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Recent development of the JT-60U charge exchange recombination spectroscopy (CXRS) diagnostic system is reported. The measurements of the radial profiles of the ion temperatures, the toroidal and poloidal rotation velocities, and the impurity density are based on CXR spectra of fully stripped carbon ions induced by neutral beam injection. Measurements are made simultaneously at 59 spatial points (23 toroidal and 36 poloidal) with a time resolution of 1/60 s throughout the full discharge pulse of 15 s. Considerable effort has been expended to ensure the automatic provision of reliable profile data, where the mechanical components of the system must cope with both a baked tokamak vessel (∼300 °C) and an expected disruption-induced acceleration of up to 60 g, where g denotes the gravitational acceleration, i.e., 9.8 m2/s. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this article, we report on the hardware and software of an eight-channel, high-resolution, spectroscopic diagnostic system that has been built for the TJ-II flexible heliac. This system is currently being used on TJ-II to measure impurity ion temperature and poloidal rotation using passive emission spectroscopy. The principal features of the diagnostic include independent focusing of its channels, high sensitivity for performing Doppler measurements in low-density ECR-heated plasmas, as well as a flexible and fast in-house-developed software program for performing integrated data reduction and analysis. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Experimental test of the radial force balance equation was done in the Compact Helical System Heliotron/Torsatron [S. Okamura et al. Nucl. Fusion 39, 1337 (1999)]. A radial electric field is measured with a heavy ion beam probe, while plasma rotation and drift velocity of fully ionized carbon are measured with charge exchange spectroscopy. The two measurements agree with each other to within 10% of the radial electric field in a wide range of electron densities of 0.3-2.0x10[sup 19] m[sup -3]. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This paper concerns experiments about the role of a radial electric field on the plasma turbulence in a toroidal magnetoplasma, and the possibility of anomalous transport reduction through the application of external biasing potentials to the plasma edge. The experiments show, for positive applied bias potential, a progressive reduction of radial anomalous particle flux, as well as electrostatic fluctuations. Some results on statistical and spectral properties of plasma and density fluctuations are reported. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents impurity toroidal rotation and transport in Alcator C-Mod ohmic high confinement mode plasmas. Observation on rotation velocities; Similarity in characteristics of ohmic H-mode plasmas and ion cyclotron range of frequencies; Presence of very long impurity confinement times.

Discusses demonstrations of causality performed in tokamak plasmas. Similarities between flow shear effects in plasmas and in neutral fluids; Examples of how flow shear reduction of turbulence in neutral fluids under the proper conditions; Model of turbulence decorrelation and stabilization by sheared E X B flow; Change in turbulence and transport.

Investigates the correlation among geodesic curvature of magnetic field lines, plasma rotation, and improved confinement regimes in tokamaks. Toroidal magnetic confinement configurations of all the charged particles; Minimization of the neoclassical transport; Reduction of the geodesic curvature.

Examines ship waves of a drift type that have a global structure of a quasimode in a poloidally rotating toroidal plasma for axisymmetric, large aspect-ratio tokamak with concentric, circular magnetic surfaces. Standard model of turbulence in tokamak plasmas; Analytical dispersion relations for global drift ship waves.

Reports that an instability with a lower frequency than the toroidicity-induced Alfven eigenmode has been identified as a beta-induced Alfven eigenmode (BAE). Instabilities with the characteristic spectral features of the BAE found in tokamak plasmas; Destabilization of the modes by circulating beam ions.

Studies the scaling of heat transport with collisionality. Proposed mechanisms of turbulent transport; Origin of power degradation and density scaling; Ion and electron thermal diffusivities.

Describes a fast charge coupled device detector for charge exchange recombination (CER) spectroscopy on the DIII-D tokamak. Applications of CER measurements; Ability of the system to detect sufficient photons to utilize the shortest time resolution only under exceptional conditions.

Focuses on the progress in anomalous transport research in toroidal magnetic confinement devices. Transport understanding in the early 1970's; Evolution of the infrastructure for transport studies; Understanding ion-channel anomalous transport mechanisms.

