Application of ${\rm MgB}_{2}$ Wire to Liquid Hydrogen Level Sensor—External-Heating-Type ${\rm MgB}_{2}$ Level Sensor

A superconducting magnesium diboride (MgB
₂
) level sensor for liquid hydrogen has been timely noted as a new sensor from a viewpoint of the worldwide storage and transport of large quantities of hydrogen. The external-heating-type level sensors (200 and 800 mm long) based on MgB
₂
wires are fabricated by an in situ method, and their level-detecting characteristics are studied in comparison with the actual liquid level using the liquid hydrogen experiment facility (LHEF). It becomes evident that an external-heating-type MgB
₂
level sensor has a high linearity, a small measurement error, and a good reproducibility even in the pressure range of up to 200 kPaG despite the evaporation loss caused by the heater used.