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Статті в журналах з теми "Simulation of magnetic fields"

Автор: Grafiati

Опубліковано: 30 травня 2022

Оновлено: 19 липня 2025

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Schnack, D. D., Z. Mikić, D. C. Barnes, and G. Van Hoven. "Magnetohydrodynamic simulation of coronal magnetic fields." Computer Physics Communications 59, no. 1 (1990): 21–37. http://dx.doi.org/10.1016/0010-4655(90)90153-r.

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Trang, Nguyen Thi Thao, Peter Lott, and Quynh Lan Nguyen. "Magnetic Field in the Universe." Journal of Physics: Conference Series 3040, no. 1 (2025): 012009. https://doi.org/10.1088/1742-6596/3040/1/012009.

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Abstract Magnetic fields permeate the universe and influence physical processes, from compact objects to large cosmic structures. Unlike electric fields, magnetic fields are closely tied to space-time dynamics, governing charged particle motion and producing radiation such as synchrotron and curvature emission. On intergalactic scales, magnetic fields are reshaped during galaxy mergers. Gravitational forces drive turbulence, shock waves, and gas inflows that amplify and reorganize magnetic fields. Radio synchrotron emission and polarization mapping observations reveal strong, coherent fields in tidal tails, bridges, and star-forming regions. These fields regulate star formation, guide cosmic ray transport, and contribute to the magnetization of the intergalactic medium. On more minor scales, in neutron stars and especially magnetars, magnetic fields reach strengths far beyond those produced in terrestrial labs. These extreme fields deform the solid crust of the star, potentially generating continuous gravitational waves through persistent asymmetric mass distributions. Simulations using general relativistic magnetohydrodynamics and crustal elasticity are essential to understanding these signals and probing the internal physics of neutron stars. This paper reviews advances in the study of magnetic fields in merging galaxies and magnetars, focusing on physical mechanisms and simulation techniques, including the velocity gradient technique and GRMHD modeling. Future advances in simulation techniques and observatories promise to deepen our understanding of the role of magnetic fields across the cosmos.

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Füzi, J. "Simulation of neutron motion in magnetic fields—magnetic monochromator." Measurement Science and Technology 19, no. 3 (2008): 034013. http://dx.doi.org/10.1088/0957-0233/19/3/034013.

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Uetake, H., N. Hirota, Y. Ikezoe, K. Kitazawa, and K. Miyoshi. "Magnetic-field simulation for shielding from high magnetic fields." Journal of Applied Physics 91, no. 10 (2002): 6991. http://dx.doi.org/10.1063/1.1452672.

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Vieira, Gregory B., Eliza Howard, Prannoy Lankapalli, Iesha Phillips, Keith Hoffmeister, and Jackson Holley. "Stray Magnetic Field Variations and Micromagnetic Simulations: Models for Ni0.8Fe0.2 Disks Used for Microparticle Trapping." Micromachines 15, no. 5 (2024): 567. http://dx.doi.org/10.3390/mi15050567.

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Patterned micro-scale thin-film magnetic structures, in conjunction with weak (~few tens of Oe) applied magnetic fields, can create energy landscapes capable of trapping and transporting fluid-borne magnetic microparticles. These energy landscapes arise from magnetic field magnitude variations that arise in the vicinity of the magnetic structures. In this study, we examine means of calculating magnetic fields in the local vicinity of permalloy (Ni0.8Fe0.2) microdisks in weak (~tens of Oe) external magnetic fields. To do this, we employ micromagnetic simulations and the resulting calculations of fields. Because field calculation from micromagnetic simulations is computationally time-intensive, we discuss a method for fitting simulated results to improve calculation speed. Resulting stray fields vary dramatically based on variations in micromagnetic simulations—vortex vs. non-vortex micromagnetic results—which can each appear despite identical simulation final conditions, resulting in field strengths that differ by about a factor of two.

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Stacy, Athena, Christopher F. McKee, Aaron T. Lee, Richard I. Klein, and Pak Shing Li. "Magnetic fields in the formation of the first stars – II. Results." Monthly Notices of the Royal Astronomical Society 511, no. 4 (2022): 5042–69. http://dx.doi.org/10.1093/mnras/stac372.

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ABSTRACT Beginning with cosmological initial conditions at z = 100, we simulate the effects of magnetic fields on the formation of Population III stars and compare our results with the predictions of Paper I. We use gadget-2 to follow the evolution of the system while the field is weak. We introduce a new method for treating kinematic fields by tracking the evolution of the deformation tensor. The growth rate in this stage of the simulation is lower than expected for diffuse astrophysical plasmas, which have a very low resistivity (high magnetic Prandtl number); we attribute this to the large numerical resistivity in simulations, corresponding to a magnetic Prandtl number of order unity. When the magnetic field begins to be dynamically significant in the core of the minihalo at z = 27, we map it on to a uniform grid and follow the evolution in an adaptive mesh refinement, MHD simulation in orion2. The non-linear evolution of the field in the orion2 simulation violates flux-freezing and is consistent with the theory proposed by Xu & Lazarian. The fields approach equipartition with kinetic energy at densities ∼1010–1012 cm−3. When the same calculation is carried out in orion2 with no magnetic fields, several protostars form, ranging in mass from ∼1 to 30 M⊙; with magnetic fields, only a single ∼30 M⊙ protostar forms by the end of the simulation. Magnetic fields thus suppress the formation of low-mass Pop III stars, yielding a top-heavy Pop III initial mass function and contributing to the absence of observed Pop III stars.

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Virtanen, I. O. I., A. A. Pevtsov, I. I. Virtanen, and K. Mursula. "Reconstructing solar magnetic fields from historical observations." Astronomy & Astrophysics 652 (August 2021): A79. http://dx.doi.org/10.1051/0004-6361/202140656.

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Context. The evolution of the photospheric magnetic field can be simulated with surface flux transport (SFT) simulations, which allow for the study of the evolution of the entire field, including polar fields, solely using observations of the active regions. However, because only one side of the Sun is visible at a time, active regions that emerge and decay on the far-side are not observed and not included in the simulations. As a result, some flux is missed. Aims. We construct additional active regions and apply them to the far-side of the Sun in an SFT simulation to assess the possible effects and the magnitude of error that the missing far-side flux causes. We estimate how taking the missing far-side flux into account affects long-term SFT simulations. Methods. We identified active regions from synoptic maps of the photospheric magnetic field between 1975 and 2019. We divided them into solar cycle wings and determined their lifetimes. Using the properties of observed active regions with sufficiently short lifetimes, we constructed additional active regions and inserted them into an SFT simulation. Results. We find that adding active regions with short lifetimes to the far-side of the Sun results in significantly stronger polar fields in minimum times and slightly delayed polarity reversals. These results partly remedy the earlier results, which show overly weak polar fields and polarity reversals that are slightly too early when far-side emergence is not taken into account. The far-side active regions do not significantly affect poleward flux surges, which are mostly caused by larger long-living active regions. The far-side emergence leads to a weak continuous flow of flux, which affects polar fields over long periods of time.

