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A 1T cryocooler-cooled oxide superconducting pulsed coil, which is a 16 layer solenoidal coil wound with an interlayer-transposed 4-strand parallel conductor composed of Bi2223 multifilamentary flat wires is fabricated. The thermal properties of the cryocooler-cooled oxide superinducting pulsed coil is described, taking into account the heat generation of ac loss and flux-flow loss and the cooling capacity of a cryocooler Ac loss and the cooling capacity of the cryocooler have been studied.

Development and testing of a cryocooler-cooled superconducting pulse coil is described and discussed.

We fabricated a cryocooler-cooled Bi2223 superconducting pulsed coil and experimentally studied the thermal runaway in dc or ac operation. We carried out numerical simulation of thermal properties of the coil in order to explain the thermal runaway of the coil. Firstly, we analyzed the total heat generation of flux-flow losses and ac losses inside the winding from the experimental results of the external field losses and the E - J characteristics for the Bi2223 strands. Secondly, we numerically simulated the thermal properties by using a 2-dimensional heat conduction equation with axial symmetry. The numerical simulation shows the relation between the initiation of thermal runaway and the temperature distribution with highly concentrated heat source in the winding. We have a semi-quantitative agreement between the numerical results and the experimental ones for the condition of the thermal runaway. [ABSTRACT FROM AUTHOR]

We studied the thermal and electromagnetic behavior of a conduction-cooled superconducting pulse coil. It was wound with a 4-strand parallel conductor composed of silver sheathed Bi2223 multifilamentary tapes and impregnated with an epoxy resin. We first investigated the temperature dependence of the thermal runaway current in dc operation. It was higher than the critical current by several tens amps at any temperature from 40 to 90 K. In order to study the mechanism of the thermal runaway, we carried out the numerical simulation of the coil behavior. We found out that the thermal runaway was caused when the heat generation at the winding end close to the cryocooler head where the flux-flow loss is the largest due to perpendicular magnetic field exceeded the cooling through thermal diffusion though the thermal runaway of the coil started at the other end of the winding. If the transport current is smaller than the thermal runaway current at the coil temperature just after applying current, the temperature distribution in the longitudinal direction of the coil varied into a monotonous gradient and the steady thermal flow was established. After that the coil temperature decreased to the balanced one. [ABSTRACT FROM AUTHOR]

We designed and fabricated a 1 T cryocooler-cooled oxide superconducting pulsed coil with Bi2223 multifilamentary flat wires. Previously we studied temperature dependence of the thermal runaway current of the pulsed coil in dc operation. The thermal runaway current was higher than the critical current that was defined as the current where the electric field 10-4 V/m was generated on average over the whole length of the conductor. In this paper, we studied the coil temperature and the ac loss dependence of the thermal runaway current in ac operation. We operated the coil at 0.5 to 5 Hz with a sinusoidal-waveform transport current. The initial coil temperature was set between 30 and 100 K. The thermal runaway current decreased monotonically with increasing temperature in a similar way to dc operation. However, in a low temperature region, the thermal runaway current was restricted to a lower level than that in dc operation due to the ac loss. We discuss the frequency dependence of thermal runaway current in ac operation. [ABSTRACT FROM AUTHOR]