Architecture and Transport Properties of Multifilamentary MgB2 Strands for MRI and Low AC Loss Applications

Standard in situ type MgB
₂
strands manufactured by Hyper Tech, Inc., have 19-36 subelements, a Monel outer sheath, and a Cu interfilamentary matrix. Typical transport J
_c
s of the strands are 2 × 10
⁵
A/cm
²
with n-values of 20-30 at 4.2 K and 5 T. This paper introduces two new MgB
₂
conductor designs. First, a new class of MgB
₂
strand is designed for magnetic resonance imaging applications. This type has a higher Cu content designed to enhance protection of a magnet wound with it, and a larger diameter to increase the critical current. Second, a new class of low ac loss MgB
₂
strand with high filament count and a high-resistance matrix is discussed. Transport properties at 4.2 K and fields up to 10 T are reported. Optical techniques are used to study the macro and microstructures of these MgB
₂
strands.