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Padoan, Paolo, Tuomas Lunttila, Mika Juvela, et al. "Magnetic Fields in Molecular Clouds." Proceedings of the International Astronomical Union 6, S271 (2010): 187–96. http://dx.doi.org/10.1017/s1743921311017601.

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AbstractSupersonic magneto-hydrodynamic (MHD) turbulence in molecular clouds (MCs) plays an important role in the process of star formation. The effect of the turbulence on the cloud fragmentation process depends on the magnetic field strength. In this work we discuss the idea that the turbulence is super-Alfvénic, at least with respect to the cloud mean magnetic field. We argue that MCs are likely to be born super-Alfvénic. We then support this scenario based on a recent simulation of the large-scale warm interstellar medium turbulence. Using small-scale isothermal MHD turbulence simulation, we also show that MCs may remain super-Alfvénic even with respect to their rms magnetic field strength, amplified by the turbulence. Finally, we briefly discuss the comparison with the observations, suggesting that super-Alfvénic turbulence successfully reproduces the Zeeman measurements of the magnetic field strength in dense MC clouds.

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Suzuki, Takeru K. "MHD in a Cylindrical Shearing Box. II. Intermittent Bursts and Substructures in MRI Turbulence." Astrophysical Journal 957, no. 2 (2023): 99. http://dx.doi.org/10.3847/1538-4357/acfb88.

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Abstract By performing ideal magnetohydrodynamical (MHD) simulations with weak vertical magnetic fields in unstratified cylindrical shearing boxes with modified boundary treatment, we investigate MHD turbulence excited by magnetorotational instability. The cylindrical simulation exhibits extremely large temporal variation in the magnetic activity compared with the simulation in a normal Cartesian shearing box, although the time-averaged field strengths are comparable in the cylindrical and Cartesian setups. Detailed analysis of the terms describing magnetic energy evolution with “triangle diagrams” surprisingly reveals that in the cylindrical simulation the compression of toroidal magnetic field is unexpectedly as important as the winding due to differential rotation in amplifying magnetic fields and triggering intermittent magnetic bursts, which are not seen in the Cartesian simulation. The importance of the compressible amplification is also true for a cylindrical simulation with tiny curvature; the evolution of magnetic fields in the nearly Cartesian shearing box simulation is fundamentally different from that in the exact Cartesian counterpart. The radial gradient of epicyclic frequency, κ, which cannot be considered in the normal Cartesian shearing box model, is the cause of this fundamental difference. An additional consequence of the spatial variation of κ is continuous and ubiquitous formation of narrow high-density (low-density) and weak-field (strong-field) localized structures; seeds of these ring gap structures are created by the compressible effect and subsequently amplified and maintained under the marginally unstable condition regarding “viscous-type” instability.

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Ye, Jun-Xian, Jia-Mian Hu, Zhan Shi, et al. "Magnetic-Field-Orientation Dependent Magnetoelectric Effect in FeBSiC/PZT/FeBSiC Composites." Advances in Materials Science and Engineering 2014 (2014): 1–5. http://dx.doi.org/10.1155/2014/249526.

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We investigate the magnetic-field-orientation dependent magnetoelectric (ME) effect in the FeBSiC/Pb(Zr,Ti)O3(PZT)/FeBSiC laminates. It is shown that, by only using the bias-magnetic-field dependent ME response measured with the magnetic-field parallel to the surface plane of PZT slab, the magnetic-field-orientation dependent ME coefficient upon magnetic-fields of various amplitudes can be obtained via computer simulations. The simulation results match well the experimental measurements, demonstrating the applicability of the ME laminates-based sensors in detecting magnetic-fields with uncertain amplitudes and/or orientations in environment.

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Inoue, Satoshi, Keiji Hayashi, and Takahiro Miyoshi. "An Evolution and Eruption of the Coronal Magnetic Field through a Data-driven MHD Simulation." Astrophysical Journal 946, no. 1 (2023): 46. http://dx.doi.org/10.3847/1538-4357/ac9eaa.

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Abstract We present a newly developed data-driven magnetohydrodynamics (MHD) simulation code under a zero-β approximation based on a method proposed by Hayashi et al. 2018 and 2019. Although many data-driven MHD simulations have been developed and conducted, there are not many studies on how accurately those simulations can reproduce the phenomena observed in the solar corona. In this study, we investigated the performance of our data-driven simulation quantitatively using ground-truth data. The ground-truth data was produced by an MHD simulation in which the magnetic field is twisted by the sunspot motions. A magnetic flux rope (MFR) is created by the cancellation of the magnetic flux at the polarity inversion line due to the converging flow on the sunspot, which eventually leads to the eruption of the MFR. We attempted to reproduce these dynamics using the data-driven MHD simulation. The coronal magnetic fields are driven by the electric fields, which are obtained from a time series of the photospheric magnetic field that is extracted from the ground-truth data, on the surface. As a result, the data-driven simulation could capture the subsequent MHD processes, the twisted coronal magnetic field and formation of the MFR, and also its eruption. We report these results and compare them with the ground-truth data, and discuss how to improve the accuracy and optimize the numerical method.

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Rodman, Payton E., та Christopher S. Reynolds. "Evolution of the Magnetic Field in High- and Low-β Disks with Initially Toroidal Fields". Astrophysical Journal 960, № 2 (2024): 97. http://dx.doi.org/10.3847/1538-4357/ad0384.

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Abstract We present the results from a pair of high-resolution, long-timescale (∼105 GM/c 3), global, three-dimensional magnetohydrodynamical accretion disk simulations with differing initial magnetic plasma β in order to study the effects of the initial toroidal field strength on the production of a large-scale poloidal field. We initialize our disks in approximate equilibrium with purely toroidal magnetic fields of strength β 0 = 5 and 200. We also perform a limited resolution study. We find that simulations of differing field strengths diverge early in their evolution and remain distinct over the time studied, indicating that the initial magnetic conditions leave a persistent imprint in our simulations. Neither simulation enters the magnetically arrested disk regime. Both simulations are able to produce poloidal fields from initially toroidal fields, with the β 0 = 5 simulation evolving clear signs of a large-scale poloidal field. We make a cautionary note that computational artifacts in the form of large-scale vortices may be introduced in the combination of initially weak field and disk-internal mesh refinement boundaries, as evidenced by the production of an m = 1 mode overdensity in the weak field simulation. Our results demonstrate that the initial toroidal field strength plays a vital role in the simulated disk evolution for the models studied.

