Full particle orbit effects in regular and stochastic magnetic fields
Abstract
We present a numerical study of charged particle motion in a timeindependent magnetic field in cylindrical geometry. The magnetic field model consists of an unperturbed reversedshear (nonmonotonic qprofile) helical part and a perturbation consisting of a superposition of modes. Contrary to most of the previous studies, the particle trajectories are computed by directly solving the full Lorentz force equations of motion in a sixdimensional phase space using a sixthorder, implicit, symplectic GaussLegendre method. The level of stochasticity in the particle orbits is diagnosed using averaged, effective Poincare sections. It is shown that when only one mode is present, the particle orbits can be stochastic even though the magnetic field line orbits are not stochastic (i.e., fully integrable). The lack of integrability of the particle orbits in this case is related to separatrix crossing and the breakdown of the global conservation of the magnetic moment. Some perturbation consisting of two modes creates resonance overlapping, leading to Hamiltonian chaos in magnetic field lines. Then, the particle orbits exhibit a nontrivial dynamics depending on their energy and pitch angle. It is shown that the regions where the particle motion is stochastic decrease as the energy increases. The nonmonotonicity of the qprofile implies themore »
 Authors:
 Aix Marseille Univ., Univ. Toulon, CNRS, CPT, Marseille (France)
 (France)
 Oak Ridge National Laboratory, Oak Ridge, Tennessee 378316169 (United States)
 CEA, IRFM, F13108 St. PaullezDurance Cedex (France)
 Publication Date:
 OSTI Identifier:
 22600020
 Resource Type:
 Journal Article
 Resource Relation:
 Journal Name: Physics of Plasmas; Journal Volume: 23; Journal Issue: 7; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; CHAOS THEORY; CHARGED PARTICLES; CHARGEDPARTICLE TRANSPORT; CYLINDRICAL CONFIGURATION; EQUATIONS OF MOTION; HAMILTONIANS; INTEGRAL CALCULUS; LORENTZ FORCE; MAGNETIC FIELDS; MAGNETIC MOMENTS; MAGNETIC SURFACES; NUMERICAL ANALYSIS; ORBITS; PARTICLES; PERTURBATION THEORY; PHASE SPACE; PITCHES; REVERSED SHEAR; STOCHASTIC PROCESSES; THERMAL BARRIERS
Citation Formats
Ogawa, Shun, Email: shun.ogawa@cpt.univmrs.fr, CEA, IRFM, F13108 St. PaullezDurance Cedex, Cambon, Benjamin, Leoncini, Xavier, Vittot, Michel, CastilloNegrete, Diego del, DifPradalier, Guilhem, and Garbet, Xavier. Full particle orbit effects in regular and stochastic magnetic fields. United States: N. p., 2016.
Web. doi:10.1063/1.4958653.
Ogawa, Shun, Email: shun.ogawa@cpt.univmrs.fr, CEA, IRFM, F13108 St. PaullezDurance Cedex, Cambon, Benjamin, Leoncini, Xavier, Vittot, Michel, CastilloNegrete, Diego del, DifPradalier, Guilhem, & Garbet, Xavier. Full particle orbit effects in regular and stochastic magnetic fields. United States. doi:10.1063/1.4958653.
Ogawa, Shun, Email: shun.ogawa@cpt.univmrs.fr, CEA, IRFM, F13108 St. PaullezDurance Cedex, Cambon, Benjamin, Leoncini, Xavier, Vittot, Michel, CastilloNegrete, Diego del, DifPradalier, Guilhem, and Garbet, Xavier. 2016.
"Full particle orbit effects in regular and stochastic magnetic fields". United States.
doi:10.1063/1.4958653.
@article{osti_22600020,
title = {Full particle orbit effects in regular and stochastic magnetic fields},
author = {Ogawa, Shun, Email: shun.ogawa@cpt.univmrs.fr and CEA, IRFM, F13108 St. PaullezDurance Cedex and Cambon, Benjamin and Leoncini, Xavier and Vittot, Michel and CastilloNegrete, Diego del and DifPradalier, Guilhem and Garbet, Xavier},
abstractNote = {We present a numerical study of charged particle motion in a timeindependent magnetic field in cylindrical geometry. The magnetic field model consists of an unperturbed reversedshear (nonmonotonic qprofile) helical part and a perturbation consisting of a superposition of modes. Contrary to most of the previous studies, the particle trajectories are computed by directly solving the full Lorentz force equations of motion in a sixdimensional phase space using a sixthorder, implicit, symplectic GaussLegendre method. The level of stochasticity in the particle orbits is diagnosed using averaged, effective Poincare sections. It is shown that when only one mode is present, the particle orbits can be stochastic even though the magnetic field line orbits are not stochastic (i.e., fully integrable). The lack of integrability of the particle orbits in this case is related to separatrix crossing and the breakdown of the global conservation of the magnetic moment. Some perturbation consisting of two modes creates resonance overlapping, leading to Hamiltonian chaos in magnetic field lines. Then, the particle orbits exhibit a nontrivial dynamics depending on their energy and pitch angle. It is shown that the regions where the particle motion is stochastic decrease as the energy increases. The nonmonotonicity of the qprofile implies the existence of magnetic ITBs (internal transport barriers) which correspond to shearless flux surfaces located in the vicinity of the qprofile minimum. It is shown that depending on the energy, these magnetic ITBs might or might not confine particles. That is, magnetic ITBs act as an energydependent particle confinement filter. Magnetic field lines in reversedshear configurations exhibit topological bifurcations (from homoclinic to heteroclinic) due to separatrix reconnection. We show that a similar but more complex scenario appears in the case of particle orbits that depend in a nontrivial way on the energy and pitch angle of the particles.},
doi = {10.1063/1.4958653},
journal = {Physics of Plasmas},
number = 7,
volume = 23,
place = {United States},
year = 2016,
month = 7
}

Full particle orbit effects in regular and stochastic magnetic fields
Here we present a numerical study of charged particle motion in a timeindependent magnetic field in cylindrical geometry. The magnetic field model consists of an unperturbed reversedshear (nonmonotonic qprofile) helical part and a perturbation consisting of a superposition of modes. Contrary to most of the previous studies, the particle trajectories are computed by directly solving the full Lorentz force equations of motion in a sixdimensional phase space using a sixthorder, implicit, symplectic GaussLegendre method. The level of stochasticity in the particle orbits is diagnosed using averaged, effective Poincare sections. It is shown that when only one mode is present, themore »Cited by 1 
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Collisional particle transport in stochastic magnetic fields is studied using a semianalytical method. The aim is to determine the influence of the nonlinear effects that occur in the magnetic field line random walk on particle transport. We show that particle transport coefficients can be strongly influenced by the magnetic line trapping. The conditions that correspond to these nonlinear regimes are determined. We also analyze the effects produced by the space variation of the largescale magnetic field. We show that an average drift is generated by the gradient of the magnetic field, which strongly increases and reverses its orientation in themore »