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Title: Density perturbation mode structure of high frequency compressional and global Alfvén eigenmodes in the National Spherical Torus Experiment using a novel reflectometer analysis technique

Reflectometry measurements of compressional (CAE) and global (GAE) Alfvén eigenmodes are analyzed to obtain the amplitude and spatial structure of the density perturbations associated with the modes. A novel analysis technique developed for this purpose is presented. The analysis also naturally yields the amplitude and spatial structure of the density contour radial displacement, which is found to be 2–4 times larger than the value estimated directly from the reflectometer measurements using the much simpler 'mirror approximation'. The modes were driven by beam ions in a high power (6 MW) neutral beam heated H-mode discharge (#141398) in the National Spherical Torus Experiment. The results of the analysis are used to assess the contribution of the modes to core energy transport and ion heating. Here, the total displacement amplitude of the modes, which is shown to be larger than previously estimated, is compared to the predicted threshold for the anomalously high heat diffusion inferred from transport modeling in similar NSTX discharges. The results of the analysis also have strong implications for the energy transport via coupling of CAEs to kinetic Alfvén waves seen in simulations with the Hybrid MHD code. Lastly, the amplitudes of the observed CAEs fall well below the thresholdmore » for causing significant ion heating by stochastic velocity space diffusion.« less
Authors:
ORCiD logo [1] ;  [1] ;  [1] ;  [1] ;  [2] ;  [2] ;  [2] ;  [2] ;  [3]
  1. Univ. of California, Los Angeles, CA (United States)
  2. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  3. Columbia Univ., New York, NY (United States)
Publication Date:
Grant/Contract Number:
AC02-09CH11466; FG02-99ER54527; SC0011810
Type:
Published Article
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 58; Journal Issue: 1; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Research Org:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Alfvén; eigenmodes; energetic ions; plasma heating; plasma transport; wave-particle interactions; reflectometry
OSTI Identifier:
1437750
Alternate Identifier(s):
OSTI ID: 1464645

Crocker, N. A., Kubota, S., Peebles, W. A., Rhodes, T. L., Fredrickson, E. D., Belova, E., Diallo, A., LeBlanc, B. P., and Sabbagh, S. A.. Density perturbation mode structure of high frequency compressional and global Alfvén eigenmodes in the National Spherical Torus Experiment using a novel reflectometer analysis technique. United States: N. p., Web. doi:10.1088/1741-4326/aa953e.
Crocker, N. A., Kubota, S., Peebles, W. A., Rhodes, T. L., Fredrickson, E. D., Belova, E., Diallo, A., LeBlanc, B. P., & Sabbagh, S. A.. Density perturbation mode structure of high frequency compressional and global Alfvén eigenmodes in the National Spherical Torus Experiment using a novel reflectometer analysis technique. United States. doi:10.1088/1741-4326/aa953e.
Crocker, N. A., Kubota, S., Peebles, W. A., Rhodes, T. L., Fredrickson, E. D., Belova, E., Diallo, A., LeBlanc, B. P., and Sabbagh, S. A.. 2017. "Density perturbation mode structure of high frequency compressional and global Alfvén eigenmodes in the National Spherical Torus Experiment using a novel reflectometer analysis technique". United States. doi:10.1088/1741-4326/aa953e.
@article{osti_1437750,
title = {Density perturbation mode structure of high frequency compressional and global Alfvén eigenmodes in the National Spherical Torus Experiment using a novel reflectometer analysis technique},
author = {Crocker, N. A. and Kubota, S. and Peebles, W. A. and Rhodes, T. L. and Fredrickson, E. D. and Belova, E. and Diallo, A. and LeBlanc, B. P. and Sabbagh, S. A.},
abstractNote = {Reflectometry measurements of compressional (CAE) and global (GAE) Alfvén eigenmodes are analyzed to obtain the amplitude and spatial structure of the density perturbations associated with the modes. A novel analysis technique developed for this purpose is presented. The analysis also naturally yields the amplitude and spatial structure of the density contour radial displacement, which is found to be 2–4 times larger than the value estimated directly from the reflectometer measurements using the much simpler 'mirror approximation'. The modes were driven by beam ions in a high power (6 MW) neutral beam heated H-mode discharge (#141398) in the National Spherical Torus Experiment. The results of the analysis are used to assess the contribution of the modes to core energy transport and ion heating. Here, the total displacement amplitude of the modes, which is shown to be larger than previously estimated, is compared to the predicted threshold for the anomalously high heat diffusion inferred from transport modeling in similar NSTX discharges. The results of the analysis also have strong implications for the energy transport via coupling of CAEs to kinetic Alfvén waves seen in simulations with the Hybrid MHD code. Lastly, the amplitudes of the observed CAEs fall well below the threshold for causing significant ion heating by stochastic velocity space diffusion.},
doi = {10.1088/1741-4326/aa953e},
journal = {Nuclear Fusion},
number = 1,
volume = 58,
place = {United States},
year = {2017},
month = {12}
}