Self consistent radio-frequency wave propagation and peripheral direct current plasma biasing: Simplified three dimensional non-linear treatment in the 'wide sheath' asymptotic regime
- CEA, IRFM, F-13108 Saint-Paul-lez-Durance (France)
- IJL-P2M UMR 7198 CNRS, F-54506 Vandoeuvre les Nancy (France)
- Department of Applied Physics, Ghent University, B-9000 Ghent (Belgium)
- LPP-ERM/KMS, Association Euratom-'Belgian State', TEC Partner, Brussels (Belgium)
A minimal two-field fluid approach is followed to describe the radio-frequency (RF) wave propagation in the bounded scrape-off layer plasma of magnetic fusion devices self-consistently with direct current (DC) biasing of this plasma. The RF and DC parts are coupled by non-linear RF and DC sheath boundary conditions at both ends of open magnetic field lines. The physical model is studied within a simplified framework featuring slow wave (SW) only and lateral walls normal to the straight confinement magnetic field. The possibility is however kept to excite the system by any realistic 2D RF field map imposed at the outer boundary of the simulation domain. The self-consistent RF + DC system is solved explicitly in the asymptotic limit when the width of the sheaths gets very large, for several configurations of the RF excitation and of the target plasma. In the case of 3D parallelepipedic geometry, semi-analytical results are proposed in terms of asymptotic waveguide eigenmodes that can easily be implemented numerically. The validity of the asymptotic treatment is discussed and is illustrated by numerical tests against a quantitative criterion expressed from the simulation parameters. Iterative improvement of the solution from the asymptotic result is also outlined. Throughout the resolution, key physical properties of the solution are presented. The radial penetration of the RF sheath voltages along lateral walls at both ends of the open magnetic field lines can be far deeper than the skin depth characteristic of the SW evanescence. This is interpreted in terms of sheath-plasma wave excitation. Therefore, the proper choice of the inner boundary location is discussed as well as the appropriate boundary conditions to apply there. The asymptotic scaling of various quantities with the amplitude of the input RF excitation is established.
- OSTI ID:
- 22086136
- Journal Information:
- Physics of Plasmas, Vol. 19, Issue 9; Other Information: (c) 2012 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ASYMPTOTIC SOLUTIONS
BOUNDARY CONDITIONS
CONFINEMENT
DC SYSTEMS
DIRECT CURRENT
ELECTRIC POTENTIAL
MAGNETIC FIELDS
NONLINEAR PROBLEMS
PHYSICAL PROPERTIES
PLASMA SCRAPE-OFF LAYER
PLASMA SHEATH
PLASMA SIMULATION
PLASMA WAVES
RADIOWAVE RADIATION
RF SYSTEMS
THERMONUCLEAR DEVICES
THREE-DIMENSIONAL CALCULATIONS
WALLS
WAVE PROPAGATION
WAVEGUIDES