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The magnetic and transport properties of magnesium diboride films representperformance goals yet to be attained by powder-processed bulk samples andconductors. Such performance limits are still out of the reach of even the bestmagnesium diboride magnet wire. In discussing the present status and prospectsfor 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 whichcurrent is transported from grain-to-grain in the conductor, an extrinsic(intergrain) property. With regard to Item-(1), the role of dopants in Hc2enhancement is discussed and examples presented. On the other hand their rolesin increasing Jc, both via Hc2 enhancement as well as directfluxoid/pining-center interaction, are discussed and a comprehensive survey ofHc2 dopants and flux-pinning additives is presented. Current transport throughthe powder-processed wire (an extrinsic property) is partially blocked by theinherent granularity of the material itself and the chemical or otherproperties of the intergrain surfaces. These and other such results indicatethat in many cases less than 15% of the conductor's cross sectional area isable to carry transport current. It is pointed out that densification inassociation with the elimination of grain-boundary blocking phases would yieldfive-to ten-fold increases in Jc in relevant regimes, enabling the performanceof magnesium diboride in selected applications to compete with that of Nb-Sn.

Prospects for Improving the Intrinsic and Extrinsic Properties of Magnesium Diboride Superconducting Strands