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Title: Evaluation of toroidal torque by non-resonant magnetic perturbations in tokamaks for resonant transport regimes using a Hamiltonian approach

Abstract

Toroidal torque generated by neoclassical viscosity caused by external non-resonant, non-axisymmetric perturbations has a significant influence on toroidal plasma rotation in tokamaks. In this article, a derivation for the expressions of toroidal torque and radial transport in resonant regimes is provided within quasilinear theory in canonical action-angle variables. The proposed approach treats all low-collisional quasilinear resonant neoclassical toroidal viscosity regimes including superbanana-plateau and drift-orbit resonances in a unified way and allows for magnetic drift in all regimes. It is valid for perturbations on toroidally symmetric flux surfaces of the unperturbed equilibrium without specific assumptions on geometry or aspect ratio. The resulting expressions are shown to match the existing analytical results in the large aspect ratio limit. Numerical results from the newly developed code NEO-RT are compared to calculations by the quasilinear version of the code NEO-2 at low collisionalities. The importance of the magnetic shear term in the magnetic drift frequency and a significant effect of the magnetic drift on drift-orbit resonances are demonstrated.

Authors:
; ; ; ;  [1];  [1];  [2]
  1. Fusion@ÖAW, Institut für Theoretische Physik - Computational Physics, Technische Universität Graz, Petersgasse 16, 8010 Graz (Austria)
  2. (Ukraine)
Publication Date:
OSTI Identifier:
22599890
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 23; Journal Issue: 8; Other Information: (c) 2016 EURATOM; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ASPECT RATIO; AXIAL SYMMETRY; COMPARATIVE EVALUATIONS; DISTURBANCES; EQUILIBRIUM; HAMILTONIANS; MAGNETIC SURFACES; NEOCLASSICAL TRANSPORT THEORY; PERTURBATION THEORY; PLASMA; QUASILINEAR PROBLEMS; TOKAMAK DEVICES; TORQUE; VISCOSITY

