C that would allow for more heating power, and possibly even deuterium–tritium (D–T) operation. This design was never formally proposed to the [[United States Department of Energy|Department of Energy]] (DOE), but continued to evolve under Coppi's direction, eventually becoming the Italian–Russian [[IGNITOR]] device planned for construction at [[Troitsk Institute of Innovative and Thermonuclear Research|TRINITY]] near [[Troitsk, Moscow Oblast|Troitsk]], Russia.
In 1982, another more ambitious device called Alcator DCT was conceived. This machine would have superconducting coils producing 7 T on axis. 4 MW of lower hybrid current drive would drive a steady-state plasma with 1.4 MA plasma current. As this design was similar to the French [[Tore Supra]], a joint French–American workshop was held in [[Cadarache]] in 1983 to compare the two designs and exchange ideas. Alcator DCT was formally proposed to the DOE in late 1983
At that time, the budget for magnetic fusion energy research in the United States had been increasing year-over-year, reaching a peak of $468.4 million in fiscal 1984. That year, the PSFC was notified that for a time, budgets would be falling, and DOE policy would be to only fund upgrades to existing devices, not new machines. Thus, design work was begun on a copper-coil machine which would reuse some of the power supplies from Alcator C, allowing the team to pitch it as a "modification" to Alcator C. The conceptual design was completed and '''Alcator C-Mod''' was formally proposed to DOE in late 1985. The project was approved and construction was authorized in 1986.
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=== Heating and current drive ===
Alcator C-Mod uses [[ion cyclotron resonance|ion cyclotron
Absorption efficiency varies with the minority concentration. It is also possible to transition between minority and mode conversion (MC) heating by varying the minority species concentration. The relative H fraction <math>\eta_H = n_H/(n_H+n_D)</math> can be scanned from roughly 2–30% via gas puffing and measured using passive charge exchange.<ref name=wuk/> The relative He3 fraction <math>\eta_{He3} = n_{He3}/n_e</math> concentration can also be scanned from roughly 2–30% via gas puffing. Phase contrast imaging (PCI) can be used to measure the mode converted waves directly in the plasma.
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{{wide image|Alcator_C-Mod_outer_wall_stitch_2013.jpg|1500px|Panorama view of the tokamak outer wall stitched from 273 photos. The rotated ion-cyclotron frequency antenna with its four copper antenna straps can be seen on the left. The Lower Hybrid Launcher with its grid of small rectangular waveguides can be seen in the middle and the non-rotated Ion-Cyclotron frequency antennas are toward the right with four copper straps. The entrance for the neutral beam is the large circular hole near the right.}}
== 2013–2016: Final operations and shutdown ==
Alcator C-Mod was slated to shut down in October 2013. However, the 2014 Congressional omnibus spending bill explicitly specified operation of the experiment, providing $22 million. The experimental operation was restarted in February 2014.
Funding was once again extended for FY 2015, although the omnibus bill that provided the funding explicitly stated that no funding would be provided beyond FY 2016.<ref>{{
In 2016
Following completion of operations at the end of September
The Alcator C-Mod plasma pressure record of 2.05 atmosphere will likely hold for some time. The only machine currently under construction that is predicted to break this record is the [[ITER]] tokamak in France. ITER is not expected to be fully operational until 2034,<ref name="auto">{{Cite web |last=Banks |first=Michael |date=2024-07-03 |title=ITER fusion reactor hit by massive decade-long delay and €5bn price hike |url=https://physicsworld.com/iter-fusion-reactor-hit-by-massive-decade-long-delay-and-e5bn-price-hike/ |access-date=2024-07-06 |website=Physics World |language=en-GB}}</ref> meaning that Alcator C-Mod's record will hold for more than 15 years unless another new device is constructed before then.<ref name=":0">{{Cite news|url=https://news.mit.edu/2016/alcator-c-mod-tokamak-nuclear-fusion-world-record-1014|title=New record for fusion|date= October 14, 2016|publisher= Plasma Science and Fusion Center|access-date=2018-03-05}}</ref>
== References ==
===Sources===
* [https://archive.today/20121211063138/http://www.psfc.mit.edu/library1/catalog/online_pubs/iap/iap2011/iap2011_index.html "An Alcator Chronicle, or: What Happened to Alcator B?" R. Parker, presentation at IAP 2011. Available online at MIT PSFC library]
* Bonoli et al. Phys. Plasmas, Vol. 7, No. 5, May 2000
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[[Category:Tokamaks]]
[[Category:Massachusetts Institute of Technology]]
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