Examines the conceptual feasibility of an active spectroscopic diagnostic on reversed field experiment (RFX) to measure the radial profiles of ion temperature, toroidal and poloidal drift velocities and main impurity densities. Charge exchange recombination spectroscopy for carbon and helium impurities; Estimation of the motional Stark effect on the beam atoms.

Describes the development of a spectroscopic diagnostic to measure poloidal velocity profiles of Tokamak fusion test reactor plasmas. Measurement of the carbon poloidal velocities; Size of poloidal velocities; Statistical errors in the chord-averaged poloidal velocity; Features of the short focal length spectrometer.

Examines the diagnostic method for radial electric fields in Tokamaks. Use of counteracting fields in preventing weak collisional ions trapping; Role of charge exchange analysis in rippled-trapped ion density; Contribution of single particle calculation to edge radial electric field.

Describes the development of a diagnostic instrumentation to study the structure and magnitude of microturbulent processes and to identify the origins of plasma loss in tokamaks. Primary instruments developed to measure fluctuating quantities associated with particle and energy transport; Techniques applicable to microturbulence.

Focuses on the development of a matrix inversion technique used to calculate local poloidal rotation velocities of impurity ions in a tokamak plasma. Recovery of radial spatial resolution that is lost due to the curvature of the field lines; Simulation of a poloidal rotation diagnostic for the tokamak.

Documents the calibration procedure for neutron counters and scintillators used to measure the neutron emission produced by the DIII-D tokamak. Detectors and calibration; Detector comparisons; Comparison with other diagnostics.

Studies the removal of helium ash in medium sized tokamaks experiments with deuterium plasmas and helium puffs. Measurement in the visible range; Examination of electron beams and a Penning discharge; Vacuum ultraviolet spectra of pure helium and deuterium which were measured by scanning the monochromator.

Discusses the use of a multianode photomultiplier to detect a collection of spectra in a high dispersion echelle spectrometer. Photomultiplier and electronics; Optics and spectrometer; Spectral and spatial instrumental functions; Algebraic deconvolution.

A high-resolution spectrometer has been developed and used to measure simultaneously impurity ion temperatures and flow velocities in high temperature plasmas with 10 μs temporal resolution (limited by digitization rate). This device is actually a duo-spectrometer: measurements from two different chordal views of the plasma can be made simultaneously via two separate quartz input fiber optic bundles coupled to the entrance slits which are tilted to compensate for line curvature. The dispersed spectra on the exit plane of the duo-spectrometer are coupled via quartz fiber optics to two arrays of 16 photomultiplier tubes each. Measurements made by recording the Doppler broadened and shifted 227.091 nm emission from the C v impurity ions in the Madison Symmetric Torus (MST) reversed-field pinch (RFP) plasma have achieved precisions of <6 eV for temperatures of 150 eV and <0.7 km/s for flow velocities of 6 km/s. Representative results from the MST RFP indicate that the toroidal flow velocity drops and ion temperature increase during sawtooth events in MST. [ABSTRACT FROM AUTHOR]

The identification of fundamental transport mechanisms in magnetically confined plasmas is a critical issue for the magnetic fusion program. Recent progress in understanding fluctuations and transport is well correlated with the development and use of new diagnostics, but a great deal of information is still missing. Some of the required measurements are well beyond our present diagnostic capabilities, but some are within reach and could answer critical questions in this area of research. Some of these critical issues are discussed. [ABSTRACT FROM AUTHOR]

Presents a unified theory of transport barriers and of subneoclassical transport that provides a nondegenerate ambipolarity constraint. Competition between nonlinear spin up of the rotation and momentum loss via charge exchange neutrals; Analysis of the local threshold condition; Physical interpretation allowing extrapolation to low collisionality plasmas.

Investigates the radial structure of parallel-velocity-shear-driven mode in toroidal plasmas by a parallel velocity shear (PVS). Analysis of the Reynolds stress created by PVS turbulence; Influence of finite ion temperature on Reynolds stress creation ability; Impact of the Reynolds stress on the sheared poloidal plasma rotation.

Measures the argon density from charge-exchange spectroscopy. Determination of the profiles of fully stripped low-Z ions in fusion plasmas; Prediction of the wavelengths of transitions; Detection of transitions in DIII-D tokamak subsequent to argon puffing into neutral-beam injected plasmas.

