Low‐purity Cu and Al sheathed multi‐core MgB₂ wires made by IMD process

Abstract

Up to now, the highest current densities of MgB2 superconducting wires have been obtained by the internal magnesium diffusion (IMD) method. MgB2 superconductors are especially suitable for DC or AC windings generating low or medium magnetic fields, where thermal stability and low AC losses are important issues. Mechanical, thermal and electrical parameters of the wires are strongly influenced by metallic materials used for the outer sheath. While highly electrical conductive sheath material is beneficial for thermally stable behaviour, it has a great effect on the generation of high eddy current losses. To minimize the contribution of eddy current losses, multi-core MgB2 wires with low purity Cu and Al sheaths were prepared by the IMD process and characterized in detail. Results of low temperature measurements are analysed and discussed in the present work.

Water ice-cooled MgB2 coil made by wind and react process

“…∼80 mW for the wire with the Al + Al 2 O 3 sheath made from 99.995% purity Al powder [7]. Figure 4(b) compares the I q /I c ratio derived from the I-V curves expressing the thermal stability for three similar multicore MgB 2 wires differing by the outer sheath [25]. One can see a low I q /I c ratio for wires with CuNi30 and low-purity Cu (99.85% > 0.15% of impurities and >0.02% oxygen content) sheaths, meaning poorer thermal stability in comparison to that with low-purity Al [25].…”

DC characterization of advanced fine-filamentary MgB2 superconducting wires

“…CuNi30 is not as strong as Monel 400 used for W342 and therefore the irreversible strain and especially the irreversible stress of this wire is increased, see figure 8. For example, Cu sheathed MgB 2 wire shows the beginning of I c degradation at much lower irreversible strain ε irr ∼ 0.15% and corresponding stress only 100 MPa [17].…”

“…Applied metallic sheath materials determine the thermal, mechanical and electrical properties of composite MgB 2 wires differently for DC and AC applications. For example, high eddy current losses are induced in pure copper or aluminum sheaths, but less pure metals or alloys can considerably suppress the conductor's heating by eddy currents [16,17]. Therefore, also low temperature filamentary NbTi superconducting wires with a resistive CuNi matrix were used for AC applications [18], which are not fully stabilized and normal transition can be easily induced by various disturbances because the CuNi matrix has a high electrical resistivity and low thermal conductivity [19].…”