Scaling trends of the critical <i>E</i>  ×  <i>B</i> shear for edge harmonic oscillation onset in DIII-D quiescent H-mode plasmas

Wilks, Theresa; Garofalo, A. M.; Diamond, P. H.; Guo, Zhifang; Hughes, J.W.; Burrell, K.H.; Chen, Xi

doi:10.1088/1741-4326/aad143

Cited by 26 publications

(28 citation statements)

References 26 publications

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“…The E × B shearing rate estimated as ω E /∆ ∼ ω A (order of MHz) is in line with the results of Ref. [45]. Finally we point out that the ω E stabilisation mechanism is independent of mode coupling.…”

Section: Is the Ion Mass) Are The Plasma Mhd And Ion Diamagnetic Velosupporting

confidence: 91%

Excitation Mechanism of Low- n Edge Harmonic Oscillations in Edge Localized Mode-Free, High Performance, Tokamak Plasmas

et al. 2019

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The excitation mechanism for low-n Edge Harmonic Oscillations in quiescent H-mode regimes is identified analytically. We show that the combined effect of diamagnetic and poloidal MHD flows, with the constraint of a Doppler-like effect of the ion flow, leads to the stabilisation of short wavelength modes, allowing lown perturbation to grow. The analysis, performed in tokamak toroidal geometry, includes the effects of large edge pressure gradients, associated with the local flattening of the safety factor and diamagnetic flows, sheared parallel and E × B rotation and a vacuum region between plasma and the ideal metallic wall. The separatrix also is modelled analytically.

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Section: Is the Ion Mass) Are The Plasma Mhd And Ion Diamagnetic Velosupporting

confidence: 91%

Excitation Mechanism of Low- n Edge Harmonic Oscillations in Edge Localized Mode-Free, High Performance, Tokamak Plasmas

et al. 2019

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“…This behaviour is reminiscent of other ‘limit cycle oscillations’ (or LCOs) in plasma such as edge harmonic oscillation (EHO) that is present owing to the action of an instability (the kink-peeling instability) in the presence of a sheared rotation (in this case the rotation), see, for example, Wilks et al. (2018).…”

Section: Resultsmentioning

confidence: 85%

“…These additional simulations also show that the period of the oscillation is controlled by the near-heteroclinic nature of the solution -as B is increased the period increases as the solution spends increasing amount of time near the invariant low vorticity state. This behaviour is reminiscent of other 'limit cycle oscillations' (or LCOs) in plasma such as edge harmonic oscillation (EHO) that is present owing to the action of an instability (the kink-peeling instability) in the presence of a sheared rotation (in this case the E × B rotation), see, for example, Wilks et al (2018).…”

Section: Resultsmentioning

confidence: 86%

Joint instability and abrupt nonlinear transitions in a differentially rotating plasma

2019

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Global magnetohydrodynamic (MHD) instabilities are investigated in a computationally tractable two-dimensional model of the solar tachocline. The model's differential rotation yields stability in the absence of a magnetic field, but if a magnetic field is present, a joint instability is observed. We analyze the nonlinear development of the instability via fully nonlinear direct numerical simulation, the generalized quasilinear approximation (GQL), and direct statistical simulation (DSS) based upon low-order expansion in equaltime cumulants. As the magnetic diffusivity is decreased, the nonlinear development of the instability becomes more complicated until eventually a set of parameters are identified that produce a previously unidentified long-term cycle in which energy is transformed from kinetic energy to magnetic energy and back. We find that the periodic transitions, which mimic some aspects of solar variability-for example, the quasiperiodic seasonal exchange of energy between toroidal field and waves or eddies-are unable to be reproduced when eddy-scattering processes are excluded from the model.

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“…Its formation and stability are crucial to high-confinement mode operation of fusion devices, e.g., the International Thermonuclear Experimental Reactor. However, a narrow edge can support either hazardous low-frequency magnetohydrodynamics (MHD) instabilities [2], i.e., edge localized mode or benign high-frequency edge harmonic oscillations (EHOs) [3][4][5]. It is a challenging problem to address the physical mechanism of which type of edge MHD phenomena will be excited in such a narrow layer.…”

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confidence: 99%

Curvature of Radial Electric Field Aggravates Edge Magnetohydrodynamics Mode in Toroidally Confined Plasmas

2020

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We show that the radial electric field (E r ) plays a dual role in edge magnetohydrodynamics (MHD) activity. While E r shear (first spatial derivative of E r ) dephases radial velocity and displacement, and so is stabilizing, a new finding here is that E r curvature (second spatial derivative of E r ) tends to synchronize the radial velocity and displacement, and so destabilizes MHD. As a highlighted result, we analytically demonstrate that E r curvature can destabilize an otherwise stable kink mode, and so form a joint vortexkink mode. The synergetic effects of E r shear and E r curvature in edge MHD extend the familiar E × B shearing paradigm. This theory thus explains the experimental findings that a deeper E × B well may aggravate edge MHD, and so trigger the formation of the edge harmonic oscillation. A simple criterion linking E r structure and the edge MHD activity is derived.

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Scaling trends of the critical E × B shear for edge harmonic oscillation onset in DIII-D quiescent H-mode plasmas

Cited by 26 publications

References 26 publications

Excitation Mechanism of Low- n Edge Harmonic Oscillations in Edge Localized Mode-Free, High Performance, Tokamak Plasmas

Excitation Mechanism of Low- n Edge Harmonic Oscillations in Edge Localized Mode-Free, High Performance, Tokamak Plasmas

Joint instability and abrupt nonlinear transitions in a differentially rotating plasma

Curvature of Radial Electric Field Aggravates Edge Magnetohydrodynamics Mode in Toroidally Confined Plasmas

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