The 'Garber Current Pattern': An Additional Contribution to AC Losses in Helical HTS Cables?

Conductors made of high-temperature (HTS) wires helically wound in one or more layers on round tubes (CORT) are compact, flexible, and can carry a large amount of current. Although these conductors were initially developed for DC applications, e.g. in magnets, it is worth considering their use for AC, e.g. in underground cables for medium voltage grids and with currents in the kA-range. In these cases, the major challenge is reducing AC losses. In contrast to a straight superconducting wire, in a helical arrangement, due to superconducting shielding, the current does not follow the direction of the wires, but takes a non-trivial zig-zag path within the individual HTS wires (Garber pattern). This includes current components across the thickness of the superconducting layers, so that the often used thin-shell approximation does not hold. In this contribution, we studied a one-layer three-wire CORT by means of fully three-dimensional simulations, based on the H-formulation of Maxwell's equations implemented in the commercial software package COMSOL Multiphysics. As a result of our simulations, the peculiar current profiles were confirmed. In addition, the influence of current, pitch angle, and frequency on the AC losses was studied. We found an optimum for the pitch angle and that the current profiles strongly depend on frequency

Project FASTGRID - Tests on 2G HTS for its Application in DC Resistive SC FCL

HVDC (High Voltage Direct Current) super-grids could become a future solution for the long-distance power-transmission. The Superconducting Fault Current Limiter (SCFCL) is a necessary facility to protect such transmission lines. In the framework of the project FASTGRID dedicated HTS wires for resistive type DC-SCFCL are under development. To reduce the cost per switching capacity: Reduction of the amount of HTS shall be achieved by increasing the allowed electrical field and the critical current density at operating conditions. A wire with an additional laminated 500 µm Hastelloy® shunt is the basic solution for FASTGRID. This work shows experiments on this prospective solution, compared with tests on bare coated conductors at lower E-field, once applied in ECCOFLOW SCFCL. The goal of this work is the validation of the HTS conductor for an electric field higher than 130 V/m for a fault clearing time of 50 ms

Efficient HTS DC- Cable for Power Distribution in Hybrid-Electric Aircraft

With respect to a substantial reduction of greenhouse gas emission, noise reduction and combustible consumption in aircraft an increasing interest in hybrid-electric propulsion systems has emerged in the last years. In the frame of a German research project we actually develop a HTS superconducting busbar system for DC currents able to join the different components as generator, motors and battery systems on the plane. Main features of this busbar system are large currents at moderate voltages and in particular low ohmic contacts, including T-type, Y-type and cross connections between system segments, this with a minimization of outer dimensions and weight. The two-pole cable consists of two stacks of REBCO tapes. Compensation of Lorentz forces between the two poles, compensation of thermal length changes and sufficient electric insulation are the major challenges. We will present details of the cable design and first test results on a lab-scale cable demonstrator

Prevalence of Coxiella burnetii in clinically healthy German sheep flocks

<p>Abstract</p> <p>Background</p> <p>Current epidemiological data on the situation of <it>Coxiella (C.) burnetii </it>infections in sheep are missing, making risk assessment and the implementation of counteractive measures difficult. Using the German state of Thuringia as a model example, the estimated sero-, and antigen prevalence of <it>C. burnetii </it>(10% and 25%, respectively) was assessed at flock level in 39/252 randomly selected clinically healthy sheep flocks with more than 100 ewes and unknown abortion rate.</p> <p>Results</p> <p>The CHECKIT™ Q-fever Test Kit identified 11 (28%) antibody positive herds, whereas real-time PCR revealed the presence of <it>C. burnetii </it>DNA in 2 (5%) of the flocks. Multiple-locus variable number of tandem repeats analysis of 9 isolates obtained from one flock revealed identical profiles. All isolates contained the plasmid QpH1.</p> <p>Conclusions</p> <p>The results demonstrate that <it>C. burnetii </it>is present in clinically inconspicuous sheep flocks and sporadic flare-ups do occur as the notifications to the German animal disease reporting system show. Although <it>C. burnetii </it>infections are not a primary veterinary concern due to the lack of significant clinical impact on animal health (with the exception of goats), the eminent zoonotic risk for humans should not be underestimated. Therefore, strategies combining the interests of public and veterinary public health should include monitoring of flocks, the identification and culling of shedders as well as the administration of protective vaccines.</p

Magnetic shielding properties of a cut superconducting hollow cylinder : modelling and experiment

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Optoelectronic Heterodyne THz Receiver for 100&#x2013;300 GHz Communication Links

Terahertz wireless communications is an increasingly interesting research topic due to the high demand for un-allocated channels and high data rates. Photonic solutions have shown great potential in this field. However, most photonics assisted THz links so far have employed optoelectronics only on the transmit side. Thus, the full potential of photonic THz communication has not been utilized yet. Here, we introduce optoelectronics also on the receive side by using a photoconductive antenna based heterodyne THz detector. This allows down-conversion of data signals from the W-, D-, and THz-band to the baseband using a laser beat signal as local oscillator. Using electromagnetic modeling, we designed passive radio frequency structures and a receiver package to handle high intermediate frequency output signals. In a homodyne spectroscopic setup, the receiver shows a frequency response superior to state-of-the-art photoconductive antennas due to an improved photoconductive material. In a heterodyne testbed, the receiver exhibits a large intermediate frequency bandwidth of 11 GHz and a conversion gain of &#x2212;47 dB. This enabled us to employ the receiver in a fully photonic wireless link at sub-terahertz and terahertz frequencies together with a PIN photodiode emitter. We achieved error-free transmission of 4-QAM signals with gross data rates up to 12 Gbit/s at carrier frequencies up to 320 GHz. This work shows the huge potential of optoelectronic receivers for THz wireless communications and enables the exploration of full photonic THz links