Tokamak
The word Tokamak, an acronym for Russian тороидальная камера с магнитными катушками -toroidal'naya kamera s magnitnymi katushkami- (in Spanish: toroidal camera with magnetic coils), is a device whose objective is to obtain the fusion of plasma particles, which would generate large amounts of energy, in order to achieve the nuclear reaction Fusion of two light particles into a more stable particle of medium weight and produce an energy relative to the Einstein equivalence:
- E=m⋅ ⋅ c2{displaystyle E={m}cdot {c^{2}}}}
The advantages of fusion over fission (used today in nuclear power plants) are: a) it does not produce direct radioactive waste and b) it does not require a non-renewable and scarce fuel such as uranium. Instead, it is much more difficult to initiate: To date, the balance point between the energy needed to accelerate and confine the plasma and that obtained by fusing some particles has not been reached. However there are no theoretical reasons for this, but only technical reasons, which the international ITER project tries to solve.
The Tokamak was devised in the 1950s by Soviet physicists Igor Tam and Andrei Sakharov, based on ideas proposed by Oleg Lavrentiev in 1950.
History
First Steps
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 or other atoms. This allowed them to measured the nuclear cross section of various fusion reactions, and determined that the deuterium-deuterium reaction occurred at a lower energy than other reactions, peaking at about 100,000 electron voltss (100 keV).
Accelerator-based fusion is impractical because the cross section of the reactor is tiny; most of the accelerator particles will disperse from the fuel, not merge with it. These scatterings cause the particles to lose energy to the point that they can no longer undergo fusion. The energy put into these particles is thus lost, and it is easy to show that it is much more energy than the resulting fusion reactions can release.
To sustain fusion and produce net energy, most fuel must be raised to high temperatures so that its atoms constantly collide at high speed; this gives rise to the name thermonuclear due to the high temperatures necessary for it to occur. In 1944, Enrico Fermi calculated that the reaction would be self-sustaining at about 50,000,000 K; at that temperature, the rate at which energy is released from the reactions is high enough to heat the surrounding fuel fast enough to maintain the temperature against losses to the environment, continuing the reaction.
During the Manhattan Project, the first practical way to achieve these temperatures was created, using an atomic bomb. In 1944, Fermi gave a talk on the physics of fusion in the context of a then-hypothetical hydrogen bomb. However, a controlled fusion device had already been thought of, and James L. Tuck and Stanislaw Ulam had attempted it using shaped charges that propelled a deuterium-infused metal foil, though without success.
The first attempts to build a practical fusion machine took place in the United Kingdom, where George Paget Thomson had selected clamping as a promising technique in 1945. After several unsuccessful attempts to obtain funding, he gave up and asked two graduate students, Stanley (Stan) W. Cousins and Alan Alfred Ware (1924-2010), to build a device out of leftover radar equipment. This device was successfully operated in 1948, but it did not show any clear evidence of fusion and failed to gain the interest of the Atomic Energy Research Establishment.
Letter from Lavrentiev
In 1950, Oleg Lavrentiev, then a Red Army sergeant stationed in Sakhalin, wrote a letter to the Central Committee of the Communist Party of the Soviet Union. The letter outlined the idea of using an atomic bomb to ignite a fusion fuel, and then went on to describe a system that used electrostatic fields to contain hot, steady-state plasma for power production. {efn|The system described by Lavrentiev is very similar to the concept now known as a fuser.}}
The letter was sent to Andrei Sakharov for comment. Sakharov noted that "the author formulates a very important problem and not necessarily an irremediable one", and considered that his main concern in the provision was that the plasma hit the electrode cables, and that "the meshes wide and a thin current-conducting part that will have to reflect almost all incident nuclei back into the reactor. In all probability, this requirement is incompatible with the mechanical resistance of the device".
An indication of the importance given to Lavrentiev's letter can be seen in the speed with which it was processed; the letter was received by the Central Committee on July 29, Sakharov sent his revision on August 18, by October Sakharov and Igor Tamm had completed the first detailed study of a fusion reactor, and had applied for funding to build it in January 1951.
