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Title: Axisymmetric global Alfvén eigenmodes within the ellipticity-induced frequency gap in the Joint European Torus

Abstract

Alfvén eigenmodes (AEs) with toroidal mode number n = 0 (i.e., axisymmetric) have been observed in the ellipticity-induced frequency range in the Joint European Torus. The axisymmetric modes are of interest because they can be used to diagnose fast particle energy distributions at the mode location. The modes were identified here as global Alfvén eigenmodes (GAEs), with the ellipticity of the plasma cross-section preventing strong continuum damping of the modes. The MHD codes CSCAS, MISHKA, and AEGIS were used to compute the n = 0 Alfvén continuum, eigenmode structure, and continuum damping. For zero ellipticity, a single mode exists at a frequency below the Alfvén continuum branch. This mode has two dominant poloidal harmonics with poloidal mode numbers m = ±1 that have the same polarity; therefore, it is an even mode. For finite ellipticity, the continuum branch splits into two branches and the single GAE splits into two modes. An even mode exists below the minimum of the top continuum branch, and the frequency of this mode coincides with the experimentally observed AE frequency. The other mode is found below the lower continuum branch with opposite signs between the two poloidal harmonics (an odd mode structure). This mode wasmore » not excited in our experiment. Analytical theory for the n = 0 GAE in an elliptical cylinder shows the n = 0 Alfvén continuum agrees with the numerical modelling.« less

Authors:
 [1];  [2];  [3]; ORCiD logo [3]
  1. Univ. of Texas, Austin, TX (United States). Inst. for Fusion Studies; Culham Science Centre, Abingdon (United Kingdom). Culham Centre for Fusion Energy (CCFE)
  2. Culham Science Centre, Abingdon (United Kingdom). Culham Centre for Fusion Energy (CCFE)
  3. Univ. of Texas, Austin, TX (United States). Inst. for Fusion Studies
Publication Date:
Research Org.:
Univ. of Texas, Austin, TX (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
Contributing Org.:
JET Contributors
OSTI Identifier:
1523265
Alternate Identifier(s):
OSTI ID: 1412628
Grant/Contract Number:  
FG02-04ER54742; AC02-05CH11231
Resource Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 24; Journal Issue: 12; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Oliver, H. J. C., Sharapov, S. E., Breizman, B. N., and Zheng, L. -J. Axisymmetric global Alfvén eigenmodes within the ellipticity-induced frequency gap in the Joint European Torus. United States: N. p., 2017. Web. doi:10.1063/1.5005939.
Oliver, H. J. C., Sharapov, S. E., Breizman, B. N., & Zheng, L. -J. Axisymmetric global Alfvén eigenmodes within the ellipticity-induced frequency gap in the Joint European Torus. United States. doi:10.1063/1.5005939.
Oliver, H. J. C., Sharapov, S. E., Breizman, B. N., and Zheng, L. -J. Mon . "Axisymmetric global Alfvén eigenmodes within the ellipticity-induced frequency gap in the Joint European Torus". United States. doi:10.1063/1.5005939. https://www.osti.gov/servlets/purl/1523265.
@article{osti_1523265,
title = {Axisymmetric global Alfvén eigenmodes within the ellipticity-induced frequency gap in the Joint European Torus},
author = {Oliver, H. J. C. and Sharapov, S. E. and Breizman, B. N. and Zheng, L. -J.},
abstractNote = {Alfvén eigenmodes (AEs) with toroidal mode number n = 0 (i.e., axisymmetric) have been observed in the ellipticity-induced frequency range in the Joint European Torus. The axisymmetric modes are of interest because they can be used to diagnose fast particle energy distributions at the mode location. The modes were identified here as global Alfvén eigenmodes (GAEs), with the ellipticity of the plasma cross-section preventing strong continuum damping of the modes. The MHD codes CSCAS, MISHKA, and AEGIS were used to compute the n = 0 Alfvén continuum, eigenmode structure, and continuum damping. For zero ellipticity, a single mode exists at a frequency below the Alfvén continuum branch. This mode has two dominant poloidal harmonics with poloidal mode numbers m = ±1 that have the same polarity; therefore, it is an even mode. For finite ellipticity, the continuum branch splits into two branches and the single GAE splits into two modes. An even mode exists below the minimum of the top continuum branch, and the frequency of this mode coincides with the experimentally observed AE frequency. The other mode is found below the lower continuum branch with opposite signs between the two poloidal harmonics (an odd mode structure). This mode was not excited in our experiment. Analytical theory for the n = 0 GAE in an elliptical cylinder shows the n = 0 Alfvén continuum agrees with the numerical modelling.},
doi = {10.1063/1.5005939},
journal = {Physics of Plasmas},
number = 12,
volume = 24,
place = {United States},
year = {2017},
month = {12}
}

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