Electromagnetic ELM and inter-ELM filaments detected in the COMPASS Scrape-Off Layer

Spolaore, M.; Kovařík, K.; Ştöckel, J.; Adámek, Jiřı́; Dejarnac, R.; Ďuran, I.; Komm, M.; Markovič, T.; Martines, E.; Pánek, R.; Seidl, J.; Vianello, N.

doi:10.1016/j.nme.2016.12.014

Cited by 20 publications

(23 citation statements)

References 18 publications

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“…The parallel current density exhibits both positive and negative oscillation throughout the time window, which is a signature of a multipolar structure. Similar behaviour has been observed within an ELM-cycle in the COMPASS tokamak [72]. The maximum parallel current density estimated by conditional averaging blobs in L and H-mode are |δj L | ≈ 0.04 kA/m 2 and |δj H | ≈ 0.1 kA/m 2 , respectively.…”

Section: Filaments: Magnetic Fluctuationssupporting

confidence: 79%

Turbulent filament properties in L and H-mode regime in the RFX-mod operating as a tokamak

et al. 2020

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The dynamics of turbulent filaments in L and ELM-free H-mode in the RFX-mod device operating as a tokamak is discussed in the present work. L-H transition and sustained H-mode have been achieved in the RFX-mod with the aid of an external electrode biasing (M. Spolaore et al. 2017 Nucl. Fusion 57 116039). Through advanced statistical techniques, turbulent filaments are detected and tracked from the edge to the Scrape-Off Layer (SOL) in a two-dimension floating potential map (measured with a 2D array of Langmuir probes) related with extreme events of a fixed ion saturation current signal in the SOL. While in L-mode filaments travel almost freely, their motion becomes restricted to the near SOL during the induced biasing H-mode. In this region, the background shear decorrelation time becomes shorter than the convective filament time, favouring its suppression. However, the experimental observation of a nearly 'trapped' monopole potential points out the possible role of the vortex selection mechanism. The sign and magnitude of the turbulent parallel vorticity are consistent with the E × B background vorticity in the SOL in this regime, while in L-mode, the inferred turbulent vorticity is always above the background one. The sparse filamentary transport in the far SOL during H-mode is further confirmed from the measurements of a poloidally symmetric array of electrostatic sensors on the wall. Lastly, the radial velocity of filaments in both regimes was discussed in the framework of analytical scalings. Filaments in L-mode exhibit a reasonable agreement with the sheath-limited regime in the cold ion approximation, with a non-negligible associated parallel current density measured with a set of 3-axial pickup coils installed in the probe head. In H-mode, the collisionality increases near the separatrix while filaments seem to follow the inertial regime before becoming trapped.

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Section: Filaments: Magnetic Fluctuationssupporting

confidence: 79%

Turbulent filament properties in L and H-mode regime in the RFX-mod operating as a tokamak

et al. 2020

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“…It is difficult to decide whether the current within the filaments is monopolar, bipolar or even composite from our measurements, except for the observations that the hodograph seems like a highly skewed ellipse. Similar results have been observed in recent studies [14]. The significant change in the direction of B r indicates that filaments have swept across the probes in the radial direction, implying that v r is at least comparable with the poloidal velocity v .…”

Section: Magnetic Fluctuationssupporting

confidence: 90%

Combined Langmuir-magnetic probe measurements of type-I ELMy filaments in the EAST tokamak

Yang

Zhong

et al. 2018

Plasma Sci. Technol.

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Detailed investigations on the filamentary structures associated with the type-I edge-localized modes (ELMs) should be helpful for protecting the materials of a plasma-facing wall on a future large device. Related experiments have been carefully conducted in the Experimental Advanced Superconducting Tokamak (EAST) using combined Langmuir-magnetic probes. The experimental results indicate that the radially outward velocity of type-I ELMy filaments can be up to 1.7 km s −1 in the far scrape-off layer (SOL) region. It is remarkable that the electron temperature of these filaments is detected to be ∼50 eV, corresponding to a fraction of 1/6 to the temperature near the pedestal top, while the density 3 10 m 19 3´-() of these filaments could be approximate to the line-averaged density. In addition, associated magnetic fluctuations have been clearly observed at the same time, which show good agreement with the density perturbations. A localized current on the order of ∼100 kA could be estimated within the filaments.

