Magnetic ripple and the modeling of 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 behavior is first depicted for a cylindrical equilibrium periodically modulated along the axial direction. 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 behavior is found when the ray trajectory crosses a high ripple region. By coupling ray tracing with a one-dimensional relativistic Fokker-Planck code, simulations of LH experiments have been performed for the TORE SUPRA tokamak. It is shown that magnetic ripple may induce significant modifications in the LH power deposition profiles, mainly in the ''few passes'' regime when the wave makes some, but not many, passes inside the plasma before being absorbed. The effect of magnetic ripple leads then to a broadening of the power deposition profile and a shift towards the center of the plasma, and a better coupling with high energy electrons. This behavior may be explained by an increase in the overall ray stochasticity.
Bibliographic Reference: Article: Physics of Plasmas, Vol. 3 (1996) No. 10, pp. 3668-3688
Record Number: 199611533 / Last updated on: 1997-01-27
Original language: en
Available languages: en