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Title: Numerical study on wave-induced beam ion prompt losses in DIII-D tokamak

Abstract

A numerical study is performed on the coherent beam ion prompt losses driven by Alfven eigenmodes (AEs) in DIII-D plasmas using realistic parameters and beam ion deposition profiles. The synthetic signal of a fast-ion loss detector (FILD) is calculated for a single AE mode. The first harmonic of the calculated FILD signal is linearly proportional to the AE amplitude with the same AE frequency in agreement with the experimental measurement. The calculated second harmonic is proportional to the square of the first harmonic for typical AE amplitudes. The coefficient of quadratic scaling is found to be sensitive to the AE mode width. The second part of this work considers the AE drive due to coherent prompt loss. As a result, it is shown that the loss-induced mode drive is much smaller than the previous estimate and can be ignored for mode stability.

Authors:
 [1];  [1]; ORCiD logo [2];  [3];  [4]
  1. Zhejiang Univ., Hangzhou (China)
  2. Zhejiang Univ., Hangzhou (China); Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  3. Univ. of California, Irvine, CA (United States)
  4. General Atomics, San Diego, CA (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) (SC-24)
OSTI Identifier:
1398341
Grant/Contract Number:
AC02-09CH11466; FC02-04ER54698
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 24; Journal Issue: 8; 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; toroidal Alfven eigenmodes

Citation Formats

Feng, Zhichen, Zhu, Jia, Fu, Guo -Yong, Heidbrink, W. W., and Van Zeeland, M. A.. Numerical study on wave-induced beam ion prompt losses in DIII-D tokamak. United States: N. p., 2017. Web. doi:10.1063/1.5000073.
Feng, Zhichen, Zhu, Jia, Fu, Guo -Yong, Heidbrink, W. W., & Van Zeeland, M. A.. Numerical study on wave-induced beam ion prompt losses in DIII-D tokamak. United States. doi:10.1063/1.5000073.
Feng, Zhichen, Zhu, Jia, Fu, Guo -Yong, Heidbrink, W. W., and Van Zeeland, M. A.. 2017. "Numerical study on wave-induced beam ion prompt losses in DIII-D tokamak". United States. doi:10.1063/1.5000073.
@article{osti_1398341,
title = {Numerical study on wave-induced beam ion prompt losses in DIII-D tokamak},
author = {Feng, Zhichen and Zhu, Jia and Fu, Guo -Yong and Heidbrink, W. W. and Van Zeeland, M. A.},
abstractNote = {A numerical study is performed on the coherent beam ion prompt losses driven by Alfven eigenmodes (AEs) in DIII-D plasmas using realistic parameters and beam ion deposition profiles. The synthetic signal of a fast-ion loss detector (FILD) is calculated for a single AE mode. The first harmonic of the calculated FILD signal is linearly proportional to the AE amplitude with the same AE frequency in agreement with the experimental measurement. The calculated second harmonic is proportional to the square of the first harmonic for typical AE amplitudes. The coefficient of quadratic scaling is found to be sensitive to the AE mode width. The second part of this work considers the AE drive due to coherent prompt loss. As a result, it is shown that the loss-induced mode drive is much smaller than the previous estimate and can be ignored for mode stability.},
doi = {10.1063/1.5000073},
journal = {Physics of Plasmas},
number = 8,
volume = 24,
place = {United States},
year = 2017,
month = 8
}

Journal Article:
Free Publicly Available Full Text
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  • A numerical model describing the expected measurements of neutral beam prompt-losses by a newly commissioned fast ion loss detector (FILD) in DIII-D is presented. This model incorporates the well understood neutral beam deposition profiles from all eight DIII-D beamlines to construct a prompt-loss source distribution. The full range of detectable ion orbit phase space available to the FILD is used to calculate ion trajectories that overlap with neutral beam injection footprints. Weight functions are applied to account for the level of overlap between these detectable orbits and the spatial and velocity (pitch) properties of ionized beam neutrals. An experimental comparisonmore » is performed by firing each neutral beam individually in the presence of a ramping plasma current. Fast ion losses determined from the model are in agreement with measured losses.« less
  • A new non-linear feature has been observed in fast-ion loss from tokamak plasmas in the form of oscillations at the sum, difference and second harmonic frequencies of two independent Alfvén eigenmodes (AEs). Full orbit calculations and analytic theory indicate this non-linearity is due to coupling of fast-ion orbital response as it passes through each AE — a change in wave-particle phase k • r by one mode alters the force exerted by the next. Furthermore, the loss measurement is of barely confined, non-resonant particles, while similar non-linear interactions can occur between well-confined particles and multiple AEs leading to enhanced fast-ionmore » transport.« less
  • The effect of the radial electric field on neoclassical orbits in a tokamak using the integrals of drift motion is considered. It is shown that for the most interesting case of high radial electric field shear, due to a dramatic change of the particle orbit topology at a distance of the order of one particle orbit width, it is not correct to apply local theory to describe neoclassical transport processes. For step-like electrostatic potentials typical for the tokamak plasma periphery in the high (H) mode, the trajectories of the particles can be either squeezed or expanded depending on the locationmore » of the potential jump with respect to the unperturbed particle trajectories. The widening of the orbits decreases the threshold energy of suprathermal particles which can be promptly lost and enhances the ion prompt losses which might increase the amplitude of the potential step. It is shown that these effects are more pronounced for a diverted tokamak with the X point located at the inner side of the torus. Simultaneous growth of prompt losses and potential magnitude might be the reason for the fast formation of the narrow electrostatic barrier during the low''-- high'' (L--H) transition. Toroidal plasma rotation induced by the radial electric field can strongly enhance the destabilizing effect of the step-like potential.« less