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Wu, Haohao, Dedong Gao, Shan Wang, Shengzhe Xu, Tengfei Ma, and Lirong Li. "Design and optimization of large-scale single-crystal furnaces asymmetric hooked magnetic fields." Journal of Physics: Conference Series 2351, no. 1 (2022): 012002. http://dx.doi.org/10.1088/1742-6596/2351/1/012002.

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The solar photovoltaic power generation industry and large-scale integrated circuit industry put forward higher requirements for the size and quality of monocrystalline silicon. However, there are some problems in the production of large-diameter and high-quality monocrystalline silicon, such as uneven crucible thermal field and strong melt convection, which affect the quality of monocrystalline silicon. Therefore, by adopting the finite element 2D modeling method, this paper established the asymmetric hook magnetic field model of the 40-inch crucible. Hence the key magnetic field parameters affecting the growth of a single crystal were determined by controlling the melt convection in the crucible. Meanwhile, through finite element static magnetic field simulations, the effect of the magnetic field at the crucible wall was analyzed by adding the upper and lower guide rings of the magnetic shield structure, the magnetic shield structure with intermediate permeability ring, and the coil parameters. In addition, the parameters of the asymmetric hooked magnetic field structure were also optimized based on the simulation data. On the above basis, a numerical simulation analysis of the key parameters of the magnetic field was carried out. The simulation results show that the optimized asymmetric hook magnetic field structure can effectively control the melt convection in the crucible. In addition, the magnetic field strength at the crucible wall can meet the target of restraining convection by a magnetic field. Hence, it provides a certain reference value for the design of a large-scale single crystal furnace magnetic field.

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Amiri Roodan, Venoos, Jenifer Gómez-Pastora, Ioannis H. Karampelas, et al. "Formation and manipulation of ferrofluid droplets with magnetic fields in a microdevice: a numerical parametric study." Soft Matter 16, no. 41 (2020): 9506–18. http://dx.doi.org/10.1039/d0sm01426e.

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Integrated computational fluid dynamics and magnetics simulation is employed to analyze the effects of magnetic force on the formation and manipulation of ferrofluid droplets within a flowing non-magnetic continuous phase in a microfluidic device.

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Shelyag, S., Y. E. Litvinenko, V. Fedun, G. Verth, J. J. González-Avilés, and F. S. Guzmán. "Flows and magnetic field structures in reconnection regions of simulations of the solar atmosphere: Do flux pile-up models work?" Astronomy & Astrophysics 620 (December 2018): A159. http://dx.doi.org/10.1051/0004-6361/201833752.

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Aims. We study the process of magnetic field annihilation and reconnection in simulations of magnetised solar photosphere and chromosphere with magnetic fields of opposite polarities and constant numerical resistivity. Methods. Exact analytical solutions for reconnective annihilations were used to interpret the features of magnetic reconnection in simulations of flux cancellation in the solar atmosphere. We used MURaM high-resolution photospheric radiative magneto-convection simulations to demonstrate the presence of magnetic field reconnection consistent with the magnetic flux pile-up models. Also, a simulated data-driven chromospheric magneto-hydrodynamic simulation is used to demonstrate magnetic field and flow structures, which are similar to the theoretically predicted ones. Results. Both simulations demonstrate flow and magnetic field structures roughly consistent with accelerated reconnection with magnetic flux pile-up. The presence of standard Sweet–Parker type reconnection is also demonstrated in stronger photospheric magnetic fields.

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Venkatesh, Vavilala, K. Srinibas Rao, and Rama Rao J.V.G. "Calculation of electric field and magnetic field in a 245 kV GIS." E3S Web of Conferences 616 (2025): 03034. https://doi.org/10.1051/e3sconf/202561603034.

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In India, the implementation of Gas Insulated Substation (GIS) has been accelerated for two decades. In the case of GIS, the electric and magnetic field estimation is very important because of the shorter distances of bus bars and line sections. Several others have given the estimation of electric and magnetic fields by solving nonlinear differential equations using numerical techniques. In this paper, the advanced simulation tools ELECNET and MAGNET have been used to estimate these fields. A typical 245k V GIS is considered for Modeling and simulation. The four important locations, XLPE cable termination, gas-to-air bushing, bus link, and current transformer (CT) position, have been considered. The resultant fields were obtained. These values are compared with Electric and Magnetic field measurements at the same substation. For these measurements, a Gauss meter and an E-field meter were used. These meters are calibrated per IEEE 644-1994 and IEEE 644-2019. The measured values are in good agreement with the simulation results. Hence, the triangular grid model and Modeling are dependable for further simulations. The results show that the bus link and CT position fields are higher than those of other locations.

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Kim, Woong-Tae. "Effects of Magnetic Fields on Bar Substructures in Barred Galaxies." Proceedings of the International Astronomical Union 10, H16 (2012): 389. http://dx.doi.org/10.1017/s1743921314011582.

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AbstractTo study the effects of magnetic fields on the properties of bar substructures, we run two-dimensional, ideal MHD simulations of barred galaxies under the influence of a non-axisymmetric bar potential. In the bar regions, magnetic fields reduce density compression in the dust-lane shocks, while removing angular momentum further from the gas at the shocks. This evidently results in a smaller and more distributed ring, and a larger mass inflows rate to the galaxy center in models with stronger magnetic fields. In the outer regions, an MHD dynamo due to the combined action of the bar potential and background shear operates, amplifying magnetic fields near the corotation resonance. In the absence of spiral arms, the amplified fields naturally shape into trailing magnetic arms with strong fields and low density. The reader is refereed to Kim & Stone (2012) for a detailed presentation of the simulation outcomes.

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NISHIKAWA, K. I., J. NIMIEC, M. MEDVEDEV, et al. "RADIATION FROM RELATIVISTIC SHOCKS WITH TURBULENT MAGNETIC FIELDS." International Journal of Modern Physics D 19, no. 06 (2010): 715–21. http://dx.doi.org/10.1142/s0218271810016865.

