The Tokamak Fusion Test Reactor (TFTR) was an experimental
tokamak
A tokamak (; russian: токамáк; otk, 𐱃𐰸𐰢𐰴, Toḳamaḳ) is a device which uses a powerful magnetic field to confine plasma in the shape of a torus. The tokamak is one of several types of magnetic confinement devices being d ...
built at
Princeton Plasma Physics Laboratory
Princeton Plasma Physics Laboratory (PPPL) is a United States Department of Energy national laboratory for plasma physics and nuclear fusion science. Its primary mission is research into and development of fusion as an energy source. It is known ...
(PPPL) circa 1980 and entering service in 1982. TFTR was designed with the explicit goal of reaching scientific
breakeven
Break-even (or break even), often abbreviated as B/E in finance, (sometimes called point of equilibrium) is the point of balance making neither a profit nor a loss. Any number below the break-even point constitutes a loss while any number above i ...
, the point where the heat being released from the
fusion reaction
Nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles (neutrons or protons). The difference in mass between the reactants and products is manifeste ...
s in the
plasma
Plasma or plasm may refer to:
Science
* Plasma (physics), one of the four fundamental states of matter
* Plasma (mineral), a green translucent silica mineral
* Quark–gluon plasma, a state of matter in quantum chromodynamics
Biology
* Blood pla ...
is equal or greater than the heating being supplied to the plasma by external devices to warm it up.
[
The TFTR never achieved this goal, but it did produce major advances in confinement time and energy density. It was the world's first magnetic fusion device to perform extensive scientific experiments with plasmas composed of 50/50 deuterium/tritium (D-T), the fuel mix required for practical fusion power production, and also the first to produce more than 10 MW of fusion power. It set several records for power output, maximum temperature, and ]fusion triple product
The Lawson criterion is a figure of merit used in nuclear fusion research. It compares the rate of energy being generated by fusion reactions within the fusion fuel to the rate of energy losses to the environment. When the rate of production is ...
.
TFTR shut down in 1997 after fifteen years of operation. PPPL used the knowledge from TFTR to begin studying another approach, the spherical tokamak
A spherical tokamak is a type of fusion power device based on the tokamak principle. It is notable for its very narrow profile, or '' aspect ratio''. A traditional tokamak has a toroidal confinement area that gives it an overall shape similar to ...
, in their National Spherical Torus Experiment
The National Spherical Torus Experiment (NSTX) is a magnetic fusion device based on the ''spherical tokamak'' concept. It was constructed by the Princeton Plasma Physics Laboratory (PPPL) in collaboration with the Oak Ridge National Laboratory, ...
. The Japanese JT-60
JT-60 (short for Japan Torus-60) is a large research tokamak, the flagship of Japan's magnetic fusion program, previously run by the Japan Atomic Energy Research Institute (JAERI) and currently run by the Japan Atomic Energy Agency's (JAEA) Naka ...
is very similar to the TFTR, both tracing their design to key innovations introduced by Shoichi Yoshikawa (1934-2010) during his time at PPPL in the 1970s.
General
In nuclear fusion, there are two types of reactors stable enough to conduct fusion: magnetic confinement reactors and inertial confinement reactors. The former method of fusion seeks to lengthen the time that ions spend close together in order to fuse them together, while the latter aims to fuse the ions so fast that they do not have time to move apart. Inertial confinement reactors, unlike magnetic confinement reactors, use laser fusion and ion-beam fusion in order to conduct fusion. However, with magnetic confinement reactors you avoid the problem of having to find a material that can withstand the high temperatures of nuclear fusion reactions. The heating current is induced by the changing magnetic fields in central induction coils and exceeds a million amperes. Magnetic fusion devices keep the hot plasma out of contact with the walls of its container by keeping it moving in circular or helical paths by means of the magnetic force on charged particles and by a centripetal force acting on the moving particles.
