High Energy Milled Ex Situ MgB₂ as Precursor for Superconducting Tapes Without Critical Current Anisotropy

Abstract

One lane of the present MgB₂ research is focused on scale-up of the conductor preparation for magnet applications. One limitation is the deformation of long length powder in tube conductors since the composite structure leads to a couple of complications. Therefore, a combination of various methods is commonly used: swaging, drawing, and flat rolling. In dense tapes deformed via distinct routes, a critical current anisotropy with respect to an external magnetic field is observed. The in situ method (unreacted Mg+B) is preferably used for conductor preparation, with the advantage offering more doping possibilities for the precursors to create flux pinning centers and to enhance the upper critical field and supporting a dense filament. In this work, we show in concurrence to the commonly preferred route, the possibility and potential of ex situ conductor preparation schemes, with the option of carbon doping, using high energy milling. Long multifilament tapes with 20 hours milled powder without carbon and with 5 wt% C were successfully deformed to wires and tapes. Tapes with 21 cores show critical current densities with J _c=10⁴ A/cm² at B=8.8 T without any current anisotropy in different field-direction different to the case of the in situ conductors.