Reciprocating probe measurements in the test divertor operation phase of Wendelstein 7-X

Killer, C.; Drews, P.; Grulke, O.; Knieps, A.; Nicolai, D.; Satheeswaren, Guruparan; Team, W X

doi:10.1088/1748-0221/17/03/p03018

Cited by 6 publications

(4 citation statements)

References 63 publications

(61 reference statements)

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“…4 % theoretically predicted in [35]), could actually correspond to tens of kW. Moreover, excitation of electrostatic daughter waves in the edge may generate supra-thermal populations of ions and/or electrons and consequently overheat and degrade plasma facing probes, as observed in the previous W7-X campaign [42]. As recently reported in ASDEX Upgrade [39], daughter microwaves excited by PDI may not only corrupt the measurements of such systems, but also overload and permanently damage the diagnostic hardware.…”

Section: Discussionmentioning

confidence: 77%

“…Parametrically driven daughter microwaves can also damage key components of microwavebased diagnostics [33] if these are not properly shielded. Finally, electrostatic daughter modes can interact with plasma populations and generate supra-thermal ion/electron populations [39,40], which, on the one hand, could potentially represent an auxiliary heating mechanism, while on the other hand, could degrade plasma facing probes [41,42]. A deeper understanding of low-threshold PDI in W7-X is, thus, not only essential to validate the current theoretical models for absolute instabilities in non-monotonic density profiles, but also to optimize the efficiency of microwave-based systems, essential components on the way to a burning fusion plasma.…”

Section: Introductionmentioning

confidence: 99%

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Inhibition of parametric decay in heating microwave beams during fluctuations of the density profile in the edge island of Wendelstein 7-X

Tancetti¹,

Nielsen²,

Rasmussen³

et al. 2022

Plasma Phys. Control. Fusion

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Experimental evidence of parametric decay instability (PDI) is observed in Wendelstein 7-X (W7-X) stellarator, when high-power microwave beams cross a stationary magnetic island in the plasma edge. Here, trapping and build-up of upper hybrid waves (UHWs) within a density bump (measured within the island by alkali beam emission spectroscopy, ABES) is responsible for the reduction of the instability power threshold below the maximum gyrotron power. In this paper, we provide first experimental evidence of the connection between the trapping mechanism in the island density bump and excitation of PDI-related signals. We show correlation of periodic crashes in the PDI-related signals with quasi-continuous fluctuations in the plasma edge, which, additionally, cause a flattening of the density profile in the island. We demonstrate that flattening of the experimental density profiles can suppress the trapping mechanism and inhibit the low-threshold PDI. PDI in the edge island could alter the power deposition profile and reduce the efficiency of the electron cyclotron resonance heating system, simultaneously posing a serious threat to the optimal operation of microwave-based diagnostics and plasma-facing components.

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Section: Discussionmentioning

confidence: 77%

Section: Introductionmentioning

confidence: 99%

Inhibition of parametric decay in heating microwave beams during fluctuations of the density profile in the edge island of Wendelstein 7-X

Tancetti¹,

Nielsen²,

Rasmussen³

et al. 2022

Plasma Phys. Control. Fusion

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“…We use ASCOT for this purpose. By way of example the fast-particle loads, caused by ICRH, on the multi-purpose manipulator (MPM) [17] as well as on the ICRH antenna are shown in Fig. 9 on the left-and right-hand side, respectively.…”

Section: Resultsmentioning

confidence: 99%

Simulation of radio-frequency heating and fast-ion generation in Wendelstein 7-X

Slaby

Machielsen

Lazerson

et al. 2022

J. Phys.: Conf. Ser.

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The next scientific operation phase of Wendelstein 7-X (W7-X) is scheduled to begin in late autumn of 2022 and will, for the first time, include experiments in which the ICRH (ion-cyclotron-resonance heating) antenna will be used. In addition to heating the plasma, this system will generate fast ions and thus offers a new way to assess fast-ion confinement in a stellarator such as W7-X. The first plasmas that will be used for the upcoming ICRH operation will be Helium-4 plasmas with a small Hydrogen minority on the order of about 10%. In tokamaks such plasmas typically offer good power absorption and are thus considered a safe way for gaining first experiences with the new antenna in W7-X. This assessment is confirmed by the SCENIC simulations carried out in this contribution that use profiles foreseen for the upcoming campaign as input. The simulations are carried out in the standard configuration of W7-X in low-beta (0.3% ≲ 〈β〉 ≲ 1%) plasmas. However, also scans over minority concentration and background-plasma density are performed. We find that the power absorbed by the Hydrogen minority directly from the radio-frequency wave is typically (provided that the minority concentration is not too high) on the order of about 90% with the rest going to the electrons. Very little power goes to the Helium-4 ions. Under the present simulation conditions only fast-ion energies up to about E ≈ 50 keV can be reached. Combining SCENIC and ASCOT simulations enables us to track lost particles through the scrape-off-layer to the 3D wall of W7-X and to compute wall loads caused by ICRH. The results show that the wall loads that can be expected from ICRH under the first operating conditions are benign.

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“…The second diagnostic used for comparison is the multipurpose manipulator (MPM). The MPM can be equipped with different probe heads to provide profiles of various plasma parameters such as T e , n e , poloidal mach number and more [24,25].…”

Section: W7-x Diagnosticsmentioning

confidence: 99%

Parametrisation of target heat flux distribution and study of transport parameters for boundary modelling in W7-X

et al. 2022

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Modelling the scrape-off layer of a stellarator is challenging due to the complex magnetic 3D geometry. The here presented study analyses simulations of the scrape-off layer (SOL) of the stellarator Wendelstein 7-X (W7-X) using the EMC3-EIRENE code for the magnetic standard configuration. Comparing with experimental observations, the transport model is validated. Based on the experimentally observed strike line width, the anomalous transport coefficients, used as input to the code are determined to around $0.2\,$m$^2/$s. This is however in disagreement with upstream measurements, where such small cross-field transport leads to temperatures higher than measured experimentally.

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Reciprocating probe measurements in the test divertor operation phase of Wendelstein 7-X

Cited by 6 publications

References 63 publications

Inhibition of parametric decay in heating microwave beams during fluctuations of the density profile in the edge island of Wendelstein 7-X

Inhibition of parametric decay in heating microwave beams during fluctuations of the density profile in the edge island of Wendelstein 7-X

Simulation of radio-frequency heating and fast-ion generation in Wendelstein 7-X

Parametrisation of target heat flux distribution and study of transport parameters for boundary modelling in W7-X

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