Magnetic Wind Research Articles

Spin evolution of neutron stars in wind-fed high-mass X-ray binaries

Abstract The observed X-ray pulse period of OB-type high-mass X-ray binary (HMXB) pulsars is typically longer than 100 seconds. It is considered that the interaction between the strong magnetic field of a neutron star and the wind matter could cause such a long pulse period. In this study, we follow the spin evolution of neutron stars, taking into account the interaction between the magnetic field and wind matter. In this line, as new challenges, we solve the evolution of the magnetic field of the neutron star at the same time, and additionally we focus on the effects of the wind properties of the donor. As a result, evolutionary tracks were obtained in which the neutron star spends some duration in the ejector phase after birth, then rapidly spins down, becomes quasi-equilibrium, and gradually spins up. Such evolution is similar to previous studies, but we found that its dominant physics depends on the velocity of the donor wind. When the wind velocity is fast, the spin-down occurs due to magnetic inhibition, while the classical propeller effect and settling accretion shell causes rapid spin-down in the slow wind accretion. Since the wind velocity of the donor could depend on the irradiated X-ray luminosity, the spin evolution track of the neutron star in a wind-fed HMXB could be more complicated than considered.

Quench detection using Hall sensors in high-temperature superconducting CORC®-based cable-in-conduit-conductors for fusion applications

Advanced magnet systems for fusion applications would greatly benefit from the use of high-temperature superconductors (HTS). These materials allow fusion magnets to operate at higher magnetic fields, allowing for more compact fusion machines, and allow for operation at elevated temperatures, enabling demountable coils that provide access for maintenance of the fusion reactor. Quench detection remains a major challenge in the protection of HTS magnets that are vulnerable to localized conductor burnout due to their low quench propagation velocities. One of the methods explored is the use of Hall sensors that are incorporated in or near the magnet terminations that can detect local field variations that occur as a result of current redistribution within the conductor to bypass a hotspot within the magnet winding. This method is potentially well suited for Cable in Conduit Conductors, such as those made from Conductor on Round Core (CORC) cables, in which sub-cables containing HTS tapes are connected to the terminations at a low resistance. To demonstrate the technique, a CORC® triplet consisting of three sub-cables, rated for 4 kA operation at 77 K, was manufactured and Hall sensors were used to measure local field variations next to the terminations due to current redistribution between the cables. The Hall response was compared to voltages that developed over the cables and terminations as a local hotspot was applied to different cables in the triplet. It was found that the Hall sensors were faster and more sensitive than voltage contact measurements and were able to reliably detect current redistribution of only a few amperes caused by a hotspot, well before the triplet exceeded its critical current. The method also allowed the detection of heater-induced hotspots during high ramp rates of 2 kA s−1 relevant for fusion applications. Hall sensors have a distinct benefit of being less sensitive to inductive pickup of AC interference compared to voltage contact measurements that make quench detection through voltage measurements in magnets especially challenging. The method can also be used for diagnostic measurements of current redistribution caused by other sources such as inhomogeneous current injection from faulty joints, or localized conductor damage. The Hall sensors are likely capable of detecting the onset of a quench that may occur a far distance away from the sensor location, presenting a breakthrough in HTS quench detection that potentially removes one of the remaining barriers to reliable operation of large HTS magnet systems.

Plasmoid Ejection by Alfvén Waves and the Fast Radio Bursts from SGR 1935+2154

Abstract Using numerical simulations we show that low-amplitude Alfvén waves from a magnetar quake propagate to the outer magnetosphere and convert to “plasmoids” (closed magnetic loops) that accelerate from the star, driving blast waves into the magnetar wind. Quickly after its formation, the plasmoid becomes a thin relativistic pancake. It pushes out the magnetospheric field lines, and they gradually reconnect behind the pancake, generating a variable wind far stronger than the normal spindown wind of the magnetar. Repeating ejections drive blast waves in the amplified wind. We suggest that these ejections generate the simultaneous X-ray and radio bursts detected from SGR 1935+2154. A modest energy budget of the magnetospheric perturbation ∼1040 erg is sufficient to produce the observed bursts. Our simulation predicts a narrow (a few milliseconds) X-ray spike from the magnetosphere, arriving almost simultaneously with the radio burst emitted far outside the magnetosphere. This timing is caused by the extreme relativistic motion of the ejecta.

