Ham, C. J., Cowley, S. C., Brochard, G. et al. (1 more author) (2018) Nonlinear ballooning modes in tokamaks:stability and saturation. Plasma Physics and Controlled Fusion. 075017. ISSN 1361-6587
Abstract
The nonlinear dynamics of magneto-hydrodynamic ballooning mode perturbations is conjectured to be characterised by the motion of isolated elliptical flux tubes. The theory of stability, dynamics and saturation of such tubes in tokamaks is developed using a generalised Archimedes' principle. The equation of motion for a tube moving against a drag force in a general axisymmetric equilibrium is derived and then applied to a simplified 's-' equilibrium. The perturbed nonlinear tube equilibrium (saturated) states are investigated in an 's-α' equilibrium with specific pressure and magnetic shear profiles. The energy of these nonlinear (ballooning) saturated states is calculated. In some cases, particularly at low magnetic shear, these finitely displaced states can have a lower energy than the equilibrium state even if the profile is linearly stable to ballooning modes (infinitesimal tube displacements) at all radii. Thus nonlinear ballooning modes can be metastable. The amplitude of the saturated tube displacement in such cases can be as large as the pressure gradient scale length. We conjecture that triggering a transition into these filamentary states can lead to hard instability limits. A short survey of different pressure profiles is presented to illustrate the variety of behaviour of perturbed elliptical flux tubes.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2018 CCFE. 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. |
Keywords: | ballooning modes,filaments,nonlinear |
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: | 18 Oct 2018 09:50 |
Last Modified: | 23 Jan 2025 00:16 |
Published Version: | https://doi.org/10.1088/1361-6587/aac4fb |
Status: | Published |
Refereed: | Yes |
Identification Number: | 10.1088/1361-6587/aac4fb |
Related URLs: | |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:137348 |