A new benchmark problem for electromagnetic modelling of superconductors: the high-Tc_{c} superconducting dynamo

The high-T$_{c}$ superconducting (HTS) dynamo is a promising device that can inject large DC supercurrents into a closed superconducting circuit. This is particularly attractive to energise HTS coils in NMR/MRI magnets and superconducting rotating machines without the need for connection to a power supply via current leads. It is only very recently that quantitatively accurate, predictive models have been developed which are capable of analysing HTS dynamos and explain their underlying physical mechanism. In this work, we propose to use the HTS dynamo as a new benchmark problem for the HTS modelling community. The benchmark geometry consists of a permanent magnet rotating past a stationary HTS coated-conductor wire in the open-circuit configuration, assuming for simplicity the 2D (infinitely long) case. Despite this geometric simplicity the solution is complex, comprising time-varying spatially-inhomogeneous currents and fields throughout the superconducting volume. In this work, this benchmark problem has been implemented using several different methods, including H-formulation-based methods, coupled H-A and T-A formulations, the Minimum Electromagnetic Entropy Production method, and integral equation and volume integral equation-based equivalent circuit methods. Each of these approaches show excellent qualitative and quantitative agreement for the open-circuit equivalent instantaneous voltage and the cumulative time-averaged equivalent voltage, as well as the current density and electric field distributions within the HTS wire at key positions during the magnet transit. Finally, a critical analysis and comparison of each of the modelling frameworks is presented, based on the following key metrics: number of mesh elements in the HTS wire, total number of mesh elements in the model, number of degrees of freedom, tolerance settings and the approximate time taken per cycle for each model. This benchmark and the results contained herein provide researchers with a suitable framework to validate, compare and optimise their own methods for modelling the HTS dynamo

A new benchmark problem for electromagnetic modelling of superconductors: the high- T c superconducting dynamo

Abstract: The high-T c superconducting (HTS) dynamo is a promising device that can inject large DC supercurrents into a closed superconducting circuit. This is particularly attractive to energise HTS coils in NMR/MRI magnets and superconducting rotating machines without the need for connection to a power supply via current leads. It is only very recently that quantitatively accurate, predictive models have been developed which are capable of analysing HTS dynamos and explain their underlying physical mechanism. In this work, we propose to use the HTS dynamo as a new benchmark problem for the HTS modelling community. The benchmark geometry consists of a permanent magnet rotating past a stationary HTS coated-conductor wire in the open-circuit configuration, assuming for simplicity the 2D (infinitely long) case. Despite this geometric simplicity the solution is complex, comprising time-varying spatially-inhomogeneous currents and fields throughout the superconducting volume. In this work, this benchmark problem has been implemented using several different methods, including H-formulation-based methods, coupled H-A and T-A formulations, the Minimum Electromagnetic Entropy Production method, and integral equation and volume integral equation-based equivalent circuit methods. Each of these approaches show excellent qualitative and quantitative agreement for the open-circuit equivalent instantaneous voltage and the cumulative time-averaged equivalent voltage, as well as the current density and electric field distributions within the HTS wire at key positions during the magnet transit. Finally, a critical analysis and comparison of each of the modelling frameworks is presented, based on the following key metrics: number of mesh elements in the HTS wire, total number of mesh elements in the model, number of degrees of freedom, tolerance settings and the approximate time taken per cycle for each model. This benchmark and the results contained herein provide researchers with a suitable framework to validate, compare and optimise their own methods for modelling the HTS dynamo

The Physics of the High-Temperature Superconducting Dynamo and No-Insulation Coils

High-Tc superconducting (HTS) dynamos are a fascinating topic as practical engineering research preceded fundamental understanding, a lead then maintained for at least a decade. These devices, counter to expectation, produce a dc voltage where ‘textbook’ electromagnetism would predict a zero dc component. Simply by replacing a normal conducting stator in a standard dynamo with HTS conductor a dc — auto-rectifying — effect is created. This thesis reports my work in uncovering and codifying the underlying mechanism that gives rise to this effect — namely the broken symmetry that is usually present with Ohm’s law. An explanation of the dc voltage then leads to an explanation of the internal resistivity of such devices, which in turn allows more efficient dynamos to be designed, and modelled. The underlying logic of the HTS dynamo mechanism is also sufficiently strong to predict a complimentary electromagnetic device, a semiconducting dynamo, which remains to be experimentally verified. Ultimately, such HTS dynamos could be used to energise powerful HTS magnets. The modelling techniques developed in this thesis also provide insight into the operational behaviour of no-insulation coils (NI coils). Such coils are extremely robust to mechanical, thermal, and electrical stresses and faults. A simple model of such coils is presented that captures their essential physics with enough fidelity to predict shielding and magnetisation currents inherent with HTS conductors and turn-to-turn current flow. These two technologies represent key topics for the future of high field HTS magnet technologies and their supporting systems.</p

