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Cold high pressure densification (CHPD) is presented as a new way tosubstantially enhance the critical current density of in situ MgB2 wires at 4.2and 20 K at fields between 5 and 14 T. The results on two binary MgB2 wires andan alloyed wire with 10 wt.% B4C are presented The strongest enhancement wasmeasured at 20K, where cold densification at 1.85 GPa on a binary Fe/MgB2 wireraised both Jcpara and Jcperp by more than 300% at 5T, while Birr was enhancedby 0.7 T. At 4.2K, the enhancement of Jc was smaller, but still reached 53% at10 T. After applying pressures up to 6.5 GPa, the mass density dm of theunreacted (B+Mg) mixture inside the filaments reached 96% of the theoreticaldensity. After reaction under atmospheric pressure, this corresponds to ahighest mass density df in the MgB2 filaments of 73%. After reaction, theelectrical resistance of wires submitted to cold densification was found todecrease, reflecting an improved connectivity. A quantitative correlationbetween filament mass density and the physical properties was established.Monofilamentary rectangular wires with aspect ratios a/b < 1.25 based on lowenergy ball milled powders exhibited very low anisotropy ratios, Gamma =Jcpara/Jcperp being < 1.4 at 4.2 K and 10T. The present results can begeneralized to alloyed MgB2 wires, as demonstrated on a wire with B4Cadditives. Based on the present data, it follows that cold densification hasthe potential of further improving the highest Jcpara and Jcperp valuesreported so far for in situ MgB2 tapes and wires with SiC and C additives.Investigations are under work in our laboratory to determine whether thedensification method CHPD can be applied to longer wire or tape lengths.

Strong enhancement of Jc in binary and alloyed in-situ MgB2 wires by a new approach: Cold high pressure densification