After many years of fusion research, the conditions needed for a D–T fusion reactor have been approached on the Tokamak Fusion Test Reactor (TFTR) [Fusion Technol. 21, 1324 (1992)]. For the first time the unique phenomena present in a D–T plasma are now being studied in a laboratory plasma. The first magnetic fusion experiments to study plasmas using nearly equal concentrations of deuterium and tritium have been carried out on TFTR. At present the maximum fusion power of 10.7 MW, using 39.5 MW of neutral-beam heating, in a supershot discharge and 6.7 MW in a high-βp discharge following a current rampdown. The fusion power density in a core of the plasma is ≊2.8 MW m−3, exceeding that expected in the International Thermonuclear Experimental Reactor (ITER) [Plasma Physics and Controlled Nuclear Fusion Research (International Atomic Energy Agency, Vienna, 1991), Vol. 3, p. 239] at 1500 MW total fusion power. The energy confinement time, τE, is observed to increase in D–T, relative to D plasmas, by 20% and the ni(0) Ti(0) τE product by 55%. The improvement in thermal confinement is caused primarily by a decrease in ion heat conductivity in both supershot and limiter-H-mode discharges. Extensive lithium pellet injection increased the confinement time to 0.27 s and enabled higher current operation in both supershot and high-βp discharges. Ion cyclotron range of frequencies (ICRF) heating of a D–T plasma, using the second harmonic of tritium, has been demonstrated. First measurements of the confined alpha particles have been performed and found to be in good agreement with TRANSP [Nucl. Fusion 34, 1247 (1994)] simulations. Initial measurements of the alpha ash profile have been compared with simulations using particle transport coefficients from He gas puffing experiments. The loss of alpha particles to a detector at the bottom of the vessel is well described by the first-orbit loss mechanism. No loss due to alpha-particle-driven instabilities has yet been observed. D–T experiments on TFTR will continue to explore the assumptions of the ITER design and to examine some of the physics issues associated with an advanced tokamak reactor.

Optical fibers are ubiquitous on today’s plasma devices, and will play a major role in future machines. However, radiation causes luminescence and transmission loss in fibers at troubling levels even on today’s machines when they operate in DT. We have evaluated these effects and studied the use of elevated operating temperatures to reduce them. Using high-purity UV grade silica-silica fibers at 400 °C reduces transmission loss by a factor of at least 100, but has little or no effect on radioluminescence. The radioluminescent spectrum appears to be Cerenkov radiation. The transmission loss spectrum depends on the fiber material and details of the manufacture. The mode structure of transmission loss is mainly simple path length attenuation, with a suggestion of internal reflection degradation.

A model for stimulated Raman scattering (SRS) in a homogeneous plasma has been designed to account for the presence of stimulated Brillouin scattering (SBS) and the nonlinear coupling between Langmuir and ion waves described by Zakharov equations. The nonlinear evolution of electron plasma waves also includes an effective damping resulting from electron diffusion in localized Langmuir fields produced during simultaneous SRS and SBS evolutions. Numerical results based on this model show two distinct SRS behaviors. Close to ncr/4 the Langmuir collapse dominates nonlinear evolution of the instability. At lower densities low level SRS is observed for a relatively long time after which SRS is terminated as a result of ion fluctuations produced by SBS. In addition, the anomalous absorption of backscattered SRS radiation by ion fluctuations produced by the collapse is proposed as a mechanism that may explain some recent experimental observations showing a gap in the SRS spectrum.