High performance of high-temperature-superconducting MPD thrusters: analytical MHD modeling and experimental demonstration

Fabrication and test results of 2 T conduction cooled HTS magnet

Chapter 144 - Design study of conduction-cooled high temperature superconducting magnet

본 논문은 초전도 에너지 저장장치(SMES)용 전도냉각형 고온초전도 자석의 설계, 제작 및 평가에 대해 기술한다. 고온초전도 자석은 황동 안정화재를 갖는 2개의 Bi-2223 다심 선재가 적층된 4-ply 도체로 제작된 22개의 double pancake coil(DPC)로 구성된다. 그리고, 각 DPC는 내경과 외경이 각각 500 mm, 691 mm이고 높이가 10 mm인 2개의 single solenoid coil로 구성된다. 코일 내부의 전기적 손실에 의해 발생된 열의 냉각을 위하여 DPC 사이에 두께 3 mm의 알루미늄 판이 내재된다. 고온초전도 자석은 2단 Gifford McMahon 냉동기에 의해 5.6 K까지 냉각된다. 충전전류가 증가할수록 방전시 고온초전도에서의 최대 온도가 증가 하였다. 충전전류가 360 A일 때 ��치 없이 고온초전도 자석에 1 MJ의 자기에너지가 성공적으로 저장되었다. 본 연구에서는 SMES용 전도 냉각형 고온초전도자석에 대한 열적, 전자기적 특성을 보이고, 본 연구를 통해 얻어진 결과는 전도냉각형 고온초전도자석의 최적설계 및 안정도 평가에 활용될 것이다. This paper describes design, fabrication, and evaluation of the conduction cooled high temperature superconducting (HTS) magnet for superconducting magnetic energy storage (SMES). The HTS magnet is composed of twenty-two of double pancake coils made of 4-ply conductors that stacked two Bi-2223 multi-filamentary tapes with the reinforced brass tape. Each double pancake coil consists of two solenoid coils with an inner diameter of 500 mm, an outer diameter of 691 mm, and a height of 10 mm. The aluminum plates of 3 mm thickness were arranged between double pancake coils for the cooling of the heat due to the power dissipation in the coil. The magnet was cooled down to 5.6 K with two stage Gifford McMahon (GM) cryocoolers. The maximum temperature at the HTS magnet in discharging mode rose as the charging current increased. 1 MJ of magnetic energy was successfully stored in the HTS magnet when the charging current reached 360A without quench. In this paper, thermal and electromagnetic behaviors on the conduction cooled HTS magnet for SMES are presented and these results will be utilized in the optimal design and the stability evaluation for conduction cooled HTS magnets.

Design, fabrication and evaluation of a conduction cooled HTS magnet for SMES

An active magnetic regenerator (AMR) system requires fast ramp rate of magnetic field variation. The magnetic field change enables a magnetic refrigerant to create magnetocaloric effect for magnetic refrigeration. In this paper, a conduction-cooled high-temperature superconducting (HTS) magnet has been thermally analyzed and tested for an AMR system. A GdBCO conductor insulated with polyimide tape was wound by dry winding and standard double-pancake coil method. Stycast 2850FT was applied to the edge of the tape conductor so that the cooling plates, which were located at the top and bottom of the coil, should effectively cool the magnet. The whole thermal bridging between the magnet and a two-stage GM cryocooler is analyzed by the numerical simulation and a Joule heating experiment of the HTS magnet at normal state. The inductance of the HTS magnet was measured as 350 mH. The HTS magnet is intended to be operated with maximum 1 T/s at 20 K, cooled by the cryocooler. A solenoid switch and an external dump resistor were employed in order to discharge the HTS magnet. A continuous ramping operation test was conducted with a 60-A peak current and a maximum 20-A/s ramp rate by 3-kW dc power supply. This paper describes the experimental results of the ramping operation of the HTS magnet for an AMR system, and the technical issues on the results are discussed.

