Alcator C-Mod: Difference between revisions

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{{shortShort description|TokamakNuclear fusion research device at MIT, United States (1991–2016)}}

{{Use mdy dates|date=September 2022}}

{{Infobox fusion devices

|name = Alcator C-Mod

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'''Alcator C-Mod''' was a [[tokamak]] (a type of [[Magnetic confinement fusion|magnetically confined fusion]] device) that operated between 1991 and 2016 at the [[Massachusetts Institute of Technology]] (MIT) [[MIT Plasma Science and Fusion Center|Plasma Science and Fusion Center]] (PSFC). Notable for its high toroidal magnetic field (of up to 8 [[Tesla (unit)|Tesla]]), Alcator C-Mod holds the world record for volume averaged plasma pressure in a magnetically confined fusion device.<ref name=":0" /> 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 ('''''Al'''to '''Ca'''mpo '''Tor'''o'', High Field Torus) tokamak series, following Alcator A (1973–1979) and Alcator BC (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.

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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]] atin [[Princeton, University]]New Jersey 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 (≥&nbsp;10&nbsp;T). In 1968, Coppi attended the third [[International Atomic Energy Agency|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&nbsp;eV in a tokamak device ([[T-3 (tokamak)|T-3]]).

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&nbsp;m major radius), high-field (10&nbsp;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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=== Heating and current drive ===

Alcator C-Mod uses [[ion cyclotron resonance|ion cyclotron rangeradio frequenciesfrequency (ICRF) heating]] as its primary auxiliary heating source. The source frequency is 80&nbsp;MHz and the standard minority heating scenarios are D(H) for 4.4–6.9 T and D(3He) for high field operation (7.3–8.0 T).<ref name=wuk/> A minority species (Hydrogen or He3) is indicated, and ICRH scenarios use a two-component plasma.

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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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&nbsp;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>{{citeCite web|url=http://www.fusionenergyleague.org/index.php/blog/article/fusion_budget_2015|title=Fusion Budget 2015: The Omnibus bill passed, Fusion budget lives to fight another year|accessdate=10 May 2023|archive-date=June 27, 2015|archive-url=https://web.archive.org/web/20150627020005/http://www.fusionenergyleague.org/index.php/blog/article/fusion_budget_2015|url-status=dead}}</ref><ref>{{cite web|url=http://www.fusionfuture.org/|title=Information about FY2013 budget and Alcator C-Mod shutdown|url-status=dead|archive-url=https://web.archive.org/web/20120304185900/http://www.fusionfuture.org/|archive-date=2012-03-04}}</ref>

In 2016 Alcator C-Mod set a world record for plasma pressure in a magnetically confined fusion device, reaching 2.05 atmospheres – a 15 percent jump over the previous record of 1.77 atmospheres (also held by Alcator C-Mod). This record plasma had a temperature of 35 million degrees C, lasted for 2 seconds, and yielded 600 trillion fusion reactions.<ref>{{Cite news|url=http://www.zmescience.com/ecology/renewable-energy-ecology/fusion-energy-record-pressure-16102016|title=New record gets us closer to fusion energy|last=ANDREI|first=MIHAI|date=2016-10-17|newspaper=ZME Science|language=en-US|access-date=2016-10-18}}</ref> The run involved operation with a toroidal magnetic field of 5.7 tesla. It reached this milestone on its final day of operation.<ref>{{Cite web|url=http://newatlas.com/nuclear-fusion-record/45932|title=Under pressure: New world record set on path to nuclear fusion|last=Franco|first=Michael|date=October 14, 2016|website=newatlas.com|access-date=2016-10-18}}</ref>

Following completion of operations at the end of September 2016, the facility has been placed into safe shutdown, with no additional experiments planned at this time. There is a wealth of data archived from the more than 20 years of operations, and the experimental and theoretical teams continue to analyze the results and publish them in the scientific literature.<ref>http{{cite web | title=Alcator C Mod Tokamak| website=psfc.mit.edu| url=https://www.psfc.mit.edu/research/topics/alcator-c-mod-tokamak | access-date=10 May 2023}}</ref>

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 20322034,<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.istoday/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