Advanced Conductor Technologies (United States)

<sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">REBCO</small> coated conductors have a strong potential for high-field magnet applications. The <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">REBCO</small> technology, however, is still in its infancy for accelerator magnet applications. As part of the U.S. Magnet Development Program (MDP), we developed a six-layer canted <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\cos \theta$</tex-math></inline-formula> dipole magnet, C3a, using <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CORC^®</small> wires developed by Advanced Conductor Technologies LLC. All the layers were wound using a semi-automated winding machine. Three layers of the magnet used <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CORC^®</small> wires containing the SuperPower “AP” <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">REBCO</small> tapes and the remaining layers used the wires containing the “HM” tapes. At 77 K, both kinds of <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CORC^®</small> wires showed 5% to 10% degradation, after bending to a minimum bend radius of 30 or 35 mm, with respect to the self-field critical current measured before winding. At 4.2 K, the magnet reached 9.5 kA at a ramp rate of 9 A s<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{-1}$</tex-math></inline-formula> and generated a dipole field of 1.4 T. The critical current of one layer degraded by 4% after a current transient up to 10.5 kA ramped in an averaged rate of 175 kA s<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{-1}$</tex-math></inline-formula> or 20 T s<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{-1}$</tex-math></inline-formula>. We confirmed the HM <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CORC^®</small> wire can carry a higher current than the AP <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CORC^®</small> wire at 4.2 K. The test results of the C3a magnet showed that the fabrication and assembly procedure can be used for the upcoming full-scale C3 magnet.

Abstract This manuscript presents the design, fabrication, and operation of high temperature superconducting conductor on round core (CORC®) wires utilizing variable critical current REBCO tapes that contain occasional dropouts of critical current (I c). Performance evaluations conducted at temperatures ranging from 25 K to 77 K demonstrated comparable superconducting characteristics between CORC® wires with and without intrinsic variations in I c within the REBCO tapes. This is a clear indication that the high level of current sharing between tapes in CORC® wires allows current to bypass local defects. A 70 mm bore, 4-layer CORC® solenoid in which 25 m of CORC® wire was wound into 81.5 turns, generated a peak magnetic field of 4.6 T at an I c of 4460 A at 25 K. The I c of the solenoid corresponds closely with the sum of the expected average tape I c, not its minimum I c driven by the tape dropouts. Experimental results confirmed stable dissipative operation at 4021 A (87% I c) continuous current with minimal power losses, highlighting the feasibility of manufacturing longer-length CORC® conductors from tapes with significant local dropouts for superconductor applications including fusion, accelerators, power transmission, and rotating machinery.

Abstract Conductor-on-round-core (CORC®) cables composed of rare-earth-barium-copper-oxide high-temperature superconducting (HTS) tapes are of great interest for power transmission applications due to their many advantages such as high power density, light weight, and low loss. Closed circulation loops of cryogenic helium gas can be used to cool HTS cables down to low temperatures to significantly improve their current-carrying capacity. Coupled circuit-electromagnetic-thermal finite element simulations implemented in the COMSOL Multiphysics package were developed, validated, and then used for simulating the fault current limiting (FCL) performance and the cooling processes of an 8-layer CORC® cable cooled with a flow of cryogenic helium gas. In the simulations, the temperature dependence of the electrical and thermal properties of all component materials is implemented for improved accuracy. To overcome computational challenges caused by the considerable difference in geometrical scales (i.e. few-µm-thick HTS layers versus 10 m-long HTS cable), the model is divided into two separate simulations. The first simulation is performed on the transverse cross-section of the cable to calculate the electric field, heating power and temperature rise in each component of a CORC® cable during FCL operation. The heating power calculated in the first simulation is transferred to the second model to simulate the cooling of a 10 m-long cable after the fault is cleared. The effect of the helium gas flow rate on the cooling process is also investigated to develop strategic approaches for optimizing cooling systems for HTS cables with FCL capability. The simulations indicated that a 40 ms fault with a voltage drop of 20 V m−1 along the cable can result in a temperature increase from 60 K to about 165 K inside the cable, and it takes about 500 s to cool the cable back to nearly 60 K with a flow of cold helium gas at a rate of 5 g s−1.

