Zhu, Yi-Ren, Li, Ze-Yu, Chan, V et al. (7 more authors) (2020) Achieving a robust grassy-ELM operation regime in CFETR. Nuclear Fusion. 046014. ISSN 1741-4326
Abstract
We have identified a robust grassy-edge localized mode (ELM) operation regime for future tokamak reactors. The regime exists within a pedestal top electron collisionality (ν *) window at high global poloidal beta (β p). The existence of an upper ν * limit for grassy-ELMs is consistent with results previously reported in experiments (Oyama et al 2010 Nucl. Fusion 50 064014), while the existence of a lower ν * limit has not been reported previously. Using EPED and BOUT + +, a theoretical model that quantitatively explains the physics of the grassy-ELMs within the window, which distinguishes them from the small mixed-ELMs at lower ν *, is presented for the first time. A peeling-ballooning stability boundary is obtained by scanning the operating density space. The change in density corresponds to a change in ν * that affects the pedestal bootstrap current. High β p leads to a strong Shafranov shift, which affects the flux surface averaged pressure drive. The two effects combine to create a peeling-dominated window in intermediate ν * buffered by ballooning-dominated regimes. Only the peeling-dominated regime shows a cyclic behavior in the perturbed pressure during the nonlinear simulation of an ELM crash, reminiscent of grassy-ELM dynamics. Similarly, the energy released across the separatrix is demonstrated to be significantly smaller. The quick recovery of the ELM crash is explainable by the rapid rise of a low n kink-peeling instability when the pedestal current Iped exceeds a threshold at high β p. It minimizes the excursion beyond marginal stability and is absent in the ballooning-dominated regime. Comparison with recent experiments over a range of β p and ν * strongly supports the physical picture proposed by the modeling.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2020 IAEA, Vienna. This is an author-produced version of the published paper. Uploaded in accordance with the publisher’s self-archiving policy. Further copying may not be permitted; contact the publisher for details. |
Dates: |
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Institution: | The University of York |
Academic Units: | The University of York > Faculty of Sciences (York) > Physics (York) |
Depositing User: | Pure (York) |
Date Deposited: | 21 Apr 2020 15:20 |
Last Modified: | 16 Oct 2024 16:33 |
Published Version: | https://doi.org/10.1088/1741-4326/ab72c0 |
Status: | Published |
Refereed: | Yes |
Identification Number: | 10.1088/1741-4326/ab72c0 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:159698 |
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