Examines the variation of the electrostatic fields in tokamaks. Association of ion orbits with significantly reduced neoclassical transport; Occurrence of an analogous process for steeper field variation; Implication of the distortion of the gyro-orbits by the ion gyro-radius for the modification of the classical transport.

Examines toroidal drift waves in rotating tokamak plasmas. Basis on the eigenmode equations with poloidal mode numbers; Determination of analytical dispersion relations for global and propagating drift waves; Observation of plasma rotation velocities in high-mode confinement regime.

Examines the improvement of the Ohmic confinement phase during the turbulent heating pulse in the Hefei Tokamak-6M. Factor affecting the steepness of the electron temperature and density profiles; Role of the radial electric field during the transition of L mode and H mode; Effect of radial electric field on the suppression of the plasma potential fluctuation.

Examines the structure and scaling of the High-mode pedestal for discharges in the DIII-D tokamak. Indication of ion measurement and C[sup 6+]; Prediction on pressure gradient magnitude in the barrier; Description of scalings based on the poloidal ion gyroradius.

Examines the effects of E[sub r] shear on edge turbulence of the China Tokamak-6B, a Nuclear Fusion in the United States. Application of negative limiter radius; Correlation of turbulence with enhanced E[sub r] shear; Importance to the existence of E[sub r] shear with turbulence and shear-induced shift.

Focuses on notched velocity profiles and the radial electric field in high ion temperature plasmas in the Tokamak Fusion Test Reactor. Calculations of neoclassical velocities; Effect of temperature gradients; Discussion on the behavior of the radial electric field and nonlinear shearing rate for turbulence.

Identifies characteristics of electrostatic microturbulence observed during negative central magnetic shear (NCS) discharges which may be significant for attainment of enhanced performance. Increase in temperature, confinement and fusion reactivity; Differences in the level and location of microturbulence in discharges with and without NCS.

Investigates the effect of a radial electric field on nonthermal ripple-trapped ions using toroidal Monte Carlo simulations for edge tokamak plasmas. Increase in the neutral particle flux from the ions trapped in local magnetic wells observed by the charge exchange detector at a low to high confinement transition at the Axially Symmetric Divertor Experiment.

Reports on the radial electric field inside a separatrix that has been deduced from spectroscopic measurements of impurities on Tokamak de Varennes, using the reduced radial momentum balance and two neoclassical models. Role of electric fields in the confinement of both particles and energy.

Focuses on low and improved confinement modes in the H-1 heliac in radio frequency (rf)-sustained argon discharges at low magnetic fields. Increase in high ion temperature across the transition to improved confinement mode; Retention of both toroidal and poloidal plasma flow velocities across the transition.

Investigates the microinstability properties of discharges with negative magnetic shear in the Tokamak Fusion Test Reactor (TFTR) experiments with and without confinement transitions. Use of a kinetic linear eigenmode calculation employing the ballooning representation; Variety of physical effects associated with differing q-profiles.

Reports that a finite-banana-width correction to the neoclassical ion thermal conductivity is obtained in a tokamak plasma. Assumption that the particle flow parallel to magnetic-field lines dominates the trapped particle's orbital dynamics; Making ion thermal conductivity itself to be a function of radial plasma density gradient and magnetic shear.

Studies the effects of E x B velocity shear and magnetic shear on turbulence and transport in magnetic confinement devices. Formation of a transport barrier at the plasma edge in tokamaks after the low-to-high transition; Transport decrease associated with E x B velocity shear effects; Effect on broader classes of microturbulence.

Investigates the effect of radial electric field on motional-Stark effect (MSE) measurements of q-profile of the plasma in toroidal magnetic confinement configurations. Sensitivity of MSE measurements to the electric field; Requirement of significant corrections for rotating plasmas; Comparison of results with those obtained from neoclassical theory.

Shows that, in toroidal collisionless plasmas, the ion temperature gradient and the trapped electron modes are weakly (strongly) coupled when both the temperature gradients and the driving mechanism of trapped electrons are moderate to strong (weak but finite). Coexistence of two independent unstable modes for the weak coupling case.

