Turbulence-reduced high-performance scenarios in Wendelstein 7-X

Ford, O. P.; Beurskens, M.; Bozhenkov, S. A.; Lazerson, S.; Vanó, L.; Alonso, A.; Baldzuhn, J.; Beidler, C. D.; Biedermann, C.; Burhenn, R.; Fuchert, G.; Hartmann, D.; Hirsch, M.; Langenberg, A.; Laqua, H.; McNeely, P.; Pablant, N.; Pasch, E.; Reimold, F.; Romba, T.; Rust, N.; Schroeder, R.; Scott, E. R.; Stange, T.; Smith, H. M.; Gradic, D.; Wolf, R. C.; Zhang, D.

doi:10.1088/1741-4326/ad5e99

Title: Turbulence-reduced high-performance scenarios in Wendelstein 7-X

Journal Article · Mon Jul 15 00:00:00 UTC 2024 · Nuclear Fusion

DOI: https://doi.org/10.1088/1741-4326/ad5e99 · OSTI ID:2426360

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Max Planck Institute for Plasma Physics, Greifswald (Germany)
Research Centre for Energy, Environment and Technology (CIEMAT), Madrid (Spain)
Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)

In the Wendelstein 7-X (W7-X) stellarator, turbulence is the dominant transport mechanism in most discharges. This leads to a 'clamping' of ion temperature over a wide range of heating power, predominantly flat density profiles where hollow profiles driven by neoclassical thermo-diffusion would be expected and by rapid impurity transport in injection experiments. Significantly reduced turbulent transport is observed in the presence of strong core density gradients found transiently after core pellet injection and irregularly after boronisation or boron pellet injection. Density peaking is also achieved in a controlled manner in purely neutral beam heated discharges where particle transport analysis reveals an abrupt reduction in the main-ion particle flux leading to significant density profile peaking not explained by the NBI particle source alone. The plasmas exhibit a heat diffusivity of around $$\chi = 0.25 \pm 0.1\,\mathrm{m}^2\ \mathrm{s}^{-1}$$ at mid radius, a factor of around 4 lower than ECRH dominated discharges. Despite the improved confinement, the achieved ion temperature is limited by broader heat deposition and the lower power-per-particle given the higher density. This is overcome with limited reintroduction of ECRH power, where the low heat diffusivity diffusivity is maintained, the density rise supressed and ion temperatures above the clamping limit are achieved. The applicability of these plasmas for a high performance scenario on transport relevant time scales is assessed, including initial predictions for planned heating upgrades of W7-X, based on a range of assumptions about particle transport.

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Research Organization:: Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)

Sponsoring Organization:: USDOE

Contributing Organization:: W7-X Team

Grant/Contract Number:: AC02-09CH11466

OSTI ID:: 2426360

Journal Information:: Nuclear Fusion, Journal Name: Nuclear Fusion Journal Issue: 8 Vol. 64; ISSN 0029-5515

Publisher:: IOP ScienceCopyright Statement

Country of Publication:: United States

Language:: English

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