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Using our new 3D relativistic electromagnetic particle (REMP) code parallelized with MPI, we investigated long-term particle acceleration associated with a relativistic electron–positron jet propagating in an unmagnetized ambient electron–positron plasma. We have also performed simulations with electron-ion jets. The simulations were performed using a much longer simulation system than our previous simulations in order to investigate the full nonlinear stage of the Weibel instability for electron–positron jets and its particle acceleration mechanism. Cold jet electrons are thermalized and ambient electrons are accelerated in the resulting shocks for pair plasma case. Acceleration of ambient electrons leads to a maximum ambient electron density three times larger than the original value for pair plasmas. Behind the bow shock in the jet shock strong electromagnetic fields are generated. These fields may lead to time-dependent afterglow emission. We calculated radiation from electrons propagating in a uniform parallel magnetic field to verify the technique. We also used the new technique to calculate emission from electrons based on simulations with a small system with two different cases for Lorentz factors (15 and 100). We obtained spectra which are consistent with those generated from electrons propagating in turbulent magnetic fields with red noise. This turbulent magnetic field is similar to the magnetic field generated at an early nonlinear stage of the Weibel instability.

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Peng, Xiao Ling, Xiao Yang, Hai Biao Wei, Rui Ping Yue, and Hong Liang Ge. "Theoretical Modeling and Simulations of Magnetic Fluids in Gradient Magnetic Fields." Advanced Materials Research 146-147 (October 2010): 1510–13. http://dx.doi.org/10.4028/www.scientific.net/amr.146-147.1510.

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When a magnetic field is applied to magnetic fluids (MF), various structures of MF are formed: chain-like structures in low fields, columnar, lamellar and striped structures in high fields, ellipsoidal structures in pulsed fields, and layered structures in rotating fields. The inner structures and particle distributions of MF in gradient magnetic fields are quite interesting, but very few works have been done on this. In the present study, the effects of magnetic field gradient on the structures of MF are investigated using a two-dimensional Monte Carlo simulation. The results show that a gradient distribution of magnetic particles is formed under gradient magnetic fields. Moreover, with increasing the field gradient, more magnetic particles are pushed to the right region and particle distribution changes from grass-like clusters to needle-like ones.

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Li, Shibang, Haoyu Lu, Jinbin Cao, et al. "Deflection of O₂ ⁺ Ion Flow by Magnetic Fields in the Martian Ionosphere." Astrophysical Journal 941, no. 2 (2022): 198. http://dx.doi.org/10.3847/1538-4357/aca32b.

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Abstract The effect of the Martian crustal magnetic field on ion escape is the focus of considerable interest. Directions of magnetic fields near Mars determined by the interaction between Mars’ crustal and interplanetary magnetic fields have been suggested to play a significant role on ion transport around Mars. In this study we investigate the physical mechanism of deflection of O 2 + ion flow in two typical magnetic field orientations at the horizontal plane in the Martian ionosphere by performing 3D multifluid Hall magnetohydrodynamic simulations. Cross validation of the simulation results from two cases with the G110 crustal field model and equivalent source dipole model reveals that due to the Hall electric force, O 2 + ion flow tends to be accelerated eastwards in the region occupied by outward magnetic fields, and westwards in the region with inward magnetic fields. These results are helpful for understanding the impact of magnetic fields on the deflection of ionospheric ions in the Martian space environment.

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Brandenburg, A., R. L. Jennings, Å. Nordlund, M. Rieutord, R. F. Stein, and I. Tuominen. "Magnetic structures in a dynamo simulation." Journal of Fluid Mechanics 306 (January 10, 1996): 325–52. http://dx.doi.org/10.1017/s0022112096001322.

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We use three-dimensional simulations to study compressible convection in a rotating frame with magnetic fields and overshoot into surrounding stable layers. The, initially weak, magnetic field is amplified and maintained by dynamo action and becomes organized into flux tubes that are wrapped around vortex tubes. We also observe vortex buoyancy which causes upward flows in the cores of extended downdraughts. An analysis of the angles between various vector fields shows that there is a tendency for the magnetic field to be parallel or antiparallel to the vorticity vector, especially when the magnetic field is strong. The magnetic energy spectrum has a short inertial range with a slope compatible with k+1/3 during the early growth phase of the dynamo. During the saturated state the slope is compatible with k−1. A simple analysis based on various characteristic timescales and energy transfer rates highlights important qualitative ideas regarding the energy budget of hydromagnetic dynamos.

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Virtanen, I. O. I., I. I. Virtanen, A. A. Pevtsov, L. Bertello, A. Yeates, and K. Mursula. "Reconstructing solar magnetic fields from historical observations." Astronomy & Astrophysics 627 (June 25, 2019): A11. http://dx.doi.org/10.1051/0004-6361/201935606.

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Aims. The evolution of the photospheric magnetic field has only been regularly observed since the 1970s. The absence of earlier observations severely limits our ability to understand the long-term evolution of solar magnetic fields, especially the polar fields that are important drivers of space weather. Here, we test the possibility to reconstruct the large-scale solar magnetic fields from Ca II K line observations and sunspot magnetic field observations, and to create synoptic maps of the photospheric magnetic field for times before modern-time magnetographic observations. Methods. We reconstructed active regions from Ca II K line synoptic maps and assigned them magnetic polarities using sunspot magnetic field observations. We used the reconstructed active regions as input in a surface flux transport simulation to produce synoptic maps of the photospheric magnetic field. We compared the simulated field with the observed field in 1975−1985 in order to test and validate our method. Results. The reconstruction very accurately reproduces the long-term evolution of the large-scale field, including the poleward flux surges and the strength of polar fields. The reconstruction has slightly less emerging flux because a few weak active regions are missing, but it includes the large active regions that are the most important for the large-scale evolution of the field. Although our reconstruction method is very robust, individual reconstructed active regions may be slightly inaccurate in terms of area, total flux, or polarity, which leads to some uncertainty in the simulation. However, due to the randomness of these inaccuracies and the lack of long-term memory in the simulation, these problems do not significantly affect the long-term evolution of the large-scale field.

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Dilmieva, E. T., A. P. Kamantsev, V. V. Koledov, et al. "Experimental simulation of a magnetic refrigeration cycle in high magnetic fields." Physics of the Solid State 58, no. 1 (2016): 81–85. http://dx.doi.org/10.1134/s1063783416010108.

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Xu, Yi, Junhua Wang, Haoli Hou, and Jianwei Shao. "Simulation analysis of coupled magnetic-temperature fields in magnetic fluid hyperthermia." AIP Advances 9, no. 10 (2019): 105317. http://dx.doi.org/10.1063/1.5127919.

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Siu-Tapia, A., A. Lagg, M. van Noort, M. Rempel, and S. K. Solanki. "Superstrong photospheric magnetic fields in sunspot penumbrae." Astronomy & Astrophysics 631 (October 29, 2019): A99. http://dx.doi.org/10.1051/0004-6361/201834083.

