Transport-driven Toroidal Rotation in the Tokamak Edge
Event details
| Date | 11.09.2012 |
| Hour | 14:00 › 15:00 |
| Speaker | Dr. T. Stolzfus-Dueck, MPI-Greifswald, Germany |
| Location |
PPB 019
|
| Category | Conferences - Seminars |
The edge of H-mode tokamak plasmas without external momentum input almost always rotates toroidally in the co-current direction, which has prompted a theoretical search for non-diffusive momentum transport mechanisms. In contrast to these efforts, the present work treats a model kinetic ion equation for the pedestal and SOL containing only parallel free streaming, magnetic drifts, and spatially inhomogeneous but purely diffusive transport. The solution demonstrates that passing-ion orbits and spatially inhomogeneous diffusion interact to cause a variation of the orbit-averaged diffusivities that depends on the sign of the parallel velocity, typically resulting in preferential transport of counter-current ions. The resulting rotation drive is independent of the toroidal velocity and its radial gradient, representing a residual stress. When momentum transport through the pedestal is required to vanish (intrinsic rotation case), the pedestal-top rotation reaches experimentally relevant values and exhibits several features in qualitative agreement with experiment. It is almost always in the co-current direction, with a rate that is proportional to ion temperature over plasma current, in accord with experimental observations. A co-current spin-up at the transition to H-mode is predicted, due to an increase of ion temperature and steepening gradients. Untested predictions of the model include a sensitivity of the rotation to the major-radial position of the X-point, with a more inboard (outboard) X-point leading to more co-current (counter-current) rotation. Beyond intrinsic rotation predictions, comparison of heat and momentum transport reveals that neutral beam injection must be significantly unbalanced in the counter-current direction to cause zero toroidal rotation at the pedestal top.
Practical information
- Expert
- Free
Organizer
- CRPP
Contact
- Prof. P. Ricci