Magnetic confinement
When heated to melting temperatures, electrons from atoms dissociate, giving rise to a fluid of nuclei and electrons known as plasma. Unlike electrically neutral atoms, a plasma is electrically conductive and therefore can be manipulated by electric or magnetic fields.
Sakharov's concern with electrodes led him to consider using magnetic rather than electrostatic confinement. In the case of a magnetic field, the particles will revolve around the lines of force. Since the particles move at high speed, their resulting trajectories resemble a helix. If a magnetic field is arranged so that the lines of force are parallel and close together, particles orbiting adjacent lines can collide and merge.
Such a field can be created in a solenoid, a cylinder with magnets wrapped around the outside. The combined fields of the magnets create a set of parallel magnetic lines that run the length of the cylinder. This arrangement prevents the particles from moving laterally towards the cylinder wall, but does not prevent them from exiting the end. The obvious solution to this problem is to fold the cylinder into a donut, or torus, shape so that the lines form a series of continuous rings. In this arrangement, the particles spin endlessly.
Sakharov discussed the concept with Igor Tamm, and by the end of October 1950 the two had drafted a proposal and sent it to Igor Kurchatov, director of the USSR atomic bomb project, and his deputy, Igor Golovin. However, this initial proposal ignored a fundamental problem; when arranged along a straight solenoid, the outer magnets are evenly spaced, but when bent into a toroidal shape, they are closer together on the inside of the ring than on the outside. This causes unequal forces that cause the particles to move away from their magnetic lines.
During his visits to the Laboratory of Measuring Instruments of the USSR Academy of Sciences (LIPAN), the Soviet nuclear research center, Sakharov suggested two possible solutions to this problem. One was to suspend a current-carrying ring in the center of the torus. The current in the ring would produce a magnetic field that would mix with that of the magnets outside. The resulting field would twist into a helix, so that any particle would repeatedly find itself outside and then inside the torus. The drifts caused by the unequal fields occur in opposite directions on the inside and outside, so over the course of multiple orbits around the long axis of the torus, the opposite drifts would cancel out. As an alternative, he suggested using an external magnet to induce a current in the plasma itself, rather than a separate metal ring, which would have the same effect.
In January 1951, Kurchatov organized a meeting at LIPAN to study Sakharov's concepts. They found widespread interest and support, and a report on the subject was sent in February to Lavrentiy Beria, who was overseeing the atomic efforts in the USSR. For a time, no response was received.
Richter and the birth of fusion research
On March 25, 1951, Argentine President Juan Perón announced that a former German scientist, Ronald Richter, had succeeded in producing fusion on a laboratory scale as part of what is now known as the Huemul Project. Scientists around the world were excited by the announcement, but soon came to the conclusion that it was not true; Simple calculations showed that his experimental setup could not produce enough power to heat the fusion fuel to the necessary temperatures.
Although nuclear researchers dismissed it, the widespread news coverage made politicians suddenly aware and receptive to the fusion investigation. In the UK, Thomson suddenly received considerable funding. In the months that followed, two projects based on the pinch system were launched. In the United States, Lyman Spitzer read Huemul's story, realized it was false, and set about designing a working machine. May was awarded $50,000 to start researching his leading man concept. Jim Tuck had briefly returned to the UK and saw Thomson's pinch machines. When he returned to Los Alamos he too received $50,000 directly from the Los Alamos budget.
Similar events occurred in the USSR. In mid-April, Dmitri Efremov of the Scientific Research Institute of Electrophysical Apparatus burst into Kurchatov's studio with a magazine containing an article on Richter's work, demanding to know why they had been defeated by the Argentines. Kurchatov immediately contacted Beria to propose the creation of an independent fusion research laboratory with Lev Artsimovich as director. Just a few days later, on May 5, the proposal had been signed by Joseph Stalin.
New Ideas
By October, Sakharov and Tamm had completed much more detailed consideration of their original proposal, calling for a device with a larger radius (of the torus as a whole) of 12 meters (13.1 yd) and a smaller radius (the inside the cylinder) of 2 meters (2.2 yd). The proposal suggested that the system could produce 100 grams (3.5 oz) of tritium per day, or reproduce 10 kilograms (22.0 lb) of U233 per day.
