Abstract In previous current sharing simulation studies, we showed that a current sharing ratio can be defined, and that it is inversely proportional to the number of defects in the cable. We also gave a specific function for this, for a given set of boundary conditions, defect pattern, and thermal and electrical parameters. In this work, we explore the relationship between the current sharing ratio and different patterns of defects. A COMSOL simulation model, a four-tape stack model was used; a simple stack of tapes (a “carpet stack” or tape stack cable). The center two tapes had three pre-existing defects each, and each defect was 0.1 mm I n length with a critical current density of 0.1 J c . The defects in the center tapes were arranged either (i) at three equally spaced lengths along the stack length, but the same lengthwise position in both tapes (“column” pattern) or (ii) with the defects in the second tape positioned halfway between the lengthwise positions of those of the first tape (“zig-zag” pattern). The cable was modelled as being fully immersed in liquid helium. A stationary model was employed using an error tolerance of 1e-3 with a fine physics-controlled mesh. Other important parameters include an interstrand contact resistance (ICR) = 5400μΩ*cm 2 and an Interstrand thermal resistance (ITR) = 5.54 K*m 2 /W. Results show that the zig-zag defect pattern allows a higher current sharing ratio.

Abstract Superconductivity was discovered more than a century ago, and it has achieved full commercialization for MRI and NMR applications. Superconducting technology has got on spotlight recent years for transportation, power network, and fusion energy, due to the significant advantages offered against its counterpart technologies, including lighter weight, compacter size, lower losses, higher efficiency, and higher power density. Therefore, many superconducting applications are moving towards higher technology readiness levels, with a fast pace. The accelerated research around superconducting applications for modern transportation is due to unique features of this technology towards decarbonisation via electrified systems. Meeting the Net Zero targets to decelerate global warming issue is the main driver of implementing the superconducting technology for aerospace, marine, and railway transport. However, many challenges still remain to be addressed for superconducting devices and applications, which will in turn pave the way for the commercialization of superconducting technology. In this article, a roadmap on electrification of transportation systems for aerospace, marine, and railway application is presented, covering challenges and solutions in design analysis, modelling, monitoring, and operation. A series of short articles are presented to outline the potential applications and solutions. These potential futuristic routes and their materials/technologies are considered/suggested for a 10-20 years time-frame.

This study investigates the role of surface modification on current sharing from defected YBCO tapes. Specifically, it explores the impact of nickel-plating on the current sharing ratio (CSR) in tape stacks, as compared to those of as-received (un-plated) tapes as a function of applied pressure and contact length. Prior computer simulation work has shown a correlation between the interstrand contact resistance (ICR) between tapes and measured current sharing ratio in tape stacks. Ni plating is known to reduce ICR (and may reduce thermal contact resistance (ITR) as well), because its native oxide is thinner than that of the Cu. Our basic approach was to (1) test the I-c and quench current (I-q) of an un-defected tape, (2) introduce a defect and re-test I-c and I-q, (3) The add a second tape on top of the first, creating a two tape "tape stack" (the simplest kind), and measure again the I-c and I-q. In this case the current was only injected into the first tape, and thus the only current in the second tape was that current shared from the first (the second tape did not extend to the current injection lugs), with CSR = I-q,I-defected/I-q,I-undefected. We tested tape pairs as received and with Ni-plating, each measured under a variety of applied transverse pressures (also known to affect ICR). We tested in each case face-to-face, back-to-back, and face-to-back tape arrangements. All measurements were performed in liquid nitrogen. Ni plated samples and those with higher applied pressured were seen to achieve higher CSR. The length of the top tape was also explored, and larger CSR was seen for longer top tapes.

Abstract This research explored thermal and electrical sharing, as well as quench, in the cable/composite winding cross-section of an epoxy-impregnated HEP dipole accelerator magnet using HTS (ReBCO) Cables. While HTS insert designs can vary, and in some cases, either no insulation tape windings or fully cooled cable windings are being contemplated, this design is for cables with indirect cooling (epoxy-infiltration) with specified electrical and thermal inter-cable resistances. The cables also have a defined level of defects within them, both in terms of severity and density. A direct simulation of the magnet winding with full detail in the cable structures would be far too computationally expensive to give sensible run times. However, our approach was to use results from previous modeling runs on cables to develop simple cable structures which replicated the main results of the cable properties (temperature and voltage distribution at a given current) but were averaged over length scales smaller than the cable length scale, but larger than that of the tape. These proxies were then used to construct a magnet winding cross-section, where inter-cable electrical and thermal interlayer values could be specified. Due to the complexity of structure, we simplified the epoxy layers in the model. For the present study, the magnet was designed with sixteen cables in each of the four quadrants, and one quadrant was studied. The cables themselves were constructed from thirty tapes each. The tendency for quench as a function of current was explored and compared to the performance of the isolated cables.

