Configuration Effect on LH Transition in Tohoku University Heliac


Hiromi Takahashia), Sumio Kitajimaa), Masayuki Yokoyamab), Yutaka Tanakaa),
Hiroyasu Utoha), Mamiko Sasaoa) and Masakazu Takayamac)

a) Department of Quantum Science and Energy Engineering, Tohoku University, Aramaki, Aoba, Sendai, Miyagi, 980-8578, Japan
b) National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
c) Department of Electronics and Information Systems, Akita Prefectural University, Ebinokuchi, Tsuchiya, Honjyo, Akita, 015-0055, Japan

In Tohoku University Heliac, a strong negative radial electric field is successfully formed by a negatively biased hot cathode of LaB6, and the bifurcation phenomena of radial electric field are clearly observed [1, 2]. Measured driving forces for poloidal rotation due to j×B qualitatively agree well with the neoclassical theory with a standard magnetic configuration (magnetic axis position Rax = 79mm), which has good poloidal symmetry. In order to study the influence of poloidal viscosity on LH transition, experiments with different magnetic configurations are carried out.
The heliac configurations are produced by three sets of coils: toroidal field coils, a center conductor coil and vertical field coils. Various kinds of magnetic configurations can be easily formed by selecting ratios of coil currents and Fourier magnetic components can be widely varied. In the present experiments, the position of magnetic axis is scanned from Rax = 73mm to 84mm. Dependence of driving force required for LH transition is studied as a function of magnetic axis position, keeping a similar profile of rotational transform. The preliminary experimental results show that the normalized poloidal driving force tends to be higher in the configuration with inward shifted magnetic axis.

References

[1]S. Kitajima et al., Int. J. Appl. Electromagnetics and Mechanics, 13, 381 (2002)
[2]S. Kitajima et al., IEEE Conference Record of 2003 IEEE International Conference on Plasma Science, 465 (2003)