TY - JOUR

T1 - Resonance and chaotic trajectories in magnetic field reversed configuration

AU - Landsman, A. S.

AU - Cohen, S. A.

AU - Edelman, M.

AU - Zaslavsky, G. M.

N1 - Funding Information:
This work was supported, in part, by US Department of Energy contract no. DE-FG02-92ER54184.
Copyright:
Copyright 2008 Elsevier B.V., All rights reserved.

PY - 2005/9

Y1 - 2005/9

N2 - The nonlinear dynamics of a single ion in a field reversed configuration (FRC) were investigated. FRC is a toroidal fusion device which uses a specific type of magnetic field to confine ions. As a result of angular invariance, the full three-dimensional Hamiltonian system can be expressed as two coupled, highly nonlinear oscillators. Due to the high nonlinearity in the equations of motion, the behavior of the system is extremely complex, showing different regimes, depending on the values of the conserved canonical angular momentum and the geometry of the fusion vessel. Perturbation theory and averaging were used to derive an integrable Hamiltonian and frequencies of the two degrees of freedom. The derived equations were then used to find resonances and compare to Poincare surface-of-section plots. A regime was found where the nonlinear resonances were clearly separated by KAM curves. The structure of the observed island chains was explained. The condition for the destruction of KAM curves and the onset of strong chaos was derived, using Chirikov island overlap criterion, and shown qualitatively to depend both on the canonical angular momentum and geometry of the device. After a brief discussion of the adiabatic regime, the paper goes on to explore the degenerate regime that sets in at higher values of angular momenta. In this regime, the unperturbed Hamiltonian can be approximated as two uncoupled linear oscillators. In this case, the system is near-integrable, except in cases of a universal resonance, which results in large island structures, due to the smallness of nonlinear terms, which bound the resonance. The linear force constants, dominant in this regime, were derived and the geometry for a large one-to-one resonance identified. The above analysis showed good agreement with numerical simulations and was able to explain characteristic features of the dynamics.

AB - The nonlinear dynamics of a single ion in a field reversed configuration (FRC) were investigated. FRC is a toroidal fusion device which uses a specific type of magnetic field to confine ions. As a result of angular invariance, the full three-dimensional Hamiltonian system can be expressed as two coupled, highly nonlinear oscillators. Due to the high nonlinearity in the equations of motion, the behavior of the system is extremely complex, showing different regimes, depending on the values of the conserved canonical angular momentum and the geometry of the fusion vessel. Perturbation theory and averaging were used to derive an integrable Hamiltonian and frequencies of the two degrees of freedom. The derived equations were then used to find resonances and compare to Poincare surface-of-section plots. A regime was found where the nonlinear resonances were clearly separated by KAM curves. The structure of the observed island chains was explained. The condition for the destruction of KAM curves and the onset of strong chaos was derived, using Chirikov island overlap criterion, and shown qualitatively to depend both on the canonical angular momentum and geometry of the device. After a brief discussion of the adiabatic regime, the paper goes on to explore the degenerate regime that sets in at higher values of angular momenta. In this regime, the unperturbed Hamiltonian can be approximated as two uncoupled linear oscillators. In this case, the system is near-integrable, except in cases of a universal resonance, which results in large island structures, due to the smallness of nonlinear terms, which bound the resonance. The linear force constants, dominant in this regime, were derived and the geometry for a large one-to-one resonance identified. The above analysis showed good agreement with numerical simulations and was able to explain characteristic features of the dynamics.

KW - Chaotic trajectories

KW - Magnetic confinement

KW - Nonlinear oscillators

KW - Resonances

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U2 - 10.1016/j.cnsns.2004.01.002

DO - 10.1016/j.cnsns.2004.01.002

M3 - Article

AN - SCOPUS:11144263229

SN - 1007-5704

VL - 10

SP - 617

EP - 642

JO - Communications in Nonlinear Science and Numerical Simulation

JF - Communications in Nonlinear Science and Numerical Simulation

IS - 6

ER -