Editing Stellarator (section)

=== Stellarator ===
After [[World War II]], a number of researchers began considering different ways to confine a plasma. [[George Paget Thomson]] of [[Imperial College London]] proposed a system now known as [[z-pinch]], which runs a current through the plasma.{{sfn|Herman|1990|p=40}} Due to the [[Lorentz force]], this current creates a magnetic field that pulls the plasma in on itself, keeping it away from the walls of the reactor. This eliminates the need for magnets on the outside, avoiding the problem Fermi noted. Various teams in the UK had built a number of small experimental devices using this technique by the late 1940s.{{sfn|Herman|1990|p=40}}

Another person working on controlled fusion reactors was [[Ronald Richter]], a German scientist who moved to [[Argentina]] after the war. His ''thermotron'' used a system of electrical arcs and mechanical compression (sound waves) for heating and confinement. He convinced [[Juan Perón]] to fund development of an experimental reactor on an isolated island near the Chilean border. Known as the [[Huemul Project]], this was completed in 1951. Richter soon convinced himself fusion had been achieved in spite of other people working on the project disagreeing.{{sfn|Mariscotti|1992|pp=9–10}} The "success" was announced by Perón on 24 March 1951, becoming the topic of newspaper stories around the world.<ref>{{cite conference |first=Regis |last=Cabral |editor-first=Juan José |editor-last=Saldaña |chapter=The Perón-Richter Fusion Program: 1948–1953 |title=Cross Cultural Diffusion of Science: Latin America |year=1987 |location=Berkeley, California |page=85 }}</ref>

While preparing for a ski trip to Aspen, Lyman Spitzer received a telephone call from his father, who mentioned an article on Huemul in ''[[The New York Times]]''.{{sfn|Ellis|1958|p=12}} Looking over the description in the article, Spitzer concluded it could not possibly work; the system simply could not provide enough energy to heat the fuel to fusion temperatures. But the idea stuck with him, and he began considering systems that would work. While riding the [[ski lift]], he hit upon the stellarator concept.<ref>{{cite web |last=Greenwald |first=J. |date=23 October 2013 |title=Celebrating Lyman Spitzer, the father of PPPL and the Hubble Space Telescope |url=http://www.pppl.gov/news/2013/10/celebrating-lyman-spitzer-father-pppl-and-hubble-space-telescope |publisher=Princeton Plasma Physics Lab |access-date=12 April 2017 |archive-date=25 April 2017 |archive-url=https://web.archive.org/web/20170425033914/http://www.pppl.gov/news/2013/10/celebrating-lyman-spitzer-father-pppl-and-hubble-space-telescope |url-status=dead }}</ref>{{efn|Sources disagree on when the stellarator concept emerged in its current form, Bromberg puts the figure-8 arrangement being part of later work after he returned to Princeton.}}

The basic concept was a way to modify the torus layout so that it addressed Fermi's concerns through the device's geometry. By twisting one end of the torus compared to the other, forming a figure-8 layout instead of a circle, the magnetic lines no longer travelled around the tube at a constant radius, instead they moved closer and further from the torus' center. A particle orbiting these lines would find itself constantly moving in and out across the minor axis of the torus. The drift upward while it travelled through one section of the reactor would be reversed after half an orbit and it would drift downward again. The cancellation was not perfect, but it appeared this would so greatly reduce the net drift rates that the fuel would remain trapped long enough to heat it to the required temperatures.{{sfn|Bromberg|1982|p=17}}

His 1958 description was simple and direct:
{{quotation|Magnetic confinement in the stellarator is based on a strong magnetic field produced by solenoidal coils encircling a toroidal tube. The configuration is characterized by a 'rotational transform', such that a single line of magnetic force, followed around the system, intersects a cross-sectional plane in points which successively rotate about the magnetic axis. ... A rotational transform may be generated either by a solenoidal field in a twisted, or figure-eight shaped, tube, or by the use of an additional transverse multipolar helical field, with helical symmetry.{{sfn|Spitzer|1958|p= 253}}}}