<p dir="ltr">Applied-field magnetoplasmadynamic (AF-MPD) thrusters represent a promising category of electric propulsion for satellites and spacecraft, boasting high-power, efficiency and specific impulse. These thrusters use electric fields and strong external magnetic fields to propel plasma to substantial velocities. The integration of high-temperature superconducting (HTS) electromagnets plays a pivotal role in minimising the mass, power, and volume requirements of AF-MPD thrusters, facilitating their application in space. To validate this critical technology, a collaborative effort led by the Paihau-Robinson Research Institute and Nanoracks LLC aims to send an HTS magnet to the International Space Station (ISS), titled the 'Hēki magnet mission.' Taking advantage of the Nanoracks External Platform (NREP), this technology demonstration will validate and mitigate risks associated with the use of miniaturised cryocoolers, HTS magnets and flux pumps in space. This endeavour marks a crucial advancement towards the in-space utilisation and potential commercialisation of HTS-powered thrusters. This paper presents on-orbit simulations of the thermal and electromagnetic performance of the Hēki payload. We developed thermal models to resolve the complex radiative thermal environment in space on-board the ISS to ensure that a 90 W miniaturised cryocooler can successfully cool an HTS magnet to a 75 K operating temperature, and we simulate the design of thermal radiators to prevent the cryocooler from overheating. We also investigate the time varying changes to the thermal environment in space as a function of ISS orbital changes throughout the year. Circuit and electromagnetic models of the HTS magnet and flux pump were developed to inform of the required performance to meet our mission goal of generating a central field of 0.3-0.5 T. Critical safety considerations are also simulated, such as a magnet quench because of a sudden loss of power, and the design of a rapid de-energisation system. </p>

Since conduction cooling system is environmental friendly and easy operating, the conduction-cooled method is widely used in cryogenic cooling system of high-temperature superconducting (HTS) magnet. The eddy-current losses are generated in the cooling structures when HTS magnet is charging and discharging or the current in the magnet is alternating. In this paper, a 3D model of analyzing the eddy-current loss was built. The eddy-current losses of a HTS magnet with different cooling structures were calculated. Thermal analysis of the HTS magnet was carried out together with the electromagnetic analysis. The effect of the cooling structures’ geometric parameters on the eddy-current losses was discussed. The methods of reducing the eddy-current loss were proposed. The analysis results demonstrate that the optimization of the geometric parameters would greatly benefit the reduction of the eddy-current losses.

In a High Temperature Superconducting (HTS) magnet consisting of pancake windings, HTS tape with the same width has been used for all pancake windings. If a wider HTS tape is used for the outer pancake windings, the critical current of the HTS magnet can be increased. This paper shows the properties of BSCCO magnets in which the outer pancake windings are wound with a wider HTS tape. In order to examine the effects of a wider HTS tape, a HTS magnet with an inner radius of 20 mm and a height of 202.4 mm was used. The number of turns of each pancake winding was 150, and the number of pancake windings was 46. The critical current of the pancake winding was determined by using E-J relation. Results of calculation show that the critical current was higher in the HTS magnet with a wider HTS tape at the outer pancake windings than in the HTS magnet with the same width of HTS tape for all pancake windings.

Under transient operating conditions, especially in the case of alternating current or pulse current, the high temperature superconducting (HTS) magnet will suffer ac losses leading to changes in the temperature and critical current distribution throughout the magnet. A magneto-thermal model is needed to simulate this process. In fact, the state change of the magnet will lead to a nonlinear performance of the HTS magnet in the power system. This paper introduces a coupling simulation and modeling method for the HTS magnet based on a cosimulation model built in MATLAB and COMSOL. The HTS magnet element is a customized module created via the self-code S-Function in MATLAB. A magneto-thermal finite element model based on the PDE and Heat Transfer modules of COMSOL is built into the S-Function. This model allows the state of the HTS magnet to be monitored during the operating process. A small-scale HTS magnet including three single pancake coils with a dc excitation system is illustrated to verify the nonlinear characteristic of the HTS magnet and the effectiveness of this coupling simulation and modeling method.

A plasma beam irradiation facility was developed based on the applied-field magnetoplasmadynamic (AF-MPD) thruster concept for studying plasma-surface interactions. The AF-MPD thruster was chosen because it can produce a plasma beam with high plasma density in continuous-wave mode. Two types of AF-MPD thruster were developed and used in this study: a type I source with a wide thruster channel was used for a heat flux test with Ar or Xe gas, while a type II source with a narrow thruster channel was used for an ion flux test with H2 or He gas. The plasma initially showed the characteristics of abnormal glow discharges and then a transition to arc occurred when the plasma current exceeded a threshold value. It was found that a cathode made of thoriated tungsten significantly lowered the threshold current for the transition from abnormal glow to arc. The maximum heat flux provided by our facility was measured to be 7 MW m−2 using a custom-made heat flux sensor, while the maximum hydrogen ion flux was measured to be 1 × 1023 m−2 s−1 using a Langmuir probe. The electron temperature ranged between (4–5) eV, while the electron density at the plasma plume (downstream) ranged between (1–4) × 1018 m−3.