Radio emission from a decade old Type I superluminous supernova, PTF10hgi: comparison with FRB121102

ABSTRACT We perform a comparative study between the only radio-detected Type I superluminous supernova (SLSN) PTF10hgi, and the most active repeating fast radio burst FRB121102. This study has its root in the hypothesized FRB-SLSN connection that states that magnetars born in SLSN can power FRBs. The wide-band spectrum (0.6–15 GHz) of PTF10hgi presented here, provides strong evidence for the magnetar wind nebular origin of the radio emission. The same spectrum also enables us to make robust estimates of the radius and the magnetic field of the radio-emitting region and demonstrates that the nebula is powered by the rotational energy of the magnetar. This spectrum is then compared with that of FRB121102 which we extend down to 400 MHz using archival data. The newly added measurements put very tight constraint on the emission models of the compact persistent source associated with FRB121102. We find that while both sources can be powered by the rotational energy of the underlying magnetar, the average energy injection rate is much higher in FRB121102. Hence, we hypothesize that, if PTF10hgi is indeed emitting fast radio bursts, those will be much weaker energetically than those from FRB121102.

Understanding FRB 200428 in the Synchrotron Maser Shock Model: Consistency and Possible Challenge

Abstract Recently, the discovery of Galactic FRB 200428 associated with an X-ray burst (XRB) of SGR 1935+2154 has built a bridge between FRBs and magnetar activities. In this Letter, we assume that the XRB occurs in the magnetar magnetosphere. We show that the observational properties of FRB 200428 and the associated XRB are consistent with the predictions of synchrotron maser emission at ultrarelativistic magnetized shocks, including radiation efficiency, similar energy occurrence frequency distributions, and simultaneous arrive times. It requires that the upstream medium is a mildly relativistic baryonic shell ejected by a previous flare. The energy injection by flares responsible for the radio bursts will produce a magnetar wind nebula, which has been used to explain the persistent radio source associated with FRB 121102. We find that the radio continuum around SGR 1935+2154 can be well understood in the magnetar wind nebula model, by assuming the same energy injection rate as FRB 121102. The required baryonic mass is also estimated form the observations of FRB 121102 by the Green Bank Telescope and the Five-hundred-meter Aperture Spherical Telescope. By assuming the same radiation efficiency , the total baryonic mass ejected from the central magnetar is about 0.005 solar mass. This value is much larger than the typical mass of a magnetar outer crust, but is comparable to the total mass of a magnetar crust.

Partitioned Stator Switched Flux Machine: Novel Winding Configurations

Torque density is one of the major limiting factors in machine design. In this paper, we propose the hybrid excited partitioned stator switched flux machine3 (HE-PSSFM3). In HE-PSSFM3, armature winding is positioned on the outer stator whereas the permanent magnet (PM) and field winding are placed at the inner stator, while the rotor is free from excitation sources and armature winding. Moreover, concentrated field winding is replaced by toroidal winding. The power splitting ratio between two stators/rotor pole combinations is analytically optimized and are validated through genetic algorithm (GA) in order to enhance average torque and flux regulation capability. The electromagnetic characteristics of the improved and initial design are evaluated and compared with existing designs, i.e., HE-PSSFM1 and HE-PSSFM2. The proposed HE-PSSFM3 has achieved high average torque, i.e., 2.0015 Nm, at same armature and field current densities of 5 A/mm. The results show that the average torques of the proposed design are 35% and 15% greater than HE-PSSFM1 and HE-PSSFM2, respectively. Furthermore, the analysis of various parameters such as flux linkage, flux regulation, electromagnetic performances, cogging torque, back EMF, electromagnetic torque, and torque ripples are investigated using two dimensional (2D) finite element analysis (FEA). Moreover, the simulation results of the proposed design are validated through GA and analytical modeling.

