State of the art powder-in-tube niobium–tin superconductors

Abstract

Powder-in-Tube (PIT) processed Niobium-Tin wires are commercially manufactured for nearly three decades and have demonstrated a combination of very high current density (presently up to 2500 Amm -2 non-Cu at 12 T and 4.2 K) with fine (35 /im), well separated filaments. We review the developments that have led to the present state of the art PIT Niobium-Tin wires, discuss the wire manufacturing and A15 formation processes, and describe typical superconducting performance in relation to magnetic field and strain. We further highlight successful applications of PIT wires and conclude with an outlook on possibilities for further improvements in the performance of PIT Niobium-Tin wires.

Assessing composition gradients in multifilamentary superconductors by means of magnetometry methods

“…The slope dβ/dx computed from linear fits in the fine grain region of the data obtained from EDX and AC magnetometry is 0.11 at.%/µm in both cases, in agreement with results obtained by others in similar studies on PIT wires. 5,9,10 In section II A we state that the introduction of an intra-granular Sn gradient is necessary to achieve agreement between the histogram obtained from the AC magnetometry method and the actual calorimetry data. One might therefore argue that the method is only useful if the intra-granular Sn gradient or the calorimetry histogram is known.…”

“…This gradient is sensitive to the reaction temperature and duration, and, given a sensible choice for the heat treatment, takes on values of typically 0.1 -0.4 at.%/µm. 5,9,10 Another characteristic feature of PIT Nb 3 Sn wires is their twofold grain morphology: the sub-elements consist of fine grains (∼ 150 nm) on the outside, whereas large grains (∼ 1 -2 µm) dominate near the core. It was found that these two grain types exhibit significantly different T c and B c2 distributions.…”

“…The actual A-15 phase is obtained by applying a heat treatment, leading to a solid state diffusion reaction in which -after the formation of some intermediate phasestubular Nb 3 Sn sub-elements are formed. 5 Modeling this process is a complex matter, but recently progress was made in this field. 8 This diffusion process results in a Sn concentration gradient inside of each sub-element, pointing from the outer edge towards the core.…”

“…First, in this material the critical temperature exhibits a strong dependence on stoichiometry, and such wires are prone to compositional gradients due to their production method, which makes them an ideal model system. 4,5 And second, research on Nb 3 Sn is currently experiencing a renaissance driven by the desire to equip the Future Circular Collider with 16 T dipoles based on this material. 6 The stoichiometry of Nb 3 Sn is usually expressed in terms of the atomic Sn content β, casting the chemi- * tbaumgartner@ati.ac.at cal composition in the form Nb 1−β Sn β .…”

COMPARISON OF A15 STOICHIOMETRY AND GRAIN MORPHOLOGY IN INTERNAL Sn AND TUBE TYPE STRANDS; INFLUENCE OF STRAND DESIGN, HTs AND ALLOYING

“…The general idea of tube type conductors, where Cu and Sn are inserted into Nb tubes, has been pursued before [7][8][9][10][11], and these conductors do have some similarities to powderin-tube (PIT) strands (as well as differences) [12][13][14][15][16][17][18][19][20][21]. Early on, geometrically similar conductors were fabricated by Murase and associates [7].…”