高温超伝導テープ線材の交流損失特性と運転電磁条件

In many high-temperature superconducting (HTS) applications, HTS-coated conductors carry a DC current under an external AC magnetic field. In such operating conditions, dynamic resistance will occur when the traversing magnetic flux across the HTS conductors. Consequently, AC loss within the superconductors is composed of the dynamic loss component arising from dynamic resistance and the magnetization loss component due to the AC external magnetic field. This AC loss is one of the critical issues for HTS applications, such as persistent current switches, flux pumps, and rotating machines. In this work, the dynamic resistance and the total loss in a three-tape HTS coated conductor stack were measured at 77 K under perpendicular AC magnetic fields up to 80 mT and DC currents (I dc) up to the critical current (I c). The stack was assembled from three serial-connected 4 mm wide Superpower wires. The measured dynamic resistance results for the stack were well supported by the results from 2D H-formulation finite element modelling (FEM) and broadly agree with the analytical values for stacks. The FEM analysis shows asymmetric transport DC current profiles in the central region of the superconductor. We attribute the result to the superposition of DC currents and the induced subcritical currents which explains why the measured magnetization loss values increase with DC current levels at low magnetic field. The onset of dynamic loss for the stack for low i (I dc/I c) values is much slower when compared to that of the single tape and hence the contribution of the dynamic loss component to the total loss in the stack is much smaller than that of the single tape. Dynamic loss in the stack becomes comparable to the magnetization loss at i = 0.5 and becomes greater than the magnetization loss at i = 0.7. Both magnetization loss and dynamic loss in the stack are smaller than those of the single tape due to shielding effects. The difference between the Q total behaviours in the stack and single tape is due to the variation of the penetration depths of the stack and single tape at the different magnetic field amplitudes.

Four 5 mm wide YBCO conductors were assembled face to face to obtain a stacked YBCOconductor (YBCO stack). The space between the conductors composing the YBCO stackwas set at 1.0 mm to investigate the influence of the space on AC loss characteristics. Themagnetization losses without transport current, the transport losses without externalmagnetic field, and total AC losses of the YBCO stack carrying various transport currentsin transverse magnetic fields with various orientations were measured. The measured AClosses in the YBCO stack were compared with those in a 0.2 mm space YBCO stackcomposed of the same conductors used in the 1.0 mm space YBCO stack as well asa single YBCO conductor. Magnetization loss without transport current in aYBCO stack decreases with decreasing space between the conductors in low andintermediate magnetic field. Transport loss without external magnetic field in aYBCO stack increases with decreasing space between conductors. There are threecharacterized regions, when comparing the total AC losses in the two YBCO stacks withdifferent space between the conductors composing the stacks: (a) in the low magneticfield region, the total AC losses in the YBCO stack with smaller space are largerthan those in the YBCO stack with larger space, (b) in the intermediate magneticfield region, the total AC losses in the YBCO stack with smaller space are largerthan those in the YBCO stack with larger space, (c) in the high magnetic fieldregion, the total AC losses in both YBCO stacks agree well with those in thesingle YBCO conductor as well as Brandt and Indembom’s analytical values.

In some high temperature superconducting (HTS) applications, HTS coated conductors carry DC current under external AC magnetic fields. Dynamic resistance occurs when the amplitude of the magnetic field is greater than the threshold magnetic field of the coated conductors. The resulting AC loss, termed as total loss, consists of dynamic loss due to dynamic resistance and magnetization loss due to the shielding currents caused by the AC magnetic field. Conductor on round core (CORC) cables wound with HTS coated conductors have attracted broad attention due to their large current-carrying capability and mechanical flexibility for coil applications. However, there has been no report on dynamic resistance and total loss in CORC cables. In this work, we present 3D FEM simulation results on the dynamic resistance and total loss of a spiral tape and three CORC cables, based on the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\boldsymbol{T-A}}$ </tex-math></inline-formula> formulation. The number of layers of the CORC cables, the amplitude of the AC magnetic field and transport DC current levels have been varied to study the impact of those parameters on dynamic resistance and total loss of the three CORC cables. The simulation results show that magnetization loss without current in a spiral tape can be analytically estimated by Brandt and Indenbom’s theoretical equation for a superconducting strip under perpendicular AC magnetic field with a geometric coefficient 2/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> . Furthermore, dynamic resistance of the spiral tape and each tape in a single-layer cable can be predicted by the analytical equation for a strip carrying DC current under perpendicular AC magnetic field, also taking into account the geometric coefficient 2/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> . The simulation results also show that the difference of total loss values in the three CORC cables depends on the shielding effect: the more layers of CORC cables, the lower each loss component. The two-layer Cable with each tape in the outer layer sitting on top of the tape in the inner layer has the lowest loss and the highest threshold magnetic field.