Wind–MRI interactions in local models of protoplanetary discs – I. Ohmic resistivity

ABSTRACT A magnetic disc wind is an important mechanism that may be responsible for driving accretion and structure formation in protoplanetary discs. Recent numerical simulations have shown that these winds can take either the traditional ‘hourglass’ symmetry about the mid-plane, or a ‘slanted’ symmetry dominated by a mid-plane toroidal field of a single sign. The formation of this slanted symmetry state has not previously been explained. We use radially local 1D vertical shearing box simulations to assess the importance of large-scale MRI channel modes in influencing the formation and morphologies of these wind solutions. We consider only Ohmic resistivity and explore the effect of different magnetizations, with the mid-plane β parameter ranging from 105 to 102. We find that our magnetic winds go through three stages of development: cyclic, transitive, and steady, with the steady wind taking a slanted symmetry profile similar to those observed in local and global simulations. We show that the cycles are driven by periodic excitation of the n = 2 or 3 MRI channel mode coupled with advective eviction, and that the transition to the steady wind is caused by a much more slowly growing n = 1 mode altering the wind structure. Saturation is achieved through a combination of advective damping from the strong wind, and suppression of the instability due to a strong toroidal field. A higher disc magnetization leads to a greater tendency towards, and more rapid settling into the slanted symmetry steady wind, which may have important implications for mass and flux transport processes in protoplanetary discs.

Global wind power development leads to high demand for neodymium praseodymium (NdPr): A scenario analysis based on market and technology development from 2019 to 2040

In recent years, to cope with climate change, the global energy structure has been subject to constant transformation. Wind power has become one of the main forms of renewable energy, and as basic equipment in wind power generation, wind turbines have become more technologically advanced over the years. Neodymium praseodymium (NdPr) has become the key material for the most recent permanent magnet wind turbines. Therefore, the development of the global wind power market has a great impact on the demand for NdPr. This paper sets three scale scenarios of the future wind power market—a baseline scenario, a development scenario and a rapid development scenario—and estimates recycling potential from end-of-life (EOL) wind turbines using a dynamic material flow model. The results show that under different scales, the demand for NdPr ranges from 2.28E+05 to 7.88E+05 t during 2019–2040. In the long term, the rapid rise in offshore wind power projects will promote recycling technology as a promising strategy for diversifying the NdPr supply.

Influence of Coil Location and Current Angle in Permanent Magnet Wind Power Generators With High-Temperature Superconducting Armature Windings

In this article, the operating current and torque of surface-mounted permanent magnet (SPM) wind power generators with high-temperature superconducting (HTS) armature windings are analyzed. The influence of coil location and current angle on the electromagnetic performance is investigated systematically. The results show that the location of the HTS coils significantly affects the operating current and torque. Furthermore, the maximum torque current angle of SPM wind power generators with HTS armature windings can be different from 180° due to the interaction between the armature and magnet fields. A design optimization method for wind power generators with HTS armature windings is developed in this article. The optimal design is then identified with consideration of the coupling influence of coil location and current angle.

CORC® wires containing integrated optical fibers for temperature and strain monitoring and voltage wires for reliable quench detection

Safe operation of large superconducting magnets wound from high-temperature superconductors (HTS) requires reliable detection of the onset of a quench. A novel method to integrate optical fibers and voltage wires within the core of multi-tape HTS CORC® wires has been developed that allows real time monitoring of local changes in strain, temperature and of the superconducting state of the magnet windings. The ability to detect highly localized changes in temperature with Rayleigh scattering in the embedded optical fibers provides invaluable information about local heating at hot spots from which a quench may originate. Integrated voltage contacts allow accurate voltage measurements in long CORC® wires without being affected by high current ramp rates or electromagnetic interference. They also allow detection of inductively driven redistribution of current between tapes in CORC® wires that may occur at high current ramp rates. Continuous monitoring of temperature and voltage was used to detect the formation of local hot spots induced by a heater or by operating the CORC® wire above its critical current. The results show that, within the boundary conditions of the experiment and the method by which the optical fibers were integrated into the CORC® wire in this study, the speed and resolution with which hot spots can be detected with optical fibers lagged that of the integrated voltage wires. This study also shows that integrated voltage wires reliably detected the formation of a local hot spot in a 5.1 meter long coiled CORC® wire, down to a hot spot size covering 0.1% of the conductor length and at current ramp rates as high as 2000 A s−1. Voltage measurements thus remain an effective option for quench detection in magnets wound with HTS conductors for which current sharing between tapes allows for operation within the flux flow regime.