History
Tokamak
By the early 1960s, the fusion power
Fusion power is a proposed form of power generation that would generate electricity by using heat from nuclear fusion, nuclear fusion reactions. In a fusion process, two lighter atomic nucleus, atomic nuclei combine to form a heavier nucleus, whi ...
field had grown large enough that the researchers began organizing semi-annual meetings that rotated around the various research establishments. In 1968, the now-annual meeting was held in Novosibirsk
Novosibirsk (, also ; rus, Новосиби́рск, p=nəvəsʲɪˈbʲirsk, a=ru-Новосибирск.ogg) is the largest city and administrative centre of Novosibirsk Oblast and Siberian Federal District in Russia. As of the Russian Census ...
, where the Soviet delegation surprised everyone by claiming their tokamak
A tokamak (; russian: токамáк; otk, 𐱃𐰸𐰢𐰴, Toḳamaḳ) is a device which uses a powerful magnetic field to confine plasma in the shape of a torus. The tokamak is one of several types of magnetic confinement devices being d ...
designs had reached performance levels at least an order of magnitude
An order of magnitude is an approximation of the logarithm of a value relative to some contextually understood reference value, usually 10, interpreted as the base of the logarithm and the representative of values of magnitude one. Logarithmic dis ...
better than any other device. The claims were initially met with skepticism, but when the results were confirmed by a UK team the next year, this huge advance led to a "virtual stampede" of tokamak construction.
In the US, one of the major approaches being studied up to this point was the stellarator
A stellarator is a plasma device that relies primarily on external magnets to confine a plasma. Scientists researching magnetic confinement fusion aim to use stellarator devices as a vessel for nuclear fusion reactions. The name refers to the ...
, whose development was limited almost entirely to the PPPL. Their latest design, the Model C, had recently gone into operation and demonstrated performance well below theoretical calculations, far from useful figures. With the confirmation of the Novosibirsk results, they immediately began converting the Model C to a tokamak layout, known as the Symmetrical Tokamak
Symmetry (from grc, συμμετρία "agreement in dimensions, due proportion, arrangement") in everyday language refers to a sense of harmonious and beautiful proportion and balance. In mathematics, "symmetry" has a more precise definit ...
(ST). This was completed in the short time of only eight months, entering service in May 1970. ST's computerized diagnostics allowed it to quickly match the Soviet results, and from that point, the entire fusion world was increasingly focused on this design over any other.
Princeton Large Torus
During the early 1970s, Shoichi Yoshikawa was looking over the tokamak concept. He noted that as the size of the reactor's minor axis (the diameter of the tube) increased compared to its major axis (the diameter of the entire system) the system became more efficient. An added benefit was that as the minor axis increased, confinement time improved for the simple reason that it took longer for the fuel ions to reach the outside of the reactor. This led to widespread acceptance that designs with lower aspect ratios were a key advance over earlier models.[
This led to the ]Princeton Large Torus
The Princeton Large Torus (or PLT), was an early tokamak built at the Princeton Plasma Physics Laboratory (PPPL). It was one of the first large scale tokamak machines, and among the most powerful in terms of current and magnetic fields. Originally ...
(PLT), which was completed in 1975. This system was successful to the point where it quickly reached the limits of its Ohmic heating system, the system that passed current through the plasma to heat it. Among the many ideas proposed for further heating, in cooperation with Oak Ridge National Laboratory
Oak Ridge National Laboratory (ORNL) is a U.S. multiprogram science and technology national laboratory sponsored by the U.S. Department of Energy (DOE) and administered, managed, and operated by UT–Battelle as a federally funded research and ...
, PPPL developed the idea of neutral beam injection
Neutral-beam injection (NBI) is one method used to heat plasma inside a fusion device consisting in a beam of high-energy neutral particles that can enter the magnetic confinement field. When these neutral particles are ionized by collision with ...
. This used small particle accelerator
A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to very high speeds and energies, and to contain them in well-defined beams.
