  The MgB2 superconductor has already demonstrated its applicative potential,
in particular for DC applications such as MRI magnets, thanks to the low costs
of the raw materials and to its simple production process. However further
efforts have still to be made in order to broaden its employment also towards
the AC applications such as SFCL, motors, transformers. The main issues are
related to the reduction of the AC losses. Some of these can be faced by
obtaining multifilamentary conductors with a large number of very fine
filaments and, in this context, the powders granulometry can play a crucial
role. We have prepared MgB2 starting powders with different granulometries and
by the ex-situ P.I.T method we have realized multifilamentary wires with a
number of filaments up to 361 and an average size of each filament lowered down
to 30 microns. In particular we have studied the relationship between grain and
filament size in terms of transport properties and show that the optimization
of this ratio is possible in order to obtain suitable conductors for AC
industrial applications.