Magnetic Braking System Using Electromagnetic Force

A vehicle is a transportation that is widely used by humans as transportation for daily activities. Vehicles generally use mechanical brakes to do braking, these mechanical brakes have a system that requires friction forces to produce a slowdown in the vehicle. The frictional forces carried out will make erosion of the mechanical brake pads and the need to periodically replace the bearings. In this study discussed the design and manufacture of braking systems using electric brakes to support the performance of mechanical brakes. Electric brakes that have advantages in the media used compared to mechanical brakes, namely electric brakes do not require friction media to slow down, but electric brakes use four aluminum plates as magnetic force media, while coils or windings with the inner core will produce electromagnetic force as an actuator braking. The braking system that is carried out will maintain the speed according to the setpoint value of 5100 rpm. This electromagnetic braking results in a maximum braking of 500 rpm and takes between 9 and 15 seconds to reach the steady state position.

Alfvén-wave-driven Magnetic Rotator Winds from Low-mass Stars. I. Rotation Dependences of Magnetic Braking and Mass-loss Rate

Abstract Observations of stellar rotation show that low-mass stars lose angular momentum during the main sequence. We simulate the winds of sunlike stars with a range of rotation rates, covering the fast and slow magneto-rotator regimes, including the transition between the two. We generalize an Alfvén-wave-driven solar wind model that builds on previous works by including the magneto-centrifugal force explicitly. In this model, the surface-averaged open magnetic flux is assumed to scale as , where and Ro are the surface open-flux filling factor and Rossby number, respectively. We find that, (1) the angular-momentum loss rate (torque) of the wind is described as , yielding a spin-down law . (2) The mass-loss rate saturates at , due to the strong reflection and dissipation of Alfvén waves in the chromosphere. This indicates that the chromosphere has a strong impact in connecting the stellar surface and stellar wind. Meanwhile, the wind ram pressure scales as , which is able to explain the lower envelope of the observed stellar winds by Wood et al. (3) The location of the Alfvén radius is shown to scale in a way that is consistent with one-dimensional analytic theory. Additionally, the precise scaling of the Alfvén radius matches previous works, which used thermally driven winds. Our results suggest that the Alfvén-wave-driven magnetic rotator wind plays a dominant role in the stellar spin-down during the main sequence.

A Variable X-Ray Source Close to the Magnetar SGR 1935+2154

Abstract The recent discovery of a millisecond radio burst from the Galactic magnetar SGR 1935+2154 has initiated an intense discussion about the connection between magnetars and fast radio bursts (FRBs). Although some properties of the radio burst from SGR 1935+2154are not the same as cosmological FRBs, there are theoretical models which propose a connection between magnetars and FRBs (see review by Margalit et al. 2020). In particular, the role of a magnetar wind nebula is included in some models, and therefore it is worthwhile to investigate the X-ray environment of SGR 1935+2154 in more detail. Here, we report on the discovery of an X-ray transient feature near SGR 1935+2154 using archival Chandra data and discuss its possible origin.

Mechanical Responses of a Combined Support Structure for a Nb3Sn Sextupole Magnet During Assembly and Thermal Cycle

