Editing Princeton Plasma Physics Laboratory (section)

==History==
===Formation===
In 1950, [[John Archibald Wheeler|John Wheeler]] was setting up a secret [[H-bomb]] research lab at [[Princeton University]]. [[Lyman Spitzer|Lyman Spitzer, Jr.]], an avid mountaineer, was aware of this program and suggested the name "Project Matterhorn".<ref>{{cite web |title=Timeline |website=Princeton Plasma Physics Laboratory |url=https://www.pppl.gov/about/history/timeline |ref=CITEREFTimeline}}</ref>

Spitzer, a professor of astronomy, had for many years been involved in the study of very hot rarefied gases in interstellar space. While leaving for a ski trip to [[Aspen, Colorado|Aspen]] in February 1951, his father called and told him to read the front page of the ''[[New York Times]]''. The paper had a story about claims released the day before in [[Argentina]] that a relatively unknown German scientist named [[Ronald Richter]] had achieved nuclear fusion in his [[Huemul Project]].<ref>Burke, James (1999) ''The Knowledge Web: From Electronic Agents to Stonehenge and Back – And Other Journeys Through Knowledge'' Simon & Schuster, New York, pp.&nbsp;241–242, {{ISBN|0-684-85934-3}}.</ref> Spitzer ultimately dismissed these claims, and they were later proven erroneous, but the story got him thinking about fusion. While riding the [[chairlift]] at Aspen, he struck upon a new concept to confine a [[Plasma (physics)|plasma]] for long periods so it could be heated to fusion temperatures. He called this concept the [[stellarator]].

Later that year he took this design to the [[United States Atomic Energy Commission|Atomic Energy Commission]] in Washington. As a result of this meeting and a review of the invention by scientists throughout the nation, the stellarator proposal was funded in 1951. As the device would produce high-energy [[neutron]]s, which could be used for breeding weapon fuel, the program was classified and carried out as part of Project Matterhorn. Matterhorn ultimately ended its involvement in the bomb field in 1954, becoming entirely devoted to the fusion power field.

In 1958, this magnetic fusion research was declassified following the [[International Atomic Energy Agency#History|United Nations International Conference on the Peaceful Uses of Atomic Energy]].  This generated an influx of graduate students eager to learn the "new" physics, which in turn influenced the lab to concentrate more on basic research.<ref>Bromberg, Joan Lisa (1982) ''Fusion: Science, Politics, and the Invention of a New Energy Source'' [[MIT Press]], Cambridge, Massachusetts, [https://books.google.com/books?id=ECOvgg7b3MQC&pg=PA97 p. 97], {{ISBN|0-262-02180-3}}.</ref>

The early figure-8 stellarators included: Model-A, Model-B, Model-B2, Model-B3.<ref name=Stix/> Model-B64 was a square with round corners, and Model-B65 had a racetrack configuration.<ref name=Stix>{{Cite web|url=http://www.jspf.or.jp/JPFRS/PDF/Vol1/jpfrs1998_01-003.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.jspf.or.jp/JPFRS/PDF/Vol1/jpfrs1998_01-003.pdf |archive-date=2022-10-09 |url-status=live|title=Highlights in Early Stellarator Research at Princeton. Stix. 1997}}</ref> The last and most powerful stellarator at this time was the "racetrack" [[Model C stellarator|Model&nbsp;C]] (operating from 1961 to 1969).<ref>{{Cite journal |last=Yoshikawa |first=S. |last2=Stix |first2=T.H. |date=1985-09-01 |title=Experiments on the Model C stellarator |url=https://iopscience.iop.org/article/10.1088/0029-5515/25/9/047 |journal=Nuclear Fusion |volume=25 |issue=9 |pages=1275–1279 |doi=10.1088/0029-5515/25/9/047 |issn=0029-5515|url-access=subscription }}</ref>

===Tokamak===
By the mid-1960s it was clear something was fundamentally wrong with the stellarators, as they leaked fuel at rates far beyond what theory predicted, rates that carried away energy from the plasma that was far beyond what the fusion reactions could ever produce. Spitzer became extremely skeptical that fusion energy was possible and expressed this opinion in very public fashion in 1965 at an international meeting in the UK. At the same meeting, the Soviet delegation announced results about 10 times better than any previous device, which Spitzer dismissed as a measurement error.

At the next meeting in 1968, the Soviets presented considerable data from their devices that showed even greater performance, about 100 times the [[Bohm diffusion]] limit. An enormous argument broke out between the AEC and the various labs about whether this was real. When a UK team verified the results in 1969, the AEC suggested PPPL to convert their Model&nbsp;C to a tokamak to test it, as the only lab willing to build one from scratch, [[Oak Ridge National Laboratory|Oak Ridge]], would need some time to build theirs. Seeing the possibility of being bypassed in the fusion field, PPPL eventually agreed to convert the Model&nbsp;C to what became the Symmetric Tokamak (ST), quickly verifying the approach.

Two small machines followed the ST, exploring ways to heat the plasma, and then the [[Princeton Large Torus]] (PLT) to test whether the theory that larger machines would be more stable was true. Starting in 1975, PLT verified these "scaling laws" and then went on to add [[neutral beam injection]] from Oak Ridge that resulted in a series of record-setting plasma temperatures, eventually topping out at 78&nbsp;million [[kelvin]]s<!-- the SI unit is in lower case and pluralized regularly -->, well beyond what was needed for a practical fusion power system. Its success was major news.

