Extra large scale superconducting magnets must be used for a fusion device such as the LargeHelical Device (LHD). Because of the relatively higher current (10 kA or more), new evaluationmethods for determining the fundamental characteristics of superconductors have to be developed; suchmethods are already established for thin superconducting wires. In the paper, methods of measuringcritical current, stability margin and current distribution are discussed. Bath cooled composite andsupercritical helium force cooled NbTi conductors have been chosen for the helical and poloidal coilsof LHD, respectively. The critical current of a conductor was measured as follows: two 2 m long,parallel conductors, connected to each other at the bottom, were inserted into a 9 T split coil. Theconductor surface was to 50% covered by spacers in order to simulate the heat transfer conditions. Timedependent transition phenomena between normal and superconducting states were observed from thevoltage distribution along the conductor. After a study of the forced flow cooled conductors, the currenttransfer from a quenching strand to another strand was measured by pick-up coils on a conduit. Itsstability margin was measured by a pancake type coil employed as a long sample test. The majormeasurement results of bath and forced cooled LHD conductors using this system yielded a sufficientamount of fundamental data for high current multistrand conductors to be used in the LHD.
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