• Record plasma pressures and temperatures. The higher the plasma pressure, the more likely fusion is to occur. The TFTR set the record for pressure at near reactor-relevant temperatures. In fact, the plasma pressure at the center of the TFTR reached 6 atmospheres, comparable to that needed for a commercial fusion reactor. In 1985, the TFTR was the first tokamak to achieve the reactor temperature of 100 million degrees Celsius. In 1995, TFTR set the record for highest temperature: 510 million degrees -- more than thirty times hotter than the center of the sun.
  
  
• The first experimental confirmation of the "bootstrap current." The plasma pressure is highest in the center and falls off rapidly toward the vacuum vessel walls. Theorists had predicted that this variation of pressure would help sustain the electrical current in the plasma without the need for an external power source (hence "bootstrap"). In 1986 TFTR confirmed the existence of the bootstrap current in a tokamak plasma. Furthermore, researchers were able to drive the entire plasma current in the TFTR by means of the bootstrap effect and neutral-beam injection.
  
  The bootstrap effect could be of great importance in future reactor design. Tokamaks are pulsed for short periods, but because the bootstrap current replaces an external drive, it could lead to steady-state operation in commercial reactors.
  
  
• First observations of "ballooning modes." Variations in plasma pressure brought on by heating the plasma can cause the plasma to become unstable. Theorists had predicted a particular type of instability called "ballooning modes." TFTR experiments confirmed the prediction. Ballooning modes take place in regions where the magnetic field (whose job is to confine the plasma) is weakest. Then, if the variations in plasma pressure are large enough, the plasma breaks out, much like an aneurism or a balloon. The region expands until the plasma ruptures and collapses. In any reactor design, the ballooning instability limits the fusion power that can be produced.
  
  
• First unambiguous demonstration of how the size of machines affect particle and energy transport in the plasma. In designing larger machines, it is important to know how the plasma will behave, more specifically how the energy contained in the plasma is transported through the magnetic fields. TFTR experiments demonstrated how the confinement time of the energy and particles in the plasma is affected by the size of the machine. The effect relates the confinement time of the plasma to the ratio of the size of the particle orbits to the size of the tokamak. This discovery has a direct impact on the size of future reactors.
  
  
• The discovery of an enhanced confinement regime. "Supershots" refers to an operating regime in which the number of fusion reactions among deuterium nuclei was up to twenty-five times higher than previously observed. The supershot regime was an experimental discovery. TFTR scientists learned the importance of decreasing the influx of gas from the vacuum vessel walls. This affects the density profile of the plasma across the torus. That is, supershots were achieved not when the plasma density was uniform, but when it was kept lowest near the torus walls and peaked in the center. The supershot regime, initially confined to a small range of plasma conditions, was expanded to a large range of plasma parameters that are close to those required for a commercial fusion reactor.
  
  
• The discovery of an enhanced reversed-shear mode. In 1995, a new, fundamental mode of plasma confinement was discovered on TFTR which could reduce substantially the size and cost of fusion power plants. The plasma current which produces the twist of the magnetic field lines (magnetic shear) in a tokamak is usually strongest at the center of the plasma. As a result, the field lines wrap more tightly at the center and gradually loosen toward the walls of the vacuum chamber. In the enhanced reversed-shear mode, the plasma current profile, and hence the magnetic shear, was modified in such a way that the magnetic field configuration had a region of reversed shear in the plasma core, i.e., the shear decreased and then increased toward the torus walls. Using this enhanced reversed-shear mode, TFTR scientists increased the central density of the plasma up to three-fold and reduced particle leakage by a factor of 50. If this phenomenon can be demonstrated over a broader range of temperatures and field strengths, it could eventually lead to smaller, more economical fusion power plants.
  
  
• World-record fusion power in deuterium-tritium (D-T) experiments. In December 1993, for the first time in history, a reactor fuel mix of 50% deuterium and 50% tritium was used in a tokamak. Initial TFTR experiments yielded 6.0 million watts. By November, 1994, TFTR achieved 10.7 million watts of power, about 100 million times the power produced by tokamaks twenty years ago.
  
  Of greater importance is the fact that D-T plasmas were more well-behaved than deuterium plasmas. For D-T plasmas, higher temperatures were possible, and the energy confinement time was about 20 percent higher.
  
  TFTR allowed, for the first time, studies of whether the alpha particles produced in the D-T fusion reactions remain confined long enough to impart their energy to the plasma to help sustain its temperature. If a significant portion of the alpha particles are not confined long enough, the density and temperature requirements for ignition would increase. However alpha particles must not accumulate in the plasma, where they would eventually quench the D-T reactions.
  
  Alpha particles were detected successfully in TFTR and were found to be well confined. There were hints of alpha-particle heating. Experiments indicated that the alpha particles ultimately leave the plasma after heating it.
  
  

In addition, TFTR achieved all of its original hardware design objectives. In doing so, it made substantial contributions in many areas of fusion technology development. A few of these engineering accomplishments are:

• The first tokamak demonstration of tritium handling technology. The TFTR was the first tokamak to utilize tritium handling and processing technology to provide 1-2 grams of molecular tritium each D-T operating day. Following plasma operations, this tritium was routinely reclaimed, converted to water (HTO) and safely stored on molecular sieve beds for ultimate reprocessing or disposal. In 1996, TFTR began recycling tritium using a unique, low inventory cyrogenic distillation isotope separation system capable purifying the tokamak plasma exhaust to greater than 97% molecular tritium.
  
  
• Reliable performance of plasma heating technology. The TFTR neutral-beam heating systems established a benchmark of performance providing reliable plasma heating power at levels routinely exceeding thirty million watts. The Ion Cyclotron Radio Frequency (ICRF) heating systems demonstrated the first radio-frequency heating of D-T plasmas by coupling up to six million watts of radio-frequency energy to the plasma. The tokamak power supply and magnet systems routinely operated at full design parameters producing magnetic fields 100,000 times that of the earth's magnetic field and plasma currents up to three million amperes.
  
  
• Development of ultra-high vacuum technology for fusion plasmas. The TFTR vacuum volume exceeded 250 m³ and contained various energy absorbing materials (e.g., carbon), windows (typically quartz glass), and large gate valves (up to one meter in diameter). Utilizing turbomolecular pumps, liquid helium cryogenic pumps, bake-out, plasma discharge cleaning and wall-coating techniques, this volume was maintained at a pressure less than 10^-8 torr, and the influx of excess hydrogen isotopes and impurities from the vacuum vessel wall was minimized allowing high-performance plasmas.