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.

Toroidal Alfven Eigenmodes are shown to be capable of inducing tipple trapping of high energy particles in tokamaks, causing intense localized particle loss. The effect has been observed in TFTR.PACS numbers: 52.35. Py, 52.35.Bj Collective alpha-driven instabilities such as the toroidicity-induced Alfven eigenmodes (TAE) are of concern for future tokamak devices since they can induce anomalous alpha losses. Previously discussed mechanisms of particle loss have consisted of induced transition from passing to direct-loss trapped orbits and radial diffusion produced by stochasticity in particle orbits caused by overlapping resonances 1 . In this work we point out a very effective loss process in devices possessing magnetic ripple wells. It differs from other forms of TAE induced loss in that the mechanism possesses no threshold mode amplitude. The effect has been observed in the Tokamak Fusion Test Reactor (TFTR), where particle fluxes intense enough to damage the vacuum wall were observed.The process is very simply understood using a simple model for the magnetic field.Consider a trapped particle whose banana tip is in the vicinity of a ripple well. In guiding center approximation the particle energy is given by £=H+" fl n/invii-K (i) MASTERUtSTa'AUTiCH OF TWS D0CUHtU = q$+uidt with Ud the toroidal precession rate. Energy conservation then reduces the problem to a particle moving in a one dimensional potential given by ^B{6). A ripple well exists at points where dB/dO = 0 which requiresIn TFTR the ripple magnitude is well represented by 6 -S 0 e^R-Rr)2+bzi/wwith Rr = 223cm, w = 18.3cm, Jo = 1-4 x 10 -5 , Z = rsin(6), and b = 1.1. Consider a trapped particle whose banana tip is in the vicinity of a ripple well below the midplane (plasma current clockwise from above), i.e. the particle passes over a local well before bouncing. Ripple trapping occurs due to the fact that a particle is radially further outward after bouncing than before, due to the banana width. Field ripple increases strongly in this direction and thus the particle encounters larger ripple after bouncing, and may be trapped in the well.If this occurs it drifts vertically to the wall and is lost. Since the well location varies due to the toroidal precession, eventually all trapped particles on orbits with bounce points intercepting the ripple well domain will be lost. The presence of a time dependent magnetic perturbation such as the TAE mode produces additional modulation of the particle position which can greatly increase the phase space of particles capable of making the transition to a trapped state.To dem...

This research describes advancements in the spectral analysis and error propagation techniques associated with x-ray imaging crystal spectroscopy (XICS) that have enabled this diagnostic to be used to accurately constrain particle, momentum, and heat transport studies in a tokamak for the first time. Doppler tomography techniques have been extended to include propagation of statistical uncertainty due to photon noise, the effect of non-uniform instrumental broadening as well as flux surface variations in impurity density. These methods have been deployed as a suite of modeling and analysis tools, written in interactive data language (IDL) and designed for general use on tokamaks. Its application to the Alcator C-Mod XICS is discussed, along with novel spectral and spatial calibration techniques. Example ion temperature and radial electric field profiles from recent I-mode plasmas are shown, and the impact of poloidally asymmetric impurity density and natural line broadening is discussed in the context of the planned ITER x-ray crystal spectrometer.

