The high gas pressure HIP influence on structure and transport properties of $MgB_2$ superconductors of single and multicore composition

Superconducting $MgB_2$ wires in Cu, GlidCop or Monel sheath with Nb or Fe barrier are prepared. Wires vary by sheath material, number of superconducting cores and their chemical composition. Wires are HIP-ed (Hot Isostatic Pressing) at various temperatures ($600-800^oC$) and pressure (up to 1.4 GPa). SEM pictures of cross sections are investigated in order to investigate barrier reactivity and cracking, superconducting material density and grain sizes. Transport measurements are made in magnetic field up to 14 T leading to calculations of critical current density $j_c$ and global pinning force $F_p$. Improvement of transport properties due to higher density of superconducting material is shown.