Investigation on characteristic of vanadium trioxide insulation mixed with metal powder for rare-earth barium copper oxide coils

This study examined the turn-to-turn contact resistance (Rct) between rare-earth barium copper oxide (REBCO) tapes and layers of vanadium trioxide (V2O3) and V2O3 mixed with metal powder mixture. V2O3 in single crystal structure was electrically characterised to exhibit resistivity with negative temperature dependence, allowing the turn-to-turn insulation to self-regulate the current bypass between REBCO tapes. To facilitate effective quench protection of V2O3-insulated REBCO magnets above the metal-insulator transition temperature (Trt), Rct must be further reduced to a level similar to those of non- and metal as insulated (NI and MI) REBCO magnets. Thus, we explored the mixing of conductive metal powders such as molybdenum (Mo) with V2O3 paste and investigated the transition properties of Rct. The resistance versus temperature characteristics, microscopic morphologies of the V2O3 layers, and thermal conductivity (kv) were appropriately assessed to determine the effects of mixing the metal powder with V2O3. The Rct of virgin V2O3 exhibited variations of 107–105 μΩ·cm2 under 77–293 K. As the mixing concentration of the metal powder was increased, the reduction magnitude on Rct increased for > Trt (approximately 150 K). Furthermore, the transition slope became gentler for a wider temperature range of < Trt. For metal powder concentrations exceeding 50 wt%, Rct decreased by approximately 2 orders of magnitude (~103 μΩ·cm2) for > 150 K compared with that for virgin V2O3 paste. Moreover, compared to that of pure V2O3, kv demonstrated a remarkable increase of approximately 352% at 91 K fore Mo powder mixed at a concentration of 60 wt%. The improved electrical and thermal properties of the V2O3 insulation layer owing to the mixing of metal powders can help REBCO magnets operate in an insulated state under normal conditions and effectively convert to a non-insulated state under quenching.