TFTR experience with D-T operation

Temperatures, densities and confinement of deuterium plasmas confined in tokamaks have been achieved within the last decade that are approaching those required for a D-T reactor. As a result, the unique phenomena present in a D-T reactor plasma (D-T plasma confinement, alpha confinement, alpha heating and possible alpha-driven instabilities) can now be studied in the laboratory. Recent experiments on the Tokamak Fusion Test Reactor (TFTR) have been the first magnetic fusion experiments to study plasmas with reactor fuel concentrations of tritium. The injection of ≈20 MW of tritium and 14 MW of deuterium neutral beams into the TFTR produced a plasma with a T/D density ratio of ≈1 and yielded a maximum fusion power of ≈9.2 MW. The fusion power density in the core of the plasma was ≈1.8 MW m−3, approximating that expected in a D-T fusion reactor. A TFTR plasma with a T/D density ratio of ≈1 was found to have ≈20% higher energy confinement time than a comparable D plasma, indicating a confinement scaling with average ion mass, A, of τE ≈ A0.6. The core ion temperature increased from 30 keV to 37 keV due to a 35% improvement in ion thermal conductivity. Using the electron thermal conductivity from a comparable deuterium plasma, about 50% of the electron temperature increase from 9 keV to 10.6 keV can be attributed to electron heating by the alpha-particles. The ∼5% loss of alpha-particles, as observed on detectors near the bottom edge of the plasma, was consistent with classical first orbit loss without anomalous effects. Initial measurements have been made of the confined energetic alphas and the resultant alpha ash density. At fusion power levels of 7.5 MW, fluctuations at the toroidal Alfvén eigenmode frequency were observed by the fluctuation diagnostics. However, no additional alpha loss due to the fluctuations was observed. These D-T experiments will continue over a broader range of parameters and higher power levels.