V
3Si multifilamentary superconductors produced by a modified bronze process are promising for AC applications. The combination of adjusting the total proportion of V to Si in the Cu-Si/V composite to -3 and reducing V filaments to -1μm enables the completion of the reaction in a short time; the V
5Si
3 initially formed around V
3Si filaments appropriately decomposes and mostly V
3Si without grain growth is produced to achieve a high overall critical current density
Jc. In addition to fine grain structure of V
3Si, an increment in density of V
3Si/normal-metal interface pinning center is also responsible for the high overall
Jc of 1.3×10
9A/cm
2 at 5T, being comparable to that of Nb
3Sn multifilamentary wires produced by the bronze process for AC use. The resistivity of remaining V
5Si
3 layers (-15μΩcm at 4.2K) is likely to be high enough to separate the filaments from each other for electromagnetic decoupling. The effective filament diameter
Deff in fields ranging from 1.5 to 7T was -3.5μm for 1.2μm (the designed V filament diameter before heat treatment) composites with undecomposed V
5Si
3 layers, being one of the smallest
Deff reported so far for AC Nb
3Sn superconductors. Disappearance of V
5Si
3 layer after long heat treatments increased
Deff, suggesting that the existence of V
5Si
3 layer is effective to reduce
Deff. Thus, with optimal cross-sectional structure (bronze composition, overall V/Si ratio, filament spacing, filament size, etc.), the control of thickness and morphology of V
5Si
3 layer would furthermore reduce
Deff and hence AC losses.
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