Major examples include Wendelstein 7-X in Germany, the Helically Symmetric Experiment (HSX) in the US, and the Large Helical Device in Japan. ==History== ===Previous work=== In 1934, Mark Oliphant, Paul Harteck and Ernest Rutherford were the first to achieve fusion on Earth, using a particle accelerator to shoot deuterium nuclei into a metal foil containing deuterium, lithium or other elements.
Various teams in the UK had built a number of small experimental devices using this technique by the late 1940s. Another person working on controlled fusion reactors was Ronald Richter, a former German scientist who moved to Argentina after the war.
In 1944, Enrico Fermi demonstrated that this would occur at a bulk temperature of about 50 million Celsius, still very hot but within the range of existing experimental systems.
In 1944, Enrico Fermi calculated the D-T reaction would be self-sustaining at about . Materials heated beyond a few tens of thousand degrees ionize into their electrons and nuclei, producing a gas-like state of matter known as plasma.
But earlier studies of magnetically confined plasmas in 1949 demonstrated much higher losses and became known as Bohm diffusion.
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. His 1958 description was simple and direct: ===Matterhorn=== While working at Los Alamos in 1950, John Wheeler suggested setting up a secret research lab at Princeton University that would carry on theoretical work on H-bombs after he returned to the university in 1951.
It is one of the earliest fusion power devices, along with the z-pinch and magnetic mirror. The stellarator was invented by American scientist Lyman Spitzer of Princeton University in 1951, and much of its early development was carried out by his team at what became the Princeton Plasma Physics Laboratory (PPPL).
Known as the Huemul Project, this was completed in 1951.
The "success" was announced by Perón on 24 March 1951, becoming the topic of newspaper stories around the world. 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.
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. His 1958 description was simple and direct: ===Matterhorn=== While working at Los Alamos in 1950, John Wheeler suggested setting up a secret research lab at Princeton University that would carry on theoretical work on H-bombs after he returned to the university in 1951.
He considered Spitzer's plans "incredibly ambitious." Nevertheless, Spitzer was successful in gaining $50,000 in funding from the AEC, while Tuck received nothing. The Princeton program was officially created on 1 July 1951.
This led to the Model A design, which began construction in 1952.
Lyman's Model A began operation in 1953 and demonstrated plasma confinement.
The machine began operations in early 1953 and clearly demonstrated improved confinement over the simple torus. This led to the construction of the Model B, which had the problem that the magnets were not well mounted and tended to move around when they were powered to their maximum capacity of 50,000 gauss.
B-3's drift rate was a full three times that of the worst-case Bohm predictions, and failed to maintain confinement for more than a few tens of microseconds. ===Model C=== As early as 1954, as research continued on the B-series machines, the design of the Model C device was becoming more defined.
B-64 was completed in 1955, essentially a larger version of the B-1 machine but powered by pulses of current that produced up to 15,000 gauss.
In 1956, B-1 was rebuilt with an ultra-high vacuum system to reduce the impurities but found that even at smaller quantities they were still a serious problem.
This led to experiments in 1956 where the machine was re-assembled without the twist in the tubes, allowing the particles to travel without rotation. B-65, completed in 1957, was built using the new "racetrack" layout.
This led to experiments in 1956 where the machine was re-assembled without the twist in the tubes, allowing the particles to travel without rotation. B-65, completed in 1957, was built using the new "racetrack" layout.
B-3, also completed in 1957, was a greatly enlarged B-2 machine with ultra-high vacuum and pulsed confinement up to 50,000 gauss and projected confinement times as long as 0.01 second.
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. His 1958 description was simple and direct: ===Matterhorn=== While working at Los Alamos in 1950, John Wheeler suggested setting up a secret research lab at Princeton University that would carry on theoretical work on H-bombs after he returned to the university in 1951.
As it appeared that little could be learned from this system in its current form, in 1958 it was sent to the Atoms for Peace show in Geneva.
The last of the B-series machines was the B-66, completed in 1958, which was essentially a combination of the racetrack layout from B-65 with the larger size and energy of the B-3. Unfortunately, all of these larger machines demonstrated a problem that came to be known as "pump out".
Construction began in 1958 and was completed in 1961.
By the early 1960s, any hope of quickly producing a commercial machine faded, and attention turned to studying the fundamental theory of high-energy plasmas.
Construction began in 1958 and was completed in 1961.
Notable among these was the 1964 addition of a small particle accelerator to accelerate fuel ions to high enough energy to cross the magnetic fields, depositing energy within the reactor when they collided with other ions already inside.
By the mid-1960s, Spitzer was convinced that the stellarator was matching the Bohm diffusion rate, which suggested it would never be a practical fusion device. The release of information on the USSR's tokamak design in 1968 indicated a leap in performance.
These "modular coils" are now a major part of ongoing research. ===Tokamak stampede=== In 1968, scientists in the Soviet Union released the results of their tokamak machines, notably their newest example, T-3.
Through continual tuning of the magnetic system and the addition of the new heating methods, in 1969, Model C eventually reached electron temperatures of 400 eV. ===Other approaches=== Through this period, a number of new potential stellarator designs emerged, which featured a simplified magnetic layout.
In July 1969 Gottlieb had a change of heart, offering to convert the Model C to a tokamak layout.
When the frequency is deliberately set close to that of the ion circulation, this is known as ion-cyclotron resonance heating, although this term was not widely used at the time. ===Inherent problems=== Work on the then-new tokamak concept in the early 1970s, notably by Tihiro Ohkawa at General Atomics, suggested that toroids with smaller aspect ratios and non-circular plasmas would have much-improved performance.
The Princeton Large Torus of 1975 quickly hit several performance numbers that were required for a commercial machine, and it was widely believed the critical threshold of breakeven would be reached in the early 1980s.
The Princeton Large Torus of 1975 quickly hit several performance numbers that were required for a commercial machine, and it was widely believed the critical threshold of breakeven would be reached in the early 1980s.
Since the 1990s, the stellarator design has seen renewed interest.
In most stellarators, these changes in field strength are greater than in tokamaks, which is a major reason that transport in stellarators tends to be higher than in tokamaks. University of Wisconsin electrical engineering Professor David Anderson and research assistant John Canik proved in 2007 that the Helically Symmetric eXperiment (HSX) can overcome this major barrier in plasma research.
Construction was cancelled in 2008, throwing the future of the PPPL into doubt. Finally, another problem with stellarator designs is that they are expected to leak alpha particles.
The stellarator is an inherently steady-state machine, which has several advantages from an engineering standpoint. In 2019 a Hessian matrix was applied to simplify the math required to assess the error fields associated with important coil imperfections.
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