Alcator C-Mod: Difference between revisions

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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

{{FusionInfobox fusion devices

|image =

|typename = [[Tokamak]]Alcator C-Mod

|fullname =

|operation = 1991–2016

|sizeimage = 0.68Alcator m/0C-Mod.22 mjpg

[[File:Alcator C-Mod.jpg|thumb|imagetitle = 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.]]

|volume = 1 m³

|fieldtype = 3–8 = [[tesla (unit)|TTokamak]] (toroidal)

|city = [[Cambridge, Massachusetts|Cambridge]]

|current = 0.4–2.0 [[Ampere|MA]] (typical)

|state = [[Massachusetts]]

|___location = [[Massachusetts Institute of Technology]], [[Cambridge, Massachusetts|Cambridge]], [[United States|USA]]

|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}} -->

|current = {{val|0.4–24|-|2.0 [[Ampere|ul=MA]]}} (typical)

|temperature = <!-- {{val|00|e=6|ul=K}} -->

|construction_date =

|operation_start_year = 1991

|operation_end_year = 2016

|ongoing = <!-- set to any non-blank value -->

|nameprev = Alcator C-Mod

|next =

|related =

|website = <!-- {{url|insert here}} -->

|other_links =

}}

'''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.

[[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 [[Research Laboratory of Electronics at MIT|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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=== 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&nbsp;D, a larger version of Alcator&nbsp;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&nbsp;T on axis. 4&nbsp;MW of lower hybrid current drive would drive a steady-state plasma with 1.4&nbsp;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 but was not funded.

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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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{{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 ==

== 2013-2016 ==

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|publisheraccessdate=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|archiveurlarchive-url=https://web.archive.org/web/20120304185900/http://www.fusionfuture.org/|archivedatearchive-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|work=|newspaper=ZME Science|language=en-US|access-date=2016-10-18|via=}}</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|publisher=|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

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{{fusion experiments}}

[[Category:Fusion power]]

[[Category:Fusion reactors]]

[[Category:Massachusetts Institute of Technology]]

[[Category:Plasma physics]]

[[Category:Tokamaks]]

[[Category:Massachusetts Institute of Technology]]