Sawtooth control using electron cyclotron current drive in the presence of energetic particles in high performance ASDEX Upgrade plasmas

Chapman, I. T.; Igochine, V.; Maraschek, M.; McCarthy, Patrick J.; Tardini, G.

doi:10.1088/0741-3335/55/6/065009

Cited by 11 publications

(12 citation statements)

References 50 publications

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“…This heating setup allows for a modification of the sawtooth period [49] as well as of the MHD activity occurring in-between sawtooth crashes (figures 2 and 4), while keeping the sawtooth-averaged kinetic profiles as constant as possible (figure 5). The deposition position scan does not lead to any detectable change in the plasma energy (black in figure 2a) or in the total radiated power (blue in figure 2f).…”

Section: Description Of the Experimentsmentioning

confidence: 99%

Interplay between central ECRH and saturated (m,n) = (1, 1) MHD activity in mitigating tungsten accumulation at ASDEX Upgrade

2015

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A new method for the determination of 2D intrinsic tungsten density profiles in the presence of saturated MHD instabilities at ASDEX Upgrade is presented. For the first time the full decoupling of the impurity density from electron density and temperature contributions to experimental 2D SXR tomographic reconstructions in the presence of MHD can be performed. The analysis relies on a combination of SXR tomography with the reconstruction of 2D electron temperature profiles through harmonic decomposition of the 1D ECE electron temperature. The method is applicable to any saturated magnetic perturbation as long as the poloidal and toroidal mode numbers m and n are known, and if the concentration of the intrinsic tungsten is high enough to dominate the SXR signals. This method may help better understand the mitigation of tungsten accumulation by central ECRH which typically occurs in the presence of saturated (m, n) = (1, 1) MHD activity. The analysis of the evolution of the intrinsic tungsten density in a typical ASDEX Upgrade discharge with central ECRH and saturated (1, 1) modes is presented.

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Section: Description Of the Experimentsmentioning

confidence: 99%

Interplay between central ECRH and saturated (m,n) = (1, 1) MHD activity in mitigating tungsten accumulation at ASDEX Upgrade

2015

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“…In this paper, ECE measurements at a sample rate of 1 MHz are used and these measurements are filtered and downsampled. A set of five discharges (30538, 30543, 30550, 30552, and 31105) are chosen which are mostly performed for feedforward sawtooth control [37,25]. By looking at the ECE channels, time ranges are selected with different sawtooth characteristics.…”

Section: Ece Datasetsmentioning

confidence: 99%

A model-based, multichannel, real-time capable sawtooth crash detector

Brand

Baar

Berkel

et al. 2016

Plasma Phys. Control. Fusion

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Control of the time between sawtooth crashes, necessary for ITER and DEMO, requires real-time detection of the moment of the sawtooth crash. In this paper, estimation of sawtooth crash times is demonstrated using the model-based Interacting Multiple Model (IMM) estimator, based on simplified models for the sawtooth crash. In contrast to previous detectors, this detector uses the spatial extent of the sawtooth crash as detection characteristic. The IMM estimator is tuned and applied to multiple ECE channels at once. A model for the sawtooth crash is introduced, which is used in the IMM algorithm. The IMM algorithm is applied to 7 datasets from the ASDEX Upgrade tokamak. Five crash models with different mixing radii are used. All sawtooth crashes that have been identified beforehand by visual inspection of the data, are detected by the algorithm. A few additional detections are made, which upon closer inspection are seen to be sawtooth crashes, which show a partial reconnection. A closer inspection of the detected normal crashes shows that about 42 % are not well fitted by any of the full reconnection models and show some characteristics of a partial reconnection. In some case, the measurement time is during the sawtooth crashes, which also results in an incorrect estimate of the mixing radius. For data provided at a sampling rate of 1 kHz, the run time of the IMM estimator is below 1 ms, thereby fulfilling real-time requirements.

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“…In the first one, the population of fast particles in the core plasma is controlled using either NBI [28] or ICRH [29], thus modifying the stability of the internal kink mode and ultimately the sawtooth period. The second method relies on the use of external current-drive or heating in order to change the the current profile near the q = 1 surface, either by using external current-drive [30,31,32,33,34], or by modifying the temperature profile through localized heating so as to change the plasma resistivity and therefore the inductive current profile. This method has been demonstrated on several devices [23,26,27], and will likely be used in ITER [35], using the 20 MW EC system that is foreseen.…”

Section: Introductionmentioning

confidence: 99%

Non-linear MHD simulations of sawteeth and their control by current and power depositions

Février¹,

Nicolas²,

Maget³

et al. 2018

Nucl. Fusion

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Sawteeth in tokamak plasmas correspond to periodic relaxations of the temperature and density in the central region of the plasma, caused by the internal kink mode. They are a key player in core confinement and impurity transport in the central region of a tokamak discharge, and can trigger secondary instabilities. Being able to control their dynamics is therefore important. In this article, we explore by means of MHD simulations the control of sawteeth, relying on Electron Cyclotron Resonant Heating (ECRH) or Electron Cyclotron Current Drive (ECCD) deposition in the vicinity of the q = 1 surface. To do so, simulations with the full-MHD code XTOR-2F [1], which features power and current source terms mimicking the effects of ECCD and ECRH, are performed. Simulations show that deposition of current inside the inversion radius leads to an increase of the sawtooth frequency whereas deposition near or outside the inversion radius leads to a decrease of the sawtooth period. The modification of the sawtooth shape in presence of additional heating or current drive is also investigated. Finally, we briefly explore possible scenarios for the triggering of magnetic islands, and show that controlling the sawteeth can indeed help to prevent the triggering of tearing instabilities.

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Sawtooth control using electron cyclotron current drive in the presence of energetic particles in high performance ASDEX Upgrade plasmas

Cited by 11 publications

References 50 publications

Interplay between central ECRH and saturated (m,n) = (1, 1) MHD activity in mitigating tungsten accumulation at ASDEX Upgrade

Interplay between central ECRH and saturated (m,n) = (1, 1) MHD activity in mitigating tungsten accumulation at ASDEX Upgrade

A model-based, multichannel, real-time capable sawtooth crash detector

Non-linear MHD simulations of sawteeth and their control by current and power depositions

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