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Title: Destabilization of counter-propagating Alfvénic instabilities by tangential, co-current neutral beam injection

Abstract

Injection of high-energy neutrals is a common tool to heat the plasma and drive current non-inductively in fusion devices. Once neutrals ionize, the resulting energetic particles can drive instabilities that are detrimental for the performance and the predictability of plasma discharges. A broad deposition profile of neutrals from neutral beam injection, e.g. by aiming the beam tangentially on the outboard midplane (i.e. off-axis), is often assumed to limit those undesired effects by reducing the radial gradient of the EP density, thus reducing the drive for instabilities. However, this paper presents new evidence that tangential neutral beam injection, including off-axis injection near the plasma mid-radius, can also lead to undesired effects such as the destabilization of Alfvénic instabilities. Time-dependent analysis with the TRANSP code indicates that instabilities are driven by a combination of radial and energy gradients in the distribution function of the energetic particles. Finally, the mechanisms for wave-particle interaction revealed by the energetic particle phase space resolved analysis are the basis to identify strategies to mitigate or suppress the observed instabilities.

Authors:
ORCiD logo [1];  [1];  [1]
  1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES)
OSTI Identifier:
1459549
Grant/Contract Number:  
AC02-09CH11466
Resource Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 58; Journal Issue: 8; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Podesta, M., Fredrickson, E. D., and Gorelenkova, M. Destabilization of counter-propagating Alfvénic instabilities by tangential, co-current neutral beam injection. United States: N. p., 2018. Web. doi:10.1088/1741-4326/aab4ae.
Podesta, M., Fredrickson, E. D., & Gorelenkova, M. Destabilization of counter-propagating Alfvénic instabilities by tangential, co-current neutral beam injection. United States. doi:10.1088/1741-4326/aab4ae.
Podesta, M., Fredrickson, E. D., and Gorelenkova, M. Wed . "Destabilization of counter-propagating Alfvénic instabilities by tangential, co-current neutral beam injection". United States. doi:10.1088/1741-4326/aab4ae. https://www.osti.gov/servlets/purl/1459549.
@article{osti_1459549,
title = {Destabilization of counter-propagating Alfvénic instabilities by tangential, co-current neutral beam injection},
author = {Podesta, M. and Fredrickson, E. D. and Gorelenkova, M.},
abstractNote = {Injection of high-energy neutrals is a common tool to heat the plasma and drive current non-inductively in fusion devices. Once neutrals ionize, the resulting energetic particles can drive instabilities that are detrimental for the performance and the predictability of plasma discharges. A broad deposition profile of neutrals from neutral beam injection, e.g. by aiming the beam tangentially on the outboard midplane (i.e. off-axis), is often assumed to limit those undesired effects by reducing the radial gradient of the EP density, thus reducing the drive for instabilities. However, this paper presents new evidence that tangential neutral beam injection, including off-axis injection near the plasma mid-radius, can also lead to undesired effects such as the destabilization of Alfvénic instabilities. Time-dependent analysis with the TRANSP code indicates that instabilities are driven by a combination of radial and energy gradients in the distribution function of the energetic particles. Finally, the mechanisms for wave-particle interaction revealed by the energetic particle phase space resolved analysis are the basis to identify strategies to mitigate or suppress the observed instabilities.},
doi = {10.1088/1741-4326/aab4ae},
journal = {Nuclear Fusion},
number = 8,
volume = 58,
place = {United States},
year = {2018},
month = {3}
}

Journal Article:
Free Publicly Available Full Text
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Cited by: 1 work
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Figures / Tables:

Figure 1 Figure 1: (a) Spectrum of magnetic fluctuations measured by Mirnov coils. Counter-propagating modes are here shown with negative frequency. (b) Waveforms of plasma current (black) and injected NB power (red). (c) Time evolution of central electron density and temperature. (d) Evolution of central and edge values of the safety factor.more » (e) Electron density and temperature profiles at t = 350ms. The magnetic axis is at R ≈ 105 cm.« less

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