As the idea developed, it was seen that a current in the plasma could create a field strong enough to confine the plasma as well, eliminating the need for external magnets. At this point, Soviet researchers had reinvented the pinch system being developed in the UK, although they had arrived at this design from a very different starting point.
Once the idea of using the pinch effect for confinement was floated, a much simpler solution became apparent. Instead of a large toroid, current could simply be induced in a linear tube, which could cause the plasma within it to collapse into a filament. This had a great advantage; the current in the plasma would heat it through normal resistive heating, but this would not heat the plasma to melting temperatures. However, by collapsing the plasma, the adiabatic process would cause the temperature to rise dramatically, more than enough for fusion. With this development, only Golovin and Natan Yavlinsky continued to consider the more static toroidal arrangement.
Instability
On July 4, 1952, Nikolai Filippov's group measured the release of neutrons from a linear pinch machine. Lev Artsimovich required them to check everything before concluding that the merger had occurred, and during these checks, they discovered that the neutrons were not coming from the merger at all. This same linear arrangement had also occurred to the Kingdom researchers. United and United States, and their machines showed the same behavior. But the great secrecy surrounding the type of research meant that neither group was aware that others were also working on it, much less that they had the same problem.
After many studies, it was discovered that some of the neutrons released were produced by instabilities in the plasma. There were two common types of instability, the sausage that was seen primarily in linear machines, and the kink that was more common in toroidal machines. The groups of the three Countries began to study the formation of these instabilities and possible ways to address them. Important contributions to the field were made by Martin David Kruskal and Martin Schwarzschild in the US, and Shafranov in the USSR.
An idea that emerged from these studies became known as the 'stabilized pinch'. This concept added additional magnets to the outside of the chamber, which created a field that would be present in the plasma prior to the pinch discharge. In most concepts, the external field was relatively weak, and since plasma is diamagnetic, it only penetrated the outer areas of the plasma. When the pinch discharge occurred and the plasma contracted rapidly, this field was &# 34;froze" in the resulting filament, creating a strong field in its outer layers. This is known as 'giving the plasma a backbone'.
Sakharov revised his original toroidal concepts and came to a slightly different conclusion about how to stabilize the plasma. The arrangement would be the same as the stabilized pinch concept, but the role of the two camps would be reversed. Instead of weak external fields providing the stabilization and a strong clamping current responsible for the confinement, in the new arrangement, the external magnets would be much more powerful to provide most of the confinement, while the current would be much smaller and responsible. of the stabilizing effect.
Steps towards declassification
In 1955, with linear approximations still subject to instability, the first toroidal device was built in the USSR. The TMP was a classic pinch machine, similar to UK and US models of the same era. The vacuum chamber was ceramic, and the spectra of the discharges showed silica, meaning that the plasma was not perfectly confined by the magnetic field and was striking the walls of the chamber. Two smaller machines, using shells, followed. of copper. The conductive shells were intended to help stabilize the plasma, but were not completely successful in any of the machines that tested it.
With progress seemingly stalled, in 1955, Kurchatov convened an all-Union conference of Soviet researchers with the ultimate goal of opening up fusion research within the USSR. In April 1956, Kurchatov traveled to the United Kingdom. as part of a widely publicized visit by Nikita Khrushchev and Nikolai Bulganin. He offered to give a talk at the Atomic Energy Research Establishment, at the former RAF Harwell, where he surprised the hosts by presenting a detailed historical overview of Soviet fusion efforts. He took the time to point out, in particular, neutrons observed in the first machines and realized that neutrons did not mean fusion.
Unbeknownst to Kurchatov, the British ZETA stabilized pinch machine was being built at the end of the old runway. ZETA was by far the largest and most powerful fusion machine to date. Building on experiments with earlier designs that had been modified to include stabilization, ZETA aimed to produce low levels of fusion reactions. It was apparently a great success, and in January 1958, they announced that fusion had been achieved at ZETA based on neutron release and plasma temperature measurements.