Superconducting magnets designed for high energy physics and nuclear fusion require mechanical and electrical integrity to perform at high currents and magnetic fields. Vacuum Pressure Impregnation (VPI), a process of curing epoxy in and around the superconducting wires, is often used to support and consolidate a magnet. However, the heat and mechanical stresses associated with the process can degrade the wires, significantly lowering their critical current. This study explores different methods of potting and curing CORC wire with the aim of reducing wire performance degradation to less than 3% measured at 77 K, self-field. The wires were 2.9 mm in diameter consisting of a total of six REBCO tapes (three layers of two tapes). Two bending radii (20 mm and 50 mm) were tested to mimic the winding shape of a magnet. Mix 61 epoxy was used in preliminary tests for potting. For each test, two wires were used, and their critical currents were measured simultaneously in liquid nitrogen at 77 K – in their straight form, then bent, followed by the heat treatment used for Mix 61 but without epoxy and finishing with the full epoxy impregnation test. Later tests were performed using CTD-528 to explore a room temperature cure, limiting possibility of degradation from thermal expansion and prolonged exposure of the REBCO tapes to elevated temperature. Here we report the experimental results with multiple CORC wires and different curing schedules. The results obtained are the first steps toward identifying the VPI process with minimum degradation in critical current to be implemented in high-field magnets using CORC wires.

Most cases of primary microvascular angina pectoris (PMVA) are diagnosed clinically, but the etiology and pathological mechanisms are unknown. The effect of routine clinical medications is minimal, and PMVA can progress to serious cardiovascular events. To improve the diagnosis and effective treatment of this disease, this study was designed to diagnose PMVA via cardiovascular magnetic resonance (CMR) and the coronary angiography thrombolysis in myocardial infarction (TIMI) blood flow grade, as well as to analyze vascular endothelial function to elucidate the pathogenesis of PMVA and compare the effects of routine clinical medications.The present randomized controlled trial including a parallel control group will be conducted on 63 PMVA patients in our cardiovascular department. The patients will be selected and randomly divided into the control, diltiazem, and nicorandil groups. The control group will be administered routine drug treatments (aspirin, atorvastatin, betaloc ZOK, perindopril, and isosorbidemononitrate sustained-release tablets). The diltiazem group will be additionally treated with 90 mg qd diltiazem sustained-release capsules. The nicorandil group was additionally given 5 mg tid nicorandil tablets. Coronary angiography will be performed before treatment, the severity and frequency of chest pain will be evaluated before and after 9 months of treatment, and homocysteine and von Willebrand factor levels will be measured. Electrocardiography, echocardiography, dynamic electrocardiography, a treadmill exercise test, and CMR will be performed. Sex, age, body mass index, complications, smoking, and family history will also be recorded. The SPSS19.0 statistical software package will be used to analyze the data. The measurements will be expressed as the mean ± standard deviation. Measurement data will be compared between the groups using Student's t-test. A relative number description will be used for the counting data, and the chi-squaretest will be used to compare the groups. A multivariate logistic regression analysis will be performed A P-value < .05 will be considered significant.The direct indices (CMR and coronary angiographic TIMI blood flow grade) may improve after adding diltiazem or nicorandil during routine drug treatments (such as aspirin, statins, and nitrates) in PMVA patients, and indirect indices (homocysteine and von Willebrand factor levels) may be reduced.Trial registration:Chinese Clinical Trial Registry (http://www.chictr.org.cn/showprojen.aspx?proj=41894), No. CHiCTR1900025319, Registered on August 23, 2019; pre initiation.

