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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]

A study of the properties of the turbulence-driven ion and electron heat fluxes, is presented. Dedicated H-mode experiments taking advantage of the on-axis and off-axis possibilities of both neutral beam injection and electron cyclotron resonance heating available on the ASDEX Upgrade tokamak were carried out. The experimental results are interpreted by comparisons with gyrokinetic calculations. Ion heat transport is, as expected, driven by the ion temperature gradient (ITG) instability with the features predicted by theory: increase of the driven heat flux above a threshold in normalised gradient. In addition the main effects known to impact on the stability of the turbulence, temperature ratio and fast ions population, are exhibited by the experimental results and agree with the gyrokinetic calculations. It is known that the ITG also contributes to the electron heat flux, but that an electron instability can be required in addition when the ITG contribution does not drive the whole imposed electron heating. This situation, investigated by adding electron cyclotron heating, indicates that in the experiments presented here the electron temperature gradient instability develops. [ABSTRACT FROM AUTHOR]

A newly installed core charge exchange recombination spectroscopy (CXRS) diagnostic at ASDEX Upgrade (AUG) enables the evaluation of the core poloidal rotation () through the inboard-outboard asymmetry of the toroidal rotation with an accuracy of 0.5 to 1 km . Using this technique, the total plasma flow has been measured in Ohmic L-mode plasmas across the transition from the linear to saturated ohmic confinement (LOC–SOC) regimes. The core poloidal rotation of the plasma around mid-radius is found to be always in the ion diamagnetic direction, in disagreement with neoclassical (NC) predictions. The edge rotation is found to be electron-directed and consistent with NC codes. This measurement provides as well the missing ingredient to evaluate the core velocity () from data only, which can then be compared to measurements of the perpendicular velocity of the turbulent fluctuations () to gain information on the turbulent phase velocity (). The non neoclassical from CXRS leads to good agreement between and indicating that is small and at similar values as found with gyrokinetic simulations. Moreover, the data shows a shift of in the ion-diamagnetic direction at the edge after the transition from LOC to SOC consistent with a change in the dominant turbulence regime. The upgrade of the core CXRS system provides as well a deeper insight into the intrinsic rotation. This paper shows that the reversal of the core toroidal rotation occurs clearly after the LOC–SOC transition and concomitant with the peaking of the electron density. [ABSTRACT FROM AUTHOR]

The upgrade of the edge charge exchange recombination spectroscopy diagnostic at ASDEX Upgrade has enabled highly spatially resolved measurements of the impurity ion dynamics during an edge-localized mode cycle (ELM) with unprecedented temporal resolution, i.e. 65 μs. The increase of transport during an ELM induces a relaxation of the ion, electron edge gradients in impurity density and flows. Detailed characterization of the recovery of the edge temperature gradients reveals a difference in the ion and electron channel: the maximum ion temperature gradient is re-established on similar timescales as , which is faster than the recovery of . After the clamping of the maximum gradient, Ti and Te at the pedestal top continue to rise up to the next ELM while ne stays constant which means that the temperature pedestal and the resulting pedestal pressure widen until the next ELM. The edge radial electric field Er at the ELM crash is found to reduce to typical L-mode values and its maximum recovers to its pre-ELM conditions on a similar time scale as for ne and Ti. Within the uncertainties, the measurements of Er align with their neoclassical predictions for most of the ELM cycle, thus indicating that Er is dominated by collisional processes. However, between 2 and 4 ms after the ELM crash, other contributions to flow, e.g. zonal flows or ion orbit effects, could not be excluded within the uncertainties. [ABSTRACT FROM AUTHOR]

In ASDEX Upgrade (AUG), the normalised gyroradius was varied via a hydrogen isotope scan while keeping other dimensionless parameters constant. This was done in L-mode, to minimise the impact of pedestal stability on confinement. Power balance and perturbative transport analyses reveal that the electron heat transport is unaffected by the differences in isotope mass. Nonlinear simulations with the Gene code suggest that these L-mode discharges are ion temperature gradient (ITG) dominated. The different gyroradii due to the isotope mass do not necessarily result in a change of the predicted heat fluxes. This result is used in simulations with the Astra transport code to match the experimental profiles. In these simulations the experimental profiles and confinement times are reproduced with the same transport coefficients for hydrogen and deuterium plasmas. The mass only enters in the energy exchange term between electrons and ions. These numerical observations are supported by additional experiments which show a lower ion energy confinement compared to that of the electrons. Additionally, hydrogen and deuterium plasmas have a similar confinement when the energy exchange time between electrons and ions is matched. This strongly suggests that the observed isotope dependence in L-mode is not dominated by a gyroradius effect, but a consequence of the mass dependence in the collisional energy exchange between electrons and ions. [ABSTRACT FROM AUTHOR]

Ion temperature gradient (ITG) and trapped electron modes (TEM) are two important micro-instabilities in the plasma core region of fusion devices (). They usually coexist in the same range of spatial scale (around ), which makes their discrimination difficult. To investigate them, one can perform gyrokinetic simulations, transport analysis and phase velocity estimations. In Tore Supra, the identification of trapped electron modes (TEM) is made possible due to measured frequency fluctuation spectra. Indeed, turbulent spectra generally expected to be broad-band, can become narrow in case of TEM turbulence, inducing ‘quasi-coherent’ (QC) modes named QC-TEM. Therefore the analysis of frequency fluctuation spectra becomes a possible tool to differentiate TEM from ITG. We have found indications that the TEM can have a QC signature by comparing frequency fluctuation spectra from reflectometry measurements, gyrokinetic simulations and synthetic diagnostic results. Then the scope of the analysis of QC-TEM are discussed and an application is shown, namely transitions between TEM turbulence and MHD fluctuations. [ABSTRACT FROM AUTHOR]