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Title: Properties of toroidal Alfvén eigenmode in DIII-D plasma

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Publication Date:
Sponsoring Org.:
OSTI Identifier:
Grant/Contract Number:
AC02-05CH11231; AC05-00OR22725
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 22; Journal Issue: 2; Related Information: CHORUS Timestamp: 2016-12-26 04:26:25; Journal ID: ISSN 1070-664X
American Institute of Physics
Country of Publication:
United States

Citation Formats

Wang, Zhixuan, Lin, Zhihong, Deng, Wenjun, Holod, Ihor, Heidbrink, W. W., Xiao, Y., Zhang, H., Zhang, W., and Van Zeeland, M. Properties of toroidal Alfvén eigenmode in DIII-D plasma. United States: N. p., 2015. Web. doi:10.1063/1.4908274.
Wang, Zhixuan, Lin, Zhihong, Deng, Wenjun, Holod, Ihor, Heidbrink, W. W., Xiao, Y., Zhang, H., Zhang, W., & Van Zeeland, M. Properties of toroidal Alfvén eigenmode in DIII-D plasma. United States. doi:10.1063/1.4908274.
Wang, Zhixuan, Lin, Zhihong, Deng, Wenjun, Holod, Ihor, Heidbrink, W. W., Xiao, Y., Zhang, H., Zhang, W., and Van Zeeland, M. 2015. "Properties of toroidal Alfvén eigenmode in DIII-D plasma". United States. doi:10.1063/1.4908274.
title = {Properties of toroidal Alfvén eigenmode in DIII-D plasma},
author = {Wang, Zhixuan and Lin, Zhihong and Deng, Wenjun and Holod, Ihor and Heidbrink, W. W. and Xiao, Y. and Zhang, H. and Zhang, W. and Van Zeeland, M.},
abstractNote = {},
doi = {10.1063/1.4908274},
journal = {Physics of Plasmas},
number = 2,
volume = 22,
place = {United States},
year = 2015,
month = 2

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1063/1.4908274

Citation Metrics:
Cited by: 4works
Citation information provided by
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  • Linear properties of the toroidal Alfvén eigenmode (TAE) excited by energetic particles (EP) in a DIII-D tokamak experiment have been studied in global gyrokinetic particle simulations treating self-consistently kinetic effects of EP, thermal ions, and electrons. Simulation results of the TAE frequency and mode structure agree very well with the experimental measurements. The non-perturbative EP contribution induces a radial localization of the TAE mode structure, a break-down of mode radial symmetry, as well as a frequency dependence on the toroidal mode number. The simulations further demonstrate the dependence of the growth rate and mode structure on EP pressure gradients. Themore » in-out asymmetry of the mode structure and the experimental identification of the poloidal harmonics have also been clarified.« less
  • 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 resultmore » in a frequency up-shift 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.« less
  • Recent upgrades to many of the diagnostic systems on DIII-D (Luxon J.L. 2002 Nucl. Fusion 42 614), such as the CO 2 interferometer, far-infrared scattering, beam-emission spectroscopy (BES), and quadrature reflectometer, have significantly extended their capabilities and made possible the experimental study of Alfvén eigenmodes (AEs) through observation of the AE induced density perturbation. Measurements have shown the presence of several different classes of AEs in DIII-D discharges, including the toroidal Alfvén eigenmode (TAE), reverse shear AE (RSAE or Alfvén cascade), and ellipticity induced Alfvén eigenmode. Based on a simple model for the RSAE frequency, a sensitive diagnostic for themore » evolution of the minimum magnetic safety factor (q min) is presented. Results are compared with motional Stark effect (MSE) measurements. Strong localization of high toroidal mode number RSAEs to regions near the minimum of the magnetic safety factor is exhibited on the CO 2 interferometer and BES measurements. Based on this observation, a method for providing constraints on the radial location of q min is demonstrated and a favourable comparison to MSE measurements is made. Detailed measurements of TAEs using a new all-digital large bandwidth two-colour CO 2 interferometer system reveal a strong asymmetry between vertical and radial viewing interferometer chords, confirming previously reported results. Additionally, effects related to line-integrated observations are clearly illustrated by comparison to local BES measurements. Potential issues related to this are discussed.« less
  • Here, a recent DIII-D experiment investigating the impact of electron cyclotron heating (ECH) on neutral beam driven reversed shear Alfvén eigenmode (RSAE) activity is presented. The experiment includes variations of ECH injection location and timing, current ramp rate, beam injection geometry (on/off-axis), and neutral beam power. Essentially all variations carried out in this experiment were observed to change the impact of ECH on AE activity significantly. In some cases, RSAEs were observed to be enhanced with ECH near the off-axis minimum in magnetic safety factor (more » $${{q}_{\min}}$$ ), in contrast to the original DIII-D experiments where the modes were absent when ECH was deposited near $${{q}_{\min}}$$ . It is found that during intervals when the geodesic acoustic mode (GAM) frequency at $${{q}_{\min}}$$ is elevated and the calculated RSAE minimum frequency, including contributions from thermal plasma gradients, is very near or above the nominal TAE frequency (f TAE), RSAE activity is not observed or RSAEs with a much reduced frequency sweep range are found. This condition is primarily brought about by ECH modification of the local electron temperature (T e) which can raise both the local T e at $${{q}_{\min}}$$ as well as its gradient. A q-evolution model that incorporates this reduction in RSAE frequency sweep range is in agreement with the observed spectra and appears to capture the relative balance of TAE or RSAE-like modes throughout the current ramp phase of over 38 DIII-D discharges. Detailed ideal MHD calculations using the NOVA code show both modification of plasma pressure and pressure gradient at $${{q}_{\min}}$$ play an important role in modifying the RSAE activity. Analysis of the ECH injection near the $${{q}_{\min}}$$ case where no frequency sweeping RSAEs are observed shows the typical RSAE is no longer an eigenmode of the system. What remains is an eigenmode with poloidal harmonic content reminiscent of the standard RSAE, but absent of the typical frequency sweeping behavior. The remaining eigenmode is also often strongly coupled to gap TAEs. Analysis with the non-perturbative gyro fluid code TAEFL confirms this change in RSAE activity and also shows a large drop in the resultant mode growth rates.« less