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Context. Recently, there have been some reports of unusually strong photospheric magnetic fields (which can reach values of over 7 kG) inferred from Hinode SOT/SP sunspot observations within penumbral regions. These superstrong penumbral fields are even larger than the strongest umbral fields on record and appear to be associated with supersonic downflows. The finding of such fields has been controversial since they seem to show up only when spatially coupled inversions are performed. Aims. Here, we investigate and discuss the reliability of those findings by studying in detail observed spectra associated with particularly strong magnetic fields at the inner edge of the penumbra of active region 10930. Methods. We applied classical diagnostic methods and various inversions with different model atmospheres to the observed Stokes profiles in two selected pixels with superstrong magnetic fields, and compared the results with a magnetohydrodynamic simulation of a sunspot whose penumbra contains localized regions with strong fields (nearly 5 kG at τ = 1) associated with supersonic downflows. Results. The different inversions provide different results: while the SPINOR 2D inversions consider a height-dependent single-component model and return B > 7 kG and supersonic positive vLOS (corresponding to a counter-Evershed flow), height-dependent two-component inversions suggest the presence of an umbral component (almost at rest) with field strengths ∼4 − 4.2 kG and a penumbral component with vLOS ∼ 16 − 18 km s−1 and field strengths up to ∼5.8 kG. Likewise, height-independent two-component inversions find a solution for an umbral component and a strongly redshifted (vLOS ∼ 15 − 17 km s−1) penumbral component with B ∼ 4 kG. According to a Bayesian information criterion, the inversions providing a better balance between the quality of the fits and the number of free parameters considered by the models are the height-independent two-component inversions, but they lie only slightly above the SPINOR 2D inversions. Since it is expected that the physical parameters all display considerable gradients with height, as supported by magnetohydrodynamic (MHD) sunspot simulations, the SPINOR 2D inversions are the preferred ones. Conclusions. According to the MHD sunspot simulation analyzed here, the presence of counter-Evershed flows in the photospheric penumbra can lead to the necessary conditions for the observation of ∼5 kG fields at the inner penumbra. Although a definite conclusion about the potential existence of fields in excess of 7 kG cannot be given, their nature could be explained (based on the simulation results) as the consequence of the extreme dynamical effects introduced by highly supersonic counter-Evershed flows (vLOS > 10 km s−1 and up to ∼30 km s−1 according to SPINOR 2D). The latter are much faster and more compressive downflows than those found in the MHD simulations and therefore could lead to field intensification up to considerably stronger fields. Also, a lower gas density would lead to a deeper depression of the τ = 1 surface, making possible the observation of deeper-lying stronger fields. The superstrong magnetic fields are expected to be nearly force-free, meaning that they can attain much larger strengths than expected when considering only balance between magnetic pressure and the local gas pressure.

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Yang, Bo, Jian-Fu Zhang, Alex Lazarian, and José Renan de Medeiros. "Statistical tracing of turbulent magnetic fields in the optically thick interstellar medium." Monthly Notices of the Royal Astronomical Society 503, no. 1 (2021): 768–76. http://dx.doi.org/10.1093/mnras/stab236.

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ABSTRACT Based on high-resolution 3D data cubes from a magnetohydrodynamic (MHD) turbulence simulation, we study how to reveal the direction of the magnetic field within the optically thick interstellar medium by using the velocity gradient technique (VGT), correlation function anisotropy (CFA), and principal component analysis of anisotropies (PCAA). Considering the CO molecular tracers as a tracing method for radiative transfer processes, we find that the VGT and CFA can successfully trace the orientation of mean magnetic fields, which is in good agreement with the low-resolution numerical results obtained in the case of an optically thin medium. Similar to the simulation of an optically thin ISM, our simulations show that PCCA is still unusable in optically thick media. The synergetic application of the VGT and CFA to high-resolution spectroscopic observations is expected to yield valuable information on the interstellar magnetic field.

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Panesar, J., and A. H. Nelson. "3–D Models of Galaxy Magnetic Fields with Spiral Shocks." Symposium - International Astronomical Union 140 (1990): 133–34. http://dx.doi.org/10.1017/s0074180900189752.

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We report here some preliminary results of 3–D numerical simulations of an α–ω dynamo in galaxies with differential rotation, small–scale turbulence, and a shock wave induced by a stellar density wave. We obtain the magnetic field from the standard dynamo equation, but include the spiral shock velocity field from a hydrodynamic simulation of the gas flow in a gravitational field with a spiral perturbation (Johns and Nelson, 1986).

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Fox, Peter A., Michael L. Theobald, and Sabatino Sofia. "Evolution of Large and Small Scale Magnetic Fields in the Sun." International Astronomical Union Colloquium 130 (1991): 218–22. http://dx.doi.org/10.1017/s0252921100079653.

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AbstractThis paper will discuss issues relating to the detailed numerical simulation of solar magnetic fields, those on the small scale which are directly observable on the surface, and those on larger scales whose properties must be deduced indirectly from phenomena such as the sunspot cycle. Results of simulations using the ADISM technique will be presented to demonstrate the importance of the treatment of Alfvén waves, the boundary conditions, and the statistical evolution of small scale convection with magnetic fields. To study the large scale fields and their time dependence, the magnetic resistivity plays an important role; its use will be discussed in the paper.

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Liu, Qingjun, and Chun Xia. "Formation of Quiescent Prominence Magnetic Fields by Supergranulations." Astrophysical Journal Letters 934, no. 1 (2022): L9. http://dx.doi.org/10.3847/2041-8213/ac80c6.

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Abstract To understand the formation of quiescent solar prominences, the origin of their magnetic field structures, i.e., magnetic flux ropes (MFRs), must be revealed. We use three-dimensional magnetofriction simulations in a spherical subdomain to investigate the role of typical supergranular motions in the long-term formation of a prominence magnetic field. Time-dependent horizontal supergranular motions with and without the effect of Coriolis force are simulated on the solar surface via Voronoi tessellation. The vortical motions by the Coriolis effect at boundaries of supergranules inject magnetic helicity into the corona. The helicity is transferred and accumulated along the polarity inversion line (PIL) as a strongly sheared magnetic field via helicity condensation. The diverging motions of supergranules converge opposite magnetic polarities at the PIL and drive the magnetic reconnection between footpoints of the sheared magnetic arcades to form an MFR. The magnetic network, negative-helicity MFR in the northern hemisphere, and fragmented-to-continuous formation process of magnetic dip regions are in agreement with observations. Although diverging supergranulations, differential rotation, and meridional flows are included, the simulation without the Coriolis effect cannot produce an MFR or sheared arcades to host a prominence. Therefore, Coriolis force is a key factor for helicity injection and the formation of magnetic structures of quiescent solar prominences.

