Search

A new thermal helium beam diagnostic has been implemented in the outer lower divertor of the ASDEX Upgrade tokamak. The purpose of this diagnostic is to measure two-dimensional profiles of electron density (ne) and temperature (Te) with high temporal and spatial resolution. The geometry of the lines of sight is chosen to avoid the influence of prompt recycling and to optimize the resolution without significantly impacting the divertor structure. Moreover, the effect of long-term helium recycling has been analyzed, and its amplitude compared to the active signal is negligible. Finally, the reconstruction of ne and Te is done via a collisional radiative model, while a static and a dynamic model were implemented and compared with SOLPS simulations as well as divertor Thomson scattering data. Furthermore, a new 2D parameterization of the outer divertor volume, which is required for the dynamic model, was developed. Due to its fast and local ne and Te profile measurements, the diagnostic is suitable for investigating fast processes such as divertor transitions and filaments. [ABSTRACT FROM AUTHOR]

Ion temperature, rotation, and density are key parameters to evaluate the performance of present and future fusion reactors. These parameters are critical for understanding ion heat, momentum, and particle transport, making it mandatory to properly diagnose them. A common technique to measure these properties is charge exchange recombination spectroscopy (CXRS). For characterizing positive and negative triangularity plasmas at the small aspect ratio tokamak, a poloidal array of gas puff based CXRS diagnostics will be measuring the ion properties in different poloidal positions. In this work, the modeling of the expected signal and spatial coverage using the FIDASIM code is presented. Furthermore, the design and characterization of the low field side midplane CXRS diagnostic are described. Each diagnostic is composed of a gas injection system, an optical system that collects the light emitted by the plasma, and a spectrometer. These systems will provide ion temperature, rotation, and density with a radial resolution of 3.75 mm and a temporal resolution of 2.2 ms. [ABSTRACT FROM AUTHOR]

We introduce a new correlation analysis technique for thermal helium beam (THB) diagnostics. Instead of directly evaluating line ratios from fluctuating time series, we apply arithmetic operations to all available He I lines and construct time series with desired dependencies on the plasma parameters. By cross-correlating those quantities and by evaluating ensemble averages, uncorrelated noise contributions can be removed. Through the synthetic data analysis, we demonstrate that the proposed analysis technique is capable of providing the power spectral densities of meaningful plasma parameters, such as the electron density and the electron temperature, even under low-photon-count conditions. In addition, we have applied this analysis technique to the experimental THB data obtained at the ASDEX Upgrade tokamak and successfully resolved the electron density and temperature fluctuations up to 90 kHz in a reactor relevant high power scenario. [ABSTRACT FROM AUTHOR]

An edge fast-ion D-alpha (FIDA) system consisting of lines of sight optimized for edge measurements and a newly designed prototype spectrometer have been installed at ASDEX Upgrade. The system allows for measurements of the full deuterium Balmer alpha spectrum with either good radial coverage or exposure times below 200 μs. It uses a bar, placed in front of the electron multiplying charge-coupled device camera, to partially block the intense unshifted D-alpha light which permits simultaneous measurements of the FIDA and unshifted D-alpha emission. Thus, not only active FIDA radiation present during neutral beam injection (NBI) can be studied but also detailed investigations of passive FIDA light are possible, since the unshifted D-alpha emission contains information on the density of background neutrals. First measurements show significant levels of active and passive FIDA radiation in discharges with large edge fast-ion populations from off-axis NBI heating. In addition, a particularly strong response of the passive emission to edge localized modes is observed, well explained by modifications of the edge-neutral density as well as the fast-ion density. [ABSTRACT FROM AUTHOR]

A new core charge exchange recombination spectroscopy diagnostic has been installed in the ASDEX Upgrade tokamak that is capable of measuring the impurity ion temperature, toroidal rotation, and density on both the low field side (LFS) and high field side (HFS) of the plasma. The new system features 48 lines-of-sight (LOS) with a radial resolution that varies from ±2 cm on the LFS down ±0.75 cm on the HFS and has sufficient signal to run routinely at 10 ms and for special circumstances down to 2.5 ms integration time. The LFS-HFS ion temperature profiles provide an additional constraint on the magnetic equilibrium reconstruction, and the toroidal rotation frequency profiles are of sufficiently high quality that information on the poloidal velocity can be extracted from the LFS-HFS asymmetry. The diagnostic LOS are coupled to two flexible-wavelength spectrometers such that complete LFS-HFS profiles from two separate impurities can be imaged simultaneously, albeit with reduced radial coverage. More frequently, the systems measure the same impurity providing very detailed information on the chosen species. Care has been taken to calibrate the systems as accurately as possible and to include in the data analysis any effects that could lead to spurious temperatures or rotations. [ABSTRACT FROM AUTHOR]

In this work, a new type of high through-put Czerny-Turner spectrometer has been developed which allows us to acquire multiple channels simultaneously with a repetition time on the order of 10 μs at different wavelengths. The spectrometer has been coupled to the edge charge exchange recombination system at ASDEX Upgrade which has been recently refurbished with new lines of sight. Construction features, calibration methods, and initial measurements obtained with the new setup will be presented. [ABSTRACT FROM AUTHOR]

