Comparative experiments of co‐ and counter‐helicity merging in the compact toroid merging device TS‐4

Abstract

SUMMARYFor the past 15 years, the TS-3 merging project has explored several new types of CT/ST (Compact Tori and Spherical Tokamak): merging formation of FRCs (Field Reversed Configuration), magnetic reconnection experiment, and ultrahigh beta ST formation. The successful results of these experiments have enabled us to construct an upscaled merging device, namely, the TS-4. The new TS-4 has two flux cores (major radius = 0.5 m) for inductive plasma formation, a center coil (external toroidal field coil and OH coil), for q value control and plasma sustaining, and DC external field coils. The initial operation of the TS-4 (since 2001) demonstrated co-helicity and counter-helicity merging of two spheromaks. The counter-helicity merging revealed annihilation of toroidal magnetic field with a significant overshoot motion of reconnected field lines. It resulted in the formation of a high-beta (≈ 0.8) FRC. The produced FRC has a significant field deformation, suggesting a contribution of the toroidal plasma flow to its equilibrium. The co-helicity merging doubled the toroidal fluxes of spheromak, causing its flux conversion from toroidal to poloidal. The merging spheromaks relaxed into another spheromak with beta ≈ 0, suggesting the large thermal energy loss due to its non-aximetric dynamo activity.

Onset of fast magnetic reconnection and particle energization in laboratory and space plasmas

“…Once generated at the ends of a vacuum chamber, the two opposite magnetic field polarity spheromaks can be translated in to the region in the centre where the experiment takes place (Yamada et al 1997;Kornack 2001). The plasma guns can create left-or right-handed spheromaks by switching the polarity on the stuffing field magnet, and so the polarity of the poloidal magnetic field, allowing the study of same helicity or opposite helicity merging flux tubes (see, e.g., Yamada et al 1997;Tsuruda, Ono & Katsurai 2002).…”