Magnetic ripple and the modeling of lower-hybrid current drive in tokamaks
- Departement de Recherches sur la Fusion Controlee, Association Euratom--CEA, Centre d`Etudes de Cadarache, 13108 St. Paul lez Durance Cedex (France)
- Centro de Fusao Nuclear, Associacao Euratom--IST, Instituto Superior Tecnico, 1096 Lisboa Codex (Portugal)
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. Despite the modest amplitude of the local ray perturbation, its global influence on ray trajectories may be strong, as a consequence of the combined 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 [Equipe TORE SUPRA, in {ital Proceedings of the 15{sup th} Conference on Plasma Physics and Controlled Nuclear Fusion Research}, Seville (International Atomic Energy Agency, Vienna, 1995), Vol. 1, p. 105, Paper IAEA-CN-60/A1-5]. It is shown that magnetic ripple may induce significant modifications in the LH power deposition profiles, mainly in the {open_quote}{open_quote}few passes{close_quote}{close_quote} 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. Taking into account magnetic ripple in LH simulations, a better agreement is found between numerical predictions and experimental observations. {copyright} {ital 1996 American Institute of Physics.}
- OSTI ID:
- 390378
- Journal Information:
- Physics of Plasmas, Vol. 3, Issue 10; Other Information: PBD: Oct 1996
- Country of Publication:
- United States
- Language:
- English
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