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The multi-machine International Tokamak Physics Activity (ITPA) Global H-mode Confinement Database has been upgraded with new data from JET with the ITER-like wall and ASDEX Upgrade with the full tungsten wall. This paper describes the new database and presents results of regression analysis to estimate the global energy confinement scaling in H-mode plasmas using a standard power law. Various subsets of the database are considered, focusing on type of wall and divertor materials, confinement regime (all H-modes, ELMy H or ELM-free) and ITER-like constraints. Apart from ordinary least squares (OLS), two other, robust regression techniques are applied, which take into account uncertainty on all variables. Regression on data from individual devices shows that, generally, the confinement dependence on density and the power degradation are weakest in the fully metallic devices. Using the multi-machine scalings, predictions are made of the confinement time in a standard ELMy H-mode scenario in ITER. The uncertainty on the scaling parameters is discussed with a view to practically useful error bars on the parameters and predictions. One of the derived scalings for ELMy H-modes on an ITER-like subset is studied in particular and compared to the IPB98(y, 2) confinement scaling in engineering and dimensionless form. Transformation of this new scaling from engineering variables to dimensionless quantities is shown to result in large error bars on the dimensionless scaling. Regression analysis in the space of dimensionless variables is therefore proposed as an alternative, yielding acceptable estimates for the dimensionless scaling. The new scaling, which is dimensionally correct within the uncertainties, suggests that some dependencies of confinement in the multi-machine database can be reconciled with parameter scans in individual devices. This includes vanishingly small dependence of confinement on line-averaged density and normalized plasma pressure (β), as well as a noticeable, positive dependence on effective atomic mass and plasma triangularity. Extrapolation of this scaling to ITER yields a somewhat lower confinement time compared to the IPB98(y, 2) prediction, possibly related to the considerably weaker dependence on major radius in the new scaling (slightly above linear). Further studies are needed to compare more flexible regression models with the power law used here. In addition, data from more devices concerning possible 'hidden variables' could help to determine their influence on confinement, while adding data in sparsely populated areas of the parameter space may contribute to further disentangling some of the global confinement dependencies in tokamak plasmas. [ABSTRACT FROM AUTHOR]

Two important topics for tokamak edge-localized modes (ELM) control, based on non-axisymmetric (3D) magnetic perturbations, are studied in NSTX and combined envisioning ELM control in the future NSTX-U operation: experimental observations of the edge harmonic oscillation (EHO) in NSTX (with lower frequency than EHOs in DIII-D and elsewhere), and theoretical study of its external drive using the high-harmonic fast wave (HHFW) antenna as a 3D field coil. EHOs were observed particularly clearly in NSTX ELM-free operation with very low n core modes. A number of diagnostics have confirmed n = 4–6 edge-localized and coherent oscillations in the 2–8 kHz frequency range. These oscillations seem to have a favoured operational window in rotational shear, similar to EHOs in DIII-D quiescent H modes. However, in NSTX, they are not observed to provide significant particle or impurity transport, possibly due to their weak amplitudes, of a few mm displacements, as measured by reflectometry. The external drive of these modes has been proposed in NSTX, by utilizing audio-frequency currents in the HHFW antenna straps. Analysis shows that the HHFW straps can be optimized to maximize n = 4–6 while minimizing n = 1–3. Also, ideal perturbed equilibrium code calculations show that the optimized configuration with only 1 kAt current can produce comparable or larger displacements than the observed internal modes. Thus it may be possible to use externally driven EHOs to relax the edge pressure gradient and control ELMs in NSTX-U and future devices. Fine and external control over the edge pressure gradient would be a very valuable tool for tokamak control. [ABSTRACT FROM AUTHOR]

The edge electron (Te) and ion temperature (Ti) at the time of the L–H transition increase when the X-point radius (RX) is reduced to a high-triangularity shape while maintaining constant edge density. Consequently the L–H power threshold (PLH) is larger for the high-triangularity shape. This supports the prediction that a single-particle loss hole, whose properties are strongly linked to RX and Ti, influences the edge radial electric field (Er) and Er × B flow-shearing rate available for turbulence suppression. Simulations using XGC0, a full-f drift-kinetic neoclassical code, indicate that maintaining a constant Er × B flow-shearing rate does require a larger heat flux and edge Ti as RX decreases. NSTX also observes a decrease in PLH when the divertor recycling is decreased using lithium coatings. However, the edge Te and Ti at the L–H transition appear independent of the divertor recycling for a constant shape. XGC0 calculations demonstrate that more heat flux is needed to maintain the edge Ti and the Er × B flow-shearing rate as the contribution of divertor recycling to the overall neutral fuelling rate increases. [ABSTRACT FROM AUTHOR]

Previous pedestal turbulence measurements in the National Spherical Torus Experiment assessed the spatial and temporal properties of turbulence in the steep gradient region of H-mode pedestals during edge localized mode (ELM)-free, MHD-quiescent periods. Here, we extend the analysis to fluctuation amplitudes and compare observations to pedestal turbulence simulations. Measurements indicate normalized fluctuation amplitudes are about 1–5% in the steep gradient region. Regression analysis indicates fluctuation amplitudes scale positively with electron density gradient, collisionality, and poloidal beta, and scale negatively with magnetic shear, electron density, ion temperature gradient (ITG), toroidal flow and radial electric field. The scalings are most consistent with trapped electron mode, kinetic ballooning mode, or microtearing instabilities, but, notably, least consistent with ITG turbulence. Gyrokinetic simulations of pedestal turbulence with realistic pedestal profiles show collisional instabilities with growth rates that increase at higher density gradient and decrease at higher ITG, in qualitative agreement with observed scalings. Finally, Braginskii fluid simulations of pedestal turbulence do not reproduce scalings from measurements and gyrokinetic simulations, and suggest electron dynamics can be a critical factor for accurate pedestal turbulence simulations. [ABSTRACT FROM AUTHOR]

