Abstract
MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> superconducting thin wires sheathed with stainless steel (SS) have been prepared by in-situ powder-in-tube (PIT) process. Using Magnesium hydride MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and amorphous B powders, SS sheathed MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin wires have been fabricated through drawing to form the round wires of 0.20 mm ~ 0.10 mm in diameter. The SS sheath of 0.1 mm in diameter was hardened to be a Vickers hardness of around 600 HV through cold-working at room temperature without annealing. The heat treatment was performed at 630°C for 5 h in Ar gas atmosphere. The SS sheath recovered the hardness of 400 HV after heat treatment. The MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> wires show the critical temperature (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) of around 35 K in onset and sharp transition of 2 K. The transport critical current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) at 4.2 K and self-field are 40 A and 8 A for the MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin wires of 0.2 mm and 0.1 mm in diameter, respectively. The I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> values correspond to the critical current density (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) of around 4,000-5,000 A/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The present MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin wires with low thermal conductivity are promising as level sensors for liquid hydrogen and current leads with small heat leakage.
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