Determination of electron thermal diffusivity at the WEGA stellarator

Zhang, D.; Glaubitz, M.; Laqua, H. P.; Marsen, S.; Otte, M.; Stange, T.

doi:10.1088/0029-5515/52/4/043002

Cited by 6 publications

(3 citation statements)

References 19 publications

(49 reference statements)

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“…A thin carbon layer (50 nm thick) has been sputtered onto the absorber to improve the detection efficiency for low-energy photons. A significant reduction in the reflectivity of visible light (by a factor of more than 5) has been confirmed in the laboratory by comparing the detection efficiency with that of the non-blackened detectors [38,39]. The detectors are particularly sensitive to impurity line radiation, whose spectrum is mainly in the VUV and soft x-ray (SXR) range (300 nm to 0.2 nm).…”

Section: The Bolometer Diagnosticmentioning

confidence: 91%

Bolometer tomography on Wendelstein 7-X for study of radiation asymmetry

et al. 2021

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The algorithm for bolometer tomography at Wendelstein 7-X (W7-X) has been recently improved using a novel regularization functional, based on relative gradient smoothing of the sought radiation profile. It has been validated using radiation patterns provided by 3D modeling under real plasma conditions as phantoms and then applied to bolometer measurements performed during the first divertor operation phase of W7-X. The following results are presented: (1) edge-localized 2D radiation patterns with clearly resolved magnetic island radiation structures, (2) an up-down asymmetry in the impurity radiation that is not captured by the 3D edge plasma transport modeling, (3) reversal of the asymmetry with reversed magnetic field direction. Further analysis reveals a poloidal variation of the emissivity in the outer confined plasma region with a field-direction dependent asymmetry, also supported by the soft x-ray measurements. This asymmetry is considered to be related to asymmetric impurity distributions, driven by the pronounced ion-impurity friction force at the plasma edge where the collisionality of the W7-X plasma is sufficiently high to develop impurity asymmetry as predicted by neoclassical theory of parallel impurity transport.

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Section: The Bolometer Diagnosticmentioning

confidence: 91%

Bolometer tomography on Wendelstein 7-X for study of radiation asymmetry

et al. 2021

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“…This basic fact has important, but thus far unaddressed, implications for heat pulse based thermal diffusivity measurements. Such experiments have been widely conducted in magnetic confinement devices since the 1980s [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Yet, many aspects of heat transport in plasmas remain mysterious.…”

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confidence: 99%

“…The vast majority of heat pulse experiments have fallen in the high frequency/close to source regime, where effects from ion coupling are negligible. Occasionally, however, a driving frequency on the order of the equilibration rate [3,6,8,15,18,20] or even slower [11,13,14] is used. In this case, the apparent diffusivity can be significantly different (usually smaller) from the true electron diffusivity.…”

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confidence: 99%

Coupled heat pulse propagation in two fluid plasmas

Jin,

Reiman,

Fisch

2020

Preprint

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Because of the large mass differences between electrons and ions, the heat diffusion in electron-ion plasmas exhibits more complex behavior than simple heat diffusion found in typical gas mixtures. In particular, heat is diffused in two distinct, but coupled, channels. Conventional single fluid models neglect the resulting complexity, and can often inaccurately interpret the results of heat pulse experiments. However, by recognizing the sensitivity of the electron temperature evolution to the ion diffusivity, not only can previous experiments be interpreted correctly, but informative simultaneous measurements can be made of both ion and electron heat channels.

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