The Institute of Modern Physics (IMP) in Lanzhou, China, is currently developing a complicated superconducting magnet system composed of four solenoids and six sextupole coils based on a sextupole-in-solenoid configuration. The magnet is made of a single Nb3Sn wire and designed for a fourth-generation ECR ion source operating at frequency of 45 GHz. To effectively prevent the wires motion from performance degradations and a quench, a pre-stress is essential for the superconducting magnet winding and strengthening. Focusing on the sextupole magnet's assembly and the pre-load procedure, a combined support structure with temporary bladders, load pads, and load keys, as well an aluminum shell was designed and fabricated in this work. A whole assembly process was fulfilled with a dummy structure at room temperature and a cooling-down and warming-up cycle to show its validity. Some low-temperature resistance strain gauges, together with a half-bridge compensation, were used to monitor strain of the aluminum shell during the pre-load control performance and thermal cycle process. A parametric study on the equivalent friction of the combined structure was carried out for the mechanical characteristics based on FEM simulation to show a reasonable agreement with the experiment measurements as a proper friction coefficient chosen. Finally, a real sextupole magnet was assembled with the combined support structure and tested for excitation. It was illustrated that a proper pre-load state realized by the support structure and a high excitation current about 800 A was reached so that the excited magnetic field gained 7 T as the designed value.

Measurements of the Effects of Compressive Loading on the Narrow Side of the HTS TAPE

Brookhaven National Laboratory (BNL) is involved in building high field magnets wound using Second Generation (2G) High Temperature Superconductor (HTS) tape. Certain magnet designs demand a load on the narrow edge of the tape approaching 170 MPa. While significant experimental data is available on the performance of the 2G HTS tape under radial and azimuthal stresses [1] , limited experimental data is available for the load on the narrow edge of the tape. To validate the design of a 25 Tesla, 100 mm cold bore Non-Insulated (NI) HTS solenoid, a series of compressive tests were performed on coils wound using 12 mm 2G HTS tape from SuperPower with an Hastelloy substrate thickness of 50 µm and varying copper stabilizer layer thicknesses of 65 μm, 40 μm, and 20 μm. This paper summarizes the initial design, several iterations, and results in the development of this test to simulate the conditions of the coils in a solenoid energized to 25 Tesla.

Heterogeneous Integration of Magnetic Component Windings on Ceramic Substrates

Heterogeneous integration and the converter in package concept have been highlighted as enabling technologies to unlock the full potential of silicon carbide (SiC) and gallium nitride (GaN) devices. Control of parasitic elements in the commutation loops and passive filter integration within the power module reduces the risk of overcurrent and overvoltage stresses for the transistors and can improve the containment of high-frequency noise at source, resulting in safer operation of the whole converter. However, at present, the major limitation to filter integration is posed by the low energy density of commercial magnetic components. This article further investigates on the integration of more reliable high-power-density magnetic components within the power module structure. The proposed approach consists of bonding individual copper parts, representative of single winding turns, onto an appropriately patterned ceramic substrate, thus improving the filters thermal management. At first, an experimental comparison between different bonding techniques has been carried out based on mechanical performance. Finally, to prove the feasibility and repeatability of the proposed route, a complete inductor has been manufactured using the solder bonding technique. Both thermal tests and simulations confirmed that due to the enhanced heat exchange between the inductor and cooling system, the maximum current density can be increased above commercial standards while maintaining the temperature in a safe range for the nearby active devices.

Mitigating Noncirculating Bearing Currents by a Correct Stator Magnetic Circuit and Winding Design

Different mechanisms by which bearing currents flow inside the electrical machine are well studied. In contrast, investigation and development of different techniques to mitigate these currents remain a field for improvement, and the final common solution to the problem has not been provided yet. In pursuit of addressing the problem, this article deals with noncirculating (or capacitive) bearing currents. The circuit mechanism of capacitive currents is explained in brief, and an approach for their mitigation is introduced. This article studies the influence of the stator winding and the slot geometry and presents different geometries to modify the motor to reduce the capacitive bearing currents. The effectiveness of the proposed mitigation technique is shown by finite-element-based modeling and verified by laboratory tests with different induction motor designs, where the winding and magnetic circuit geometries are varied. The technique can be used, in particular, for the mitigation of noncirculating currents, but it also offers potential for further research.

