To establish the worldwide storage and marine transportation of hydrogen, it is important to develop liquid hydrogen tanks/carriers as well as a long level sensor such as a superconducting magnesium diboride (MgB2) level sensor. An external-heating-type MgB2 level sensor is expected to be an excellent choice for liquid hydrogen because of its high linearity, resolution, and reproducibility. The dynamic level-detecting characteristics of three 500-mm-long MgB2 level sensors have been evaluated under conditions of oscillating liquid level using an optical cryostat and a high-speed microscope. The response time to variations of the liquid hydrogen level is about 0.1 s, and the difference between the level read optically and that detected by the MgB2 level sensors is about 5 mm under these conditions. Thus, the MgB2 level sensors have superior response performance for the sloshing measurement of liquid hydrogen.

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Synopsis:We are currently developing an external-heating-type superconducting magnesium diboride (MgB 2 )-level sensor for a large liquid hydrogen tank as one of the basic technologies for the marine transportation of liquid hydrogen. Optimization of the sensor performance and effect of sensor length on thermal response were previously reported. However, the performance variation of the MgB 2 sensor caused by individual differences in the wire rod has not yet been clarified. In this study, we developed a simultaneous calibration system for five MgB 2 -level sensors, and examined the level-detecting characteristics of five 500-mm-long MgB 2 -level sensors. It was found that the maximum performance variation of the MgB 2 sensors was about 2% for the full scale of the sensor length, although the four fifth sensors indicated the same results. Therefore, the performance variation in MgB 2 sensors caused by individual differences in the wire rods was minimal.

Synopsis We are currently developing an external-heating-type superconducting magnesium diboride (MgB 2) level sensor for a liquid hydrogen tank. The heating effect of an external heater on an 800-mm-long MgB 2 level sensor was previously reported. However, the heating effect of an external heater on the MgB 2 level sensor has not yet been clarified in the case of changing the sensor length. In this study, we examined the temperature distribution and level-detecting characteristics of a 200mm-long MgB 2 level sensor. It was found that the temperature of the sensor above the liquid surface was higher than T c at a heater input of 6 W or more. Regarding the level-detecting characteristics of the MgB 2 sensor, the linear correlation coefficient was 0.99 or more at a heater input of 3 W and above. Moreover, the ratio of the effective level-detecting length to the total length remained constant at a heater input of 6 W or more. Similar results were observed for different sensor lengths. Therefore, the optimum heater input was 6 W regardless of the sensor length.