Vitaly Shafranov and Stanislav Braginskii looked at the news and tried to figure out how it worked. One possibility they considered was the use of "frozen" weak fields, but they rejected it, believing that the fields would not last long enough. They then concluded that ZETA was essentially identical to the devices they had been studying, with strong external fields.
First tokamaks
By then, Soviet researchers had decided to build a larger toroidal machine along the lines suggested by Sakharov. In particular, an important point found in the works of Kruskal and Shafranov was taken into account in its design; if the helical trajectory of the particles caused them to circle the circumference of the plasma faster than they circled the long axis of the torus, the instability of the curvature would be strongly suppressed.
Today this basic concept is known as factor of safety. The relationship between the number of times the particle orbits the major axis compared to the minor axis is denoted q, and the Kruskal-Shafranov Limit stated that the kink is would suppress whenever q > 1. This trajectory is controlled by the relative forces of the external magnets compared to the field created by the internal current. So that q > 1, the external magnets must be much stronger, or alternatively, the internal current has to be reduced.
Following this criteria, design began for a new reactor, the T-1, which is now known as the first real tokamak. The T-1 used both stronger external magnets and reduced current compared to machines pinch stabilized like ZETA. The success of the T-1 led to its recognition as the first tokamak in operation.. For his work on "high impulse discharges in a gas, to obtain unusually high temperatures necessary for thermonuclear processes", Yavlinskii was awarded the Lenin Prize and the Stalin Prize in 1958. Yavlinskii was already preparing the design of an even larger model, later to be built as the T-3. With ZETA's seemingly successful announcement, Yavlinskii's concept was viewed very favorably.
Details of ZETA were made public in a series of articles in Nature in late January. To Shafranov's surprise, the system did use the "frozen" field concept. He remained skeptical, but a team at the Ioffe Institute in Saint Petersburg began planning to build a similar machine known as Alpha. Only a few months later, in May, the ZETA team issued a statement stating that they had failed to achieve fusion, and had been misled by erroneous plasma temperature measurements.
The T-1 began operating at the end of 1958. It demonstrated very high energy losses due to radiation. This was attributed to impurities in the plasma due to the vacuum system causing outgassing of the container materials. To explore solutions to this problem, another small device, the T-2, was built. This used a corrugated metal inner lining that was baked at 550 degrees Celsius (1,022.0 °F) to cook any trapped gases.
Atoms for peace and depression
In the framework of the second meeting of Atoms for Peace held in Geneva in September 1958, the Soviet delegation released numerous documents on their investigations into fusion. Among them was a set of initial results on their toroidal machines, which up to that point had shown nothing of significance.
The "star" of the exhibit was a large model of Spitzer's stellarizer, which immediately caught the attention of the Soviets. Unlike their designs, the stellarizer produced the required twisted paths in the plasma without driving a current through it, using a series of magnets that could operate in the steady state instead of the pulses of the induction system. Kurchatov began asking Yavlinskii to trade his T-3 design for a stellarizer, but was convinced that the current provided a useful second function in heating, something the stellarizer lacked.
At the time of exposure, the stellarizer had suffered from a long series of minor issues that were being resolved. Resolution of these revealed that the diffusion rate of the plasma was much faster than predicted by theory. Similar problems were observed in all contemporary designs, for one reason or another. The stellarator, various pinch concepts, and magnetic mirror machines in both the US and USSR demonstrated problems limiting their confinement times.
Since the earliest studies of controlled fusion, there was a problem lurking in the background. During the Manhattan Project, David Bohm had been part of the team working on the isotopic separation of uranium. In the postwar period he continued to work with plasmas in magnetic fields. Using basic theory, plasma would be expected to diffuse through the lines of force at a rate inversely proportional to the square of the field strength, which means that small increases in force would greatly improve confinement. But based on his experiments, Bohm developed an empirical formula, now known as Bohm's diffusion, which suggested that the rate was linear with the magnetic force, not its square.
If Bohm's formula was correct, there was no hope of building a fusion reactor based on magnetic confinement. To confine the plasma to the temperatures necessary for fusion, the magnetic field would have to be orders of magnitude larger than any known magnet. Spitzer attributed the difference between the classical and Bohmian diffusion rates to turbulence in the plasma, and believed that the stellator's stable fields would not suffer from this problem. Various experiments at the time suggested that Bohm's rate did not apply and that the classical formula was correct.
