Relationship between MHD events, magnetic resonances and transport barriers in TJ-II plasmas

López‐Bruna, D.; Ochando, M. A.; Löpez‐Fraguas, A.; Medina, F.; Ascasíbar, E.

doi:10.1088/0029-5515/53/7/073051

Cited by 15 publications

(17 citation statements)

References 40 publications

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“…At present, the rotational transform profiles of a given experiment have to be inferred from the theoretical expectations (e.g. vacuum rotational profiles, current diffusion) and MHD activity as measured with magnetic and radiation diagnostics [58] .…”

Section: Feedback Options For Magnetic Configuration Sweep Controlmentioning

confidence: 99%

Magnetic configuration sweep control in heliac type stellarators

Romero

Pacios²,

Peña³

et al. 2014

Nucl. Fusion

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A novel magnetic configuration sweep control system for the TJ-II Heliac device is described. The system is prepared to establish a reference for plasma, torus or vessel current while the coil configuration currents are swept during a single plasma discharge. It can also be run in a special simulation mode, which does not require powering the TJ-II device, intended for commissioning and experiment preparation purposes. Preliminary tests with the system have shown its ability to perform rotational transform scans while establishing a waveform for torus current independently, despite variable plasma conditions. This opens up new experimental possibilities to study the influence of rotational transform and shear independently.

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Section: Feedback Options For Magnetic Configuration Sweep Controlmentioning

confidence: 99%

Magnetic configuration sweep control in heliac type stellarators

Romero

Pacios²,

Peña³

et al. 2014

Nucl. Fusion

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“…However, the stability of ITB is a critical concern. A continuous growth of the m/n = 1/1 mode can lead to the collapse of ITB, especially when the minimum safety factor, q min , approaches to unity [5,6]. Furthermore, three-dimensional nonlinear magnetohydrodynamic (MHD) simulations within tokamak geometry suggest that an increase in β p might mitigate the saturation amplitude of such infernal-type m/n = 1/1 modes [7].…”

Section: Introductionmentioning

confidence: 99%

Observation of fast electron redistribution during saturated kink mode in high β

Xu,

Lin,

Mai

et al. 2024

Nucl. Fusion

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In the EAST tokamak, we have developed an internal transport barrier (ITB) high- confinement mode (H-mode) scenario characterized by dominant electron heating and centrally peaked electron temperature profiles, facilitated primarily through the combustion of lower hybrid current drive (LHCD) and electron cyclotron radio heating (ECRH). Hard X-ray (HXR) diagnostics reveal a marked increase in the population of fast electrons with energy from 30 keV to 80 keV, concurrent with augmented ECRH power during H-mode plasma operations. This surge in fast electron population precedes the formation of the electron temperature ITB (Te-ITB). Within the Te-ITB H-mode discharge, a mild and long-lived m/n=1/1 mode (where m and n denote the toroidal and poloidal mode numbers, respectively) emerges proximal to the ITB region. This mode precipitates a redistribution of fast electrons, contributing to an increase in the safety factor near the magnetic axis and thereby promoting the stability of the Te-ITB. Furthermore, we explore the influence of fast electrons on plasma pressure and examine the effects of ion cyclotron radio heating (ICRF) on the distribution of fast electrons. Strategies to maintain the m/n=1/1 mode at a moderate amplitude are also discussed, highlighting their significance in the sustained management of Te-ITB.

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“…ELM‐like events have also been observed in the heliotron LHD and the heliac TJ‐II. In the case of TJ‐II, such events are first seen in low‐density electron cyclotron resonance heated (ECRH) plasmas (average electron density n e < 10 19 m −3 ) and later in NBI heated plasmas (1.5 × 10 19 m −3 < n e < 4 × 10 19 m −3 ) . For both heating modes in TJ‐II, it was found that the instability pivotal position is located near low‐order resonant (rational) magnetic surfaces, typically around iota central values of ι ≈ 1.5 (where iota, ι , is value of the rotational transform, which is the inverse of the safety factor, q , in tokamaks).…”

Section: Introductionmentioning

confidence: 99%

Discrete fast‐ion detection with energy discrimination in plasmas having edge‐localized mode‐like instabilities in the stellarator TJ‐II

Martínez

Zurro²,

Baciero³

et al. 2018

Contributions to Plasma Physics

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The existence of a population of ions, with energies well above the corresponding thermal values, in plasmas heated by neutral beam injection (NBI) in the stellarator TJ-II and in other magnetically confined plasmas devices is well known. Moreover, during the NBI phase of the TJ-II, edge-localized mode-like (ELM-like) instabilities often appear. This work studies the relationship between fast ions escaping from TJ-II plasmas and such ELM-like events. For this, an ion luminescent probe (LP), operated with a fast scintillator (decay time = 27 ns) and high-speed conditioning electronics (100 MHz), is used to measure, without pile-up effects, the energy distribution of suprathermal ions across the energy range, from 1 to 30 keV. It is found that the LP detects suprathermal ion populations that can be related to ELM-like events whose temperatures oscillate between 0.5 and 3 keV and that can be distinguished in a spectrogram of the LP response as an increase in frequencies from 15 to 150 kHz. Finally, observations of substructures within ELM-likes events, consisting of bursts of ions, with times between 5 and 15 μs are also reported. Such substructures have been observed previously in both tokamaks and stellarators in ion saturation current, high-speed camera images, etc. However, understanding the fast-ion component can provide new and relevant information about the behaviour of ions.

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Relationship between MHD events, magnetic resonances and transport barriers in TJ-II plasmas

Cited by 15 publications

References 40 publications

Magnetic configuration sweep control in heliac type stellarators

Magnetic configuration sweep control in heliac type stellarators

Observation of fast electron redistribution during saturated kink mode in high β

Discrete fast‐ion detection with energy discrimination in plasmas having edge‐localized mode‐like instabilities in the stellarator TJ‐II

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