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Title: Self-consistent perturbed equilibrium with neoclassical toroidal torque in tokamaks

Abstract

Toroidal torque is one of the most important consequences of non-axisymmetric fields in tokamaks. The well-known neoclassical toroidal viscosity (NTV) is due to the second-order toroidal force from anisotropic pressure tensor in the presence of these asymmetries. This work shows that the first-order toroidal force originating from the same anisotropic pressure tensor, despite having no flux surface average, can significantly modify the local perturbed force balance and thus must be included in perturbed equilibrium self-consistent with NTV. The force operator with an anisotropic pressure tensor is not self-adjoint when the NTV torque is finite and thus is solved directly for each component. This approach yields a modified, non-self-adjoint Euler-Lagrange equation that can be solved using a variety of common drift-kinetic models in generalized tokamak geometry. The resulting energy and torque integral provides a unique way to construct a torque response matrix, which contains all the information of self-consistent NTV torque profiles obtainable by applying non-axisymmetric fields to the plasma. This torque response matrix can then be used to systematically optimize non-axisymmetric field distributions for desired NTV profiles. Published by AIP Publishing.

Authors:
ORCiD logo [1]; ORCiD logo [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) (SC-24)
OSTI Identifier:
1377823
Alternate Identifier(s):
OSTI ID: 1348951
Grant/Contract Number:
AC02-76CH03073
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 24; Journal Issue: 3; 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; banana-drift transport; momentum dissipation; plasmas; stability

Citation Formats

Park, Jong-Kyu, and Logan, Nikolas C. Self-consistent perturbed equilibrium with neoclassical toroidal torque in tokamaks. United States: N. p., 2017. Web. doi:10.1063/1.4977898.
Park, Jong-Kyu, & Logan, Nikolas C. Self-consistent perturbed equilibrium with neoclassical toroidal torque in tokamaks. United States. doi:10.1063/1.4977898.
Park, Jong-Kyu, and Logan, Nikolas C. Wed . "Self-consistent perturbed equilibrium with neoclassical toroidal torque in tokamaks". United States. doi:10.1063/1.4977898. https://www.osti.gov/servlets/purl/1377823.
@article{osti_1377823,
title = {Self-consistent perturbed equilibrium with neoclassical toroidal torque in tokamaks},
author = {Park, Jong-Kyu and Logan, Nikolas C.},
abstractNote = {Toroidal torque is one of the most important consequences of non-axisymmetric fields in tokamaks. The well-known neoclassical toroidal viscosity (NTV) is due to the second-order toroidal force from anisotropic pressure tensor in the presence of these asymmetries. This work shows that the first-order toroidal force originating from the same anisotropic pressure tensor, despite having no flux surface average, can significantly modify the local perturbed force balance and thus must be included in perturbed equilibrium self-consistent with NTV. The force operator with an anisotropic pressure tensor is not self-adjoint when the NTV torque is finite and thus is solved directly for each component. This approach yields a modified, non-self-adjoint Euler-Lagrange equation that can be solved using a variety of common drift-kinetic models in generalized tokamak geometry. The resulting energy and torque integral provides a unique way to construct a torque response matrix, which contains all the information of self-consistent NTV torque profiles obtainable by applying non-axisymmetric fields to the plasma. This torque response matrix can then be used to systematically optimize non-axisymmetric field distributions for desired NTV profiles. Published by AIP Publishing.},
doi = {10.1063/1.4977898},
journal = {Physics of Plasmas},
number = 3,
volume = 24,
place = {United States},
year = {Wed Mar 01 00:00:00 EST 2017},
month = {Wed Mar 01 00:00:00 EST 2017}
}

Journal Article:
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  • Established results of neoclassical kinetic theory are used in a fluid model to show that in low collisionality regimes ({nu} and 1/{nu}) the propagation velocity of Neoclassical Tearing Modes (NTM) magnetic islands of sufficient width is determined self-consistently by the Neoclassical Toroidal Viscosity (NTV) appearing because of broken symmetry. The NTV effect on bulk plasma rotation, may also explain recent observations on momentum transport. At the same time this affects the role of the neoclassical ion polarization current on neoclassical tearing modes (NTM) stability.
  • Bumpiness in a magnetic field enhances the magnitude of the plasma viscosity and increases the rate of the plasma flow damping. A general solution of the neoclassical toroidal plasma viscosity (NTV) torque induced by nonaxisymmetric magnetic perturbation (NAMP) in the collisionless regimes in tokamaks is obtained in this Letter. The plasma angular momentum can be strongly changed, when there is a small deviation of the toroidal symmetry caused by a NAMP of the order of 0.1% of the toroidal field strength.
  • It is shown that when tokamaks are perturbed, the kinetic energy principle is closely related to the neoclassical toroidal torque by the action invariance of particles. Especially when tokamaks are perturbed from scalar pressure equilibria, the imaginary part of the potential energy in the kinetic energy principle is equivalent to the toroidal torque by the neoclassical toroidal viscosity. A unified description therefore should be made for both physics. It is also shown in this case that the potential energy operator can be self-adjoint and thus the stability calculation can be simplified by minimizing the potential energy.
  • The presence of the magnetic stochasticity induced by resonant magnetic perturbations in fusion experiments leads to radial electron particle and heat diffusivities which are substantially different from quasilinear predictions. In this paper, using neoclassical simulation, the effects of the self-consistent electric field on the radial electron particle and heat transports are investigated. The presence of stochasticity produces positive contribution to the radial electric field, consistent with experimental observations. Bringing both radial and poloidal components of the electric field into the simulation might help recover some of the trends observed in the experiment and is currently under investigation.