In this work we propose semi-analytical models for computing alternating current (AC) power loss of stacks of $N$ high-temperature superconductor YBa2Cu3O7-x (or Y-Ba-Cu-O) tapes with non-standard arrangements of tapes. Each stack is subjected to time-dependent magnetic fields perpendicular to the wide surface of the tapes with zero transport current. The models take into account screening of the interior superconducting layers in the stack from the external magnetic field. These models are validated by our experimental studies. As is also shown, the AC loss dependence on the arrangement of tapes in the stack can be quite strong, varying by factors up to similar to 180x for temperatures 20-65 K, magnetic fields 2-5 T and frequencies up to 2 kHz.

The magnetization of ReBCO tape stacks and tape stack cables in high magnetic fields (up to 30 T) are not commonly reported. Here we report magnetization measurements of tape stack cables in magnetic fields up to 30 T at 4.2 K. We observed that flux jumps, commonly relegated to low field regimes for single tapes, persisted up to 17 T in tape stacks, an effect which could have substantial technological relevance for high field applications including fusion devices or accelerator magnets. On the other hand, with the use of small spacers, we could suppress flux jump behavior, in some cases eliminating jumps entirely. Our findings provide critical insights for the optimization of designs for ReBCO cables for high-field applications, including fusion magnets and particle accelerators.

In high energy physics magnets, superconducting cables are typically used, one for this reason is to limit inductance and thus voltages during magnet quench. For LTSC cables this also allows for current sharing in case of a local perturbation of a strand; such current sharing mitigates problems attendant to the low minimum quench energy seen in LTSC superconductors. For HTS strands, MQE is much larger, but an equally important function has emerged which is conductor redundancy. Heating due to small defects within the cable can be mitigated again by strand-to-strand current sharing. Of particular interest in this context are REBCO tape stacks, Roebel and CORC cables. Here small defects may arise in the original tapes, either during cabling or in service in the magnet. However they arise, local heating can be generated if current sharing is not present. In this article, we modelled the current sharing in non-insulated tape stacks (i.e., tape stack cables) containing seven double-sided tapes with defects present in some of the tapes. In this article, we used Finite Element Method (FEM) modeling, assuming critical current densities of these tapes relevant for operation at 4.2 K (boiling liquid He).

Previous studies have shown that APC Nb3Sn strands based on the internal oxidation of Nb-Ta-Zr or Nb-Ta-Hf alloys had higher non-Cu critical current density (J(c)s) than the state-of-the-art strands at high fields (e.g., >= 12 T) while having lower non-Cu J(c)s at low fields (e.g., <= 5 T), which helps to reduce the undesired persistent-current magnetization. Moreover, APC strands reacted at lower temperature tend to have flatter J(c)(B) curves, possibly allowing the targeting of even better J(c) performance at high fields, while at the same time suppressing J(c)s at low fields. However, it is required that APC strands attain large fine-grain (FG) area fractions and suppressed coarse-grain (CG) area fractions at low reaction temperature. In this work, the influence of reaction temperature on the evolution of FG and CG Nb3Sn phases in APC Nb3Sn strands was investigated. Our goal is to find more effective methods to increase the FG area fraction as well as the overall performance of APC strands.

High-power electric aircraft motors and generators require high current density conductors to meet the required performance metrics, which are beyond those achievable using ambient temperature metals. MgB2 superconductors and high-purity aluminum (HPAL) hyperconductors are being considered for this work because of their combination of high current density/ampacity in combination with relatively low AC loss and their ability to work at the temperature of liquid hydrogen and above. In this work, we calculated the AC losses of MgB2 and HPAL conductors of various wire architectures in applied magnetic fields of 0.5 T and frequencies, f, up to 1 kHz. In particular, we estimated the contributions of several AC loss components, including eddy current and coupling losses, in AC magnetic fields and frequencies relevant to AC motors and generators in electric aircraft. The losses were then summed up and presented in terms of power loss per length, per unit current [W/(m*A)] in order to fairly compare the AC losses of superconductors to hyperconductors over various frequency regimes. Additionally, we accounted for the anomalous magnetoresistance component of the HPAL conductor, using data from a newly developed composite, measured at 20 K in fields up to 9 T in a PPMS. We conclude that for a 0.5 T, externally applied, time varying field, MgB2 is the lowest loss conductor for f < 180 Hz, while multifilamentary HPAL conductors are better for f > 180 Hz (explored up to 1 kHz), based on our chosen conductor design assumptions. However, the best place to transition from MgB2 to HPAL composites lies somewhere in the 200 Hz to 1 kHz regime, depending on the parameters of the conductors, the value of Bm, and the relative tradeoffs in Je and power loss per unit volume the application demands.

