Shear Alfvén Eigenmodes in Compact Stellarators
Abstract
Fast ion destabilized shear Alfvén modes are of interest in stellarators due to the fast ion losses and lowered heating efficiency they can cause, their potential diagnostic use (MHD spectroscopy), and the possibility of direct channeling of fast ion energy to core ions through wave-particle mechanisms (i.e., bypassing the slower collisional transfer mechanisms). Low aspect ratio stellarators offer much stronger poloidal/toroidal couplings in |B| and the g^ρρ metric coefficient (which enter into the Alfvén continuum equation) than either tokamaks or large aspect ratio stellarators. Also, since low aspect ratio devices generally are designed at low field periods (N_fp = 2 - 3), more closely spaced toroidal mode families must be taken into account in calculating the Alfvén spectrum. We have developed a numerical procedure for rapidly calculating the Alfvén continuum structure that uses VMEC coordinates and MPI parallelism over flux surfaces. We find a number of qualitative differences between the continuum structures of low and high aspect ratio devices that can impact Alfvén stability properties. We also expect to extend this calculation to obtain the discrete Alfvén modes located in the gaps of the continuum and examine their thresholds to excitation by fast ion components..
- Publication:
-
APS Division of Plasma Physics Meeting Abstracts
- Pub Date:
- October 2001
- Bibcode:
- 2001APS..DPPCP1048F