Optimization of stellarator geometry for low transport from ITG/TEM modes *

Gyrokinetic analysis advances indicate that the transport barriers can arise because of the existence of a regime of strongly weakened ITG/TEM instabilities [1]. It should be possible to optimize the geometry of a stellarator to be in this regime. Both the Wendelstein 7-X geometry and the National Compact Stellarator eXperiment (NCSX) geometry have been found to lie in this regime, and many transport barriers in tokamaks also lie in it [1]. Here, a very fast implementation of a Simplified Kinetic Model (SKiM) [1] is being developed for incorporation into the STELLOPT optimization code [2]. The SKiM often gives an acceptably accurate estimate of the ITG/TEM growth rate, but is many orders of magnitude faster than gyrokinetic simulations. Together with optimization of neoclassical transport, this can be used to develop stellarator geometries with exceptionally high energy confinement.

1 M. Kotschenreuther, X. Liu, S. Mahajan, and D.R. Hatch, Submitted to Physical Review Letters

2  D.Spong et al, NF 41 (2001) 711