As a bellwether transportation mode, albeit with hot controversy, evacuated tube transport (ETT) can dramatically reduce air friction, and incorporating Maglev technology could also thoroughly eliminate wheel-rail friction. It is not difficult to imagine that incorporation of these two technologies could establish an innovative transportation system, with particular advantages in terms of high speed, safety, energy saving, and environmental protection. The integration of these two technologies has been a great challenge, however, due to the composite technology. To realize this revolutionary idea, we have successfully developed the first proof-of-principle prototype of a 45-m-long high-temperature superconducting Maglev evacuated tube transport (HTS Maglev-ETT) test system, called the “Super-Maglev,” based on the passive self-stable HTS Maglev conceived in our group in 2000. The system mainly consists of three parts: an HTS Maglev-vehicle-guideway coupling system with 1-t load capability at a levitation gap of 10 mm, a 45-m-long racetrack-type evacuated tube with a 2-m-diameter circular cross section pumped by a hybrid air extraction system, and a 3-m linear induction motor to provide sectional propulsion. The system can achieve a pressure as low as 2.9 kPa in the tube. Experiments show that air drag on the vehicle is greatly reduced at that low air pressure, and a maximum speed of 50 km/h was recorded on the 6-m-diameter test guideway. Theoretically, the reduction of the aerodynamic consumed power could reach as high as to 90% under 10 kPa. This “Super-Maglev” strongly demonstrates the feasibility and potential merits of the HTS Maglev-ETT transportation concept.

A High-Temperature Superconducting Maglev-Evacuated Tube Transport (HTS Maglev-ETT) Test System

This paper describes the construction and main components of a full-scale superconducting magnetic levitation vehicle. The prototype, comprising four 1.5-m-long wagons, will travel a short test line of 200 meters, connecting two buildings inside the campus of the Federal University of Rio de Janeiro. The efforts to implement this technology started thirteen years ago with a small-scale prototype in an attempt to prove the concept. The second step was the construction of a functional prototype that could levitate more than one Ton. The actual stage of this project is the construction of an operational prototype mentioned above, designed to transport up to 24 passengers. This work has been reported in several previous editions of the ASC conference. New details about the elevated test line, the permanent magnetic (Nd-Fe-B) guideways, the cryostats with YBCO high critical temperature superconductors, the energy conditioning, the linear induction motor and its regenerative braking, as well as the automatic supply system of liquid nitrogen will be presented in the proposed paper. Tests with this operational prototype demonstrate the technology feasibility.

A Full Scale Superconducting Magnetic Levitation (MagLev) Vehicle Operational Line

In order to improve the cost performance of the present high-Tc superconducting (HTS) Maglev vehicle system for practical application, the multi-pole permanent magnet guideway (PMG) concept was introduced. A well-known double-pole Halbach PMG was chosen as a representative of multi-pole PMGs to compare with traditional monopole PMGs from the point of view of levitation efficiency and cost. Experimental results show that YBCO bulks above the double-pole Halbach PMG can exhibit better load capability and guidance performance as well as dynamics stability at the applied working height between the bulk HTSC and the PMG due to a more reasonable magnetic field distribution at the working range of bulk HTSC. Furthermore, the double-pole PMG configuration can play a more important role in improving guidance performance due to the potential-well field configuration. By comparing with former 'century' PMGs, the double-pole Halbach PMG shows another remarkable advantage in reducing the cost of levitation. As another necessary issue, magnetic field homogeneity and the corresponding magnetic drag force of a double-pole Halbach PMG has been considered by experiment in spite of the above highlights. Synthetically, the multi-pole Halbach PMG design is concluded to be one important choice for future HTS Maglev vehicle applications because of its high efficiency and low cost.

https://iopscience.iop.org/article/10.1088/0953-2048/21/11/115018/pdf

High-efficiency and low-cost permanent magnet guideway consideration for high-Tc superconducting Maglev vehicle practical application

In applications utilizing high-temperature superconductors (HTS) under high mechanical loads as high-field magnets or rotors of generators and motors, the rare-earth–barium–copper-oxide (REBCO) tapes have to be stabilized mechanically. This is achieved using support structures of structural materials and filling the voids in the support through the impregnation of the tapes. The impregnation prevents movement of the tapes and distributes mechanical loads evenly. With high mechanical strengths and low sensitivities to rapid temperature changes, epoxy resins are desired materials for the impregnation of superconductor tapes. However, a strong decrease of the current-carrying capabilities was observed in previous epoxy-impregnated REBCO coils. In this work the thermal expansion mismatches between epoxy resins and REBCO tapes are identified as the cause of these degradations. Fillers are used to reduce the thermal expansions of glues and resins. Mixtures with varying filler contents are analyzed systematically. Their thermal expansions and the corresponding degradations of short REBCO tape samples are measured. A mixture of epoxy resin and filler is found which allows degradation-free impregnation of REBCO tapes. This mixture is validated on a 1.2 m long 15 × 5 Roebel-assembled-coated-conductor (RACC) cable from Industrial Research Limited (IRL).

https://iopscience.iop.org/article/10.1088/0953-2048/26/5/055007/pdf

Degradation free epoxy impregnation of REBCO coils and cables

A novel composite control method based on disturbance observer for the precision suspension of a voltage-controlled active magnetic bearing (AMB) system is presented in this study. The voltage-controlled AMB system always suffers from the mismatched disturbances, which act on the system via different channels from the control inputs. In this study, we reconstruct a new system, which is equivalent to the original voltage-controlled AMB dynamical system. The reconstructed system targets to divide the mismatched disturbances into the matched component and the mismatched component. The matched component is attenuated by the feedback robust controller, and the mismatched component is rejected on the basis of disturbance observer. Both simulations and experiments demonstrate the effectiveness in rejecting the mismatched disturbances on the voltage-controlled AMB system in a magnetically suspended control moment gyro. The proposed control method handles the mismatched disturbances from the state variable and preserves the nominal performance of the baseline robust controller to the best.

