Magnetic configuration scans during divertor operation of Wendelstein 7-X

Andreeva, T.; Geiger, J.; Dinklage, A.; Wurden, G. A.; Thomsen, H.; Schmitt, J. C.; Hirsch, M.; Fuchert, G.; Nührenberg, C.; Alonso, A.; Beidler, C. D.; Beurskens, M.; Bozhenkov, S.; Brakel, R.; Brandt, C.; Bykov, V.; Grahl, M.; Grulke, O.; Killer, C.; Kocsis, G.; Klinger, T.; Krämer‐Flecken, A.; Lazerson, S.; Otte, M.; Pablant, N.; Schilling, J.; Windisch, T.; Team, the W7-X

doi:10.1088/1741-4326/ac3f1b

Cited by 15 publications

(12 citation statements)

References 37 publications

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“…During the configuration scan the location of the 5/5 magnetic island chain was moved inside the last closed flux surface, and the island size was varied by changing the control coil current. For these magnetic configuration scan experiments, it has already been reported that the plasma energy increased for the configurations where the 5/5 island chain is close to the plasma boundary but still inside the last close flux surface [5]. However, the reason behind the improved confinement for certain configuration from the scan is not fully understood yet.…”

Section: Introductionmentioning

confidence: 94%

“…At the start of the magnetic configuration scan experiments specially for the configurations where the magnetic island chain was moved inside the plasma [5], it was observed from the ECE diagnostic that an electron pedestal develops during the plasma buildup phase. Figure 2 shows the ECE time traces for the plasma startup phase, and around 0.27 s in the discharge (marked in figure), it can be seen that the edge channels (lower than 1 keV) start to show change in electron temperature gradient and a transport barrier develops leading to the delayed increase in the core temperature.…”

Section: Electron Temperature Pedestalmentioning

confidence: 99%

“…Due to the low magnetic shear, it is possible to shape the separatrix by large islands constituting an island divertor [4]. During the operational campaign OP 1.2 of W7-X, a magnetic configuration scan was performed by varying the rotational transform with magnetic configurations between iota = 5/4 and iota = 5/5 at the boundary [5,6]. During the configuration scan the location of the 5/5 magnetic island chain was moved inside the last closed flux surface, and the island size was varied by changing the control coil current.…”

Section: Introductionmentioning

confidence: 99%

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Radial localization of electron temperature pedestal and ELM-like events using ECE measurements at Wendelstein 7-X

et al. 2023

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A magnetic configuration scan was performed at Wendelstein 7-X stellarator by varying the rotational transform to analyze the plasma confinement for magnetic configurations with different edge magnetic island locations and sizes. For the magnetic configurations, where the 5/5 island chain was moved inside the last closed flux surface, it was observed with electron cyclotron emission measurements that an electron temperature, Te, pedestal develops in the plasma buildup phase and followed by the edge localized mode (ELM)-like crashes. From the mapping of the island to the plasma radius from HINT equilibrium, it was found that the Te pedestal is formed at the island location on the high field side of the plasma. The ELM-like crashes occur at the location of the pedestal and the transport barrier is broken typically with an energy loss of 3-4% during a single ELM-like event. The frequency and the amplitude of the ELM-like crashes were observed to be changing with island size, plasma heating power and density. Additionally during the plasma decay, after the heating was switched-off, a transition to degraded plasma confinement state was observed with changed Te profile gradients, faster decay rate of diamagnetic energy, and increased H-alpha levels.