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Duţan, Ioana, Ken-Ichi Nishikawa, Yosuke Mizuno, et al. "Particle-in-cell Simulations of Global Relativistic Jets with Helical Magnetic Fields." Proceedings of the International Astronomical Union 12, S324 (2016): 199–202. http://dx.doi.org/10.1017/s1743921316012722.

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AbstractWe study the interaction of relativistic jets with their environment, using 3-dimen- sional relativistic particle-in-cell simulations for two cases of jet composition: (i) electron-proton (e− − p+) and (ii) electron-positron (e±) plasmas containing helical magnetic fields. We have performed simulations of “global” jets containing helical magnetic fields in order to examine how helical magnetic fields affect kinetic instabilities such as the Weibel instability, the kinetic Kelvin-Helmholtz instability and the Mushroom instability. We have found that these kinetic instabilities are suppressed and new types of instabilities can grow. For the e− − p+ jet, a recollimation-like instability occurs and jet electrons are strongly perturbed, whereas for the e± jet, a recollimation-like instability occurs at early times followed by kinetic instability and the general structure is similar to a simulation without a helical magnetic field. We plan to perform further simulations using much larger systems to confirm these new findings.

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Grošelj, Daniel, Lorenzo Sironi, and Anatoly Spitkovsky. "Long-term Evolution of Relativistic Unmagnetized Collisionless Shocks." Astrophysical Journal Letters 963, no. 2 (2024): L44. http://dx.doi.org/10.3847/2041-8213/ad2c8c.

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Abstract We study a relativistic collisionless electron–positron shock propagating into an unmagnetized ambient medium using 2D particle-in-cell simulations of unprecedented duration and size. The shock generates intermittent magnetic structures of increasingly larger size as the simulation progresses. Toward the end of our simulation, at around 26,000 plasma times, the magnetic coherence scale approaches λ ∼ 100 plasma skin depths, both ahead and behind the shock front. We anticipate a continued growth of λ beyond the time span of our simulation, as long as the shock accelerates particles to increasingly higher energies. The post-shock field is concentrated in localized patches, which maintain a local magnetic energy fraction ε B ∼ 0.1. Particles randomly sampling the downstream fields spend most of their time in low field regions (ε B ≪ 0.1) but emit a large fraction of the synchrotron power in the localized patches with strong fields (ε B ∼ 0.1). Our results have important implications for models of gamma-ray burst afterglows.

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Chiba, M. "Nonlinear Interaction Between Magnetic Fields and Spiral Arms." Symposium - International Astronomical Union 157 (1993): 373–74. http://dx.doi.org/10.1017/s0074180900174443.

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The evolution of galactic magnetic fields under the influence of spiral arms is investigated numerically by 2-dimensional simulation. We compute several models, especially when the swing-excitation mechanism works. We consider also the modification of the mean velocity fields driven by the Lorentz force of the growing magnetic fields. The characteristic structure of magnetic fields around the arm in each model is compared with the observations.

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Pamyatnykh L. A., Lysov M. S., Pamyatnykh S. E., Agafonov L. Yu., Mekhonoshin D. S., and Shmatov G. A. "Mechanism of domain walls drift in pulsed magnetic fields in iron garnet crystals." Physics of the Solid State 64, no. 10 (2022): 1398. http://dx.doi.org/10.21883/pss.2022.10.54225.33hh.

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Conditions for the drift of domain walls in pulsed magnetic fields of various organization (bipolar and unipolar pulsed magnetic fields, pulse packets) are established. Dependences of domain walls drift velocity on the parameters of pulsed magnetic fields (frequency, amplitude, pulse duration) are obtained. As a result of numerical simulation of domain walls drift in a uniaxial sample, an experimentally confirmed mechanism of domain walls drift in pulsed magnetic fields is proposed. Keywords: pulsed magnetic fields, iron garnets, domain walls, dynamic domain structures, drift of domain walls.

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Li, H., X. Peng, and W. Chen. "Simulation of the Chain-formation Process in Magnetic Fields." Journal of Intelligent Material Systems and Structures 16, no. 7-8 (2005): 653–58. http://dx.doi.org/10.1177/1045389x05052598.

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Oreshkin, V. I., S. A. Chaikovsky, K. V. Khishchenko, and E. V. Oreshkin. "Numerical simulation of electrical explosions in megagauss magnetic fields." Journal of Physics: Conference Series 830 (May 4, 2017): 012029. http://dx.doi.org/10.1088/1742-6596/830/1/012029.

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Bradshaw, L. A., A. Myers, J. P. Wikswo, and W. O. Richards. "A spatio-temporal dipole simulation of gastrointestinal magnetic fields." IEEE Transactions on Biomedical Engineering 50, no. 7 (2003): 836–47. http://dx.doi.org/10.1109/tbme.2003.813549.

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Fidler, J., T. Schrefl, W. Scholz, D. Suess, and V. D. Tsiantos. "Micromagnetic simulation of magnetization reversal in rotational magnetic fields." Physica B: Condensed Matter 306, no. 1-4 (2001): 112–16. http://dx.doi.org/10.1016/s0921-4526(01)00988-7.

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Martinez, D., C. Plechaty, and R. Presura. "Magnetic Fields for the Laboratory Simulation of Astrophysical Objects." Astrophysics and Space Science 307, no. 1-3 (2006): 109–14. http://dx.doi.org/10.1007/s10509-006-9275-9.

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Fujimoto, K., K. Totsuka, Y. Uesaka, et al. "Computer simulation of MR response to transverse magnetic fields." IEEE Transactions on Magnetics 33, no. 3 (1997): 2386–91. http://dx.doi.org/10.1109/20.573862.

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Machida, Mami, Takuya Akahori, Kenji Nakamura, Hiroyuki Nakanishi, and Marijke Haverkorn. "Faraday Depolarization Effects in Spiral Galaxies." Galaxies 7, no. 1 (2019): 15. http://dx.doi.org/10.3390/galaxies7010015.

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Magnetic fields in the universe play an essential role in observations of the radio synchrotron continuum; however, we do not know enough about them, either observationally or theoretically. We are interested in galactic magnetic fields because they affect the structural formation of galaxies in terms of star-forming regions, spiral arms, and threads at the galactic center. To clarify the importance of magnetic fields, we carried out numerical simulations of the galactic gaseous disk with magnetic fields. We also calculated observables, such as the rotation measure and Stokes parameters, from the results of numerical simulation. FD maps and intensity maps have been reported, and the relation between azimuthal angle and FD has been shown to depend on the inclination of the observer. Furthermore, it has been shown that a polarized intensity below 800 MHz reflects field structure in the halo region, although the intensity is weak. The present paper summarizes the effects of Faraday depolarization and the relation between magnetic-field structure and Stokes parameters.