With this string of successes, PPPL had little trouble winning the bid to build an even larger machine, one specifically designed to reach [[fusion energy gain factor|"breakeven"]] while running on an actual fusion fuel, rather than a test gas. This produced the [[Tokamak Fusion Test Reactor]], or TFTR, which was completed in 1982. After a lengthy breaking-in period, TFTR began slowly increasing the temperature and density of the fuel, while introducing [[deuterium]] gas as the fuel. In April 1986, it demonstrated a combination of density and confinement, the so-called [[fusion triple product]], well beyond what was needed for a practical reactor. In July, it reached a temperature of 200&nbsp;million kelvins, far beyond what was needed. However, when the system was operated with both of these conditions at the same time, a high enough triple product and temperature, the system became unstable. Three years of effort failed to address these issues, and TFTR never reached its goal.<ref>{{cite journal |title=Results and Plans for the Tokamak Fusion Test Reactor |first=Dale |last=Meade |journal=Journal of Fusion Energy |volume = 7|issue=2–3 |date= September 1988 |page=107|doi = 10.1007/BF01054629|bibcode=1988JFuE....7..107M |s2cid=120135196 }}</ref> The system continued performing basic studies on these problems until being shut down in 1997.<ref name="TFTR-end">Staff (1996) "Fusion Lab Planning Big Reactor's Last Run", ''[[The Record (Bergen County)|The Record]]'', 22 December 1996, p.&nbsp;N-07.</ref> Beginning in 1993, TFTR was the first in the world to use 1:1 mixtures of [[deuterium]]–[[tritium]]. In 1994 it yielded an unprecedented 10.7&nbsp;megawatts of fusion power.<ref name="TFTR-end"/>

===Later designs===
In 1999, the [[National Spherical Torus Experiment]] (NSTX), based on the spherical tokamak concept, came online at the PPPL. 

Odd-parity heating was demonstrated in the 4&nbsp;cm radius PFRC-1 experiment in 2006. PFRC-2 has a plasma radius of 8&nbsp;cm. Studies of electron heating in PFRC-2 reached 500&nbsp;[[electronvolt|eV]] with pulse lengths of 300&nbsp;ms.<ref name=":0">{{Cite web |url=https://www.nextbigfuture.com/2019/06/game-changing-direct-drive-fusion-propulsion-progress.html |title=Game Changing Direct Drive Fusion Propulsion Progress |last=Wang |first=Brian |date=June 22, 2019 |website=NextBigFuture |language=en-US |access-date=2019-06-22}}</ref>

In 2015, PPPL completed an upgrade to NSTX to produce NSTX-U that made it the most powerful experimental fusion facility, or tokamak, of its type in the world.<ref>{{Cite web |url=https://www.pppl.gov/nstx |title=National Spherical Torus Experiment Upgrade (NSTX-U) |website=Princeton Plasma Physics Lab}}</ref>

In 2017, the group received a Phase II NIAC grant along with two NASA STTRs funding the RF subsystem and superconducting coil subsystem.<ref name=":0" />

In 2024, the lab announced MUSE, a new [[stellarator]]. MUSE uses rare-earth permanent magnets with a field strength that can exceed 1.2 [[Tesla (unit)|teslas]]. The device uses quasiaxisymmetry, a subtype of [[quasisymmetry]]. The research team claimed that its use of quasisymmetry was more sophisticated than prior devices.<ref>{{Cite web |last=Paul |first=Andrew |date=2024-04-05 |title=Stellarator fusion reactor gets new life thanks to a creative magnet workaround |url=https://www.popsci.com/environment/stellarator-fusion-reactor/ |access-date=2024-04-11 |website=Popular Science |language=en-US}}</ref> Also in 2024, PPL announced a [[reinforcement learning]] model that could forecast tearing mode instabilities up to 300 milliseconds in advance. That is enough time for the plasma controller to adjust operating parameters to prevent the tear and maintain [[High-confinement mode|H-mode]] performance.<ref>{{Cite web |date=March 4, 2024 |title=AI can predict and prevent fusion plasma instabilities in milliseconds |url=https://www.ans.org/news/article-5835/ai-can-predict-and-prevent-fusion-plasma-instabilities-in-milliseconds/ |access-date=2024-05-20 |website=www.ans.org |language=en}}</ref><ref>{{Cite journal |last=Seo |first=Jaemin |last2=Kim |first2=SangKyeun |last3=Jalalvand |first3=Azarakhsh |last4=Conlin |first4=Rory |last5=Rothstein |first5=Andrew |last6=Abbate |first6=Joseph |last7=Erickson |first7=Keith |last8=Wai |first8=Josiah |last9=Shousha |first9=Ricardo |last10=Kolemen |first10=Egemen |date=2024 |title=Avoiding fusion plasma tearing instability with deep reinforcement learning |url=https://www.nature.com/articles/s41586-024-07024-9 |journal=Nature |language=en |volume=626 |issue=8000 |pages=746–751 |doi=10.1038/s41586-024-07024-9 |issn=1476-4687|pmc=10881383 }}</ref>