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Author(s):
N. Nakajima, M. Yokoyama, M. Okamoto and J. Nuhrenberg
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Title:
Optimization of M=2 Stellarator
Date of publication:
Dec. 1996
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Key words:
Stellarator optimization, Quasi-axisymmetric stellarator (QAS), Shape of the confinement region, Pfirsch-Schluter current, Bootstrap current, Boozer coordinates, Magnetic spectra, Vertical elongation, Helical modulation, Triangularity
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Abstract:
Quasi-axisyrnmetric stellarator (QAS) configurations are considered for improvement of high energy reflected particle confinement. A reference QAS configuration with the field period of M = 2 has been obtained by the optimization of the shape of the confinement region. A wide operational regime, collisional (without net plasma current) and collisionless (with bootstrap current) equilibria, have been examined. The magnetic axis shift is rather large in collisional equilibriurn in the reference QAS configuration. On the other hand, in collisionless equilibrium, the bootstrap current is evaluated self-consistently and its crucial role on reduction of magnetic axis shift is shown. The effects of important boundary harmonics on the magnetic configuration are considered, in particular, plasma boundary control has been investigated for reducing the Pfirsch-Schluter current. Based on the plasma boundary control, we have obtained two QAS(-1ike) configurations with reduced magnetic axis shift. The basic properties for these two configurations are also explained.
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