Compact solid-state sources of terahertz (THz) radiation are being sought for sensing, imaging, and spectroscopy applications across the physical and biological sciences. We demonstrate that coherent continuous-wave THz radiation of sizable power can be extracted from intrinsic Josephson junctions in the layered high-temperature superconductor Bi2Sr2CaCu2O8. In analogy to a laser cavity, the excitation of an electromagnetic cavity resonance inside the sample generates a macroscopic coherent state in which a large number of junctions are synchronized to oscillate in phase. The emission power is found to increase as the square of the number of junctions reaching values of 0.5 microwatt at frequencies up to 0.85 THz, and persists up to ∼50 kelvin. These results should stimulate the development of superconducting compact sources of THz radiation.

http://absimage.aps.org/image/MAR08/MWS_MAR08-2007-004672.pdf

Emission of Coherent THz-Radiation from Superconductors.

This paper describes the present status of high temperature superconductors (HTS) and of bulk superconducting magnet devices, their use in bearings, in flywheel energy storage systems (FESS) and linear transport magnetic levitation (Maglev) systems. We report and review the concepts of multi-seeded REBCO bulk superconductor fabrication. The multi-grain bulks increase the averaged trapped magnetic flux density up to 40% compared to single-grain assembly in large-scale applications. HTS magnetic bearings with permanent magnet (PM) excitation were studied and scaled up to maximum forces of 10 kN axially and 4.5 kN radially. We examine the technology of the high-gradient magnetic bearing concept and verify it experimentally. A large HTS bearing is tested for stabilizing a 600 kg rotor of a 5 kWh/250 kW flywheel system. The flywheel rotor tests show the requirement for additional damping. Our compact flywheel system is compared with similar HTS–FESS projects. A small-scale compact YBCO bearing with in situ Stirling cryocooler is constructed and investigated for mobile applications. Next we show a successfully developed modular linear Maglev system for magnetic train operation. Each module levitates 0.25t at 10 mm distance during one-day operation without refilling LN2. More than 30 vacuum cryostats containing multi-seeded YBCO blocks are fabricated and are tested now in Germany, China and Brazil.

http://iopscience.iop.org/article/10.1088/0953-2048/25/1/014007/pdf

Superconductor bearings, flywheels and transportation

This manuscript reports on the recent progress and the remaining materials challenges in the development of coated conductors (CCs) for power applications and magnets, with a particular emphasis on the different initiatives being active at present in Europe. We first summarize the scientific and technological scope where CCs have been raised as a complex technology product and then we show that there exists still much room for performance improvement. The objectives and CC architectures being explored in the scope of the European project EUROTAPES are widely described and their potential in generating novel breakthroughs emphasized. The overall goal of this project is to create synergy among academic and industrial partners to go well beyond the state of the art in several scientific issues related to CCs’ enhanced performances and to develop nanoengineered CCs with reduced costs, using high throughput manufacturing processes which incorporate quality control tools and so lead to higher yields. Three general application targets are considered which will require different conductor architectures and performances and so the strategy is to combine vacuum and chemical solution deposition approaches to achieve the targeted goals. A few examples of such approaches are described related to defining new conductor architectures and shapes, as well as vortex pinning enhancement through novel paths towards nanostructure generation. Particular emphasis is made on solution chemistry approaches. We also describe the efforts being made in transforming the CCs into assembled conductors and cables which achieve appealing mechanical and electromagnetic performances for power systems. Finally, we briefly mention some outstanding superconducting power application projects being active at present, in Europe and worldwide, to exemplify the strong advances in reaching the demands to integrate them in a new electrical engineering paradigm.

/pdf/coated-conductors-for-power-applications-materials-1e6nsc3j8f.pdf

Coated conductors for power applications: materials challenges

https://bura.brunel.ac.uk/bitstream/2438/14401/3/FullText.pdf

Heat pipe based systems - Advances and applications

Superconducting technology applications in electric machines have long been pursued due to their significant advantages of higher efficiency and power density over conventional technology. However, in spite of many successful technology demonstrations, commercial adoption has been slow, presumably because the threshold for value versus cost and technology risk has not yet been crossed. One likely path for disruptive superconducting technology in commercial products could be in applications where its advantages become key enablers for systems which are not practical with conventional technology. To help systems engineers assess the viability of such future solutions, we present a technology roadmap for superconducting machines. The timeline considered was ten years to attain a Technology Readiness Level of 6+, with systems demonstrated in a relevant environment. Future projections, by definition, are based on the judgment of specialists, and can be subjective. Attempts have been made to obtain input from a broad set of organizations for an inclusive opinion. This document was generated Superconductor Science and Technology Supercond. Sci. Technol. 30 (2017) 123002 (41pp) https://doi.org/10.1088/1361-6668/aa833e Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. 0953-2048/17/123002+41$33.00 © 2017 IOP Publishing Ltd Printed in the UK 1 through a series of teleconferences and in-person meetings, including meetings at the 2015 IEEE PES General meeting in Denver, CO, the 2015 ECCE in Montreal, Canada, and a final workshop in April 2016 at the University of Illinois, Urbana-Champaign that brought together a broad group of technical experts spanning the industry, government and academia.

https://iopscience.iop.org/article/10.1088/1361-6668/aa833e/pdf

High power density superconducting rotating machines—development status and technology roadmap

