Levitation Force of Bulk YBaCuO and GdBaCuO Under a Low-Pressure Environment

The high-temperature superconducting (HTS) bulk is the core component of HTS maglev systems. For the potential application of evacuated tube transportation, it is necessary to verify the loading capacity of the bulk under a low-pressure environment. Based on a home-made pressure-reducing platform, we investigated the levitation force of two kinds of typical bulks, that is, the same sized YBaCuO and GdBaCuO, above a Halbach permanent magnet guideway under different pressure conditions. The levitation force in the cases of zero-field-cooling (ZFC) and field-cooling (FC) were measured and analyzed. Experimental results show that the reduced air pressure can significantly improve the levitation force of the two kinds of bulks. The levitation force of YBaCuO and GdBaCuO has increased by 11.6% and 4.4% in the FC case, 20.3% and 13.7% in the ZFC case under 20 kPa compared with the atmospheric pressure (100 kPa), respectively. This universal phenomenon was explained by the increasing critical current density Jc of HTS bulks due to cooler liquid nitrogen under the low-pressure condition. It is interesting to find that the YBaCuO bulk was more sensitive to the pressure variation compared with the GdBaCuO bulk. This difference reflects the improvement extent of levitation force of HTS bulks with different Jc performance working in a low-pressure environment.