Heat wave experiments on TJ-II flexible heliac

Eguilior, Sonsoles; Castejón, F.; Luna, E. de la; Cappa, Á.; Likin, K. M.; Fernández, Á.; Team, Tj‐Ii

doi:10.1088/0741-3335/45/2/303

Cited by 38 publications

(47 citation statements)

References 20 publications

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“…With respect to the heating sources, the 2nd harmonic X mode ECR heating power, P ECR , is described with a Gaussian slightly displaced from the magnetic axis, which is in agreement with the profile estimated from heat wave experiments in TJ-II [17]. The P ECR profile, however, is not very important for this work because it does not change considerably until almost the cutoff density is reached.…”

Section: Simulations Of the Plasma Evolutionsupporting

confidence: 81%

Dynamic Simulation of the Electron Bernstein Wave Heating Under NBI Conditions in TJ–II Plasmas

Cappa¹,

López‐Bruna

Castejón

et al. 2011

Contrib. Plasma Phys.

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In this work, we have calculated the expected properties of the Electron Bernstein Wave (EBW) heating using the O-X-B double mode conversion scenario in a plasma that evolves from Electron Cyclotron Resonance (ECR) to Neutral Beam Injection (NBI) heating in the TJ-II device. For this purpose, a transport simulation that reproduces the time evolution of a typical collapsing plasma heated by a combination of ECR and NBI power has been used. It is seen that the predicted EBW absorption depends strongly on the plasma characteristics, whose time evolution depends in turn on the heating properties. Therefore, the need of consistently computing the ray tracing and the plasma evolution is underlined. The fraction of the absorbed EBW heating power becomes very high as soon as the O mode cutoff layer appears. This guarantees the overlapping of both EBW and ECR heating, thus avoiding excessive plasma cooling when the wave cutoff is reached. The EBW power deposition profile evolves from off-axis to a much more centred shape that persists until the radiative collapse quenches the plasma.

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Section: Simulations Of the Plasma Evolutionsupporting

confidence: 81%

Dynamic Simulation of the Electron Bernstein Wave Heating Under NBI Conditions in TJ–II Plasmas

Cappa¹,

López‐Bruna

Castejón

et al. 2011

Contrib. Plasma Phys.

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“…In tokamaks with profile resiliency, the thermal diffusivity obtained from heat pulse propagation is typically much larger than the thermal diffusivity from steady state power balance. In contrast, experiments in LHD, 3 W7-AS, 4 and TJ-II 5 have shown that heat pulse and power balance diffusivities are comparable.…”

Section: Introductionmentioning

confidence: 81%

Profile stiffness measurements in the Helically Symmetric experiment and comparison to nonlinear gyrokinetic calculationsa)

et al. 2015

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Stiffness measurements are presented in the quasi-helically symmetric experiment (HSX), in which the neoclassical transport is comparable to that in a tokamak and turbulent transport dominates throughout the plasma. Electron cyclotron emission is used to measure the local electron temperature response to modulated electron cyclotron resonant heating. The amplitude and phase of the heat wave through the steep electron temperature gradient (ETG) region of the plasma are used to determine a transient electron thermal diffusivity that is close to the steady-state diffusivity. The low stiffness in the region between 0.2 r/a 0.4 agrees with the scaling of the steady-state heat flux with temperature gradient in this region. These experimental results are compared to gyrokinetic calculations in a flux-tube geometry using the gyrokinetic electromagnetic numerical experiment code with two kinetic species. Linear simulations show that the ETG mode may be experimentally relevant within r/a 0.2, while the Trapped Electron Mode (TEM) is the dominant long-wavelength microturbulence instability across most of the plasma. The TEM is primarily driven by the density gradient. Non-linear calculations of the saturated heat flux driven by the TEM and ETG bracket the experimental heat flux. V C 2015 AIP Publishing LLC.

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“…To analyze these small amplitude, randomly occurring propagating temperature fluctuations, traditional heat pulse analysis techniques (correlation, conditional averaging [32]) do not offer sufficient clarity: the correlation tends to smear out the information over the typical duration of the heat pulses, while the conditional averaging technique tends to offer poor statistics due to the necessity to clearly identify individual (relatively large) events. For this reason, we turn to a technique from the field of Information Theory [33] that was recently applied for the first time in the context of fusion plasmas [34]: the Transfer Entropy.…”

Section: Transfer Entropymentioning

confidence: 99%

The impact of rational surfaces on radial heat transport in TJ-II

Nicolau¹,

Garcia²,

Carreras³

et al. 2017

Nucl. Fusion

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In this work, we study the outward propagation of temperature perturbations. For this purpose, we apply an advanced analysis technique, the Transfer Entropy, to ECE measurements performed in ECR heated discharges at the low-shear stellarator TJ-II. We observe that the propagation of these perturbations is not smooth, but is slowed down at specific radial positions, near 'trapping zones' characterized by long time lags with respect to the perturbation origin. We also detect instances of rapid or instantaneous (non-local) propagation, in which perturbations appear to 'jump over' specific radial regions.The analysis of perturbations introduced in a resistive Magneto-Hydrodynamic model of the plasma leads to similar results. The radial regions corresponding to slow radial transport are identified with maxima of the flow shear associated with rational surfaces (mini-transport barriers). The non-local interactions are ascribed to MHD mode coupling effects.

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Heat wave experiments on TJ-II flexible heliac

Cited by 38 publications

References 20 publications

Dynamic Simulation of the Electron Bernstein Wave Heating Under NBI Conditions in TJ–II Plasmas

Dynamic Simulation of the Electron Bernstein Wave Heating Under NBI Conditions in TJ–II Plasmas

Profile stiffness measurements in the Helically Symmetric experiment and comparison to nonlinear gyrokinetic calculationsa)

The impact of rational surfaces on radial heat transport in TJ-II

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