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The analysis of small-scale magnetic fluctuations has been performed in the TEXTOR tokamak. Runaway electrons are used as test particles for studying the turbulent transport at different toroidal magnetic fields. The flux of runaways from the plasma increases with decreasing magnetic field strength. The comparison with a model of magnetic braiding provides insight into the basic properties of the turbulence. A substantial growth of the diffusion coefficients of runaways at the plasma edge with an increase in the width of the turbulent spectrum is demonstrated. The diffusion coefficients of runaways and their flux at the plasma edge are derived from measurements by an IR camera and runaway probe. The level of the magnetic fluctuations and the poloidal spectrum of the magnetic turbulence vary between 10-5 and 5*10-5T and decrease with the magnetic field strength. In addition, the width of the spectrum can be derived to a poloidal mode spectrum of wn #&x2265; 20. [ABSTRACT FROM AUTHOR]

Measurements of the plasma edge electron density ne and temperature Te fields during application of a fast rotating, resonant magnetic perturbation (RMP) field show a characteristic modulation of both, ne and Te coherent to the rotation frequency of the RMP field. A phase delay [uppercase_phi_synonym] between the ne(t) and Te(t) waveforms is observed and it is demonstrated that this phase delay [uppercase_phi_synonym] is a function of the radius with [uppercase_phi_synonym](r) depending on the relative rotation of the RMP field and the toroidal plasma rotation. This provides for the first time direct experimental evidence for a rotation dependent damping of the external RMP field in the edge layer of a resistive high-temperature plasma which breaks down at low rotation and high resonant field amplitudes. [ABSTRACT FROM AUTHOR]

This study reports the results of a pilot experiment concerning observations of extreme ultraviolet emission from plasma produced by the capillary discharges. A few kA current was applied across the gas-filled alumina capillary (1 mm diameter and 8 mm long) to generate radiation in the EUV region (12–63 nm). Spectroscopic studies were carried out by means of a XEUV spectrometer which was upgraded for special lithography purposes. The results obtained from the EUV spectroscopic measurements provided information about the radiation processes from xenon and argon plasma and testifies that given capillary is an effective source of EUV emission. Additionally we showed a simulation which describes plasma dynamics parameters and dynamics of various ionization stages in capillary discharge. Our computer simulation confirmed the presence of ions, which spectra was registered in the experiment. [ABSTRACT FROM AUTHOR]

Interpretation of spectroscopic measurements in the edge region of high-temperature plasmas can be a challenge since line of sight integration effects make direct interpretation in terms of quantitative, local emission strengths often impossible. The EMC3-EIRENE code--a 3D fluid edge plasma and kinetic neutral gas transport code--is a suitable tool for full 3D reconstruction of such signals. A versatile synthetic diagnostic module has been developed recently which allows the realistic 3D setup of various plasma edge diagnostics to be captured.We highlight these capabilities with two examples for Wendelstein 7-X (W7-X): a visible camera for the analysis of recycling, and a coherent-imaging system for velocity measurements. [ABSTRACT FROM AUTHOR]

A generic approach to study the stochastic field lines formed near the magnetic separatrix of poloidal divertor tokamaks due to nonaxisymmetric magnetic perturbations is proposed. The method is based on the determination of the so-called Poincaré integral [S. S. Abdullaev, Phys. Rev. E 70, 046202 (2004)] defined as an integral over the vector potential of the perturbation field taken along the closed field lines orbit. This integral allows us to obtain the analytical estimations for the characteristics of chaotic field lines near the magnetic separatrix, like the Chirikov parameter, the widths of the stochastic layer and magnetic footprints, also the statistical characteristics of chaotic field lines, the quasilinear field line diffusion coefficients, and the Kolmogorov lengths. These estimations are in good agreement with the direct numerical calculations of corresponding quantities. A field line convection coefficient is introduced to describe the preferential outward drift of open chaotic field lines near the separatrix. [ABSTRACT FROM AUTHOR]