Large accelerators are used for fundamental research in particle ...
s to inject fuel atoms directly into the plasma, both heating it and providing fresh fuel.[
After a number of modifications to the beam injection system, the newly equipped PLT began setting records and eventually made several test runs at 60 million K, more than enough for a fusion reactor. To reach the ]Lawson criterion
The Lawson criterion is a figure of merit used in nuclear fusion research. It compares the rate of energy being generated by fusion reactions within the fusion fuel to the rate of energy losses to the environment. When the rate of production is ...
for ignition, all that was needed was higher plasma density, and there seemed to be no reason this would not be possible in a larger machine. There was widespread belief that break-even would be reached during the 1970s.[
]
TFTR concept
After the success of PLT and other follow-on designs, the basic concept was considered well understood. PPPL began the design of a much larger successor to PLT that would demonstrate plasma burning in pulsed operation.[
In July 1974, the ]Department of Energy A Ministry of Energy or Department of Energy is a government department in some countries that typically oversees the production of fuel and electricity; in the United States, however, it manages nuclear weapons development and conducts energy-rel ...
(DOE) held a large meeting that was attended by all the major fusion labs. Notable among the attendees was Marshall Rosenbluth, a theorist who had a habit of studying machines and finding a variety of new instabilities that would ruin confinement. To everyone's surprise, at this meeting he failed to raise any new concerns. It appeared that the path to break-even was clear.
The last step before the attack on break-even would be to make a reactor that ran on a mixture of deuterium
Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two Stable isotope ratio, stable isotopes of hydrogen (the other being Hydrogen atom, protium, or hydrogen-1). The atomic nucleus, nucleus of a deuterium ato ...
and tritium
Tritium ( or , ) or hydrogen-3 (symbol T or H) is a rare and radioactive isotope of hydrogen with half-life about 12 years. The nucleus of tritium (t, sometimes called a ''triton'') contains one proton and two neutrons, whereas the nucleus o ...
, as opposed to earlier machines which ran on deuterium alone. This was because tritium was both radioactive
Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consid ...
and easily absorbed in the body, presenting safety issues that made it expensive to use. It was widely believed that the performance of a machine running on deuterium alone would be basically identical to one running on D-T, but this assumption needed to be tested. Looking over the designs presented at the meeting, the DOE team chose the Princeton design.[
]Bob Hirsch
Bob, BOB, or B.O.B. may refer to:
Places
*Mount Bob, New York, United States
* Bob Island, Palmer Archipelago, Antarctica
People, fictional characters, and named animals
*Bob (given name), a list of people and fictional characters
* Bob (surnam ...
, who recently took over the DOE steering committee, wanted to build the test machine at Oak Ridge National Laboratory
Oak Ridge National Laboratory (ORNL) is a U.S. multiprogram science and technology national laboratory sponsored by the U.S. Department of Energy (DOE) and administered, managed, and operated by UT–Battelle as a federally funded research and ...
(ORNL), but others in the department convinced him it would make more sense to do so at PPPL. They argued that a Princeton team would be more involved than an ORNL team running someone else's design. If an engineering prototype of a commercial system followed, that could be built at Oak Ridge. They gave the project the name TFTR and went to Congress for funding, which was granted in January 1975. Conceptual design work was carried out throughout 1975, and detailed design began the next year.[
TFTR would be the largest tokamak in the world; for comparison, the original ST had a plasma diameter of , while the follow-on PLT design was , and the TFTR was designed to be .] This made it roughly double the size of other large-scale machines of the era; the 1978 Joint European Torus
The Joint European Torus, or JET, is an operational magnetically confined plasma physics experiment, located at Culham Centre for Fusion Energy in Oxfordshire, UK. Based on a tokamak design, the fusion research facility is a joint European pro ...
and roughly concurrent JT-60
JT-60 (short for Japan Torus-60) is a large research tokamak, the flagship of Japan's magnetic fusion program, previously run by the Japan Atomic Energy Research Institute (JAERI) and currently run by the Japan Atomic Energy Agency's (JAEA) Naka ...
were both about half the diameter.
As PLT continued to generate better and better results, in 1978 and 79, additional funding was added and the design amended to reach the long-sought goal of "scientific breakeven" when the amount of power produced by the fusion reactions in the plasma was equal to the amount of power being fed into it to heat it to operating temperatures. Also known as ''Q'' = 1, this is an important step on the road to useful power-producing designs. To meet this requirement, the heating system was upgraded to 50 MW, and finally to 80 MW.
