An extensive statistical characterization of the electromagnetic turbulence in the edge region of RFX-mod, operated as a tokamak and as a Reversed Field Pinch, is presented. Striking similarity are ...observed on the intermittent character of the electrostatic turbulence between the two configurations whereas the difference between magnetic turbulence is likely to be imputed to the different β value of the two configurations. Blobs are characterized in terms of their spatial structure, the associated enstrophy and energy and the mechanism of energy and enstrophy transfer between intermittent fluctuation at different scales is addressed.
We report the first case of
Listeria monocytogenes
meningoencephalitis associated with anti-GQ1b antibody syndrome in an immunocompetent adult. A prompt diagnosis, made thanks to the ...multidisciplinary contribution, allowed a combined therapeutic approach leading to final favourable outcome, despite several intercurrent complications.
Density and magnetic fluctuation measurements in low-β type-III ELM discharges are obtained in the Joint European Torus (JET). They are observed during the inter-ELM pedestal evolution, after the LH ...transition phase, at about 60-70 kHz. Density fluctuations are measured with a correlation reflectometer system installed on the low-field side and they are localized at the pedestal top. Magnetic fluctuations with a spatial scale kyρi∼0.1 are measured through a high resolution coil array. The main features and the relations with local plasma parameters are presented. The nature of these fluctuations is discussed along with linear gyrokinetic simulations. Ion temperature gradient (ITG) modes are the dominant instabilities in the frequency range of interest. In terms of radial localization, typical oscillation frequency and qualitative relation with the possible linear drive, ITG modes are consistent with the experimental density fluctuations measurements. Micro-tearing modes (MTMs), found unstable with a lower growth rate, appear a possible explanation for magnetic fluctuations in terms of typical wavenumbers and direction of propagation.
Filament or blob structures have been observed in all magnetic configurations with very similar features despite the difference in the magnetic geometry, and are believed to play an important role in ...convecting particles and energy towards the wall. Despite their different generation mechanism, turbulent structures and edge-localized mode (ELM) filaments share some common physical features. The electromagnetic effects on filament structures deserve particular interest, among others reasons for the implication they could have for ELM, related for instance to their dynamics in the transition region between closed and open field lines or to the possibility, at high beta regimes, of causing line bending which could enhance the interaction of blobs with the first wall. A direct characterization of the effects of active modification of the edge topology on EM turbulent filament structures is presented, comparing reversed field pinch and tokamak configurations. Measurements are obtained in the RFX-mod device, which allows operation in both configurations and with different equilibria. The RFX-mod experiment versatility is exploited also from the point of view of the active control of the edge magnetic topology, equipped with an advanced system for edge boundary feedback control. Three different case studies of actively controlled magnetic perturbations are shown, focusing on the filament interaction with local magnetic islands. High-frequency fluctuations, characterizing electrostatic and magnetic filament features, and the associated transport coefficients have been observed to be strongly affected by the island proximity and topology.
•Waveguide phase reference can be compensated directly in quadrature raw data.•Vessel features can be observed along plasma reflection in reflectometry data.•X-mode first fringe estimation algorithms ...should use amplitude and spectral details.•X-mode lower cut off reflection influences first fringe estimation algorithms.
The new multichannel X-mode reflectometer installed on ASDEX Upgrade measures the plasma density profile evolution at different positions in front of the ICRF antenna. The reflectometer operates in the extended U-band (40–68GHz) microwave region, measuring density profiles up to 2×1019m−3 with magnetic fields between 1.5T and 2.7T. In this heterodyne reflectometer architecture, the signal reflected by the plasma is down-shifted and quadrature detectors demodulate its in-phase and quadrature (IQ) components. In this work we analysed the acquired IQ signals from the different reflectometer antennas, and describe the waveguide dispersion calibration and filtering of the raw signal. The effect of spurious reflections, such as the multiple reflections from the ICRF antenna metal straps, are analysed and taken into account on the data processing software. In high plasma density and high magnetic field scenarios, both the lower and upper X-mode cut off frequencies are detected in the probing range. The first fringe (FF) reflection of the upper cut off indicates the start of the plasma signal and must be determined robustly to reduce density profile errors. Existing FF estimation algorithms based on signal amplitude and spectral information may still fail in the presence of both upper and lower cut off reflections.
In the reversed field pinch RFX-mod at the highest plasma current of 2 MA, when error fields are not effectively feedback controlled, localized thermal loads up to tens of MW m−2 can be produced. The ...graphite tiles withstand such high power loads, but the high hydrogen retention makes density control extremely difficult. Several wall conditioning techniques have been optimized in the last campaigns, including helium glow discharge cleaning and wall boronization by diborane glow discharges. More recently, lithium conditioning has been applied for the first time in a reversed field pinch by the evaporation technique. The main results are discussed in this paper. Lithization leads to important operational advantages: a significant improvement of the density control is obtained. Densities up to n/nG 0.5 can be produced in a controlled way. At the same value of input power, plasmas at higher densities can be sustained. However, due to the short particle confinement time, such densities are reached with high rates of gas puffing and the resulting profiles at high density are edge peaked. A lithium multipellet injector, to be applied in order to obtain a more uniform deposition, has been tested.
The traditional and widely used reflectometric schemes are not able to probe the edge density layers of the reversed field pinches (RFPs) due to the presence of a high level of density fluctuations. ...In order to overcome this limitation, an ultrafast microwave reflectometer has been developed and the first Ka-band has been successfully operational on the RFX-mod experiment 1 since mid-2009. The actual diagnostics configuration (frequency sweep 26.5–30.5 GHz in 1 µs) allows us to evaluate the radial distance of the relative cut-off density layer with a high time resolution. The first results are presented and discussed in this paper. In particular, a relation between edge density and local magnetic topology is proposed as well as a systematic study of the average behaviour over several global operative conditions of the machine. An outlook on the future diagnostic developments is also given.
We report results of an extensive world-wide observing campaign devoted to the recently discovered dwarf nova SDSS J162520.29+120308.7 (SDSS J1625). The data were obtained during the July 2010 ...eruption of the star and in August and September 2010 when the object was in quiescence. During the July 2010 superoutburst, SDSS J1625 clearly displayed superhumps with a mean period of Psh = 0.095942(17) days (138.16 ± 0.02 min) and a maximum amplitude reaching almost 0.4 mag. The superhump period was not stable, decreasing very rapidly at a rate of Ṗ = −1.63(14) × 10-3 at the beginning of the superoutburst and increasing at a rate of Ṗ = 2.81(20) × 10-4 in the middle phase. At the end of the superoutburst, it stabilized around the value of Psh = 0.09531(5) day. During the first twelve hours of the superoutburst, a low-amplitude double wave modulation was observed whose properties are almost identical to early superhumps observed in WZ Sge stars. The period of early superhumps, the period of modulations observed temporarily in quiescence, and the period derived from radial velocity variations are the same within measurement errors, allowing us to estimate the most probable orbital period of the binary to be Porb = 0.09111(15) days (131.20 ± 0.22 min). This value clearly indicates that SDSS J1625 is another dwarf nova in the period gap. Knowledge of the orbital and superhump periods allows us to estimate the mass ratio of the system to be q ≈ 0.25. This high value poses serious problems for both the thermal and tidal instability (TTI) model describing the behaviour of dwarf novae and for some models explaining the origin of early superhumps.
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