CORC ReBCO cables are promising conductors for the next generation of high-performance cables for high-field accelerator magnets. However, because significant mechanical stress is inevitable in high field magnet applications, the deformation and damage of these cables under large stresses should be explored. Focusing on high field accelerator dipole inserts for a moment, various mechanical configurations for the winding are under consideration, which may affect cable performance. Therefore, the relationship between mechanical support conditions and the mechanical performance of CORC ReBCO cable under transverse compressive stress should be explored. In this study, the effects of transverse pressure on CORC cables with either side support during pressure application, or epoxy impregnation, or both, were investigated. Several segments of a particular CORC cable were used in four different mechanical configurations; (i) as received, (ii) unpotted but with side support, (iii) potted without side support, and (iv) potted and with side support. A material Testing System (MTS model 43) was utilized to compress our samples up to 30kN in four different supporting conditions as listed above. Samples were autopsied using optical as well as scanning electron microscopy after the completion of the mechanical tests. As a result, we found that the support conditions enhance the mechanical performance of the CORC cable by extending the elastic-plastic transition load to a larger stress level, and we also observe cleavage cracks after the completion of the compressive stress test.

This research explored current sharing and quench evolution in rare-earth barium copper oxide (ReBCO) based su-perconducting cables intended for use in the High Energy Physics (HEP) accelerator magnets. We used 3D finite element simulation studies of three-tape stack (carpet stack) cables. A given number of defects per tape length was assumed, along with specified electrical and thermal resistance values within and between tapes. Previous studies with a single defect in a three-tape stack cable showed that in addition to intra and inter-tape electrical resistivity, values of thermal resistivity and thermal boundary conditions were needed to determine a current sharing level. Here we defined the current sharing level as CSR = I-cable_defect/I-cable_no_defect just before thermal runaway. The current sharing level varied with inter strand contact resistance (ICR), inter-strand thermal resistance (ITR), and thermal boundary conditions. As one example a three-tape stack cable with an interlayer electrical contact efficiency, eta = 5400 mu Omega*cm(2), an interlayer thermal contact efficiency, w= 5.54 K*m(2)/W, liquid helium cooling on the outer surface of the cable, and one defect (set at 10% I-c) in the central tape had a current sharing value of 0.91 (ie., the ability to achieve 95% of nominal (defect free) I-c,I-cable before a quench). Increasing the number of defects per unit length in the central tape reduced the achievable I/I Gamma I-c,I-cable from 0.95 to 0.87.

Superconducting windings are enabling for the development of the highest power density motors and generators for aircraft use. Targets for motors with normal conducting windings are at best 20 kW/kg, while those for superconducting windings are on the order of 45 kW/kg. While superconducting wires can carry high currents and do not have ohmic losses, they have other kinds of loss with AC excitation. These loss components; hysteretic, eddy current, and coupling loss predominantly, have interesting functional dependencies. Much of the work on AC loss in superconductors has been performed at lower frequencies, but higher frequencies are of interest for electric aircraft motors, particular with respect to harmonics, which can be high frequency (up to 10s of kHz) but are typically low amplitude. This work calculates the losses for superconductors at these higher frequencies to see when their competitive advantages drop off with frequency. Another contender for high power density windings are fine filament normal state conductors operated at a cryogenic temperature. These conductors have drastically reduced ohmic losses, but they are not zero. On the other hand, they have no hysteretic losses per se, and their eddy current losses can be tuned by trading off against filament diameter, matrix resistivity, and frequency of operation. The high field regime and harmonics contributions of both advanced conductor types is given and compared to ambient temperature conductor.

The rapid development of electric aircraft technology drives the need for highly effective cooling systems to manage the significant heat generated by high-power electronic components. In this work, liquid ammonia, with its excellent thermophysical properties including a high specific heat, and volumetric energy density, is evaluated as a good coolant (especially relevant when it will also serve aviation fuel at the same time). This work focuses on designing fuel storage and cooling strategies to address thermal management challenges both globally and locally for the electric aircraft. Aluminum was chosen as the material for the heat exchanger/heat sink due to its excellent resistance to liquid ammonia corrosion, high thermal conductivity, and low density. Using computational fluid dynamics (CFD) simulations, we analyzed the heat transfer performance and liquid ammonia flow characteristics within the aluminum heat sink. Temperature distribution of aluminum heat sink and flowing liquid are simulated to determine the viability and effectiveness of this cooling strategy. In addition, various design configurations, including fluid storage methods (cold-temperature or high-pressure) and flow channel topology, are explored to optimize the cooling efficiency. The results shows that liquid ammonia cooling is feasible to maintain the power electronics within safe operating temperatures under the given flow rates and operating conditions, especially for the cold-temperature storage strategy. This research provides valuable insights into the design and implementation of advanced cooling systems for next-generation electric aircraft, indicating the potential of liquid ammonia as an effective and innovative cooling media good cooling media, despite challenges related to environmental, safety, and corrosion concerns.