This paper presents a study of the total ac loss characteristics of a rolling-assisted biaxially textured substrate (RABiTS) YBa2Cu3O7 (YBCO) sample exposed to a parallel ac magnetic field. The results have shown that, for a given applied magnetic field and transport current, a RABiTS YBCO tape can generate very different magnitudes of ac loss, depending on whether the transport current and applied field have the same phase or opposite phase. The results of this study are very important for the optimization of the design of a RABiTS YBCO cable because they can suggest an appropriate arrangement of RABiTS tapes in a cable to minimize the cable ac loss. In this study, both experimental and finite-element method simulation approaches were employed. A modeling model that takes the magnetic field dependent permeability and ferromagnetic loss of the substrate into account reproduced well the experimental data for both self-field and total ac losses.

Parallel magnetic field dependence of AC losses in periodically arranged superconductors with ferromagnetic substrates

Influence of longitudinal magnetic field on current distribution and AC loss in twisted multifilamentary high Tc superconducting tapes

Electromagnetic interfilament coupling of silver-sheathed Bi-2223 multifilamentary tapes in transverse AC magnetic fields

Magnetisation loss of BSCCO/Ag superconducting tape exposed to applied field with arbitrary angle

AC loss characteristics of copper-stabilized YBCO coated conductor

The paper reports an experimental study on AC loss characteristics of a YBCO coated tape conductor carrying AC transport current in AC external magnetic field. In the experiment we electrically measured total losses that were transport current losses plus magnetization losses in AC external magnetic fields perpendicular to the tape surfaces. The transport current losses were measured by a four terminal method and the magnetization losses by a method using a pick-up coil. To measure the total losses electrically we need to pay proper attentions to prevent electromagnetic coupling between the sample currents and the external magnetic fields and to suppress inductive voltage in signals from the pick-up coil and voltage taps. The total losses were purely hysteretic for the amplitude of the external field up to 20 mT and the peak transport current up to the critical current. The loss characteristics can be explained by a theory based on the Bean model if the dependence of the critical current on the external magnetic field is taken into consideration.

Recently, it is proposed to make striations on the YBCO coated conductor and to transpose each other as one of the solutions to decrease the perpendicular magnetization loss. For large power application using HTS, the stacked conductor packing the YBCO coated conductors should be used because the current carrying capacity of a single conductor is limited. The stacked conductor has different AC loss characteristics from single conductor because the screening currents in the adjacent conductors affect the local magnetic field at the position of each conductor in the stacked conductors. In this paper, we research the effect by the stack, striation and transposition on magnetization loss of YBCO coated conductors in perpendicular magnetic field. To estimate the reduction effects of perpendicular magnetization loss, several short samples as the stacked conductor with striation and transposition are prepared and tested. We compare the measured results of the conductors with that of the single YBCO coated conductor to estimate the reduction effects.

High-temperature superconducting (HTS) devices, such as magnets and flux pumps, often carry DC current when exposed to AC magnetic fields. Under these conditions, the total loss within the superconductor comprises the magnetization loss caused by the external AC magnetic field and the dynamic loss resulting from the interaction between the DC current and the AC field. In practice, AC fields with arbitrary orientations can alter the superconductor’s electromagnetic properties, affecting the efficiency and safety of HTS devices. However, a comprehensive study on the dynamic resistance and total loss in REBCO stacks under various field orientations is still lacking, and the effect of Jc(B,θ) dependence on these characteristics still requires more systematic investigation. This work employs the H-formulation to investigate the dynamic resistance and total loss of two three-tape YBCO stacks—assembled from nearly isotropic Shanghai Creative (SCST) tapes and strongly anisotropic SuperOx tapes—under field angles of 0° (perpendicular to the wide surface of a tape) to 85° at 77 K, and external magnetic fields up to 1 T. We elucidated the mechanism responsible for the differing behaviors of magnetization loss and dynamic resistance between the two stacks at various field angles, and clarified the correspondence between the angular dependence of loss components and that of Jc when Ba,⊥ is fixed. Furthermore, the correspondence between the angular dependence of Jc and that of the flux flow loss and the corner field was also established. More importantly, we clarified how the interplay among the loss components influences the total loss characteristics under different field angles. Furthermore, based on the same critical current (Ic0_stack), the total loss and loss components for the two stacks were fairly quantitatively compared at different field angles. Finally, case studies confirmed that the findings can be generalized beyond specific stack geometries.

Critical Currents and AC Losses in YBCO Coils

Chapter 114 - AC loss characteristics of Bi-2212 multifilamentary round wires and their cables

A large negative magnetoresistance (NMR) is anticipated in topological semimetals in parallel magnetic fields, demonstrating the chiral anomaly, a long-sought high-energy-physics effect, in solid-state systems. Recent experiments reveal that the Dirac semimetal Cd3As2 has the record-high mobility and positive linear magnetoresistance in perpendicular magnetic fields. However, the NMR has not yet been unveiled. Here we report the observation of NMR in Cd3As2 microribbons in parallel magnetic fields up to 66% at 50 K and visible at room temperatures. The NMR is sensitive to the angle between magnetic and electrical fields, robust against temperature and dependent on the carrier density. The large NMR results from low carrier densities in our Cd3As2 samples, ranging from 3.0 × 1017 cm−3 at 300 K to 2.2 × 1016 cm−3 below 50 K. We therefore attribute the observed NMR to the chiral anomaly. In perpendicular magnetic fields, a positive linear magnetoresistance up to 1,670% at 14 T and 2 K is also observed.