Confirmation of theoretical evaluation of equilibrium current in helical systems - through the Heliotron E result for dipole current suppression and reversal

Equilibrium current (EC) suppression or even reversal was experimentally demonstrated in Heliotron E (HE) [Besshou, S., et al., Nucl. Fusion 35 (1995) 173] when the initial magnetic configuration is shifted inwards by vertical field control. The EC properties are systematically investigated on the basis of the Boozer magnetic spectrum, which gives rather good agreement with the experimental results. This agreement provides the experimental evidence for the basis of the theoretical optimization study of stellarator configurations for EC. Equilibrium current suppression seems rather difficult in present experimental conditions for LHD due to its lower aspect ratio with a larger poloidal inhomogeneity of the magnetic field strength than that of HE. For comparison, the EC property in Wendelstein 7-X is also examined on the basis of the same approach, which demonstrates the successful reduction of EC. (author)