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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.

Order of magnitude improvements in the level and curation of current driven by lower hybrid waves have been chieved in the PLT tokamak. Steady currents up to 175 kA have been maintained for three seconds and 400 kA for 0.3 sec by the rf power alone. The principal current carrier appears to be a high energy (-100 keV) electron component, concentrated in the central 20-40 cm diameter core of the 80 cm PLT discharge. DISimtOTI OF THIS DOCUMENT is mump .\JLA

A study is made of the spectral distribution of the soft X-ray emission produced by the thermal part of the electron velocity distribution in the ST Tokamak. The slopes of the spectra are in good agreement with the prediction from laser measurement of electron temperature if radial profile effects are taken into account. The absolute intensity is a factor 5 to 100 larger than is expected for hydrogen bremsstrahlung. This enhancement can be quantitatively accounted for by recombination radiation from oxygen and heavy-metal impurities. The enhancement factor ζ was measured at different radii, in order to study the impurity distribution in the tokamak. These, as well as other experiments, in which high-Z gases (Xe, Kr, A) were pulsed into the discharge, indicated that, within the measuring accuracy, Zeff does not vary substantially with radius.

Wall conditioning in the Tokamak Fusion Test Reactor ͑TFTR͒ ͓K. M. McGuire et al., Phys. Plasmas 2, 2176 ͑1995͔͒ by injection of lithium pellets into the plasma has resulted in large improvements in deuterium-tritium fusion power production ͑up to 10.7 MW͒, the Lawson triple product ͑up to 10 21 m Ϫ3 s keV͒, and energy confinement time ͑up to 330 ms͒. The maximum plasma current for access to high-performance supershots has been increased from 1.9 to 2.7 MA, leading to stable operation at plasma stored energy values greater than 5 MJ. The amount of lithium on the limiter and the effectiveness of its action are maximized through ͑1͒ distributing the Li over the limiter surface by injection of four Li pellets into Ohmic plasmas of increasing major and minor radius, and ͑2͒ injection of four Li pellets into the Ohmic phase of supershot discharges before neutral-beam heating is begun.

Lower-hybrid current drive requires the generation of a high-energy electron tail anisotropic in velocity. Measurements of bremsstrahlung emission produced by this tail are compared with the calculated emission from reasonable model distributions. The physical basis and the sensitivity of this modelling process are described, and the plasma properties of current-driven discharges which can be derived from the model are discussed.

Alpha-particle-driven toroidal Alfvén eigenmodes (TAEs) have been observed for the first time in deuterium-tritium (D-T) plasmas on the tokamak fusion test reactor (TFTR). These modes are observed 100-200 ms following the end of neutral beam injection in plasmas with reduced central magnetic shear and elevated central safety factor ͓q͑0͒ . 1͔. Mode activity is localized to the central region of the discharge ͑r͞a , 0.5͒ with magnetic fluctuation levelB Ќ ͞B k ϳ 10 25 and toroidal mode numbers in the range n 2 4, consistent with theoretical calculations of a-TAE stability in TFTR.[S0031-9007 (97)02857-3] PACS numbers: 52.55.Fa, 52.35.Bj, 52.35.Py, 52.55.PiDeuterium-tritium (D-T) plasma operation on the tokamak fusion test reactor (TFTR) provides the first opportunity to investigate the interaction of fusion alpha particles with plasma waves under reactor relevant conditions. Such investigations are crucial for assessing the impact of plasma instabilities on the confinement of energetic alpha particles, which are required to sustain ignition in a D-T reactor. One candidate instability with the potential for affecting alpha particle confinement in tokamaks is the toroidal Alfvén eigenmode (TAE) [1]. This Letter describes the first observation of purely alpha-particledriven TAEs in TFTR with central b a as low as 0.02% (b a ϵ alpha particle pressure͞magnetic pressure), well below that expected in the International Thermonuclear Experimental Reactor (ITER) [central b a ϳ ͑0.5 1͒%].TAEs are discrete frequency modes occurring inside toroidicity induced gaps in the shear Alfvén spectrum which can be destabilized by the pressure gradient of energetic ions. These modes can potentially cause internal redistribution and enhanced loss of energetic alpha particles in a D-T reactor due to their extended radial structure, relatively low instability threshold, and resonant interaction with 3.5 MeV alpha particles near the Alfvén velocity [2,3]. The characteristics of TAEs and associated fast ion losses have been studied in experiments utilizing circulating neutral beam ions ͑E b # 100 keV͒ [4-6], deeply trapped minority ions in the MeV range of energy [7-9], nonlinear beat wave excitation using fast magnetosonic waves [10], and external excitation using saddle coils [11]. Until recently alpha-driven TAEs had not been observed in TFTR, even in the highest fusion power D-T "supershot" plasmas ͑P fus ഠ 10.7 MW͒ with b a ഠ 0.3% in the core of the discharge [12]. These results were consistent with theoretical calculations of alpha-driven TAE stability in TFTR, after taking into account beam ion Landau damping and radiative damping due to coupling to the kinetic Alfvén wave (KAW) [13]. However, a better comparison with theory requires the actual observation of purely alpha particle driven TAEs in D-T plasmas, as described in this Letter. The present experiment was motivated by recent theoretical calculations for low-n modes ͑n , 6͒ in TFTR indicating a significant reduction in the central b a required for destabilizing TAEs under condi...

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