Vitaly S. Vysotsky

Thermal quench study in HTSC pancake coil

Abstract In spite of rather high general stability of high temperature superconducting (HTSC) Bi-based magnets, catastrophic thermal quench (TQ) may appear in them under certain circumstances. It happens because of non-linearity of voltage–current characteristics in HTSC superconductors. Starting with small samples in our previous works, we continue to study the TQ with large samples. We prepared a highly instrumented HTSC pancake coil. It is wound using the Bi-2223-based tape. We attached many potential taps to the tape and installed in the winding 10 cryogenic thermocouples (TC) and two heaters. Quench development in the coil was measured under different temperatures, different magnetic fields and different cooling conditions. In this paper, the experimental details and the results obtained are presented. The results are discussed from the point of view of scaling theory for quenching in HTSC devices.

30 m HTS Power Cable Development and Witness Sample Test

In the framework of the Russian R&D Program for superconducting power devices, an experimental 30 m HTS power cable has been developed. Three 30 m phases with nominal current of ~2 kA and 20 kV operating voltage were delivered as the result of the project. Variations were used in basic HTS materials, cryostats and current leads for the cable design in this research project. All phases were made of 1G HTS Bi-based tape. The details of the design of the cable are discussed. Before the full length cable test a 5 m witness sample has been cut, heavily instrumented and tested. Results of the witness sample tests and analysis of fault current behavior of the cable are presented.

AC Loss and Other Researches with 5 m HTS Model Cables

The test facility developed in Russian Scientific R&D Cable Institute permits to perform extensive tests of heavily instrumented HTS cable models with length up to 5 m. Several HTS cables with different design have been developed and tested at this facility. The test programs included, besides usual critical current measurements, current distribution measurements among layers, joint resistance test, etc. The facilitys equipment permits digital measurements of voltage and current with high accuracy and, therefore, digital ac loss analysis in model cables. In this paper we present the details of the test facility and results of tests and ac loss measurements in few 5 m model cables. ac losses in model cables made of 1 G and 2 G wires and other cable parameters are discussed and compared.

Quench characteristics in HTSC devices

Quench dynamics in a YBCO HTSC film and a Bi-based small HTSC coil have been studied. While the stability margin of HTSC against a local disturbance was very large, quench current was limited by a catastrophic temperature rise originated from the nonlinear characteristic of Joule heating in HTSC. The crucial parameter for the quench becomes the nonlinear resistance in HTSC as a function of temperature and transport current. It has been shown that the dynamic characteristics of the quench in both the film and the coil can be described quantitatively by the simplified one-dimensional heat balance equation even though the time scales are different by more than six orders, i.e., several hundreds micro seconds for the film and several hundreds seconds for the tape coil.

Current non-uniformity in multistrand superconducting cables. Experimental studies and its influence on stability of superconducting magnets

It is widely acknowledged that current non-uniformity is a major source of reduction of quench currents at nonsteady state conditions in multistrand superconducting cables. It is important to study current non-uniformity in experiments. In this paper we present a review of the experimental methods used to study current non-uniformity in CICC and AC multistrand superconducting cables and results received. We discuss the influence of current non-uniformity on stability of superconducting magnets made from multistrand superconducting cables and possible ways to overcome their instability.

Heat propagation and stability in a small high Tc superconductor coil

Abstract Using a Bi-based small high T c superconductor (HTSC) coil, we have studied its stability against a local disturbance and current-induced quench in the helium gas cooling condition. While the stability margin of HTSC coil against a local disturbance was very large, quench current was limited by a catastrophic temperature rise which originated from the nonlinear characteristic of the Joule heating. The crucial parameter for the quench becomes the nonlinear resistance in HTSC as a function of temperature and transport current. It has been shown that the dynamic characteristics of the quench can be described quantitatively by the simplified one-dimensional heat balance equation.

Hybrid Energy Transfer Line With Liquid Hydrogen and Superconducting

The transfer of massive amounts of both electrical and chemical power over long distances will present a major challenge for the global energy enterprise in the future. Attraction of hydrogen is apparent as a chemical energy agent, possessing among the highest energy density content of various common fuels, whose combustive “waste” is simply water. It could be transferred via cryogenic tubes being liquid at temperatures ~18-26 K. The usage of “gratis” cold to cool a superconducting cable made of a proper superconductor permits to deliver extra electrical power with the same line. In this paper, we describe the experimental modeling of this concept via a combined MgB2-cryogenic dc superconducting cable refrigerated by “singlet” phase liquid hydrogen. We present the design, construction details, and test results of a 10-m prototype, focusing on choice of MgB2 cable and cryostat technologies. We also discuss the opportunities and possibilities for future practical deployment of such hybrid energy delivery systems.

\hbox{MgB}_{2}

We studied quench propagation in double-sided samples of YBCO thin films covered by a gold top layer and deposited on sapphire wafers. The length of the YBCO structures was up to 0.5 m. A critical current density /spl sim/2-3 MA per centimeter square at 77.8 K was found over the entire YBCO film. Quench development in large-area YBCO thin film appears to be a complicated process. Depending on test conditions and external circuit parameters, normal spots may appear and disappear during the quench process. In double-sided samples quench development is strongly affected by thermal interaction between the two films through the substrates heat conductivity. This thermal conduction should be considered during the design of fault current limiters made from such films. Mutual thermal interaction of a film through a substrate may also be used for acceleration of normal zone propagation using active or passive heaters on opposite sides of the substrate.

Cable—First Experimental Proof of Concept

In the framework of the Russian R&D Program for superconducting power devices, the 30 m HTS power cable has been developed made of 1 G Bi-2223 tapes. Before the full length cable production, as the first prototype the short 5 m cable model was produced and tested. After 30 m cable production the 5 m witness sample has been cut from the long piece and tested as well. To verify the calculations and designing principles both 5 m cables were heavily instrumented by potential taps and sensors to measure current distribution among layers, voltage-current characteristics and other parameters. AC losses in these short cable pieces have been analyzed by use of digital measurements of current and voltages along the cable. The witness sample has been provided by thermocouples to evaluate AC losses by calorimetric method. The details of AC losses measurements are discussed. Their analysis and comparison with calculations by standard theoretical models are presented.

Quench propagation in large area YBCO films

The cable-in-conduit-conductors (CICC) for the ITER Toroidal Field (TF) Coils are tested in the Sultan test facility in order to estimate their AC and DC performances under operating conditions. The tests are carried out on different stages of conductor procurement implementation starting from Nb3Sn superconducting strand layout and process development to regular checks of production unit lengths. Four TF samples provided by Russia have been successfully tested in the Sultan facility by now in the framework of the ITER collaboration, including Strand Performances Qualification Sample, Qualification Conductor Sample, Pre-production and Production Conductors sample. The test results of all four samples shows pretty good reproducibility of the conductor performances from sample to sample and at the same time good stability of conductor performance under mechanical loading caused by Lorenz force during electromagnetic (EM) cycling can be observed. In the present work a comparison of the conductors and their performance was carried out to show the development of conductor performances from R&D stage to mass production.