Abstract
Edge density profiles were measured during natural and forced magnetic axis shifts in the lowaspect-ratio heliotron/torsatron CHS, using an 8 keV fast neutral lithium beam probe. The Shafranov shift of the magnetic axis (and hence the dislocation of the LCFS) that was negligible for a low density ECH discharge became substantial (∼4.5 cm) for a high density NBI discharge (〈n e〉∼2.5× 1013cm−3) and the corresponding radius of the LCFS increased about 1.2 cm in major radius compared to the vacuum case. For NBI discharges with different settings of the vacuum magnetic axisR ax (fixed during the discharge), the measured edge density profiles indicated reasonable agreement between the theoretically and experimentally obtained LCFS radii for 90 cm <R ax<101.6cm, while forR ax<90 cm the measured radius was 10% larger than expected. When a change ofR ax from 94.7 cm to 89.9 cm during a discharge was imposed externally, a well behaved plasma boundary moved inward smoothly by about 7.5 cm, while the steepness of the edge density profile changed for different values ofR ax. The steepest profile was attained forR ax=92.1 cm when the highest energy content and average density were achieved.
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Ueda, M., Iguchi, H., Yamada, H. et al. Edge density profile variation during a magnetic axis shift in the CHS heliotron/torsatron. J Fusion Energ 12, 273–279 (1993). https://doi.org/10.1007/BF01079670
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DOI: https://doi.org/10.1007/BF01079670