  The magnetic and transport properties of magnesium diboride films represent
performance goals yet to be attained by powder-processed bulk samples and
conductors. Such performance limits are still out of the reach of even the best
magnesium diboride magnet wire. In discussing the present status and prospects
for improving the performance of powder-based wire we focus attention on (1)
the intrinsic (intragrain) superconducting properties of magnesium diboride,
Hc2 and flux pinning, (2) factors that control the efficiency with which
current is transported from grain-to-grain in the conductor, an extrinsic
(intergrain) property. With regard to Item-(1), the role of dopants in Hc2
enhancement is discussed and examples presented. On the other hand their roles
in increasing Jc, both via Hc2 enhancement as well as direct
fluxoid/pining-center interaction, are discussed and a comprehensive survey of
Hc2 dopants and flux-pinning additives is presented. Current transport through
the powder-processed wire (an extrinsic property) is partially blocked by the
inherent granularity of the material itself and the chemical or other
properties of the intergrain surfaces. These and other such results indicate
that in many cases less than 15% of the conductor's cross sectional area is
able to carry transport current. It is pointed out that densification in
association with the elimination of grain-boundary blocking phases would yield
five-to ten-fold increases in Jc in relevant regimes, enabling the performance
of magnesium diboride in selected applications to compete with that of Nb-Sn.
