Study of the interplay between magnetic shear and resonances using Hamiltonian models for the magnetic field lines

Abstract

The issue of magnetic confinement in magnetic fusion devices is addressed within a purely magnetic approach. Using some Hamiltonian models for the magnetic field lines, the dual impact of low magnetic shear is shown in a unified way. Away from resonances, it induces a drastic enhancement of magnetic confinement that favors robust internal transport barriers (ITBs) and stochastic transport reduction. When low-shear occurs for values of the winding of the magnetic field lines close to low-order rationals, the amplitude thresholds of the resonant modes that break internal transport barriers by allowing a radial stochastic transport of the magnetic field lines may be quite low. The approach can be applied to assess the robustness versus magnetic perturbations of general (almost) integrable magnetic steady states, including non-axisymmetric ones such as the important single helicity steady states. This analysis puts a constraint on the tolerable mode amplitudes compatible with ITBs and may be proposed as a possible explanation of diverse experimental and numerical signatures of their collapses.

References in corpus (3)

• Noble internal transport barriers and radial subdiffusion of toroidal magnetic lines
• Drastic facilitation of the onset of global chaos in a periodically driven Hamiltonian system due to an extremum in the dependence of eigenfrequency on energy
• Enhanced confinement with increased extent of the low magnetic shear region in tokamak plasma

Cited by in corpus (6)

• Contributions of plasma physics to chaos and nonlinear dynamics
• General formulas for adiabatic invariants in nearly-periodic Hamiltonian systems
• Heat pulse propagation in chaotic 3-dimensional magnetic fields
• Exact non-symmetric closed line vacuum magnetic fields in a topological torus
• Low-shear three-dimensional equilibria and vacuum magnetic fields with flux surfaces
• Low-shear three-dimensional equilibria in a periodic cylinder