Operations
Construction began in 1980 and TFTR began initial operations in 1982. A lengthy period of break-in and testing followed. By the mid-1980s, tests with deuterium began in earnest in order to understand its performance. In 1986 it produced the first 'supershots' which produced many fusion neutrons.[Fusion. Robin Herman. 1990. ] These demonstrated that the system could reach the goals of the initial 1976 design; the performance when running on deuterium was such that if tritium was introduced it was expected to produce about 3.5 MW of fusion power. Given the energy in the heating systems, this represented a ''Q'' of about 0.2, or about only 20% of the requirement for break-even.
Further testing revealed significant problems, however. To reach break-even, the system would have to meet several goals at the same time, a combination of temperature, density and the length of time the fuel is confined. In April 1986, TFTR experiments demonstrated the last two of these requirements when it produced a fusion triple product
The Lawson criterion is a figure of merit used in nuclear fusion research. It compares the rate of energy being generated by fusion reactions within the fusion fuel to the rate of energy losses to the environment. When the rate of production is ...
of 1.5 x Kelvin seconds per cubic centimeter, which is close to the goal for a practical reactor and five to seven times what is needed for breakeven. However, this occurred at a temperature that was far below what would be required. In July 1986, TFTR achieved a plasma temperature of 200 million kelvin (200 MK), at that time the highest ever reached in a laboratory. The temperature is 10 times greater than the center of the sun, and more than enough for breakeven. Unfortunately, to reach these temperatures the triple product had been greatly reduced to , two or three times too small for break-even.
Major efforts to reach these conditions simultaneously continued. Donald Grove, TFTR project manager, said they expected to achieve that goal in 1987. This would be followed with D-T tests that would actually produce breakeven, beginning in 1989.[Thomsen, D.E.(1986) A Plasma 10 times as hot as the Sun. Science News. 130: 102-102. ] Unfortunately, the system was unable to meet any of these goals. The reasons for these problems were intensively studied over the following years, leading to a new understanding of the instabilities of high-performance plasmas that had not been seen in smaller machines. A major outcome of TFTR's troubles was the development of highly non-uniform plasma cross-sections, notably the D-shaped plasmas that now dominate the field.
Later experiments
Although it became clear that TFTR would not reach break-even, experiments using tritium began in earnest in December 1993, the first such device to move primarily to this fuel. In 1994 it produced a then world-record of 10.7 megawatts of fusion power from a 50-50 D-T plasma (exceeded at JET in the UK, which generated 16MW from 24MW of injected thermal power input in 1997, which was the record until 2021). The two experiments had emphasized the alpha particles produced in the deuterium-tritium reactions, which are important for self-heating of the plasma and an important part of any operational design. In 1995, TFTR attained a world-record temperature of 510 million °C - more than 25 times that at the center of the sun. This later was beaten the following year by the JT-60 Tokamak which achieved an ion temperature of 522 million °C (45 keV). Also In 1995, TFTR scientists explored a new fundamental mode of plasma confinement -- enhanced reversed shear
''Enhanced'' is a 2019 Canadian-Japanese action film produced, written and directed by James Mark. The film premiered at the 2019 Toronto After Dark Film Festival.
Plot
A sinister government organization hunts down mutants, and one of such is a y ...
, to reduce plasma turbulence.
TFTR remained in use until 1997. It was dismantled in September 2002, after 15 years of operation.
It was followed by the NSTX
The National Spherical Torus Experiment (NSTX) is a Magnetic fusion energy, magnetic fusion device based on the ''spherical tokamak'' concept. It was constructed by the Princeton Plasma Physics Laboratory (PPPL) in collaboration with the Oak Ridg ...
spherical tokamak.[http://www.pppl.gov/Tokamak%20Fusion%20Test%20Reactor ("In addition to meeting its physics objectives, TFTR achieved all of its hardware design goals")]
See also
* List of fusion experiments
Experiments directed toward developing fusion power are invariably done with dedicated machines which can be classified according to the principles they use to confine the plasma fuel and keep it hot.
The major division is between magnetic co ...
References
{{fusion experiments
Tokamaks
Princeton Plasma Physics Laboratory