Mismatched Disturbance Rejection Control for Voltage-Controlled Active Magnetic Bearing via State-Space Disturbance Observer

A 45-m-long high-temperature superconducting (HTS) Maglev ring test line, named “Super-Maglev,” has been successfully developed in Chengdu, China, in February 2013, 12 years after the birth of the first man-loading HTS Maglev test vehicle. The Maglev vehicle (2.2 m in length, 1.1 m in width) is designed for one passenger with a levitation height of 10–20 mm; the permanent-magnet guideway (PMG) (45 m in length, 0.77 m of track gauge) is a racetrack shape with a curve radius of 6 m; the driving is accomplished by a linear induction motor with a maximum running speed of 50 km/h. The linear motor is composed of four submotors installed at one straight section in the middle of the double PMGs, and the total length is 3 m. This second-generation HTS Maglev vehicle system is highlighted by the cost-performance and the wireless multiparameter onboard monitoring function. The current same-level load capability has been achieved over a small-section low-cost PMG whose cross-sectional area is only 3000 mm
 2
. On the vehicle, parameters of levitation weight, levitation height, running speed, acceleration, lateral offset, online position, and total running distance of the vehicle are real-time monitored and displayed on the onboard tablet computer. The system component and test data are reported in detail in this paper.

A High-Temperature Superconducting Maglev Ring Test Line Developed in Chengdu, China

A four pole superconducting excitation system that was part of a linear synchronous motor (LSM) system, was fabricated and its thrust and normal forces studied experimentally. Four cases were investigated, air-cored, with a ferromagnetic (FM) back plate, an FM core, and with both an FM back plate and core. With a total of only 15 m of YBCO coated conductor in the form of four coils as the excitation system, thrust output of up to 95 N while operating at 77 K with a magnetic gap of 10 mm was obtained in one particular case. The results of the studied superconducting LSM system help better understand the feasibility of their applications to drive systems for Maglev trains.

Superconducting Excitation System of a Small Scale Linear Synchronous Motor

Four coils made of YBCO-coated conductor wire were fabricated and connected in series to make up the excitation system of a linear synchronous motor system with a stator made of ordinary copper wire. The electromagnetic forces experienced by the superconducting coils with respect to the stator were studied in the static case. We began with the study of one single coil, followed by two coils connected in series, and finally, four coils in series from which the largest force obtained was of 53.9 N at a gap of 10 mm at 77 K. The critical current, n-value, and inductance were also measured for the coils so that the power dissipation of the field windings can be calculated. This paper also helps us understand whether linear motors with superconducting components are currently economically feasible with present commercially available superconducting wire.

Performance of a Small-Scale High Temperature Superconducting Linear Synchronous Motor Prototype

Zero-field cooling (ZFC) and field cooling (FC) are the two most popular activation ways of the bulk high-temperature superconductors (HTSCs). The former can bring a big levitation force but a poor stability, while the latter can bring a good stability but a reduced levitation force due to the trapped flux. Under this rule, it is very difficult to improve the levitation force (load capability) and guidance force (stability) at the same time with the given bulk HTSCs and applied field in practice. In the paper, based on the re-magnetization ability of bulk HTSCs, the maglev performance of bulk HTSCs with a re-magnetization process after ZFC was experimentally investigated above a permanent magnetic guideway (PMG). The bulk HTSCs were firstly cooled down at a far distance above the PMG, but before moving to the working height, an additional process was introduced to descend the bulks to a lower height to magnetize again by the PMG field. Experimental results show that, at certain re-magnetization height above PMG, the levitation force and guidance force could be improved simultaneously compared with the results of normal FC cases, which is different from the present performance improvement with the sacrifice of one important force. This result presents a possible working way for the levitation applications of bulk HTSCs by employing a re-magnetization process after ZFC, and is also useful to optimize the performance of high-temperature superconducting Maglev vehicle systems.

Improved Maglev Performance of Bulk High-Temperature Superconductors with a Re-magnetization Process After Zero-Field Cooling

The mechanical bearing in the cryogenic liquid pump has short working life due to the low temperature environment. For conquering the disadvantage, the radial high temperature superconducting magnetic bearing (HTSB) is designed to be used in the cryogenic pump. The high temperature superconductors (HTSs) in the HTSB are cooled by the cryogenic liquid directly. The introduced cryogenic liquid pump can constrain the heat leakage. The equipment for the kinetic characteristics of the HTSB is introduced, and it can measure the axial forces of the HTS at different rotation speeds. Basic mechanical principle of the rotor of the pump is analyzed.

Qunxu Lin

Papers

A High-Temperature Superconducting Maglev Ring Test Line Developed in Chengdu, China

Superconducting Excitation System of a Small Scale Linear Synchronous Motor

Performance of a Small-Scale High Temperature Superconducting Linear Synchronous Motor Prototype

Improved Maglev Performance of Bulk High-Temperature Superconductors with a Re-magnetization Process After Zero-Field Cooling

Research of Radial High Temperature Superconducting Magnetic Bearings for Cryogenic Liquid Pumps