Stochastic electron dynamics due to drift waves in a sheared magnetic field and other drift motion problems

Technical Report · Mon Dec 01 04:00:00 EST 1986

OSTI ID:6920880

Robertson, J A

Electron motion in a single electrostatic wave in a sheared magnetic field is shown to become stochastic in the presence of a second wave at an amplitude well below that obtained from the overlapping pendulum resonance approximation. The enhanced stochasticity occurs for low parallel velocity electrons for which the parallel trapping motion from eE/sub parallel//m interacts strongly with the E x B trapping motion due to the presence of magnetic shear. The guiding-center equations for single particle electron orbits in given fields are investigated using both analytical and numerical techniques. The model assumes a slab magnetic field geometry with shear and two electrostatic plane waves propagating at an angle with respect to each other. Collisions and the self-consistent effect of the electron motion upon the fields are ignored. The guiding-center motion in an inertial reference frame moving in phase with the two waves is given by a two degree-of-freedom, autonomous Hamiltonian system. The single wave particle motion may be reduced to a two parameter family of one degree-of-freedom Hamiltonians which bifurcate from a pendulum phase space to a topology with three chains of elliptic and hyperbolic fixed points separated in radius about the mode-rational surface. In the presence of a perturbing wave with a different helicity, electrons in the small parallel velocity regime become stochastic at an amplitude scaling as the fourth root of the wave potential. The results obtained for stochastic motion apply directly to the problem of electron diffusion in drift waves occurring in toroidal fusion confinement devices. The effect of an adiabatically changing radial electric field upon guiding-center orbits in tokamaks is also investigated. This perturbation causes a radial polarization drift of trapped particle tokamak orbits.

• Research Organization: Texas Univ., Austin (USA). Inst. for Fusion Studies
• DOE Contract Number: FG05-80ET53088
• OSTI ID: 6920880
• Report Number(s): DOE/ET/53088-251; IFSR-251; ON: DE87005523
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700103* -- Fusion Energy-- Plasma Research-- Kinetics
CLOSED PLASMA DEVICES
ELECTRON DRIFT
GUIDING-CENTER APPROXIMATION
HAMILTONIANS
MAGNETIC FIELDS
MATHEMATICAL OPERATORS
PLASMA
QUANTUM OPERATORS
RESONANCE
SHEAR
STOCHASTIC PROCESSES
THERMONUCLEAR DEVICES
TOKAMAK DEVICES
TRANSPORT THEORY