The magnetic bearing is considered as one of the most prospective applications of high temperature superconductors (HTSs) which can realize stable levitation in a magnetic field generated by permanent magnet devices or coils. The exploration of this kind of HTS bearing through numerical investigation is usually made by assuming the induced current circulates only within the ab-plane and thus simplifying the actual three-dimensional problem to a two-dimensional one. In this paper, on the basis of the three-dimensional model of the HTS bulk established before, we further introduce the developed finite-element software to calculate the magnetic field generated by a magnetic rotor which is composed of permanent magnet (PM) rings and ferromagnet (FM) shims, and in this way, we can investigate the magnetic forces (radial force and axial force) of a simplified HTS bearing model, i.e., two symmetric HTS bulks and a magnetic rotor, at a three-dimensional level. The investigations performed in this paper lead to the observations: the favorable configuration to construct the HTS bearing is that the axial height of each HTS element should be equivalent to the axial heights of PM ring plus FM shim; the increase of the radial thickness of PM ring will improve both the radial force and the axial force considerably, but its margin decreases; the enhancement of critical current density of HTSs due to the decrease of operating temperature can result in a higher increase of both the radial and axial force with a lower nominal gap between the HTSs and the magnetic rotor.

Numerical Studies of Axial and Radial Magnetic Forces Between High Temperature Superconductors and a Magnetic Rotor

The research on dynamic characteristics of a high-temperature superconducting (HTS) maglev system reveals that the system is a low-damping dynamic system and an eddy-current damper is able to improve the systemic damping. The influence of the eddy-current damper on the dynamic levitation force of the HTS maglev system was studied in the paper. Several different thicknesses of copper plates were respectively set at the bottom of the superconductors to work as the eddy-current damper. Dynamic levitation forces were measured above a rotating permanent magnet guideway (PMG) under a velocity range from 15 to 120 km/h. For the sake of estimating the effect of the copper damper on the dynamic levitation force, the peak values, steady values, and attenuation ratios of dynamic levitation forces are comparatively analyzed in two conditions of no copper damper and having copper damper. We also perform the magnetic field measurement experiment in the top and bottom surface s of 0. 1 -mm- thick copper damper by two Hall sensors, the results of which indicate that the electromagnetic shielding effect of the copper plate becomes more obvious with the increase of the rotational velocity of PMG. We conclude that inserting the eddy-current damper at the bottom of the superconductors has a weakly positive effect on the promotion of dynamic levitation force. So, the eddy-current damper can be applied to the HTS maglev system to enhance systemic damping without substantially affecting the systemic dynamic levitation force under a designated running velocity.

Effect of Eddy-Current Damper on the Dynamic Levitation Force in High-Temperature Superconducting Maglev System

With the advantages of high-speed, low-noise and environment-friendly, magnetic levitation (maglev) train has the potential to become a high-speed transportation mode. High-temperature superconducting (HTS) maglev, which can remain stable levitation without any control system, is a competitive type of maglev rail transit. As a kind of high-speed transit, the vibration of the HTS maglev system is inevitable. Hence, studies about its dynamics are necessary and significant. The developments and researches for the HTS maglev vehicle dynamics in Applied Superconductivity Laboratory (ASCLab) are elaborated in detail in this paper. Based on the improved HTS maglev ring test line “Super-Maglev”, a series of research works have been carried out. First, the mathematical model of the pinning force was proposed. Second, motion stability and nonlinear vibration characteristics were studied. Then, the dynamic simulation of vehicle-bridge coupled system of the HTS maglev train was performed. Finally, certain vibration reduction optimizations were added. These dynamics researches give a strong verification for the future application prospect and feasibility of HTS maglev transportation, and the results can provide reference for the engineering application.

Dynamic Studies of the HTS Maglev Transit System

Due to the large levitation force or the large guidance force of bulk high-temperature superconducting magnets (BHTSMs) above a permanent magnet guideway (PMG), it is reasonable to employ pre-magnetized BHTSMs to replace applied-magnetic-field-cooled superconductors in a maglev system. There are two combination modes between the BHTSM and the PMG, distinguished by the different directions of the magnetization. One is the S-S pole mode, and the other is the S-N pole mode combined with a unimodal PMG segment. A multi-point magnetic field measurement platform was employed to acquire the magnetic field signals of the BHTSM surface in real time during the pre-magnetization process and the re-magnetization process. Subsequently, three experimental aspects of levitation, including the vertical movement due to the levitation force, the lateral movement due to the guidance force, and the force relaxation with time, were explored above the PMG segment. Moreover, finite element modeling by COMSOL Multiphysics has been performed to simulate the different induced currents and the potentially different temperature rises with different modes inside the BHTSM. It was found that the S-S pole mode produced higher induced current density and a higher temperature rise inside the BHTSM, which might escalate its lateral instability above the PMG. The S-N pole mode exhibits the opposite characteristics. In general, this work is instructive for understanding and connecting the magnetic flux, the inner current density, the levitation behavior, and the temperature rise of BHTSMs employed in a maglev system.

https://iopscience.iop.org/article/10.1088/0953-2048/29/9/095009/pdf

Zigang Deng

Papers

Numerical Studies of Axial and Radial Magnetic Forces Between High Temperature Superconductors and a Magnetic Rotor

Effect of Eddy-Current Damper on the Dynamic Levitation Force in High-Temperature Superconducting Maglev System

Dynamic Studies of the HTS Maglev Transit System

Magnetic and levitation characteristics of bulk high-temperature superconducting magnets above a permanent magnet guideway

Levitation performance of different bulk YBaCuO arrays above a permanent magnet guideway for HTS maglev systems