Gyroaverage effects on nontwist Hamiltonians: Separatrix reconnection and chaos suppression

Journal Article · Sun Jan 01 04:00:00 EST 2012 · Communications in Nonlinear Science and Numerical Simulations

DOI:https://doi.org/10.1016/j.cnsns.2011.07.020· OSTI ID:1036196

Del-Castillo-Negrete, Diego B ^[1]; Martinell, J. ^[2]

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1. ORNL
2. Universidad Autonoma de Mexico

A study of finite Larmor radius (FLR) effects on E x B test particle chaotic transport in non-monotonic zonal flows with drift waves in magnetized plasmas is presented. Due to the non-monotonicity of the zonal flow, the Hamiltonian does not satisfy the twist condition. The electrostatic potential is modeled as a linear superposition of a zonal flow and the regular neutral modes of the Hasegawa-Mima equation. FLR effects are incorporated by gyro-averaging the E x B Hamiltonian. It is shown that there is a critical value of the Larmor radius for which the zonal flow transitions from a profile with one maximum to a profile with two maxima and a minimum. This bifurcation leads to the creation of additional shearless curves and resonances. The gyroaveraged nontwist Hamiltonian exhibits complex patterns of separatrix reconnection. A change in the Larmor radius can lead to heteroclinic-homoclinic bifurcations and dipole formation. For Larmor radii for which the zonal flow has bifurcated, double heteroclinic-heteroclinic, homoclinic-homoclinic and heteroclinic-homoclinic separatrix topologies are observed. It is also shown that chaotic transport is typically reduced as the Larmor radius increases. Poincare sections show that, for large enough Larmor radius, chaos can be practically suppressed. In particular, changes of the Larmor radius can restore the shearless curve.

• Research Organization: Oak Ridge National Laboratory (ORNL)
• Sponsoring Organization: SC USDOE - Office of Science (SC)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1036196
• Journal Information: Communications in Nonlinear Science and Numerical Simulations, Journal Name: Communications in Nonlinear Science and Numerical Simulations Journal Issue: 5 Vol. 17; ISSN 1007-5704
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
BIFURCATION
DIPOLES
ELECTROSTATICS
HAMILTONIANS
LARMOR RADIUS
TEST PARTICLES
TRANSPORT