A new edge beam emission polarimetry diagnostic dedicated to the measurement of the magnetic field line angle has been installed on the ASDEX Upgrade tokamak. The new diagnostic relies on the motional Stark effect and is based on the simultaneous measurement of the polarization direction of the linearly polarized π (parallel to the electric field) and σ (perpendicular to the electric field) lines of the Balmer line Dα. The technical properties of the system are described. The calibration procedures are discussed and first measurements are presented. [ABSTRACT FROM AUTHOR]

At the ASDEX Upgrade tokamak a new approach has been developed to determine the profiles of the effective charge (Z[sub eff]) from bremsstrahlung emission in hot fusion plasmas. The signals of all diagnostics measuring bremsstrahlung have been incorporated into one evaluation algorithm, resulting in the possibility to check whether or not signals are disturbed during each discharge. Especially helpful to this aim is a recently installed diagnostic measuring the bremsstrahlung spectrally resolved by using a spectrometer and a charge-coupled-device (CCD) camera as a detector. The experimental results are verified qualitatively and quantitatively using a discharge with silicon laser blow-off. Modeling of the bremsstrahlung as measured with the CCD camera using the routines and data of the ADAS package reveals that the background of the spectra is dominated by bremsstrahlung for most sight lines. Only those passing mainly outside the last closed flux surface measure a considerable amount of line and molecular band radiation. This edge emission can be considered as a radiative mantle. Subtracting it from all other signals results in reduced statistical errors of the deduced Z[sub eff] profiles while not changing the profile shape inside a normalized minor radius of 0.8. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A two channel multicrystal spectrometer of Bragg geometry was constructed for measurements of absolute photon fluxes of ASDEX Upgrade plasmas in the wavelength range from 0.5 up to 26 Å. The calibration of the spectrometer was done by an ab initio calculation using the absolute reflection data from literature of four crystals. The calibration was validated by the direct comparison with other absolute calibrated diagnostics at the ASDEX Upgrade as well as by using the impurity transport code STRAHL. The absolute impurity concentrations of elements from N up to Cu have been extracted. O and F appear to be main impurity components after C, which is routinely measured by an independent diagnostic. Despite the significantly lower concentration of Ar, it contributes measurably to Z[sub eff] and can account for main plasma impurities as well. Other impurities either have never been seen or appear only sporadically (like Fe and Cu) and normally do not contribute significantly to the plasma radiation in the soft x-ray range. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A novel charge-exchange recombination spectroscopy (CXRS) diagnostic method is presented, which uses a simple thermal gas puff for its donor neutral source, instead of the typical high-energy neutral beam. This diagnostic, named gas puff CXRS (GP-CXRS), is used to measure ion density, velocity, and temperature in the tokamak edge/pedestal region with excellent signal-background ratios, and has a number of advantages to conventional beam-based CXRS systems. Here we develop the physics basis for GP-CXRS, including the neutral transport, the charge-exchange process at low energies, and effects of energy-dependent rate coefficients on the measurements. The GP-CXRS hardware setup is described on two separate tokamaks, Alcator C-Mod and ASDEX Upgrade. Measured spectra and profiles are also presented. Profile comparisons of GP-CXRS and a beam based CXRS system show good agreement. Emphasis is given throughout to describing guiding principles for users interested in applying the GP-CXRS diagnostic technique. [ABSTRACT FROM AUTHOR]

The charge exchange recombination spectroscopy (CXRS) diagnostics at ASDEX Upgrade (AUG) have been upgraded and extended to provide high-resolution measurements of impurity ion temperature, density, and rotation profiles. The existing core toroidal CXRS diagnostic has been refurbished to increase the level of signal, thus enabling shorter exposure times down to 3.5 ms. Additional lines of sight provide more detailed profiles and enable simultaneous measurements of multiple impurities. In addition, a new CXRS system has been installed, which allows for the measurement of poloidal impurity ion rotation in the plasma edge with high temporal (1.9 ms) and spatial resolution (down to 5 mm). A new wavelength correction method has been implemented to perform in situ wavelength calibrations on a shot-to-shot basis. Absolute measurements of the poloidal impurity ion rotation with uncertainties smaller than 1.5 km/s have been obtained. Comparison of all the CXRS measurements provides a consistency check of the diagnostics and good agreement has been found for all of the CXRS systems. [ABSTRACT FROM AUTHOR]

The thermal helium beam edge diagnostic has recently been upgraded at the ASDEX Upgrade (AUG) tokamak experiment. Line ratio spectroscopy on neutral helium is a valuable tool for simultaneous determination of the electron temperature and density of plasmas. The diagnostic now offers a temporal resolution of 900 kHz with a spatial resolution of up to 3 mm at 32 lines of sight (LOS) simultaneously. The LOS covers a radial region of 8.5 cm, starting at the limiter radius and reaching into the confined region beyond the separatrix. Two components are of particular importance for the aforementioned hardware improvements. The first is the optical head, which collects the light from the experiment. Equipped with an innovative clamping system for optical fiber ends, an arbitrary distribution pattern of LOS can be achieved to gain radial and poloidal profiles. The second major development is a new polychromator system that measures the intensity of the 587 nm, 667 nm, 706 nm, and 728 nm helium lines simultaneously for 32 channels with filter-photomultiplier tube arrays. Thus, the thermal helium beam diagnostic supplements the AUG edge diagnostics, offering fast and spatially highly resolved electron temperature and density profile measurements that cover the plasma edge and scrape-off layer region. Plasma fluctuations, edge localized modes, filaments, and other turbulent structures are resolved, allowing analysis of their frequency and localization or their propagation velocity.