  A significant enhancement of Jc and Hirr in MgB2 tapes has been achieved by
the in situ powder-in-tube method utilizing hollow carbon spheres (HCS) as
dopants. At 4.2 K, the transport Jc for the 850C sintered samples reached
3.1x10^4, and 1.4x10^4 A/cm^2 at 10 and 12 T, respectively, and were better
than those of optimal nano-SiC doped tapes. Furthermore, the Hirr for doped
sample was raised up to 16.8 T at 10 K due to the carbon substitution effect.
The results demonstrate that HCS is one of the most promising dopants besides
nano-carbon and SiC for the enhancement of current capacity for MgB2 in high
fields.