But in the early 1960s, with all the various designs losing plasma at prodigious rates, Spitzer himself came to the conclusion that Bohm scale was an inherent quality of plasmas, and that confinement magnetic would not work. The entire field descended into what became known as "the trough", a period of intense pessimism.
Progress in the 1960s
In contrast to the other designs, the experimental tokamaks seemed to be progressing well, so much so that a small theoretical problem was now a real concern. In the presence of gravity, there is a small pressure gradient in the plasma, previously small enough to ignore, but now becoming something that had to be addressed. This led to the addition of another set of magnets in 1962, which produced a vertical field that offset these effects. This was successful, and by the mid-1960s the machines began to show signs that they were outperforming the Bohm.
At the 1965 Second International Atomic Energy Agency conference on fusion at the newly opened Culham Center for Fusion Energy in the UK, Artsimovich reported that his systems exceeded the Bohm limit by 10 times. Spitzer, reviewing the submissions, suggested that the Bohm limit might still apply; the results were well within the experimental error range of the results seen in stellars, and the temperature measurements, based on magnetic fields, were simply not reliable.
The next major international fusion meeting was held in August 1968 in Novosibirsk. Two more tokamak designs had been completed by then, the TM-2 in 1965 and the T-4 in 1968. The results of the T-3 had continued to improve, and early trials of the new reactors yielded similar results. At the meeting, the Soviet delegation announced that T-3 was producing electron temperatures of 1000 eV (equivalent to 10 million degrees Celsius) and that the confinement time was at least 50 times the Bohm limit.
These results were at least 10 times better than any other machine. If they were correct, they represented a huge leap for the fusion community. Spitzer remained skeptical, noting that the temperature measurements were still based on indirect calculations from the magnetic properties of the plasma. Many concluded that they were due to an effect known as runaway electrons, and that the Soviets were measuring only these extremely energetic electrons and not global temperature. The Soviets responded with various arguments suggesting that the temperature they were measuring was Maxwellian, and the debate escalated.
Culham Five
Following ZETA, teams in the UK began developing new plasma diagnostic tools to provide more accurate measurements. Among these was the use of a laser to directly measure the temperature of bulk electrons using Thomson scattering. This technique was well known and respected in the fusion community; Artsimovich had publicly called it "brilliant". Artsimovich invited Bas Pease, the Culham boss, to use his devices on Soviet reactors. At the height of the Cold War, in what is still considered a major political move on Artsimovich's part, British physicists were allowed to visit the Kurchatov Institute, the heart of the Soviet nuclear bomb effort.
The British team, nicknamed 'The Culham Five,' arrived in late 1968. After a long setup and calibration process, the team measured temperatures over the course of many experiments. Initial results were available in August 1969; the Soviets were right, their results were accurate. The team telephoned the results to Culham, who transmitted them in a confidential telephone call to Washington. The final results were published in Nature in November 1969. The results of this announcement have been described as a "true stampede" construction of tokamaks around the world.
A serious problem remained. As the electrical current in the plasma was much smaller and produced much less compression than a pinch machine, this meant that the temperature of the plasma was limited to the resistive heating rate of the current. First proposed in 1950, Spitzer's resistivity stated that the electrical resistance of a plasma decreased as the temperature increased, meaning that the rate of heating of the plasma would decrease as devices improved and temperatures cooled. they will press more Calculations showed that the resulting maximum temperatures while staying within q > 1 would be limited to millions of degrees. Artsimovich was quick to point this out in Novosibirsk, stating that future progress would require the development of new heating methods.
Trouble in the United States
One of the people who attended the Novosibirsk meeting in 1968 was Amasa Stone Bishop, one of the leaders of the American fusion program. One of the few devices that showed clear evidence of exceeding the Bohm limit at that time was the multipole concept. Both Lawrence Livermore and the Princeton Plasma Physics Laboratory (PPPL), home of Spitzer's stellarator, were building variations of the multipole design. Although they were moderately successful on their own, the T-3 vastly outperformed either machine. Bishop was concerned that the multipoles were redundant and thought the United States should consider creating a tokamak of its own.