Objective: The effects of acquired obesity on lipid profile and lipoprotein composition in rare BMI-discordant monozygotic (MZ) twin pairs were studied. Design and Methods: Abdominal fat distribution, liver fat (magnetic resonance imaging and spectroscopy), fasting serum lipid profile (ultracentrifugation, gradient gel-electrophoresis, and colorimetric enzymatic methods), and lifestyle factors (questionnaires and diaries) were assessed in 15 BMI-discordant (within-pair difference [Δ] in BMI >3 kg/m2) and nin concordant (ΔBMI <3 kg/m2) MZ twin pairs, identified from two nationwide cohorts of Finnish twins. Results: Despite a strong similarity of MZ twins in lipid parameters (intra-class correlations 0.42-0.90, P < 0.05), concentrations of apolipoprotein B (ApoB), intermediate-density lipoprotein cholesterol, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein 3a% (HDL3a%), and HDL3c% were higher ( P < 0.05) and those of HDL cholesterol, HDL2-C, and HDL2b% were lower ( P < 0.01) in the heavier co-twins of BMI-discordant pairs. The composition of lipoprotein particles was similar in the co-twins. When BMI-discordant pairs were further divided into liver fat-discordant and concordant (based on median for Δliver fat, 2.6%), the adverse lipid profile was only seen in those heavy co-twins who also had high liver fat. Conversely, BMI-discordant pairs concordant for liver fat did not differ significantly in lipid parameters. In multivariate analyses controlling for Δsubcutaneous, Δintra-abdominal fat, sex, Δsmoking and Δphysical activity, Δliver fat was the only independent variable explaining the variation in ΔApoB, Δtotal cholesterol, and ΔLDL-C concentration. Conclusions: Several pro-atherogenic changes in the amounts of lipids but not in the composition of lipoprotein particles were observed in acquired obesity. In particular, accumulation of liver fat was associated with lipid disturbances, independent of genetic effects. [ABSTRACT FROM AUTHOR]

Impurity injection experiments were performed in the National Spherical Torus Experiment [NSTX, M. Ono et al., Nucl. Fusion 40, 557 (2000)] for a first assessment of low-Z impurity transport in a low field, low-aspect ratio device. Short neon puffs were injected in beam heated, co-rotating L-mode (low confinement) discharges and the radial penetration of the successive neon charge states has been monitored with arrays of filtered ultrasoft x-ray diodes. Time-dependent modeling of the neon emissivity in several spectral bands indicates a core diffusion coefficient in the neoclassical range (<1 m[sup 2]/s) in these strongly rotating plasmas, consistent with the low thermal ion transport inferred from the power balance analysis. By contrast, due to the large Larmor radii in NSTX turbulent diffusion would reach tens of m[sup 2]/s if tokamak-like instability growth rates were assumed. The much lower experimental diffusivity then suggests that turbulent ion transport must be largely suppressed in the NSTX core. It is not yet clear in what measure this is due to the large E×B flow shear characteristic of beam heated NSTX discharges, or to the long wavelength instability growth rates being intrinsically low in the NSTX core, as recently predicted. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Edge data from plasmas in the National Spherical Torus Experiment (NSTX) [S. Kaye et al., Fusion Technol. 36, 16 (1999)] have been compared to theories of transport suppression that have been used to develop a physics framework for low-confinement (L) to high-confinement (H) mode transitions. The NSTX data were obtained in low aspect ratio (R/a≃1.3) discharges taken from a variety of discharge phases, including L-modes, L-H transitions and H-modes with and without edge localized modes. The comparisons show that the group of points taken just before the L-H mode transition are well mixed with the purely L-mode group to within the measurement uncertainties, indicating that changes in these parameters leading up to the transition are subtle. One of the theory parameters, α[sub MHD]=-Rq[sup 2] dβ[sub t]/dr, does show a clear threshold (α[sub MHD]=1 to 2) between the H-mode grouping of points and those remaining in the L-mode or taken just prior to the transition. Additionally, there is no evidence for an edge temperature threshold necessary for transitioning into the H-mode. NSTX data indicate further a possible connection between L-H transitions and nonambipolar beam ion losses. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Examines the trajectories of neutral beam injected energetic ions in spherical tokamaks. Effect of a large poloidal magnetic field in the outboard region; Numerical solutions to the equations for particle motion; Possibility of additional orbit types in spherical tokamaks.

Shows that radial localization of optically thin electron cyclotron emission from superthermal electrons can be imposed by observation of emission upshifted from the thermal cyclotron resonance in the horizontal midplane of a tokamak. Superthermal electron density profile; Moments of the electron energy distribution as a function of radius.

Examines the radial profile and velocity distribution of the fast current-carrying electrons. Time evolution of the electrons; Efforts for understanding the fast electron transport; Oblique horizontal view of upshifted cyclotron emission.