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Amard, Louis, Allan Sacha Brun, and Ana Palacios. "Understanding Post-main-sequence Stellar Magnetism: On the Origin of Pollux’s Weak Surface Magnetic Field." Astrophysical Journal 974, no. 2 (2024): 311. http://dx.doi.org/10.3847/1538-4357/ad6cd0.

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Abstract The magnetic field of red giants is still poorly understood today. Close to the core, asteroseismology has revealed magnetic fields of several hundred thousand gauss, but close to the surface, spectropolarimetric observations of the red giant Pollux only showed an average field of the order of 1 G. Using the ASH code, we conduct a series of 3D nonlinear magnetohydrodynamical simulations aiming at modeling the dynamo process operating within the extended convective envelope of a star similar to the red giant Pollux. We find that the dynamo is efficient even for the slow rotation considered and that large-scale fields are generated and maintained. We further test the correlation between the scale of the convective motions and the surface magnetic field geometry by varying the Prandtl number in our simulations. We show in particular that the value and the geometry of the modeled surface field depend directly on the coupling scales between the magnetic and the velocity fields, with larger convective cells leading to a stronger large-scale magnetic field. We also verify that the dynamo and the geometry of the resulting field are robust against a change of the initial conditions. We then compare our simulations to the observed field and find average ∣B ℓ ∣ of about 7 G for the simulation with large convective cells, and down to 2 G for the smaller-scale simulation, very close to the observed value. Finally, we suggest the possibility of the reversal of the red giant’s magnetic field.

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Varma, Vishnu, and Bernhard Müller. "3D simulations of oxygen shell burning with and without magnetic fields." Monthly Notices of the Royal Astronomical Society 504, no. 1 (2021): 636–47. http://dx.doi.org/10.1093/mnras/stab883.

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ABSTRACT We present a first 3D magnetohydrodynamic (MHD) simulation of convective oxygen and neon shell burning in a non-rotating $18\, \mathrm{M}_\odot$ star shortly before core collapse to study the generation of magnetic fields in supernova progenitors. We also run a purely hydrodynamic control simulation to gauge the impact of the magnetic fields on the convective flow and on convective boundary mixing. After about 17 convective turnover times, the magnetic field is approaching saturation levels in the oxygen shell with an average field strength of $\mathord {\sim }10^{10}\, \mathrm{G}$, and does not reach kinetic equipartition. The field remains dominated by small-to-medium scales, and the dipole field strength at the base of the oxygen shell is only $10^{9}\, \mathrm{G}$. The angle-averaged diagonal components of the Maxwell stress tensor mirror those of the Reynolds stress tensor, but are about one order of magnitude smaller. The shear flow at the oxygen–neon shell interface creates relatively strong fields parallel to the convective boundary, which noticeably inhibit the turbulent entrainment of neon into the oxygen shell. The reduced ingestion of neon lowers the nuclear energy generation rate in the oxygen shell and thereby slightly slows down the convective flow. Aside from this indirect effect, we find that magnetic fields do not appreciably alter the flow inside the oxygen shell. We discuss the implications of our results for the subsequent core-collapse supernova and stress the need for longer simulations, resolution studies, and an investigation of non-ideal effects for a better understanding of magnetic fields in supernova progenitors.

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Donnert, Julius, Hanbyul Jang, Peter Mendygral, Gianfranco Brunetti, Dongsu Ryu, and Thomas Jones. "Towards Exascale Simulations of the ICM Dynamo with WENO-Wombat." Galaxies 6, no. 4 (2018): 104. http://dx.doi.org/10.3390/galaxies6040104.

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In galaxy clusters, modern radio interferometers observe non-thermal radio sources with unprecedented spatial and spectral resolution. For the first time, the new data allows to infer the structure of the intra-cluster magnetic fields on small scales via Faraday tomography. This leap forward demands new numerical models for the amplification of magnetic fields in cosmic structure formation—the cosmological magnetic dynamo. Here we present a novel numerical approach to astrophyiscal MHD simulations aimed to resolve this small-scale dynamo in future cosmological simulations. As a first step, we implement a fifth order WENO scheme in the new code WOMBAT. We show that this scheme doubles the effective resolution of the simulation and is thus less expensive than common second order schemes. WOMBAT uses a novel approach to parallelization and load balancing developed in collaboration with performance engineers at Cray Inc. This will allow us scale simulation to the exaflop regime and achieve kpc resolution in future cosmological simulations of galaxy clusters. Here we demonstrate the excellent scaling properties of the code and argue that resolved simulations of the cosmological small scale dynamo within the whole virial radius are possible in the next years.

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Palin, Denis. "FINITE ELEMENT MODELING OF MAGNETIC FIELDS OF FERROFLUIDIC SEALS." Transport engineering 2023, no. 3 (2023): 14–20. http://dx.doi.org/10.30987/2782-5957-2023-3-14-20.

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The paper shows the process of constructing a model of a magnetic system of a ferrofluidic seal by means of femm 4.2. The results of a finite element simulation of a magnetic field are presented. It is found out that finite element modeling of the magnetic field gives the opportunity to assess qualitatively the efficiency of the magnetic system of ferrofluidic seals.

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Backs, Alex, Simon Sebold, Matteo Busi, Wai Tung Lee, Markus Strobl, and Dmytro Orlov. "Development and first results of a magnetic sample environment for polarized neutron imaging of thin metal sheets." EPJ Web of Conferences 286 (2023): 05003. http://dx.doi.org/10.1051/epjconf/202328605003.

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Polarized neutron imaging brings the great advantage of analyzing bulk magnetic properties with good spatial resolution. The technique is based on the interaction of the neutron spin with magnetic samples or free magnetic fields and observing the changes to a spin-polarized neutron beam. The high sensitivity to even small magnetic fields is a benefit in obtaining magnetization information but simultaneously a challenge in instrumentation, since magnetic environments for the polarized neutron beam and for the sample, as well as the fringe field from the magnetic sample itself all affect the measurement and can give rise to unwanted effects. We have used finite element simulations and ray tracing simulations, to design and analyze a magnetic sample environment devised for the measurement of ferromagnetic metal sheets. Here we show an analysis of performance of the experimental setup based on the simulation results and compare them to first experimental results on a grain oriented silicon steel sample.