Citation Formats

Albert, Christopher G., Heyn, Martin F., Kapper, Gernot, Kernbichler, Winfried, Martitsch, Andreas F., Kasilov, Sergei V., and Institute of Plasma Physics, National Science Center “Kharkov Institute of Physics and Technology,” ul. Akademicheskaya 1, 61108 Kharkov. Evaluation of toroidal torque by non-resonant magnetic perturbations in tokamaks for resonant transport regimes using a Hamiltonian approach. United States: N. p., 2016. Web. doi:10.1063/1.4961084.
Albert, Christopher G., Heyn, Martin F., Kapper, Gernot, Kernbichler, Winfried, Martitsch, Andreas F., Kasilov, Sergei V., & Institute of Plasma Physics, National Science Center “Kharkov Institute of Physics and Technology,” ul. Akademicheskaya 1, 61108 Kharkov. Evaluation of toroidal torque by non-resonant magnetic perturbations in tokamaks for resonant transport regimes using a Hamiltonian approach. United States. doi:10.1063/1.4961084.
Albert, Christopher G., Heyn, Martin F., Kapper, Gernot, Kernbichler, Winfried, Martitsch, Andreas F., Kasilov, Sergei V., and Institute of Plasma Physics, National Science Center “Kharkov Institute of Physics and Technology,” ul. Akademicheskaya 1, 61108 Kharkov. 2016. "Evaluation of toroidal torque by non-resonant magnetic perturbations in tokamaks for resonant transport regimes using a Hamiltonian approach". United States. doi:10.1063/1.4961084.
@article{osti_22599890,
title = {Evaluation of toroidal torque by non-resonant magnetic perturbations in tokamaks for resonant transport regimes using a Hamiltonian approach},
author = {Albert, Christopher G. and Heyn, Martin F. and Kapper, Gernot and Kernbichler, Winfried and Martitsch, Andreas F. and Kasilov, Sergei V. and Institute of Plasma Physics, National Science Center “Kharkov Institute of Physics and Technology,” ul. Akademicheskaya 1, 61108 Kharkov},
abstractNote = {Toroidal torque generated by neoclassical viscosity caused by external non-resonant, non-axisymmetric perturbations has a significant influence on toroidal plasma rotation in tokamaks. In this article, a derivation for the expressions of toroidal torque and radial transport in resonant regimes is provided within quasilinear theory in canonical action-angle variables. The proposed approach treats all low-collisional quasilinear resonant neoclassical toroidal viscosity regimes including superbanana-plateau and drift-orbit resonances in a unified way and allows for magnetic drift in all regimes. It is valid for perturbations on toroidally symmetric flux surfaces of the unperturbed equilibrium without specific assumptions on geometry or aspect ratio. The resulting expressions are shown to match the existing analytical results in the large aspect ratio limit. Numerical results from the newly developed code NEO-RT are compared to calculations by the quasilinear version of the code NEO-2 at low collisionalities. The importance of the magnetic shear term in the magnetic drift frequency and a significant effect of the magnetic drift on drift-orbit resonances are demonstrated.},
doi = {10.1063/1.4961084},
journal = {Physics of Plasmas},
number = 8,
volume = 23,
place = {United States},
year = 2016,
month = 8
}
  • The toroidal torque driven by external non-resonant magnetic perturbations (neoclassical toroidal viscosity) is an important momentum source affecting the toroidal plasma rotation in tokamaks. The well-known force-flux relation directly links this torque to the non-ambipolar neoclassical particle fluxes arising due to the violation of the toroidal symmetry of the magnetic field. Here, a quasilinear approach for the numerical computation of these fluxes is described, which reduces the dimension of a standard neoclassical transport problem by one without model simplifications of the linearized drift kinetic equation. The only limiting condition is that the non-axisymmetric perturbation field is small enough such thatmore » the effect of the perturbation field on particle motion within the flux surface is negligible. Therefore, in addition to most of the transport regimes described by the banana (bounce averaged) kinetic equation also such regimes as, e.g., ripple-plateau and resonant diffusion regimes are naturally included in this approach. Based on this approach, a quasilinear version of the code NEO-2 [W. Kernbichler et al., Plasma Fusion Res. 3, S1061 (2008).] has been developed and benchmarked against a few analytical and numerical models. Results from NEO-2 stay in good agreement with results from these models in their pertinent range of validity.« less
  • By applying the principle of minimum free energy an analytical model for the plasma response to externally applied resonant magnetic perturbations (RMPs) is proposed. The results are compared with ATTEMPT code calculations [D. Reiser et al., Phys. Plasmas 16, 0042317 (2009)] and reproduce qualitatively and quantitatively the numerical results on the collisionality dependence of RMP penetration characteristics. Strong increase in the radial electric field with reduced screening at RMPs above a certain threshold is also reproduced by the model.
  • 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.
  • In divertor tokamak plasmas, an Edge Transport Barrier forms during the L-H transition. A poloidal shear flow has been shown to play a crucial role in the barrier sustainement. The H regime, obtained for a critical value of the heating power, is promising for the next generation of tokamak experiments such as ITER. However, an instability known as Edge Localized Mode (ELM) develops as the power is increased further. ELMs are characterized by intermittent bursts in the radial heat flux, therefore causing the transport barrier to relax quasi-periodically. Over the last decade, the possibility of controlling ELMs has become moremore » and more plausible, as recent experiments were carried out on DIII-D using I-coils, on JET using error field correction coils, and on TEXTOR using an ergodic divertor. These experimental studies demonstrate a qualitative control over the ELMs by imposing a magnetostatic perturbation at the plasma edge. However, in order to get any quantitative result, much work has to be done in the understanding of ELM dynamics. In this work, we present results from numerical simulations of Resistive Ballooning Mode (RBM) turbulence reproducing the stabilization of barrier relaxations by a static magnetic perturbation. We focus our study on the edge region around the resonant surface q = 3. We use the TEXTOR tokamak geometry, and plasma parameters close to those used in typical experiments on this machine.« less