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Title: "BAAE" instabilities observed without fast ion drive

Abstract

The instability that was previously identified as a fast-ion driven beta-induced Alfv´en-acoustic eigenmode (BAAE) in DIII-D was misidentified. In a dedicated experiment, low frequency modes (LFM) with characteristic “Christmas light” patterns of brief instability linked to the safety factor evolution occur in plasmas with electron temperature Te ≳ 2.1 keV but modest beta. To isolate the importance of different driving gradients on these modes, the electron cyclotron heating power and 80 keV, sub-Alfv´enic neutral beams are altered for 50-100 ms durations in reproducible discharges. Although beta-induced Alfv´en eigenmodes and reversed-shear Alfv´en eigenmodes stabilize when beam injection ceases (as expected for a fast-ion driven instability), the low frequency modes that were called BAAEs persist. Data mining reveals that characteristic LFM instabilities can occur in discharges with no beam heating but strong electron cyclotron heating. A large database of over 1000 discharges shows that LFMs are only unstable in plasmas with hot electrons but modest overall beta. The experimental LFMs have low frequencies (comparable to diamagnetic drift frequencies) in the plasma frame, occur near the minimum of the safety factor qmin, and appear when qmin is close to rational values. In conclusion, theoretical analysis suggests that the LFMs are a low frequencymore » reactive instability of predominately Alfv´enic polarization.« less

Authors:
ORCiD logo [1]; ORCiD logo [2];  [3]; ORCiD logo [4];  [5]; ORCiD logo [1];  [6];  [1];  [7]; ORCiD logo [8]
  1. Univ. of California, Irvine, CA (United States)
  2. General Atomics, San Diego, CA (United States)
  3. Univ. of Texas, Austin, TX (United States)
  4. Rokkasho Fusion Inst., Aomori (Japan)
  5. Univ. of California, Irvine, CA (United States); Zhejiang Univ., Hangzhou (China)
  6. Max Planck Inst. for Plasma Physics, Garching (Germany)
  7. Univ. of Wisconsin, Madison, WI (United States)
  8. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
General Atomics, San Diego, CA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1706625
Alternate Identifier(s):
OSTI ID: 1777705
Grant/Contract Number:  
FC02-04ER54698; SC0020337; AC05-00OR22725
Resource Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 61; Journal Issue: 1; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Heidbrink, William W., Van Zeeland, Michael A., Austin, Max E., Bierwage, Andreas, Chen, Liu, Choi, Gyungjin, Lauber, Philipp, Lin, Zhihong, McKee, George R., and Spong, Donald A.. "BAAE" instabilities observed without fast ion drive. United States: N. p., 2020. Web. https://doi.org/10.1088/1741-4326/abc4c3.
Heidbrink, William W., Van Zeeland, Michael A., Austin, Max E., Bierwage, Andreas, Chen, Liu, Choi, Gyungjin, Lauber, Philipp, Lin, Zhihong, McKee, George R., & Spong, Donald A.. "BAAE" instabilities observed without fast ion drive. United States. https://doi.org/10.1088/1741-4326/abc4c3
Heidbrink, William W., Van Zeeland, Michael A., Austin, Max E., Bierwage, Andreas, Chen, Liu, Choi, Gyungjin, Lauber, Philipp, Lin, Zhihong, McKee, George R., and Spong, Donald A.. Thu . ""BAAE" instabilities observed without fast ion drive". United States. https://doi.org/10.1088/1741-4326/abc4c3.
@article{osti_1706625,
title = {"BAAE" instabilities observed without fast ion drive},
author = {Heidbrink, William W. and Van Zeeland, Michael A. and Austin, Max E. and Bierwage, Andreas and Chen, Liu and Choi, Gyungjin and Lauber, Philipp and Lin, Zhihong and McKee, George R. and Spong, Donald A.},
abstractNote = {The instability that was previously identified as a fast-ion driven beta-induced Alfv´en-acoustic eigenmode (BAAE) in DIII-D was misidentified. In a dedicated experiment, low frequency modes (LFM) with characteristic “Christmas light” patterns of brief instability linked to the safety factor evolution occur in plasmas with electron temperature Te ≳ 2.1 keV but modest beta. To isolate the importance of different driving gradients on these modes, the electron cyclotron heating power and 80 keV, sub-Alfv´enic neutral beams are altered for 50-100 ms durations in reproducible discharges. Although beta-induced Alfv´en eigenmodes and reversed-shear Alfv´en eigenmodes stabilize when beam injection ceases (as expected for a fast-ion driven instability), the low frequency modes that were called BAAEs persist. Data mining reveals that characteristic LFM instabilities can occur in discharges with no beam heating but strong electron cyclotron heating. A large database of over 1000 discharges shows that LFMs are only unstable in plasmas with hot electrons but modest overall beta. The experimental LFMs have low frequencies (comparable to diamagnetic drift frequencies) in the plasma frame, occur near the minimum of the safety factor qmin, and appear when qmin is close to rational values. In conclusion, theoretical analysis suggests that the LFMs are a low frequency reactive instability of predominately Alfv´enic polarization.},
doi = {10.1088/1741-4326/abc4c3},
journal = {Nuclear Fusion},
number = 1,
volume = 61,
place = {United States},
year = {2020},
month = {12}
}

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