When he raised the issue at a December 1968 meeting, the laboratory directors refused to consider it. Melvin B. Gottlieb of Princeton grew exasperated and asked, "Do you think this committee can outthink the scientists?" With major labs demanding control of their own research, one of them stayed out. [Oak Ridge National Laboratory had originally entered the fusion field with studies on reactor power systems, but branched out into a mirror program of its own. By the mid-1960s, their DCX designs were running out of ideas, offering nothing that the similar program of the more prestigious and politically powerful Livermore did not offer. This made them very receptive to new concepts.
After considerable internal debate, Herman Postma formed a small group in early 1969 to consider the tokamak. They came up with a new design, later christened the Ormak, which had several novel features. The main one was that the external field was created in a single large copper block, powered by a large transformer below the torus. This was opposed to traditional designs that used coils of magnets on the outside. They considered that the single block would produce a much more uniform field. It would also have the advantage of allowing the torus to have a smaller major radius, without the need to run the wires through the donut hole, leading to a lower aspect ratio, than the Soviets already had. they had suggested that it would produce better results.
Tokamak's career in the United States
In early 1969, Artsimovich visited MIT, where he was harassed by merger stakeholders. He finally agreed to give several lectures in April and then allowed lengthy question-and-answer sessions. As these developed, MIT itself became interested in tokamak, having previously stayed out of the fusion field for various reasons. Bruno Coppi was at MIT at the time, and following the same concepts as the Postma team, he came up with his own low aspect ratio concept, Alcator. Instead of Ormak's toroidal transformer, Alcator used traditional ring-shaped magnets, but required them to be much smaller than existing designs. The MIT Francis Bitter Magnet Laboratory was the world leader in the design of magnets and they were confident they could build them.
During 1969, two additional groups entered the field. At General Atomics, Tihiro Ohkawa had been developing multipole reactors, and presented a concept based on these ideas. This was a tokamak that would have a non-circular plasma cross section; the same math that suggested a lower aspect ratio would improve performance also suggested that a C- or D-shaped plasma would do the same. He called the new design Doublet Meanwhile, a group at the University of Texas at Austin was proposing a relatively simple tokamak to explore plasma heating through deliberately induced turbulence, the Texas Turbulent Tokamak.
When members of the Atomic Energy Commission's Fusion Steering Committee met again in June 1969, they had "tokamak proposals coming out of our ears". working on a toroidal design and not proposing a tokamak was Princeton, who refused to consider it despite the fact that their model C stellarizer was almost perfect for such a conversion. They went on to offer a long list of reasons why the Model C should not be converted. Questioning them sparked a furious debate about the reliability of the Soviet results.
Watching the debate unfold, Gottlieb changed his mind. There was no point in going ahead with the tokamak if the Soviet measurements of electron temperatures weren't accurate, so he formulated a plan to prove or disprove his results. While he was swimming in the pool during his lunch break, he told Harold Furth his plan, to which Furth replied "Well, maybe you're right." After lunch, the various teams presented their designs, at which point Gottlieb pitched his idea for a "stellarator-tokamak" in the US. based on Model C.
The Standing Committee noted that this system could be completed in six months, while Ormak would take a year. The confidential results of the Culham Five were released soon after. When they met again in October, the Standing Committee released funding for all of these proposals. The new Model C configuration, soon named the Symmetrical Tokamak, was intended simply to verify the Soviet results, while the others would explore ways to go well beyond the T-3.
Warming Up: USA Takes the Lead
Experiments with the Symmetrical Tokamak began in May 1970, and early the following year confirmed the Soviet results and surpassed them. The stellarator was abandoned, and the PPPL devoted its considerable experience to the problem of plasma heating. Two concepts looked promising. PPPL proposed using magnetic compression, a technique similar to pinching to compress a hot plasma and increase its temperature, but providing that compression through magnets rather than current. Oak Ridge suggested neutral beam injection, small accelerators of particles that would shoot fuel atoms through the surrounding magnetic field, where they would collide with the plasma and heat it up.