The application of time-delay-estimation techniques to two-dimensional measurements of density fluctuations, obtained with beam emission spectroscopy in DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] plasmas, has provided temporally and spatially resolved measurements of the turbulence flow-field. Features that are characteristic of self-generated zonal flows are observed in the radial region 0.85 &les;r/a &les;1.0. These features include a coherent oscillation (approximately 15 kHz) in the poloidal flow of density fluctuations that has a long poloidal wavelength, possibly m = 0, narrow radial extent (k[SUBr]ρ[SUBI] < 0.2), and whose frequency varies monotonically with the local temperature. The approximate effective shearing rate, dv[SUBθ/dr, of the flow is of the same order of magnitude as the measured nonlinear decorrelation rate of the turbulence, and the density fluctuation amplitude is modulated at the frequency of the observed flow oscillation. Some phase coherence is observed between the higher wavenumber density fluctuations and low frequency poloidal flow fluctuations, suggesting a Reynolds stress contribution. These characteristics are consistent with predicted features of zonal flows, specifically identified as geodesic acoustic modes, observed in 3-D Braginskii simulations of core/edge turbulence. [ABSTRACT FROM AUTHOR]

Two-dimensional measurements of density fluctuations are obtained in the radial and poloidal plane of the DIII-D tokamak with the Beam Emission Spectroscopy (BES) diagnostic system. The goals are to visualize the spatial structure and time evolution of turbulent eddies, as well as to obtain the 2D statistical properties of turbulence. The measurements are obtained with an array of localized BES spatial channels configured to image a midplane region of the plasma. 32 channels have been deployed, each with a spatial resolution of about 1 cm in the radial and poloidal directions, thus providing measurements of turbulence in the wave number range 0

Discusses the application of wavelet spectral analysis to plasma fluctuation measurements using beam emission spectroscopy (BES). Measurement of localized density fluctuations in fusion plasma turbulence; Application of a wavelet transform method to BES spectral analysis; Observation of transient changes in turbulence via BES.

Energy spectral measurements of runaway electrons were performed by a scanning probe with high spatial and temporal resolution in the TEXTOR tokamak. The probe consists of ten YSO (Y2SiO5:Ce) crystals, which are shielded by tungsten filters. The probe can resolve electrons with different energies between 4 and 30 MeV. An insertion of the probe to the plasma boundary several times during the discharge allowed spectral measurements of runaway electrons at different minor radial positions at the plasma edge as well as the study of runaway production in time. The high temporal resolution of the probe, 0.05 ms, enabled measurements of runaway electrons not only during low density discharges, but also during plasma disruptions. [ABSTRACT FROM AUTHOR]

The critical issues in the development of diagnostics, which need to work robust and reliable under quasi-steady state conditions for the discharge durations of 30 min and which cannot be maintained throughout the one week duration of each operation phase of the Wendelstein 7-X stellarator, are being discussed. [ABSTRACT FROM AUTHOR]

Abstract: For given conditions, significant change in main particle and carbon transport is observed in TEXTOR under the action of the Dynamic Ergodic Divertor, DED, operating both in 6/2 and 3/1 basic modes. In particular, the stochastic layer created at the plasma edge by the applied perturbing field, is responsible for the so called pump out, PO, effect (observed in DIII-D and on JET during experiments of ELM mitigation) characterized by a decrease in the plasma density and the reduction in the intrinsic carbon concentration in the plasma core. For a sufficiently high value of the applied field strength, in DED 3/1 basic operational mode a 3/1 island connects to the wall, with related further enhancement of particle transport. With respect to carbon, this phenomenon simply leads to a further carbon de-contamination from the central plasma. [Copyright &y& Elsevier]

Abstract: Silicon samples were exposed in the scrape-off layer of the TEXTOR plasma using a fast reciprocating probe, with the aim of studying carbon deposition and deuterium retention during Dynamic Ergodic Divertor (DED) operation. Separate samples were exposed for 300ms at the flat-top phase of neutral beam heated discharges. The exposure conditions were varied on a shot-to-shot basis by external magnetic perturbations generated by the DED in the m/n =3/1, DC regime, base configuration. Nuclear Reaction Analysis (NRA) was used to characterise collector sample surfaces after their exposure. Enhanced concentrations of both carbon and deuterium (C 3–10×1016 at./cm2, D 8–60×1015 at./cm2) were found. The D/C ratio was less than unity which indicates that most of the carbon and deuterium were co-deposited. Carbon e-folding lengths of about 2cm were found on both toroidal sides of the probe independent of DED perturbations. [Copyright &y& Elsevier]

Abstract: Experimental results from the dynamic ergodic divertor (DED) at TEXTOR are given, describing the complex structure of the edge plasma and the properties of the divertor as well as its influence on the plasma rotation. [Copyright &y& Elsevier]