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K. H. Saito, M. Aizawa,
K. N. Saito, I. Kawakami, S. Shiina
Atomic Energy Research Institute, College of Science and Technology, Nihon University, Tokyo, Japan 101-8308
Abstract. A new approach to the transport improvement in helical magnetic axis
stellarator is proposed. First of all, the proposal is presented for
L=1 helical axis systems with roughly quasihelical symmetry, then its
compatibility with equilibrium and stability would be optimized and
controlled. In the optimization, three key requirements are considered; the
reduction of effective toroidal curvature
for localized trapped
particles, the suppression of indirect magnetic island formation and the
magnetic well improvement by some field modifications. The important
features is to find the field modifications to satisfy the other two
requirements. The reduced
configuration is found to be
nearly omnigenous while far from quasihelical, giving rise to the
possibility of stellarator design study in a wider parameter domain than
quasisymmetry approaches. Up-to-date results show both the negative coil
pitch modulation and the superposition of a relatively weak L=-1 field to
satisfy the compatibility within the central beta value up to 2%
calculated. The compatibility study at higher beta and lower aspect ratio is
progressing by optimizing configuration parameters with the combination of
some field modifications proposed to improve magnetic well.
IAEA 2001
