Development of Ta-matrix ${\rm Nb}_{3}{\rm Al}$ Strand and Cable for High-Field Accelerator Magnet

Kikuchi

et al. 2012

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We have been developing high-field accelerator magnets with the aim of upgrading the luminosity of the Large Hadron Collider. In this program, four kinds of Ta-matrix strands with slightly different cross-sectional structures (K1, K2, K3 and K4 strands) were designed and fabricated. The non-copper values of these strands were 700-800 at 15 T and 4.2 K. The cabling work of these strands was performed at Fermilab, and the superconducting properties of the cables were studied using the extracted strands from the cables. In this paper, we report on the fabrication experience for the strands and cables. The results obtained from this study are also presented.

Section: Fabrication Of Copper-stabilized Strandmentioning

confidence: 64%

Section: Introductionmentioning

confidence: 99%

Development of ${\rm Nb}_{3}{\rm Al}$ Rutherford Cable for High-Field Accelerator Magnet Applications

Kikuchi

et al. 2012

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“…Example of RHQ current, voltage, diameter and input power per unit volume in CC mode. The sample is Ta matrix wire (ME492) [15]. The gap at 65 m was caused by wire breaking during the RHQ operation.…”

Section: Recent Efforts and Resultsmentioning

confidence: 99%

Fabrication of Long-Length ${\rm Nb}_{3}{\rm Al}$ Wire by the Metastable Solid-Solution-Strand Restacking Method

Banno

et al. 2011

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This paper describes two subjects, both aimed at the industrialization of Nb 3 Al conductors. One is the metastable solid-solution-strand restacking method, which is expected to be a low-cost Cu-stabilization method compared with the electroplating technique. In this paper, we mainly focus on recent efforts toward long-length production. The key point here is an improvement of the contact between the Cu tube and the restacked original strands. The second subject is the first attempt at "constant voltage" control in the continuous rapid-heating and quenching operation for 300-m-class precursor wire. With constant current control, changes in the diameter of the wire lead to variations in power per unit volume, so that the processing temperature changes. With constant voltage control, changes in diameter of the wire do not lead to changes in the power per unit volume, so that the processing temperature does not change and thus the uniformity of the longitudinal performance is improved.

“…The critical current (I c ) under the optimum condition (V RHQ : 9.5-10.0 V) is characterized by a steeper magnetic field dependence than that under conditions with very small (V RHQ < 9.0 V) and with excess heating (V RHQ > 10.5 V). The non-Cu critical current density (J c ) (4.2 K) at 18 T is approximately 200 A/mm 2 for the asquenched-&-transformed Nb 3 Al filament, which is lower than that for conventional Ta barrier precursors [5], mainly because the Nb&Ta to JR ratio of 1.89 (Table I) is much larger than that of the Ta barrier precursor (0.8 [5]). Excessive heating degrades the upper critical magnetic field (B c2 ) (which is proportional to T c [ Fig.…”

Section: Reel-to-reel Rhq Treatmentmentioning

confidence: 88%

Applicability of Reel-to-Reel RHQ Treatments to $ \hbox{Nb}_{3}\hbox{Al}$ Precursors With a Ta/Cu/Ta Three-Layer Filament-Barrier Structure

Nakagawa

et al. 2013

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A tension-free rapid heating and quenching (RHQ) simulator was previously employed to demonstrate that a ductile and normal-conducting Cu layer can suppress a magnetic field instability and improve bending strain tolerance. However, a molten Cu barrier caused the filament to be shifted from the original location, and excess heating caused the Cu to locally corrode a Ta layer, through which it diffused into the filament, thereby embrittling the resulting wire. In some cases, the swelling molten-Cu tore the Ta skin. Fabrication of a long piece of Ta/Cu/Ta barrier Nb 3 Al wire is attempted using reelto-reel RHQ treatment of a modified precursor with a thicker Ta skin that would tolerate both tension forces in a section of the wire between electrodes and pressure from the swelling of molten-Cu. In the optimum RHQ condition (V RHQ : 9.5 V), a 50-m piece of Ta/Cu/Ta barrier precursor was successfully reelto-reel RHQ treated to form a bcc supersaturated-solid solution (Nb(Al) ss ) without bursting of the Ta skin. Microstructural analysis revealed that the molten Cu, into which Ta dissolved, diffused into the jelly-roll filament, mainly through a region of partially melted Al-rich Nb(Al) ss . The critical current density of the filament J c (18 T, 4.2 K) was optimized by the deformation of Nb(Al) ss and compared favorably with the conventional precursor.