Helical ripple transport in stellarators at low collision frequency

Technical Report · Tue Dec 01 04:00:00 EST 1987

OSTI ID:5498406

Beidler, C D

Numerical and analytical techniques have been developed to investigate the plasma transport which is due to particles trapping/detrapping in the local helical ripple wells of a stellarator's magnetic field. This process is of considerable importance as it provides the dominant transport mechanism in a stellarator plasma at ''low'' collision frequency: that is, when the frequency with which a particle is collisionally detrapped from a local ripple well is less than the bounce frequency of the particle in that well. A form of the longitudinal adiabatic invariant, J, is constructed and shown to describe accurately the orbits of ripple trapped particles. Unlike previous expressions for J, the form derived here correctly accounts for the local toroidal variation of the magnetic field. The expression for J is incorporated into a rapid ''hybrid'' Monte Carlo simulation of ripple transport in stellarators. The simulation is a hybrid in the sense that particle orbits in the narrow region of phase space on either side of the ripple trapping/detrapping boundary are followed using guiding center equations of motion while orbits in the remainder of phase space are described using adiabatic invariants. An analytical expression for the distribution function of ripple trapped particles in a stellarator - valid at all low collision frequencies - has been obtained by series solution of the bounce - averaged kinetic equation. This solution has been applied to both 'standard' and a class of 'transport optimized' stellarator magnetic fields. Analytical estimates of the diffusion coefficient obtained from the series solution show excellent agreement with the numerical results of the hybrid Monte Carlo code in all cases studied. 55 refs., 30 figs.

• Research Organization: Wisconsin Univ., Madison (USA). Torsatron/Stellarator Lab.
• DOE Contract Number: FG02-85ER53201; FG02-86ER53216
• OSTI ID: 5498406
• Report Number(s): DOE/ER/53201-T3; TSL-87-7; ON: DE88006431
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700103* -- Fusion Energy-- Plasma Research-- Kinetics
ANGULAR MOMENTUM
CLOSED PLASMA DEVICES
COLLISIONLESS PLASMA
COMPUTER CODES
DIFFERENTIAL EQUATIONS
EQUATIONS
EQUATIONS OF MOTION
KINETIC EQUATIONS
M CODES
MAGNETIC FIELD CONFIGURATIONS
MAGNETIC FIELD RIPPLES
MATHEMATICAL SPACE
MONTE CARLO METHOD
ORBITS
PARTIAL DIFFERENTIAL EQUATIONS
PHASE SPACE
PLASMA
PLASMA SIMULATION
SIMULATION
SPACE
STELLARATORS
THERMONUCLEAR DEVICES
TRANSPORT THEORY