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“…These observations confirm also the electromagnetic (EM) features of the observed structures as expected for ELMs [23]. In particular they are current filaments as observed in the ELM structures in the COMPASS experiment [24], and for turbulence filaments as well [25,22]. Bursty behavior of ω t (t) and δJ t , correlated with D α peaks, are observed in the Fig.…”

Section: Transient Events During H-modesupporting

confidence: 85%

H-mode achievement and edge features in RFX-mod tokamak operation

Spolaore¹,

Cavazzana²,

Marrelli³

et al. 2017

Nucl. Fusion

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The RFX-Mod experiment is a fusion device designed to operate as a Reversed Field Pinch (RFP), with a major radius R " 2 m and a minor radius a " 0.459 m. Its high versatility recently allowed operating also as an ohmic tokamak allowing comparative studies between the two configurations in the same device. The device is equipped with a state of the art MHD mode feedback control system, providing a magnetic boundary effective control and modulation, by applying resonant or nonresonant magnetic perturbations (MP) both in RFP and in tokamak configurations. In the fusion community the application of MPs is widely studied as a promising tool in particular to limit the impact of plasma filaments and ELMs, in particular on plasma facing components. An important issue is envisaged in the exploitation of the RFX-Mod active control system for ELM mitigation studies.As a first step in this direction, this paper will focus on the most recent achievements in term of RFX-Mod tokamak explored scenarios, which allowed the first investigation of the ohmic and edge biasing induced H-mode. In particular the realization of D-shaped tokamak discharges and the design and deployment of an insertable polarized electrode were accomplished. Both operations took advantage of the implementation of a real-time feedback control system of the electron density and of a multivariable shape feedback control system designed on a full modelbased approach. Indications of Ohmic H-mode were transiently observed during Single Null shaped plasmas. Stationary H-mode phases were instead obtained with insertable electrode biasing stimulation. The edge biasing is applied in new operation scenarios relatively unexplored with this technique in particular in plasma shaped Single Null discharges and in the very low-q circular plasma discharges, qpaq ă 2, achievable in RFX-Mod. Important modification of the edge plasma density and flow properties are observed as well as, in some cases, a complex "dithering" phenomenology, characterized by very fast L-H and H-L transitions. These strong fluctuations appear associated to the onset of MHD activity, whose behaviour will be analyzed and discussed in the paper along with the filamentary structures observed in the fast turbulence electromagnetic fluctuations.Published as a journal article in Nuclear Fusion http://iopscience.iop.org/article/Abstract The RFX-mod experiment is a fusion device designed to operate as a Reversed Field Pinch (RFP), with a major radius R= 2 m and a minor radius a = 0.459 m. Its high versatility recently allowed operating also as an ohmic tokamak allowing comparative studies between the two configurations in the same device. The device is equipped with a state of the art MHD mode feedback control system, providing a magnetic boundary effective control, by applying resonant or non-resonant magnetic perturbations (MP) both in RFP and in tokamak configurations. In the fusion community the application of MPs is widely studied as a promising tool to limit the impact of plasma filaments and ELMs on p...

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Electromagnetic ELM and inter-ELM filaments detected in the COMPASS Scrape-Off Layer

Cited by 20 publications

References 18 publications

Turbulent filament properties in L and H-mode regime in the RFX-mod operating as a tokamak

Turbulent filament properties in L and H-mode regime in the RFX-mod operating as a tokamak

Combined Langmuir-magnetic probe measurements of type-I ELMy filaments in the EAST tokamak

H-mode achievement and edge features in RFX-mod tokamak operation

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