Rare-earth-barium-copper-oxide (ReBCO) superconducting tapes are pivotal for emerging technologies such as fusion reactors and particle accelerators due to their superior performance in high magnetic fields. Despite extensive studies of single tapes, the magnetization behavior of ReBCO tape stack cables at high magnetic fields has been underexplored. Here, we present magnetization measurements of ReBCO tape stack cables at magnetic fields up to 30 T at 4.2 K. Remarkably, flux jump instabilities, typically confined to lower field regimes in single tapes, persisted up to 17 T and higher in tape stacks. Such instabilities could significantly impact the stability and field quality of large-scale superconducting magnets. Crucially, we demonstrate that introducing small intertape spacers substantially mitigates flux jump occurrences, sometimes eliminating them completely. Our findings offer valuable insights for designing stable, high-performance ReBCO cable-based magnets, enhancing their viability for next-generation fusion and accelerator applications.

In this paper we analyzed numerically, using a Finite Element Method (FEM), the performance of REBCO CORC cable where we have assumed defects are present. In particular, we focus on the influence of the defects on heating and thermal runaway of the magnets. Defects, which are possible in any HTS cable, may originate from the tape manufacture, or during cabling, or in service. Here we considered a design based on real Canted Cosine Theta (CCT) dipole magnet, wound using CORC cable, which was built and tested at the Lawrence Berkeley National Laboratory, USA as a stand-alone dipole magnet providing a magnetic field of 1.2 T in liquid He bath at 4.2 K. Because, thermally at least, the turns of the CCT dipole magnet behave as parallel straight wires immersed half way in the grooves of the mandrel material with their outside surfaces in direct contact with pool boiling liquid He, in our FEM model we adopted a 3D straight geometry which significantly reduces the computational time and memory. To model the REBCO superconducting material we used its measured power law E-J curve.

In accelerator magnets the magnetic field quality is an important parameter. Using REBCO tapes or cables in magnet windings affects the magnetic field quality because of a quite high magnetization generated by these conductors. In this paper we analyzed numerically (using FEM) an effect of various REBCO cables' magnetization on the field quality of canted cosine theta (CCT) dipole magnets. The magnetic properties of the cables were taken from our measurements of their M (H) curves at 4.2 K and magnetic fields up to 12 T. Also, flux creep effects were measured and their effects on field quality analyzed. Here we present a modeling of a CCT magnet containing 1 dipole double layer wound using a CORC and STAR cable. To make the FEM modeling less computationally "expensive", we modelled only a section of 10 turns of the magnet's central part and calculated b(3) fields on a circle of 2/3 of the innermost layer center line. Special M (H) curves measured during various field cycles (the so called "pre-injection cycles") are effective in decreasing b(3) fields of the magnets. Flux creep effects suppress the b(3) fields further. Using these techniques b(3) fields less than 10 units can be achieved.

Vapor-solid reactions were applied to monofilament and 6-filament AIMI MgB2 wires. A layer J(c) of similar to 10(5) A cm(-2) was achieved by the generation of a highly dense MgB2 layer after reaction at 625 degrees C for 8 to 16 h. It was found that the critical current, I-c, and engineering current density, Je, reached maximum values of 92.3 A and 1.15 x 10(4) A cm(-2) at 4.2 K, 10 T when the multifilament AIMI wire was heat-treated at 625 degrees C for 14 h. Transport I(c)s were also measured at 10-20 K for the wire heat-treated at 625 degrees C for 16 h. Phase formation investigations suggested that even better performance of I-c and J(e) could be attained in multifilamentary AIMI MgB2 wires after further conductor optimization.

Optimization techniques can significantly improve the performance of electrical machines. The analysis and the optimization algorithms focus on computational efficiency. In this paper, the optimization of a high frequency electrical machine in cryogenic conditions is proposed. The losses introduced by AC current in a conductor are directly proportional with the applied frequency in terms of skin effect and proximity effect. The stator coil, made from two aluminium (Al) turns, in the presence of cryogenic coolants has been analysed at frequencies up to 1000 Hz. In order to reduce the AC losses introduced by the magnetic fields, Nonlinear Conjugate Gradient (NCG) method has been applied for the stator coil thickness optimization. Frequency dependence is observed in most simulations. In the presence of Liquid Hydrogen (LH2) coolant, Al 1100 conductor presents the minimum power loss.