A new method of actively modifying the plasma-wall interaction was tested on the Tokamak Fusion Test Reactor. A laser was used to introduce a directed lithium aerosol into the discharge scrape-off layer. The lithium introduced in this fashion ablated a n d migrated preferentially to the limiter contact points. This allowed the plasma-wall interaction to be influenced in situ and in real t i m e by external means. Significant improvement in energy confinement and fusion neutron production rate as well as a reduction in t h e plasma Z eff have been documented in a neutral-beam-heated plasma. The introduction of a metallic aerosol into the plasma e d g e increased the internal inductance of the plasma column and also resulted in prompt heating of core electrons in Ohmic plasmas. Preliminary evidence also suggests that the introduction of a n aerosol leads to both edge poloidal velocity shear and edge electric field shear. . I n t r o d u c t i o nIt has been well documented that the fusion performance of discharges in the Tokamak Fusion Test Reactor (TFTR) was strongly dependent on the physical and chemical condition of the graphite surface forming its limiter [1,2]. In particular, the highperformance supershot mode of operation was attainable at high currents (>2.0 MA) only when the graphite inner wall had previously been "scoured" by repeated discharges heated by high-power neutral beam injection (NBI) in order to render the limiter surface free of loosely-bound carbon and loosely-adsorbed hydrogenic material. At the end of a series of such pre-conditioning discharges, plasma fueling from the limiter typically reached a minimum.Moreover, only when this low-recycling condition had been attained did high levels of fusion performance become accessible.It has also been well documented that dramatic improvements in supershot fusion performance were attainable by the deposition of elemental lithium (Li) onto the limiter surface once it had been brought into the low-recycling condition. This deposition was carried out in earlier experiments by the injection and ablation of a few small (3 mg each) Li pellets [3,4,5,6]. In order to improve plasma performance during NBI, Li pellets were typically injected into the Ohmic phase of discharges and the ablated Li was allowed to 3 condense out of the plasma column and onto the limiter surface before the application of auxiliary heating. While the use of Li pellets did improve plasma performance, the technique was, nonetheless, highly perturbing. In order to reduce the perturbation to the plasma, brief but successful experiments with a Li effusion oven were also carried out on TFTR and are described elsewhere [7,8].While the use of an oven did result in an increase in the amount of Li deposited onto the inner wall as compared to pellet injection, deposition could only take place between discharges and not during the discharge of interest.In this work, an alternate wall-conditioning technique is described in which Li was injected into the scrape-off layer (SOL), during pl...

Results from the investigation of neoclassical core transport and the role of the radial electric field profile (E r) in the first operational phase of the Wendelstein 7-X (W7-X) stellarator are presented. In stellarator plasmas, the details of the E r profile are expected to have a strong effect on both the particle and heat fluxes. Investigation of the radial electric field is important in understanding neoclassical transport and in validation of neoclassical calculations. The radial electric field is closely related to the perpendicular plasma flow (u ⊥) through the force balance equation. This allows the radial electric field to be inferred from measurements of the perpendicular flow velocity, which can be measured using the x-ray imaging crystal spectrometer (XICS) and correlation reflectometry diagnostics. Large changes in the perpendicular rotation, on the order of ∆u ⊥ ∼ 5 km/s (∆E r ∼ 12 kV /m), have been observed within a set of experiments where the heating power was stepped down from 2 M W to 0.6 M W. These experiments are examined in detail to explore the relationship between heating power, temperature and density profiles and the radial electric field. Finally the inferred E r profiles are compared to initial neoclassical calculations using measured plasma profiles. The results from several neoclassical codes, sfincs, fortec-3d and dkes, are compared both with each other and the measurements. These comparisons show good agreement, giving confidence in the applicability of the neoclassical calculations to the W7-X configuration.

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The bremsstrahlung emission from the PLT tokamak during lowerhybrid current drive has been measured as a function of angle between the magnetic fiela and the emission direction. The emission is peaked atrongly in the forward direction, indicating a strong anisotropy of the electron-velocity distribution. The data demonstrate the existence of a nearly flat tail of the velocity distribution, which extends out to approximately 500 JteV ^nd whiffh is interpreted as the plateau created by Landau damping of the lowftr-hybrid

The Tokamak Fusion Test Reactor ͑TFTR͒ ͑R. J. Hawryluk, to be published in Rev. Mod. Phys.͒ experiments on high-temperature plasmas, that culminated in the study of deuterium-tritium D-T plasmas containing significant populations of energetic alpha particles, spanned over two decades from conception to completion. During the design of TFTR, the key physics issues were magnetohydrodynamic ͑MHD͒ equilibrium and stability, plasma energy transport, impurity effects, and plasma reactivity. Energetic particle physics was given less attention during this phase because, in part, of the necessity to address the issues that would create the conditions for the study of energetic particles and also the lack of diagnostics to study the energetic particles in detail. The worldwide tokamak program including the contributions from TFTR made substantial progress during the past two decades in addressing the fundamental issues affecting the performance of high-temperature plasmas and the behavior of energetic particles. The progress has been the result of the construction of new facilities, which enabled the production of high-temperature well-confined plasmas, development of sophisticated diagnostic techniques to study both the background plasma and the resulting energetic fusion products, and computational techniques to both interpret the experimental results and to predict the outcome of experiments.