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Tokamak Fusion Test Reactor
The Tokamak Fusion Test Reactor (TFTR) was an experimental tokamak built at Princeton Plasma Physics Laboratory (PPPL) circa 1980 and entering service in 1982. TFTR was designed with the explicit goal of reaching scientific breakeven, the point where the heat being released from the fusion reactions in the plasma 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.
TFTR shut down in 1997 after fifteen years of operation. PPPL used the knowledge from TFTR to begin studying another approach, the spherical tokamak, in their National Spherical Torus Experiment. The Japanese JT-60 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.
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.
By the early 1960s, the fusion power 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, where the Soviet delegation surprised everyone by claiming their tokamak designs had reached performance levels at least an order of magnitude 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, 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 (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.
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 (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, PPPL developed the idea of neutral beam injection. This used small particle accelerators to inject fuel atoms directly into the plasma, both heating it and providing fresh fuel.
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Tokamak Fusion Test Reactor
The Tokamak Fusion Test Reactor (TFTR) was an experimental tokamak built at Princeton Plasma Physics Laboratory (PPPL) circa 1980 and entering service in 1982. TFTR was designed with the explicit goal of reaching scientific breakeven, the point where the heat being released from the fusion reactions in the plasma 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.
TFTR shut down in 1997 after fifteen years of operation. PPPL used the knowledge from TFTR to begin studying another approach, the spherical tokamak, in their National Spherical Torus Experiment. The Japanese JT-60 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.
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.
By the early 1960s, the fusion power 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, where the Soviet delegation surprised everyone by claiming their tokamak designs had reached performance levels at least an order of magnitude 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, 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 (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.
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 (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, PPPL developed the idea of neutral beam injection. This used small particle accelerators to inject fuel atoms directly into the plasma, both heating it and providing fresh fuel.