Superconductor electromagnetic simulation, particularly inductance extraction, plays a critical role in the design of superconductor integrated circuits. However, existing London-equation-based models, such as 3D-MLSI and SuperScreen, suffer from the difficulty of systematic calibration due to their complexity, are incompatible with current-voltage data, and cannot capture interactions between bias current and control current. To address this problem, we propose a double-layer calibration method along with a flux-based inductance extraction method for London-equation-based superconductor electromagnetic simulation tools. Experiments based on the SIMIT Nb03 process demonstrate that our method achieves an average inductance extraction error of $4\%$, which is comparable to those achieved by InductEx. Furthermore, with calibration, our method reduces the error by over $10\%$ compared to the same superconductor simulation tool without calibration. These results confirm that the proposed double-layer calibration framework effectively bridges the gap between physical simulation and actual fabrication processes, providing a robust and scalable solution for superconductor circuit design based on the SIMIT Nb03 process. Additionally, the calibration framework has the capability to utilize current-voltage data and reflect the interaction between the bias current and the control current.
The DyBa2Cu3O7-δ (DyBCO) bulk superconductors prepared by the Single-Direction Melt Growth (SDMG) process and treated by high-temperature post annealing (HTPA) in a 1% O2/Ar atmosphere were microstructurally analysed by scanning electron microscopy to clarify their behaviour during high-temperature post-annealing. The microstructural analysis indicates that high-temperature post-annealing enables partial sintering of oxygenation cracks. The meandering residual porosity along the oxygenation cracks allows oxygen to flow into the sample, and cracks formed during oxygenation of as-grown samples are not required for oxygenation. Thus, HTPA increases the effective cross-section of the sample for superconducting current.
Traveling wave parametric amplifiers are promising sources of broadband microwave squeezing for quantum technologies. Recent studies suggest that, in addition to loss, spontaneously generated spurious spectral tones may limit the achievable squeezing performance. Motivated by this, we experimentally investigate pump-induced spurious tones generation in a traveling wave parametric amplifier based on the sign-reversal of the Kerr nonlinearity phase matching. By measuring the output spectrum as a function of pump frequency and magnetic flux bias, we identified operating regimes with improved spectral purity. We found that increasing the pump frequency suppresses both the number and the amplitude of parasitic spectral tones in the device under test, resulting in wider operating regions with minimal unwanted spectral content. Complementing existing studies on spurious tones generation, these results provide practical guidelines for optimizing the operating conditions of this family of amplifiers for future squeezing experiments and other quantum applications.
Electric machines for aviation applications are currently being intensively developed. Increasing performance to 30 kW/kg at the 10-20 MW scale requires a step change in air-gap magnetic field and hence the wire current density. Fully superconducting machines greatly increase the current density in the motor windings and show promise for achieving the power-to-weight ratios required, and the use of liquid hydrogen as the aircraft propulsion energy source presents the opportunity to cool the superconductors with minimal additional refrigeration plant. In this paper we simultaneously evaluate the superconductor AC losses and cryogenic cooling system requirements for two different armature conductors: a magnesium diboride (MgB2) winding at a nominal 20 K operating temperature, and a REBCO cable winding operating at a nominal 35 K. A 3 MW synchronous air-core motor model is used as the basis for comparison, in order to define relevant AC coil currents and alternating magnetic fields. For these initial comparisons, AC losses generated in the cables are estimated using electromagnetic FEA, and heat transfer from the cable to the coolant is evaluated using a combination of thermal FEA and pipe-flow correlations. This in turn allows us to estimate coolant flows, temperatures and pressures required in the aircraft cryogenic cooling system. We found that the performance of MgB2 exhibits a strong temperature dependency above 20 K which affects the physical dimensions of the cable as well as the losses generated, and this in turn impacts the heat transfer characteristics. The dependency on temperature is lower with REBCO cable, but losses are higher due to tape geometry. The two conductors lead to very different cooling system options and we can compare the advantages of each from an overall powertrain complexity and performance perspective.