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Section: Introductionmentioning

confidence: 94%

Section: Electron Temperature Pedestalmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Radial localization of electron temperature pedestal and ELM-like events using ECE measurements at Wendelstein 7-X

et al. 2023

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“…Ignoring magnetic field errors and field line diffusion, field-lines launched within one island of the five islands in the 5/5 edge will never connect to any of the other islands. Through a combination of coil currents [8] and plasma currents (Pfirsch-Schlüter, bootstrap, ECCD, induced) it is possible to move the locations and affect the size of these 5/5 islands. For the purpose of the analysis here, only vacuum fields generated by coil currents were considered, however, the inclusion of plasma currents should be straightforward as the routines to perform field line following in stellarators with finite beta and net toroidal current already exist [9][10][11][12].…”

Section: Edge Islands In W7-xmentioning

confidence: 99%

Radial coordinate maps, radial vectors, and binormal vectors for 5/6, 5/5 and 5/4 edge island domains in W7-X

Schmitt¹,

Kriete²,

Andreeva³

et al. 2022

Plasma Phys. Control. Fusion

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The edge island domain in Wendelstein 7-X consists of divertor islands whose position coincide with the location of rational values of the rotational transform - ι ≈ ( 5 / 6 , 5 / 5 , 5 / 4 ) and surround the main confinement volume (the ‘main plasma’), providing the magnetic topology for an island divertor. The 5/5 edge consists of five individual islands that are unconnected. In contrast, a single island connects onto itself after 6 or 4 toroidal transits in the 5/6 or 5/4 edge, respectively. Many interesting phenomena are related to these islands and diagnostic analyses require a mapping from ‘laboratory’ or real space coordinates to the island coordinate system (ICS). A procedure is described here to calculate several scalar and vector quantities for closed island structures which can be utilized in fast interpolation schemes for inverse maps. For the 5/5 edge, a fixed-boundary vacuum (zero beta) magneto-hydrodynamic solution of the 5/5 island is found with the Variational Moments Equilibrium Code, VMEC. The solution is compatible with already existing routines which determine the radial and binormal vectors of VMEC solutions at arbitrary laboratory coordinates. VMEC does not support solutions for the 5/4 and 5/6 islands, but the radial and binormal vectors are available in a local 2D Fourier ICS.

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“…The different width may be attributed by the change of the magnetic curvature effect and/or the pressure profiles in the plasma edge region. It is observed that the plasma pressure is the highest in the FMM configuration, yielding an increase of the diamagnetic energy (W dia ) and confinement time [34,35].…”

Section: ⊥ Comparison In the Magnetic Configuration Scanmentioning

confidence: 99%

Application of the elliptic approximation model for the edge turbulence rotation measurement via the poloidal correlation reflectometer in Wendelstein 7-X

Han¹,

Krämer‐Flecken²,

Xiang³

et al. 2021

Nucl. Fusion

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The perpendicular velocity (v ⊥) of turbulence is measured by means of a hopping poloidal correlation reflectometer diagnostic for the study of turbulence rotation in the plasma edge region in Wendelstein 7-X. An elliptic approximation (EA) model is applied for calculating the space-time correlation in the edge region. The v ⊥ profile is compared in the high-ι (edge ι ≈ 1.2) and limiter (edge ι < 1) configurations. It is found that the v ⊥ gradient is inversely proportional to the heating power in the high-ι configuration, which could be attributed to the turbulence activities in the plasma edge. In the limiter configuration, the v ⊥ spike is observed near the island boundary, which is corresponded to the plasma current crash. In the standard configuration (edge ι ≈ 1), the v ⊥ profile in the island region distributes as a function of the perpendicular separation. With increasing of the plasma current, the island enlarges the size as is referred from the v ⊥ scope, accompanying with steepening of the v ⊥ gradient at the boundary of the island.

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Magnetic configuration scans during divertor operation of Wendelstein 7-X

Cited by 15 publications

References 37 publications

Radial localization of electron temperature pedestal and ELM-like events using ECE measurements at Wendelstein 7-X

Radial localization of electron temperature pedestal and ELM-like events using ECE measurements at Wendelstein 7-X

Radial coordinate maps, radial vectors, and binormal vectors for 5/6, 5/5 and 5/4 edge island domains in W7-X

Application of the elliptic approximation model for the edge turbulence rotation measurement via the poloidal correlation reflectometer in Wendelstein 7-X

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