Sawtooth pacing with on-axis ICRH modulation in JET-ILW

Lerche, E.; Lennholm, M.; Carvalho, I.; Dumortier, P.; Durodié, F.; Eester, D. Van; Graves, J. P.; Jacquet, P.; Murari, A.

doi:10.1051/epjconf/201715703029

Cited by 5 publications

(8 citation statements)

References 32 publications

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“…A second typology of test has been performed, aimed at investigating the causality horizon [ 26 , 27 , 28 , 29 ], i.e., the maximum time interval into which two physical quantities are synchronized and in which one observable can be thought as the “drive mechanism” of the second observable, for periodic and quasiperiodic signals of the same nature as those encountered in real experiments in thermonuclear scenarios [ 30 , 31 ]. In this kind of experiment, particular instabilities of the plasma, with potential harmful effects on the machine integrity, are paced by triggering them frequently enough that they do not have time to become dangerous for either the performance or safety of the reactor.…”

Section: Numerical Tests: Causality Horizonmentioning

confidence: 99%

“…Besides practical implementation difficulties, the evaluation of the pacing efficiency is difficult because the instabilities are quasi periodic, and therefore after a perturbation induced by the control systems, if enough time is allowed to pass, they are bound to reoccur. Typical pacing techniques are the injection of frozen deuterium pellets for controlling ELM instabilities [ 31 ] or ICRH power modulation for the control of sawtooth instabilities [ 30 ]. The latter experiment has been considered in this paper, by means of a simple synthetic model.…”

Section: Numerical Tests: Causality Horizonmentioning

confidence: 99%

“…A delay of 50 samples has been added to the fastest sawteeth function with respect to the square wave, then the two have been summed as shown in Figure 6 . The resulting time series are meant to simulate the modulation of a fast (paced) sawtooth by a square wave modulation in presence of a slower (natural) sawtooth behavior [ 30 , 31 ].…”

Section: Numerical Tests: Causality Horizonmentioning

confidence: 99%

See 2 more Smart Citations

A Refinement of Recurrence Analysis to Determine the Time Delay of Causality in Presence of External Perturbations

Peluso

Murari

2020

Entropy

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This article describes a refinement of recurrence analysis to determine the delay in the causal influence between a driver and a target, in the presence of additional perturbations affecting the time series of the response observable. The methodology is based on the definition of a new type of recurrence plots, the Conditional Joint Recurrence plot. The potential of the proposed approach resides in the great flexibility of recurrence plots themselves, which allows extending the technique to more than three quantities. Autoregressive time series, both linear and nonlinear, with different couplings and percentage of additive Gaussian noise have been investigated in detail, with and without outliers. The approach has also been applied to the case of synthetic periodic signals, representing realistic situations of synchronization experiments in thermonuclear fusion. The results obtained have been very positive; the proposed Conditional Joint Recurrence plots have always managed to identify the right interval of the causal influences and are very competitive with alternative techniques such as the Conditional Transfer Entropy.

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Section: Numerical Tests: Causality Horizonmentioning

confidence: 99%

Section: Numerical Tests: Causality Horizonmentioning

confidence: 99%

Section: Numerical Tests: Causality Horizonmentioning

confidence: 99%

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A Refinement of Recurrence Analysis to Determine the Time Delay of Causality in Presence of External Perturbations

Peluso

Murari

2020

Entropy

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“…A need for control of the sawtooth instability is also anticipated in ITER, in order to avoid long period sawteeth with large amplitude crashes that could trigger an NTM instability [23], and several schemes using ECCD or ICRF heating have been proposed [24]. Recent JET experiments have shown that the sawtooth period can be controlled with low field side ICRF heating (as will be available in ITER) near the q=1 surface [25], and that sawtooth pacing can be achieved with modulated central ion cyclotron heating [26], a method that is less sensitive to the deposition location. Further work is needed to validate ICRF sawtooth control in ITER-relevant H-mode discharges.…”

Section: Plasma Configuration Controlmentioning

confidence: 99%

Progress in disruption prevention for ITER

Strait¹,

Barr²,

Baruzzo³

et al. 2019

Nucl. Fusion

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Key plasma physics and real-time control elements needed for robustly stable operation of high fusion power discharges in ITER have been demonstrated in US fusion research. Optimization of the current density profile has enabled passively stable operation without n " 1 tearing modes in discharges simulating ITER's baseline scenario with zero external torque. Stable rampdown of the discharge has been achieved with ITER-like scaled current ramp rates, while maintaining an X-point configuration. Significant advances have been made toward real-time prediction of disruptions: machine learning techniques for prediction of disruptions have achieved 90% accuracy in offline analysis, and direct probing of ideal and resistive plasma stability using 3D magnetic perturbations has shown a rising plasma response before the onset of a tearing mode. Active stability control contributes to prevention of disruptions, including direct stabilization of resistive-wall kink modes in high-β discharges, forced rotation of magnetic islands to prevent wall locking, and localized heating/current drive to shrink the islands. These elements are being integrated into stable operating scenarios and a new event-handling system for off-normal events in order to develop the physics basis and techniques for robust control in ITER.

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“…In the case of ELMs, the periodic injection of small frozen pellets of fusion fuel into the plasma edge at high frequency is a very promising solution [ 2 ]. The modulation of the Ion Cyclotron Radiofrequency Heating (ICRH) power has proven to be an efficient solution for sawteeth pacing, reducing the fast ion component, which has a stabilizing effect [ 3 ]. Pellets and ICRH notches represent time localized perturbations of the natural evolution of the plasma, with a clear causal direction.…”

Section: Introductionmentioning

confidence: 99%

Image-Based Methods to Investigate Synchronization between Time Series Relevant for Plasma Fusion Diagnostics

Murari

Lerche

Gelfusa

et al. 2020

Entropy

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Advanced time series analysis and causality detection techniques have been successfully applied to the assessment of synchronization experiments in tokamaks, such as Edge Localized Modes (ELMs) and sawtooth pacing. Lag synchronization is a typical strategy for fusion plasma instability control by pace-making techniques. The major difficulty, in evaluating the efficiency of the pacing methods, is the coexistence of the causal effects with the periodic or quasi-periodic nature of the plasma instabilities. In the present work, a set of methods based on the image representation of time series, are investigated as tools for evaluating the efficiency of the pace-making techniques. The main options rely on the Gramian Angular Field (GAF), the Markov Transition Field (MTF), previously used for time series classification, and the Chaos Game Representation (CGR), employed for the visualization of large collections of long time series. The paper proposes an original variation of the Markov Transition Matrix, defined for a couple of time series. Additionally, a recently proposed method, based on the mapping of time series as cross-visibility networks and their representation as images, is included in this study. The performances of the method are evaluated on synthetic data and applied to JET measurements.

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Sawtooth pacing with on-axis ICRH modulation in JET-ILW

Cited by 5 publications

References 32 publications

A Refinement of Recurrence Analysis to Determine the Time Delay of Causality in Presence of External Perturbations

A Refinement of Recurrence Analysis to Determine the Time Delay of Causality in Presence of External Perturbations

Progress in disruption prevention for ITER

Image-Based Methods to Investigate Synchronization between Time Series Relevant for Plasma Fusion Diagnostics

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