PPPL's Adiabatic Toroidal Compressor (ATC) began operation in May 1972, followed soon after by an Ormak equipped with a neutral beam. Both proved to have significant problems, but PPPL preempted Oak Ridge by installing beam injectors at ATC and provided clear evidence of a successful warm-up in 1973. This success "carried away" to Oak Ridge, who fell out of favor with the Washington Steering Committee.
A much larger design based on beam heating, the Princeton Large Torus, or PLT, was being built by then. The PLT was specifically designed to "give a clear indication of whether the tokamak concept plus auxiliary heating can form a basis for a future fusion reactor". The PLT was a huge success, continually raising its temperature internal until reaching 60 million Celsius (8,000 eV, eight times the T-3 record) in 1978. This is a key point in the development of the tokamak; fusion reactions become self-sustaining at temperatures between 50 and 100 million Celsius, PLT demonstrated that this was technically achievable.
These experiments, especially the PLT, put the United States at the very forefront of tokamak research. This is largely due to budget; a tokamak cost about $500,000, and the US annual budget for fusion was about $25 million at the time. They were able to afford to explore all promising methods of heating, eventually discovering that neutral beams were among the most promising. more effective.
During this period, Robert Hirsch took over the Directorate of Fusion Development at the United States Atomic Energy Commission. Hirsch felt that the program could not be sustained at current funding levels without demonstrating tangible results. He began to reformulate the entire program. What was once a laboratory-led scientific exploration effort was now a Washington-led effort to build a power-producing reactor. The 1973 oil crisis gave a boost to this initiative, leading to a large increase in power. of research in alternative energy systems.
1980s: great hope, great disappointment
By the late 1970s, tokamaks had achieved all the necessary conditions for a practical fusion reactor; in 1978 the PLT had demonstrated ignition temperatures, the following year the Soviet T-7 successfully used superconducting magnets for the first time, The doublet proved to be a success and led to almost all future designs adopting this &# 34;molded plasma". It seemed that all that was needed to build a power-producing reactor was to put all of these design concepts into a single machine, one that was capable of running on radioactive tritium in its fuel mix.
The race was on. During the 1970s, four large second-generation proposals were funded around the world. The Soviets continued their line of development with the T-15, while a pan-European effort developed the Joint European Torus (JET) and Japan began the JT-60 effort (originally known as the "Breakeven Plasma Test Facility"). In the United States, Hirsch began formulating plans for a similar design, skipping proposals for another design to go directly to a tritium-burning one. This emerged as the Tokamak Fusion Test Reactor (TFTR), run directly from Washington and not tied to any specific lab. Hirsch initially favored Oak Ridge as the site, but moved it to PPPL after others told him. convinced that they would be the ones who would work the most on it because they had the most to lose.
Development
In 1956, experimental investigations of these systems began at the Institute of Atomic Energy «I. V. Kurchatov» of the USSR Academy of Sciences. The first Tokamak consisted of a toroidal-shaped vacuum chamber that contained hydrogen and an electrical device that ionized the gas through strong discharges until it reached a plasmatic state. A strong helical magnetic field produced with powerful electromagnets achieved the confinement of the plasma at very high temperatures.
On May 21, 2000, it is announced that American physicists have overcome one of the problems of nuclear fusion, the phenomenon called edge localized modes, or ELMs.) that would cause an erosion of the interior of the reactor, forcing its frequent replacement. In an article published Sunday May 21, 2000 in the British journal Nature Physics, a team led by Todd Evans of General Atomics, California, announces the discovery that a small resonant magnetic field from special coils located inside the reactor vessel, it creates “chaotic” magnetic interference at the edge of the plasma that stops the formation of flux.
On May 24, 2006, the seven partners of the ITER project -- the European Union, Japan, the United States, South Korea, India, Russia and China -- signed the agreement in Brussels international for the launch of the international fusion reactor, to be built at Cadarache, in South-East France using the Tokamak design. The construction costs of the reactor were estimated at 4,570 million euros and the duration of the construction at 10 years. The EU and France agreed to contribute 50% of the cost, while the other six parties agreed to each contribute around 10%.