Research data supporting "Modeling stator versus magnet width effects in high-Tc superconducting dynamos"

Research data supporting [Modelling and measurements of stator vs magnet width effects in high-Tc superconducting dynamos]. AMSC_Jc_B_theta_T.txt: J_c(B, theta) data used in the H-formulation model, calculated by normalising experimental I_c(B, theta) by the cross-section of the modelled wire. Data was measured at 35, 53 and 83 K in magnetic fields up to 0.7 T from a short sample of AMSC 46 mm wide superconducting wire. The four columns in the data file relate to temperature [units of kelvin], magnitude of magnetic field B [units of tesla], magnetic field angle [units of degrees] and I_c/w [units of A/cm]

Research data supporting "Modelling the Frequency Dependence of the Open-Circuit Voltage of a High-Tc Superconducting Dynamo"

Research data supporting [Modelling the Frequency Dependence of the Open-Circuit Voltage of a High-Tc Superconducting Dynamo]. The data were obtained from numerical models built in COMSOL Multiphysics 5.4 - see the main manuscript for more details

Research data supporting "Origin of the DC output voltage from a high-Tc superconducting dynamo"

Research data supporting [Origin of the DC output voltage from a high-Tc superconducting dynamo]. Please see the README file for a description of the dataset

Modeling the charging process of a coil by an HTS dynamo-type flux pump

The high-Tc superconducting (HTS) dynamo exploits the nonlinear resistivity of an HTS tape to generate a DC voltage when subjected to a varying magnetic fie ld. This leads to the so-called flux pumping phenomenon and enables the injection of DC current into a superconducting coil connected to the dynamo without current leads. In this work, the process of charging a coil by an HTS dynamo is examined in detail using two numerical models: the Minimum Electromagnetic Entropy Production and the segregated H-formulation fi nite element model. The numerical results are compared with an analytical method for various airgaps and frequencies. Firstly, the I-V curves of the modeled HTS dynamo are calculated to obtain the open-circuit voltage, short-circuit current and internal resistance. Afterward, the process of charging a coil by the dynamo including the charging current curve and its dynamic behavior are investigated. The results obtained by the two models show excellent quantitative and qualitative agreement with each other and with the analytical method. Although the general charging process of the coil can be obtained from the I-V curve of the flux pump, the current ripples within a cycle of dynamo rotation, which can cause ripple AC loss in the HTS dynamo, can only be captured via the presented models.Engineering and Physical Sciences Research Council (EPSRC) Early Career Fellowship, EP/P020313/1; Slovak grant agencies APVV (contract number APVV-19-0536) and VEGA (contract number 2/0097/18

Research data supporting "Modeling the charging process of a coil by an HTS dynamo-type flux pump"

Research data supporting [Modeling the charging process of a coil by an HTS dynamo-type flux pump]. The data were obtained from numerical models using the MEMEP method programmed in C++ and the segregated H-formulation built in COMSOL Multiphysics 5.4 - see the main manuscript for more details

A new benchmark problem for electromagnetic modelling of superconductors: the high- T c superconducting dynamo

Abstract: The high-T c superconducting (HTS) dynamo is a promising device that can inject large DC supercurrents into a closed superconducting circuit. This is particularly attractive to energise HTS coils in NMR/MRI magnets and superconducting rotating machines without the need for connection to a power supply via current leads. It is only very recently that quantitatively accurate, predictive models have been developed which are capable of analysing HTS dynamos and explain their underlying physical mechanism. In this work, we propose to use the HTS dynamo as a new benchmark problem for the HTS modelling community. The benchmark geometry consists of a permanent magnet rotating past a stationary HTS coated-conductor wire in the open-circuit configuration, assuming for simplicity the 2D (infinitely long) case. Despite this geometric simplicity the solution is complex, comprising time-varying spatially-inhomogeneous currents and fields throughout the superconducting volume. In this work, this benchmark problem has been implemented using several different methods, including H-formulation-based methods, coupled H-A and T-A formulations, the Minimum Electromagnetic Entropy Production method, and integral equation and volume integral equation-based equivalent circuit methods. Each of these approaches show excellent qualitative and quantitative agreement for the open-circuit equivalent instantaneous voltage and the cumulative time-averaged equivalent voltage, as well as the current density and electric field distributions within the HTS wire at key positions during the magnet transit. Finally, a critical analysis and comparison of each of the modelling frameworks is presented, based on the following key metrics: number of mesh elements in the HTS wire, total number of mesh elements in the model, number of degrees of freedom, tolerance settings and the approximate time taken per cycle for each model. This benchmark and the results contained herein provide researchers with a suitable framework to validate, compare and optimise their own methods for modelling the HTS dynamo