Critical Current Densities and n-Values of MgB2 Conductors for SMES, MRI, and Low AC Loss Applications

Multifilamentary MgB
₂
strands (filament numbers 36 to 114) prepared by the in-situ power-in-tube (PIT) route with carbon doping contents of 0, 2, and 3.2% were wound on barrels for transport
J_c
and
n
-value measurement at 4.2 K in fields of up to 12 T. The strand and gauge lengths were 1 m and 0.5 m. Heat treatments at 675 °C and 650 °C centered around the melting point of Mg (650 °C) and both utilized the liquid-solid reaction. A pair of strands, with and without 2% C doping exhibited the
J_c
(B) crossover effect. Studied were the dependencies of
J_c
on field strength, dopant concentration, and cabling and the dependence of
n
-value on field strength.