Introduction of superconductor to magnetic levitation (maglev) trains greatly enhances the performances compared to those of normal conductor maglevs, e.g. from 430 km/h of the Transrapid (in Shanghai) to 603 km/h of the L0 Series in Japan. However, one of the important constraints on development of superconducting maglevs is limited wireless feeding power for on-board superconducting magnets and cryogenic cooling. In this paper, a persistent-current superconducting magnets system with solid nitrogen (SN₂) cooling preservation is proposed for liberation of its demanding on-board power feeding requirement. The magnets are optimally designed with no-insulation technique guaranteeing a safe operation with magnetic field over 0.8 T. Lasting time of persistent current (at 96.5% magnetic field retained) and SN₂ cooling preservation (up to 40 K) is all >9 h, covering a maglev traveling distance of >5400 km at average designed speed of >600 km/h. The magnets have anti-vibration ability of 15 g (147 m/s²) up to 350 Hz, which has covered the vibratory motion range in maglevs. This work is intended to provide a reference for superconducting maglev developments.

We have designed and built a novel high-temperature superconducting (HTS) flux pump device to charge a second-generation (2G) HTS double pancake coil (DPC). This device generates dc-biased ac travelling wave on sections of 2G HTS coated conductor (superconducting stator), which pumps flux into the superconducting closed loop formed by the DPC and superconducting stator. In this paper, we discuss the importance of the dc-biased field, ac travelling wave, and the travelling direction in the flux pump process, and how to control the magnetization of an HTS coil with the above factors. We have found that a pure ac travelling wave can only transport net flux into the superconducting closed loop in the presence of dc-bias field. The magnetization direction of the DPC can be reversed by reversing the dc-bias direction of the dc background field or travelling direction of the ac travelling wave. This paper shows the versatility and flexibility of this novel flux pump device in controlling the magnetization of the HTS coils, which will work as a wireless dc power source to help persistent current mode operation of a small-scale MRI magnet built by HTS DPCs later in this project.

An experimental platform of high temperature superconducting (HTS) synchronous motor with HTS flux pump has been designed and under construction. The HTS flux pump as an exciter eliminates thermal load from the metal current leads, which will reduce the cryogenic volume and improve the efficiency of the HTS machine. A finite element model (FEM) using T-A formulation was developed to analyze the electromagnetic characteristics of a double-pancake (DP) racetrack coil. The no-insulation (NI) racetrack coil wound by YBCO tapes was fabricated with a winding machine in our lab. We proposed a novel mechanical structure to avoid the impregnation of epoxy resin and make the coil more reliable. The turn-to-turn pressure of the racetrack coil can be changed by driving the screws on the straight section. Besides, we manufactured a rotating HTS flux pump as a DC power supply to charge the racetrack coil without contact. The self-field critical current test with a direct current (DC) power supply and the charging experiment with the HTS flux pump of the constructed YBCO racetrack coil were performed at 77 K.