Magnetic Ripple and the Modeling of the Lower-Hybrid Current Drive in Tokamaks
Using ray tracing, a detailed investigation of the lower hybrid (LH) wave propagation in presence of toroidal magnetic field ripple is presented. The local ray behaviour is depicted for a cylindrical equilibrium periodically modulated along the axial detection. Variations along ray trajectories in the component of the wave vector parallel to the equilibrium magnetic field are observed, with a maximum relative amplitude that is locally of the order of the ripple level. For the full rippled toroidal equilibrium, a similar local behaviour is found when the ray trajectory crosses a high ripple region at the outboard plasma edge. However, despite the rather modest amplitude of the local ray perturbation that results from magnetic ripple, its global influence on ray trajectories may be strong, as a consequence of the combining effects of toroidal and poloidal inhomogeneities. By coupling ray tracing with a one-dimensional relativistic Fokker-Planck code, simulations of LH experiments have been performed for the TORE SUPRA tokamak which has a large magnetic ripple at the plasma edge (7%). It is shown that magnetic ripple may induce significant modifications in the LH power deposition profiles mainly in the "few passes" regime.
Bibliographic Reference: Report: 1572 EN (1996) 52pp.
Availability: Available from Association Euratom-CEA, CEN Cadarache, 13108 Saint-Paul-lez-Durance (FR)
Record Number: 199610656 / Last updated on: 1996-06-10
Original language: en
Available languages: en