The thermal-radiative wind in low-mass X-ray binary H1743−322 – II. Iron line predictions from Monte Carlo radiation transfer

ABSTRACT We show the best current simulations of the absorption and emission features predicted from thermal-radiative winds produced from X-ray illumination of the outer accretion disc in binary systems. We use the density and velocity structure derived from a radiation hydrodynamic code as input to a Monte Carlo radiation transport calculation. The initial conditions are matched to those of the black hole binary system H1743−322 in its soft, disc dominated state, where wind features are seen in Chandra grating data. Our simulation fits well to the observed line profile, showing that these physical wind models can be the origin of the absorption features seen, rather than requiring a magnetically driven wind. We show how the velocity structure is the key observable discriminator between magnetic and thermal winds. Magnetic winds are faster at smaller radii, whereas thermal winds transition to a static atmosphere at smaller radii. New data from XRISM (due for launch 2022 January) will give an unprecedented view of the physics of the wind launch and acceleration processes, but the existence of static atmospheres in small disc systems already rules out magnetic winds which assume self-similar magnetic fields from the entire disc as the origin of the absorption features seen.

Study of the fractality in a magnetohydrodynamic shell model forced by solar wind fluctuations

Abstract. The description of the relationship between interplanetary plasma and geomagnetic activity requires complex models. Drastically reducing the ambition of describing this detailed complex interaction and, if we are interested only in the fractality properties of the time series of its characteristic parameters, a magnetohydrodynamic (MHD) shell model forced using solar wind data might provide a possible novel approach. In this paper we study the relation between the activity of the magnetic energy dissipation rate obtained in one such model, which may describe geomagnetic activity, and the fractal dimension of the forcing. In different shell model simulations, the forcing is provided by the solution of a Langevin equation where a white noise is implemented. This forcing, however, has been shown to be unsuitable for describing the solar wind action on the model. Thus, we propose to consider the fluctuations of the product between the velocity and the magnetic field solar wind data as the noise in the Langevin equation, the solution of which provides the forcing in the magnetic field equation. We compare the fractal dimension of the magnetic energy dissipation rate obtained, of the magnetic forcing term, and of the fluctuations of v⋅bz, with the activity of the magnetic energy dissipation rate. We examine the dependence of these fractal dimensions on the solar cycle. We show that all measures of activity have a peak near solar maximum. Moreover, both the fractal dimension computed for the fluctuations of v⋅bz time series and the fractal dimension of the magnetic forcing have a minimum near solar maximum. This suggests that the complexity of the noise term in the Langevin equation may have a strong effect on the activity of the magnetic energy dissipation rate.

Competing effect of wind braking and interior coupling in the rotational evolution of solar-like stars

Solar-like stars (M ≲ 1.3 M⊙) lose angular momentum through their magnetized winds. The resulting evolution of the surface rotation period, which can be directly measured photometrically, has the potential to be an accurate indicator of stellar age, and is constrained by observations of rotation periods of coeval stars, such as members of Galactic open clusters. A prominent observational feature of the mass–rotation period diagrams of open clusters is a sequence of relatively slower rotators. The formation and persistence of this slow-rotator sequence across several billion years imply an approximately coherent spin-down of the stars that belong to it. In particular, the sequence is observed to evolve coherently toward longer periods in progressively older clusters. Recent observations of the ≈700 Myr Praesepe and the 1 Gyr NGC 6811 clusters, however, are not fully consistent with this general pattern. While the stars of 1 M⊙ on the slow-rotator sequence of the older NGC 6811 have longer periods than their counterparts in the younger Praesepe, as expected, the two sequences essentially merge at lower masses (≲0.8 M⊙). In other words, it seems that low-mass stars have not been spinning down in the intervening 300 Myr. Here we show that this behavior is a manifestation of the variable rotational coupling in solar-like stars. The resurfacing of angular momentum from the interior can temporarily compensate for that lost at the surface due to wind braking. In our model the internal redistribution of angular momentum has a steep mass dependence; as a result, the re-coupling occurs at different ages for stars of different masses. The semi-empirical mass dependence of the rotational coupling timescale included in our model produces an evolution of the slow-rotator sequence in very good agreement with the observations. Our model, in particular, explains the stalled surface spin-down of low-mass stars between Praesepe and NGC 6811, and predicts that the same behavior should be observable at other ages in other mass ranges.