Conductor on Round Core (CORC®) technology has achieved a long sought-after benchmark by enabling the production of round, multifilament, (RE)Ba2Ca3O7−x coated conductors with practical current densities for use in magnets and power applications. Recent progress, including the demonstration of engineering current density beyond 300 Amm−2 at 4.2 K and 20 T, indicates that CORC® cables are a viable conductor for next generation high field magnets. Tapes with 30 μm substrate thickness and tape widths down to 2 mm have improved the capabilities of CORC® technology by allowing the production of CORC® wires as thin as 3 mm in diameter with the potential to enhance the engineering current density further. An important benefit of the thin CORC® wires is their improved flexibility compared to thicker (7–8 mm diameter) CORC® cables. Critical current measurements were carried out on tapes extracted from CORC® wires made using 2 and 3 mm wide tape after bending the wires to various diameters from 10 to 3.5 cm. These thin wires are highly flexible and retain close to 90% of their original critical current even after bending to a diameter of 3.5 cm. A small 5-turn solenoid was constructed and measured as a function of applied magnetic field, exhibiting an engineering current density of 233 Amm−2 at 4.2 K and 10 T. CORC® wires thus form an attractive solution for applications between 4.2 and 77 K, including high-field magnets that require high current densities with small bending diameters, benefiting from a ready-to-use form (similar to NbTi and contrary to Nb3Sn wires) that does not require additional processing following coil construction.

For high-current REBCO superconductors in high magnet fields with currents on the order of 50 kA, single coated conductors must be assembled in a cable. Under operating conditions, such cables are subjected to combined torsion, axial, and transverse loads in the tapes and tape joints. As such, the single tape performance under applied axial strain is crucial to understand cable limitations, and important for choosing an appropriate tape geometry and tape supplier. The critical current (I c ) versus applied uniaxial strain and the relative strain irreversibility limit were measured on HTS tapes produced by five manufacturers. The I c measurements were performed at 77 K in self-field with the sample tapes soldered to the U-shaped bending spring (U-spring). It has been observed that most of the tapes perform well under applied compressive strain. The dependence of I c on applied strain and the irreversibility limits were found to be unique for each tape. The n-values of the tapes, unlike the I c , are less sensitive to applied strain in the reversible regime. The results of different tapes are presented and compared.

Within CERN the development of REBCO-CORC (Conductor On Round Core) type cables is pursued in view of possible application in future detector and accelerator magnets. An important issue is the design and qualification of terminations for connecting CORC cables mutually or to bus-bars. A termination design is envisaged that combines a simple manufacturing process with a lowest possible joint terminal resistance in the few nΩ range at 4.2 K, first for a single CORC cable and subsequently for CORC based Cable-in-Conduit Conductors. The investigation concerns the effect of tapering the CORC cable within the joint to form a staircase like geometry, which allows current to pass more directly from the copper joint casing to the inner REBCO layers of the CORC cable. Simulations have shown a substantial decrease in joint resistance at operating current in the case both CORC cable and joint casing are tapered. The CORC cable and new joint were tested at CERN. In this paper, some details of the new joint design, fabrication process, and model are presented and the results are summarized.

Described are the results of magnetization loss measurements made at 77 K on several YBCO conductor-on-round-core (CORC) cables in ac magnetic fields of up to 80 mT in amplitude and frequencies of 50 to 200 Hz, applied perpendicular to the cable axis. The cables contained up to 40 tapes that were wound in as many as 13 layers. Measurements on the cables with different configurations were made as functions of applied ac field amplitude and frequency to determine the effects of their layout on ac loss. In large scale devices such as e.g. Superconducting Magnetic Energy Storage (SMES) magnets, the observed ac losses represent less than 0.1% of their stored energy.

The structure of LaSr2CuTiO6.5, a novel (ABO3)nAO n ) 2 Ruddlesden-Popper phase, has been solved by powder X-ray diffraction and electron microscopy. The diffraction patterns are consistent with I4/mmm symmetry, with tetragonal lattice parameters a ) 3.8816(1) A and c ) 20.296(2) A. The structure of LaSr2CuTiO6.5 is similar to Sr3Ti2O7, with copper and titanium disordered over the single B-cation site, and lanthanum and strontium almost perfectly disordered over the two A-cation sites. The oxygen content, determined by thermogravimetric reduction to be 6.5 ((0.1), is consistent with divalent copper with the oxygen vacancies distributed within the perovskite layers. The absence of local order and strategies for inducing a layered arrangement of the B-cations are discussed.