Pumping sequence effect on levitation and guidance forces of YBCO bulks for evacuated tube transportation

Abstract

As a part of high temperature superconducting Maglev-evacuated tube transport (HTS Maglev-ETT), ETT technology provides a potential new solution to realize the proposition of higher ground speed transportation. In this system, due to the low pressure caused by tube evacuation, the temperature of liquid nitrogen (LN2) changes and ultimately affects the performance of HTS bulks. Considering the significant necessity to guarantee HTS Maglev-ETT operational stability and safety, this paper focuses on the levitation and guidance performance variations of YBCO bulks caused by the pumping sequence under low pressure. One working condition is to pump the air out during the field cooling stage before levitating the vehicle, defined as “evacuating and then levitating” (E-L case). The other working condition is to pump the air out after the field cooling stage when the vehicle is already levitated, defined as “levitating and then evacuating” (L-E case). Based on the superconducting maglev measurement system (SCML-01) and a self-developed ambient pressure-reducing platform, the working conditions’ effect on levitation and guidance force in the two sequences above is experimentally explored. Simultaneously, the difference between the two sequences is also discussed specifically. For a larger levitation force, the E-L case with high field cooling height (FCH) and low working height (WH) is an efficient condition; The L-E case with low FCH and low WH is suitable for a larger guidance force. In addition, the two specific conditions perform better under lower air pressure. All these conclusions are anticipated to provide a reference for practical startup procedures and future engineering design of HTS Maglev-ETT systems.