MgB 2 superconducting thin wires sheathed with stainless steel (SS) and pure iron (Fe) have been prepared by in situ powder in tube process. Using Magnesium hydride MgH 2 and amorphous B powders with and without SiC nano sized powder addition, SS/Fe/MgB 2 composites have been fabricated through grooved rolling and drawing to form the round wires of 0.53~ 0.10 mm in diameter. Both SS and Fe sheaths were hardened to be a Vickers hardness of around Hv 650 and Hv 510 through cold working at room temperature. The transport critical current (I c ) at 4.2 K for the MgB 2 wire increases with decreasing the amount of SiC addition in lower magnetic field than 1 T. The I c at 4.2 K and self field for the MgB 2 wire of 0.10 mm in diameter without SiC addition is 14 A, which corresponds to the critical current density ( J c ) of around 1×10 4 A/mm 2 . The present MgB 2 thin wires are promising as current leads and level sensor for liquid hydrogen.
An electric pump composed of an MgB2 motor is combined with superconducting level sensors using thin CuNi-sheathed MgB2 wires to transfer liquid hydrogen. An impeller is attached to the lower end of a rotating shaft on the MgB2 motor and covered with an outer casing to form a centrifugal pump. Then, the MgB2 motor and impeller are placed vertically inside a cryostat with an infill of liquid hydrogen. A glass Dewar vessel is prepared to receive the liquid hydrogen transferred from the cryostat containing the MgB2 motor. The MgB2 sensors are used not only to detect the level of liquid hydrogen but also to control the electric pump on the basis of their pre-estimated calibration curves. By using the assembled pump system, the liquid hydrogen is successfully transferred from the cryostat to the glass Dewar vessel via a transfer tube.
/ 21Highlights: A pump system composed of an MgB 2 motor and MgB 2 level sensors was constructed. The centrifugal pump was formed by attaching an aluminum impeller to the motor. A glass Dewar vessel receives the liquid hydrogen from a cryostat for the pump. The MgB 2 sensors were used to detect the liquid level and to control the motor. Transfer of liquid hydrogen was successfully carried out with the pump system. liquid hydrogen but also to control the electric pump on the basis of their pre-estimated calibration curves. By using the assembled pump system, the liquid hydrogen is successfully transferred from the cryostat to the glass Dewar vessel via a transfer tube.
Synopsis:As a thermal property of MgB 2 wires, we observed the propagation velocity of a normal zone for those immersed in liquid helium. The normal zone propagation was initiated by a resistive heater and the propagation velocity was estimated from the response of voltage difference between potential taps attached to the wire in a transverse magnetic field. The specimen was a mono-filamentary bare wire with a composite sheath of iron and copper. A part of the wire was cooled directly by liquid helium and the other was covered with a vacuum-grease layer for thermal insulation. The propagation velocity observed in each part was of a very low level in comparison with typical ones for usual NbTi wires, which may come from the high critical temperature and the low overall current density. We numerically calculate the propagation velocity with transient cooling models and discuss the normal zone propagation in relation to the cooling processes. We also evaluated the propagation of the normal zone in the MgB 2 wires with advanced transport properties, which were attained in short specimens, under the condition of conduction cooling in a wide range of operation temperatures.
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