Double-Gap Alfvén Eigenmodes: Revisiting Eigenmode Interaction with the Alfvén Continuum

Gorelenkov, N. N.

doi:10.1103/physrevlett.95.265003

Cited by 15 publications

(23 citation statements)

References 11 publications

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“…They present all the features reported in Ref. [16] for so-called double-gap Alfvén eigenmodes, i.e. AEs that can tunnel through the continuum without discontinuities and couple to a different AE type that resides in an adjacent AE gap.…”

Section: /2mentioning

confidence: 52%

Properties of Alfven Eigenmodes in the TAE range on the National Spherical Torus Experiment-Upgrade

Author¹

2013

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A second Neutral Beam (NB) injection line is being installed on the NSTX Upgrade device, resulting in six NB sources with different tangency radii that will be available for heating and current drive. This work explores the properties of instabilities in the frequency range of the Toroidal Alfvén Eigenmode (TAE) for NSTX-U scenarios with various NB injection geometries, from more perpendicular to more tangential, and with increased toroidal magnetic field with respect to previous NSTX scenarios. Predictions are based on analysis through the ideal MHD code NOVA-K. For the scenarios considered in this work, modifications of the Alfvén continuum result in a frequency upshift and a broadening of the radial mode structure. The latter effect may have consequences for fast ion transport and loss. Preliminary stability considerations indicate that TAEs are potentially unstable, with ion Landau damping representing the dominant damping mechanism.

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Section: /2mentioning

confidence: 52%

Properties of Alfven Eigenmodes in the TAE range on the National Spherical Torus Experiment-Upgrade

Author¹

2013

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“…13,18 Damping was then calculated for the same case using CKA, which is a finite element code incorporating the resistive term found in Eq. (4).…”

Section: Comparison Of Perturbative and Resistive Methodsmentioning

confidence: 99%

“…The perturbative technique for computing continuum resonance damping has been applied in the ideal MHD code NOVA and the hybrid MHD/kinetic code NOVA-K. 13 Borba et al conducted a study comparing the results calculated by NOVA-K to the overall damping calculated by various MHD and gyro-kinetic codes with experiment. 12 This total damping had significant contributions from both continuum and radiative damping components.…”

Section: Introductionmentioning

confidence: 99%

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Comparison of methods for numerical calculation of continuum damping

et al. 2014

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Continuum resonance damping is an important factor in determining the stability of certain global modes in fusion plasmas. A number of analytic and numerical approaches have been developed to compute this damping, particularly in the case of the toroidicity-induced shear Alfv\'en eigenmode. This paper compares results obtained using an analytical perturbative approach with those found using resistive and complex contour numerical approaches. It is found that the perturbative method does not provide accurate agreement with reliable numerical methods for the range of parameters examined. This discrepancy exists even in the limit where damping approaches zero. When the perturbative technique is implemented using a standard finite element method, the damping estimate fails to converge with radial grid resolution. The finite elements used cannot accurately represent the eigenmode in the region of the continuum resonance, regardless of the number of radial grid points used.Comment: 19 pages, 9 figure

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“…Figure 1 (a) shows the difference between the continuum and the RSAE eigenfrequency with the continuum frequency 23.6kHz. The NOVA-K code is able to compute the continuum damping in a perturbative manner [15]. The continuum damping of RSAE computed using NOVA-K is given in Fig.…”

Section: Numerical Study Of the Pressure Gradient Effect On Rsaementioning

confidence: 99%

Interpretation of the Finite Pressure Gradient Effects in the Reversed Shear Alfv?n Eigenmode Theory

Kramer¹

2008

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Ideal MHD equations employed in the NOVA code are analyzed analytically and numerically in order to investigate the role of the pressure gradient on global reversed shear Alfvén eigenmodes (RSAEs) or Alfvén cascades. We confirm both numerically and analytically conclusions obtained earlier using the ideal MHD code NOVA [1] and analytically [2] that the plasma pressure gradient plays a key role in the existence condition and in the dispersion relation for the mode. The effect of the plasma pressure gradient is to shift the mode frequency up at the low part of the RSAE frequency chirp and downshift the mode frequency when the frequency approaches the TAE gap.This finding is opposite to predictions in a recent publication [3], where the pressure gradient is found to be always stabilizing by means of downshifting the RSAE frequency and enhancing its interaction with the continuum. We resolve this discrepancy by showing that neglecting the pressure gradient effect on the plasma equilibrium (modification of the Shafranov shift and the averaged curvature) leads to conclusions at variance to the numerical and analytical results presented here.A new variational approximation of the RSAE is introduced which compares remarkably well with NOVA solutions. With this new approximation we clearly demonstrate the diagnostic potential and limitations of the RSAE frequency measurement for MHD spectroscopy.

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Double-Gap Alfvén Eigenmodes: Revisiting Eigenmode Interaction with the Alfvén Continuum

Cited by 15 publications

References 11 publications

Properties of Alfven Eigenmodes in the TAE range on the National Spherical Torus Experiment-Upgrade

Properties of Alfven Eigenmodes in the TAE range on the National Spherical Torus Experiment-Upgrade

Comparison of methods for numerical calculation of continuum damping

Interpretation of the Finite Pressure Gradient Effects in the Reversed Shear Alfv?n Eigenmode Theory

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