A test facility for high heat and particle loads relevant to a fusion divertor has been developed using an applied-field magnetoplasmadynamic (AF-MPD) thruster. The AF-MPD thruster can provide high heat and particle fluxes to a target at a relatively low pressure with a relatively strong magnetic field. Several diagnostics for heat and particle fluxes such as a calorimeter and Langmuir probe were utilized to confirm that a heat flux of 4.0 MW m−2 and particle flux of 4.2 × 1022 m−2 s−1 were achieved using a 0.17 T permanent magnet. The electron temperature and electron density were estimated to be 4 eV and 1013 cm3, respectively, using optical emission spectroscopy based on the collisional-radiative model.

Sustainability in space is now the centre of attention for different space research organisations given the scale of current investment in planetary search activities, ambitious plans for habitation in future, and focus on electric space propulsion systems. One potential propulsive means for future spacecraft is the applied-field magnetoplasmadynamic thruster (AF-MPDT). This type of thruster uses the principle of the Lorentz force, where ionized gas is propelled through the interaction of a current and a magnetic field. These thrusters are characterized by nonlinear and complex interaction between controllable parameters, such as current and magnetic field, and structural attributes like part dimensions including anode and cathode radii. Consequently, traditional empirical modelling approaches have encountered challenges in predicting certain outputs, such as thrust, with sufficient precision across different operational regimes. As an alternative to analytical/empirical formulas that approximate the true physics only partially, this paper demonstrates the potential of artificial intelligence (AI) techniques to predict thrust in AF-MPDTs. Through training and meticulous hyperparameter tuning, this study compares 7 different AI models fed with experimental data from 21 thrusters and their different configurations, reaching a total of 58 thruster designs, spanning decades of thruster research and development work. Results indicate that the supervised ensemble algorithm, eXtreme Gradient Boosting (XGBoost), outperforms all other utilized techniques such as random forest, Gradient Boosting Regressor, support vector regression, kernel ridge regression, K-nearest neighbors, and Gaussian process regression. With a Goodness of Fit (R 2) of 98.55%, root mean square error of 1.421 N, and mean absolute error of 0.453 N, XGBoost specifically, and AI in general, has demonstrated its superiority, by significantly improving on the accuracy of previously published empirical models for AF-MPDT thrust prediction. Additionally, the fast response associated with these techniques further expands their applicability to real-time data operation or to being used as a subroutine in thruster design procedure. This can potentially become a fundamental component of AF-MPDT designing software, whereby it may be used to check a configuration’s functionality, applicability and feasibility all in a few milliseconds. This data-driven approach can be helpful in upscaling or specially down-scaling AF-MPDTs to make them better suited for many lower power space applications.

High Temperature Superconducting (HTS) magnets may offer an attractive alternative to both water-cooled copper and conventional low temperature superconducting magnets in many accelerators and beam lines. With energy cost rising and conductor cost falling, HTS magnets operating in the 20-60 K temperature range are gaining renewed interest for the lower cost of ownership (capital + operation). Moreover, in a few low to medium field R&D applications, HTS magnets not only provided a better technical solution but also proved to be less expensive to build and test than the magnets made with conventional Low Temperature Superconductors (LTS). In addition, HTS magnets can tolerate large energy and radiation loads and can operate with a simpler cryogenic system. This paper will present several specific examples.

High-temperature superconductor-based power and propulsion system architectures as enablers for high power missions

This paper considers the insulationless high-temperature superconducting (HTS) magnet as a new and innovative concept for dc applications due to its benefits as compared to conventional HTS magnets with insulation layers between HTS conductors. The purpose of this paper is to study the operating characteristics of an insulationless HTS magnet. The normal operating characteristics of the insulationless HTS magnet were investigated according to the various current levels. Thermal stability of the insulationless HTS magnet was also analyzed. The critical current of the insulationless HTS magnet was measured at 40 K. The temperature distribution of the insulationless HTS magnet was measured using thermocouples. The experiment results demonstrate superior thermal stability characteristics in the insulationless HTS magnet. Thus, it is confirmed that the thermal performance of large-scale HTS magnets can be enhanced by applying insulationless magnets instead of general insulated HTS magnets.