Studies the turbulence driven by the ion temperature gradient, the mass shear flow parallel to the magnetic field, and the impurity ion density gradient in confined plasma, in a sheared slab magnetic configuration. Enhancement of the turbulence drive by the shear flow and the negative density gradient of the impurity ions.

The effect of isotope on confinement in high-recycling, L-mode plasmas is studied on the Tokamak Fusion Test Reactor (TFTR) [see D. M. Meade, J. Fusion Energy 7, 107 (1988)] by comparing hydrogen and deuterium plasmas with the same magnetic field and similar electron densities and heating power, with both Ohmic and deuterium-neutral-beam heating. Following a long operational period in deuterium, nominally hydrogen plasmas were created through hydrogen glow discharge and hydrogen gas puffing in Ohmic plasmas, which saturated the exposed limiter surface with hydrogen and raised the H/(H+D) ratio from 10±3% to 65±5%. Ohmic deuterium discharges obtained higher stored energy and lower loop voltage than hydrogen discharges with similar limiter conditions. Neutral-beam power scans were conducted in L-mode plasmas at minor radii of 50 and 80 cm, with plasma currents of 0.7 and 1.4 MA. To minimize transport differences from the beam deposition profile and beam heating, deuterium neutral beams were used to heat the plasmas of both isotopes. Total stored energy increased approximately 20% from nominally hydrogen plasmas to deuterium plasmas during auxiliary heating. Of this increase about half can be attributed to purely classical differences in the energy content of unthermalized beam ions. Kinetic measurements indicate a consistent but small increase in central electron temperature and total stored electron energy in deuterium relative to hydrogen plasmas, but no change in total ion stored energy. No significant differences in particle transport, momentum transport, and sawtooth behavior are observed. Overall, only a small improvement (∼10%) in global energy confinement time of the thermal plasma is seen between operation in hydrogen and deuterium. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A breaking of the up–down symmetry due to the inductive electric field E&fgr; is analyzed in detail for particles describing quasibanana orbits in the large aspect ratio approximation. Time-independent and time-dependent electric fields are considered. In the first case it is proved that the classical ∇B drift and the breaking of up–down symmetry due to E&fgr; lead to a net inward radial drift, which agrees with the well-known Ware pinch formula. The weak points of previous treatments of the Ware pinch, e.g. taking only leading terms in the Taylor expansion of A&fgr;, are discussed. Yet the results obtained here lead to the same pinch formula, even for banana orbits with a large amplitude of poloidal angle and for more general conditions than previously considered. A more general formula for a time-dependent E&fgr; has also been found. Our results show from a very general basis that the corresponding polarization type of drift does not play any role in the inward pinch; however, the second time derivative of the inductive electric field E&fgr; could significantly increase or decrease the usual Ware pinch. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Analyzes the kinetic stability properties in a number of high performance discharges from the DIII-D tokamak, using a comprehensive kinetic eigenvalue code. Toroidal drift mode; Computation of magnetohydrodynamic equilibria; Presence of a wide region of instability.

Presents an extension of the phase transition model for the transition from the low-confinement region to high-confinement regime to incorporate the effect of neutral particles on the transition threshold. Increase of effective poloidal viscosity through charge exchange damping; Reduction of the effective fluxes by both ionization and charge exchange.

Reports on the effects of dissipative trapped electrons on ion temperature gradient-driven instability in tokamak plasmas. Adoption of a sheared slab geometry and a linearized fluid model of ion temperature gradient mode; Existence of an intrinsic oscillation mode in a tokamak plasma.

Studies a system of equations that couples rapidly varying fluctuations of resistive ballooning modes to slowly varying transport of the density, vorticity and parallel momentum for low-high transition in tokamaks. Fluctuations associated with resistive ballooning modes; Reductions in particle transport; Effects of strong damping that prevents average poloidal flow.

Studies model equations describing dynamics of a toroidal eta[sub i] mode in a rotating plasma. Stationary solution of the model equations; Condition for global vortex formation; Effects of the shear of the plasma poloidal rotation on the shape of global vortices.

Presents a study that carried out self-consistent predictive transport simulations of temperature and density profiles for ten dimensionally similar low mode discharges. Combination of theoretically derived transport models; Weiland model for transport due to drift waves; Ion temperature gradient and trapped electron modes.