Edge-localized-mode-like events in the TJ-II stellarator

Garcı́a-Cortés, I.; Luna, E. de la; Castejón, F.; Jiménez, Javier; Ascasíbar, E.; Brañas, B.; Estrada, T.; Herranz, J.; Löpez‐Fraguas, A.; Pastor, I.; Qin, Jie; Sánchez, J.; Tabarés, F.L.; Tafalla, D.; Tribaldos, V.; Zurro, B.; Team, Tj‐Ii; Shchepetov, S. V.

doi:10.1088/0029-5515/40/11/306

Cited by 36 publications

(36 citation statements)

References 10 publications

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“…These ELM-like bursts, however, frequently appear in LHD discharges without such an H-mode-like transition. A similar phenomenon to the ELM-like bursts is also observed in the W7-AS and the TJ-II stellarators [9][10][11]. In tokamaks the control of high-heat flux on divertor plates derived by the ELM is one of the key issues in the future reactor-grade experiment.…”

Section: Introductionsupporting

confidence: 58%

H-mode-like transition and ELM-like bursts in LHD with thick ergodic layer

et al. 2007

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In H2 discharges of large helical device (LHD), H-mode-like transition has been obtained with edge localized mode (ELM)-like bursts in an outwardly shifted configuration of R ax = 4.00 m with an extremely thick ergodic layer, where the ι/2π = 1 position is located in the middle of the ergodic layer. This H-mode-like transition can be triggered by changing P NBI (<12 MW) from 3 beams to 2 beams in a density range (4–8) × 1013 cm−3. The spontaneous H-mode-like transition is also observed during a stable discharge with constant heating power and density, where a steep edge pressure gradient is formed at the ι/2π = 1 position. The ELM-like bursts occurred in the ergodic layer accompanied with density bursts. It is found that the density bursts triggered at the ι/2π = 1 position in the ergodic layer instantaneously propagate outward beyond the ergodic layer with positive density pulse, and a few ms later also begin to propagate inward from the ergodic layer with negative density pulse to recover the previous edge density profile. In the case of He discharges no H-mode-like transition and ELM-like bursts are observed. The frequency of the ELM-like bursts increases with heating power, e.g. 50 Hz (3 MW)–100 Hz (5 MW) at n e = 4 × 1013 cm−3. The external resonant magnetic field to generate a static m/n = 1/1 island inside the ergodic layer is supplied to the ELM-like bursts. It is also found that the externally supplied magnetic field makes a clear response even in the ergodic layer. As a result, the frequency of the ELM-like bursts decreases, e.g. from 60 to 45 Hz. The present study strongly indicates that those phenomena observed in LHD are quite different from the ones which have been observed in tokamaks until now.

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Section: Introductionsupporting

confidence: 58%

H-mode-like transition and ELM-like bursts in LHD with thick ergodic layer

et al. 2007

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“…The experimentally measured characteristics of the features associated to the observed transport events depend on the position of the resonance [27,28]. Examples are: fast transient drops of the electron temperature associated to the 3/2 and 8/5 resonant surfaces close to the plasma centre [29]; or transient flattenings of the electron temperature profile (ELM-like events) associated to the presence of the 3/2 resonant surface in the density gradient region [30,31].…”

Section: Degraded Confinement Due To Low Order Resonances At Low βmentioning

confidence: 99%

Effect of Rotational Transform and Magnetic Shear on Confinement of Stellarators

Ascasíbar

López‐Bruna

Castejón

et al. 2008

Plasma and Fusion Research

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This work surveys the main results concerning the effects of the rotational transform, its low order rational values and its shear on the confining properties of low shear devices. It is meant to promote further studies aimed at clarifying their role in future, reactor grade, devices. 1-D transport studies are encouraged as the effects of rotational transform on confinement appear to be of local nature. Low order rational values of the rotational transform are associated with both degraded and improved confinement, being the magnetic shear a plausible cause for the difference. Very small shear values are enough to avoid deletereous effects of the low order rationals in high rotational transform discharges, but further experiments are needed to elucidate whether there is a threshold shear that depends on the rotational transform itself.

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“…These two cases correspond approximately to the ECRH operation regimes described in Refs. [35,36] and where the net current was measured. Unfortunately, it was not possible to use these experimental results directly since not all necessary pro- files were available (ion temperature and Z ef f profiles) or were not available with the required accuracy for all radii (edge electron density and temperature).…”

Section: Resultsmentioning

confidence: 99%

“…The results obtained are consistent with the neoclassical ordering since the radial electric field is small enough to neglect radial momentum transport effects (even for the lowest collisionality and the central electron root E r R/ ιv i th rB is below 0.2) and the ion parallel flow is small compared with the ion thermal velocity, j i /q i n i v i th < 0.3. It is difficult to compare the bootstrap current values obtained with the net currents measured during ECRH operation, ranging from -0.5 to -1. kA 35,36 since on the one hand experimental values might be influenced by ECCD and on the other hand because of the sensitivity of the total current on the edge profiles and the Z = 1 value. Nevertheless, neoclassical estimations have the same current sign and are less than a factor of two larger than the experimental measurements.…”

Section: Resultsmentioning

confidence: 99%