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Yu, Chunkai, Zhongwei Yang, Xinliang Gao, Quanming Lu та Jian Zheng. "Electron Acceleration by Moderate-Mach-number Low-β Shocks: Particle-in-Cell Simulations". Astrophysical Journal 930, № 2 (2022): 155. http://dx.doi.org/10.3847/1538-4357/ac67df.

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Abstract Particle acceleration is ubiquitous at shock waves, occurring on scales ranging from supernova remnants in the universe to coronal-mass-ejection-driven shocks and planetary bow shocks in the heliosphere. The most promising mechanism responsible for the almost universally observed power-law spectra is diffusive shock acceleration (DSA). However, how electrons are preaccelerated by different shocks to the energy required by the DSA theory is still unclear. In this paper, we perform two-dimensional particle-in-cell plasma simulations to investigate how the magnetic field orientations, with respect to simulation planes, affect electron preacceleration in moderate-Mach-number low- β shocks. Simulation results show that instabilities can be different as the simulation planes capture different trajectories of particles. For magnetic fields perpendicular to the simulation plane, electron cyclotron drift instability dominates in the foot. Electrons can be trapped by the electrostatic wave and undergo shock-surfing acceleration. For magnetic fields lying in the simulation plane, whistler waves produced by modified two-stream instability dominate in the foot and scatter the electrons. In both cases, electrons undergo multistage acceleration in the foot, shock surface, and immediate downstream, during which process shock-surfing acceleration takes place as part of the preacceleration mechanism in moderate-Mach-number quasi-perpendicular shocks.

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Chávez, José Antonio Manco Chávez, Joel Núñez Mejía, Haydeé Verónica Túllume Huayanay, Daniel Enrique Terrones Rojas, Rolando Juan Borja Torres, and Carlos Héctor Cerna Gonzales. "Simulation of magnetic field produced by induction in toroid and solenoid using GeoGebra software." Journal of Posthumanism 5, no. 2 (2025): 85–104. https://doi.org/10.63332/joph.v5i2.406.

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In today’s era of modernity and the appearance of new knowledge-construction approaches supported by technological tools such as A.I., various instruments contribute to enhancing educational quality like GeoGebra, an open-source software with extensive capabilities for simulations. This research established three objectives, all of which are answered in its conclusions. The study focused on simulating magnetic fields with predefined geometric shapes, analyzed using mathematical principles. Computational simulation was the primary methodology, involving the implementation of Ampere’s law, Biot-Savart law, and electromagnetism, as well as their applications in solenoids and toroids. The simulations were developed using GeoGebra’s virtual simulation tools and Java Script application. As a result, a functional simulation was created to model the behavior of a normally closed solenoid valve, allowing manipulation of parameters such as radius, length, number of turns, diameter and current intensity. Similarly, a toroidal transformer simulation was developed, enabling adjustments to coil count, toroidal surface area, voltage, primary and secondary toroids to control each parameter in the respective model. The discussion highlights that similar applications have been successfully developed by other researchers, demonstrating their effectiveness in supporting university students’ learning. The study concludes that simulations significantly strengthen foundational physics knowledge in engineering education.

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Zhong, Y. S., G. Qin, and S. S. Wu. "Modeling the Transport of Solar Energetic Particles in a Corotating Interaction Region." Astrophysical Journal 968, no. 2 (2024): 75. http://dx.doi.org/10.3847/1538-4357/ad3fb0.

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Abstract We present a new three-dimensional (3D) magnetohydrodynamic (MHD) model and a new 3D energetic particle transport (EPT) model. The 3D MHD model numerically solves the ideal MHD equations using the relaxing total variation diminishing scheme. In the 3D MHD simulations, we use simple boundary conditions with a high-speed flow, and we can clearly identify a corotating interaction region (CIR) with the characteristics of forward shock and reverse shock. The 3D EPT model solves the Fokker–Planck transport equation for the solar energetic particles (SEPs) using backward stochastic processes, with the magnetic field and solar wind velocity field from MHD results. For comparison, the 3D EPT model results with Parker fields are also obtained. We investigate the transport of SEPs with particle sources and observers in different positions in MHD fields with a CIR, and we compare the results with those in the Parker fields. Our simulation results show that the compression region with local enhancement of the magnetic field, i.e., CIR, can act as a barrier to scatter energetic particles back, and particles can struggle to diffuse through the strong magnetic field regions. Usually, a normal anisotropy profile is commonly present in SEP simulation results with Parker fields, and it is also typically present in that with MHD fields. However, because of the compression region of the magnetic field, energetic particles may exhibit anomalous anisotropy. This result may be used to replicate the spacecraft observation phenomena of the anomalous anisotropy.

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Nishikawa, K. I., J. Niemiec, M. Medvedev, et al. "Simulation of relativistic shocks and associated radiation from turbulent magnetic fields." Proceedings of the International Astronomical Union 6, S275 (2010): 354–57. http://dx.doi.org/10.1017/s174392131001639x.

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AbstractRecent PIC simulations of relativistic electron-positron (electron-ion) jets injected into a stationary medium show that particle acceleration occurs in the shocked regions. Simulations show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields and for particle acceleration. These magnetic fields contribute to the electron's transverse deflection behind the shock. The “jitter” radiation from deflected electrons in turbulent magnetic fields has different properties from synchrotron radiation calculated in a uniform magnetic field. This jitter radiation may be important for understanding the complex time evolution and/or spectral structure of gamma-ray bursts, relativistic jets in general, and supernova remnants. In order to calculate radiation from first principles and go beyond the standard synchrotron model, we have used PIC simulations. We will present detailed spectra for conditions relevant to various astrophysical sites of collisionless shock formation. In particular we will discuss application to GRBs and SNRs.

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Liu, Jianjun, Zixing Xue, Zhenhai Dong, et al. "Multiphysics Modeling Simulation and Optimization of Aerodynamic Drum Magnetic Separator." Minerals 11, no. 7 (2021): 680. http://dx.doi.org/10.3390/min11070680.

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Aerodynamic Drum Magnetic Separator (ADMS) uses an adjustable air flow to enhance the separation of magnetic particles from gangue. In order to explore the matching relationship between the magnetic field, the flow field, and the gravity field, as well as the capture and separation behavior of particles under the action of multi-physics, a related simulation model is established using the finite element software COMSOL Multiphysics and the accuracy of the simulation results is verified by measurement, formula calculation, and magnetic separation experiment. The trajectories and capture probabilities of particles in different magnetic fields and flow fields are calculated, as well as the critical airflow velocity corresponding to a specific capture probability. In addition, the magnetic field characteristics and particle capture effect of N-S alternate arrangement and N-N homopolar arrangement are compared by optimizing the permutation of magnetic poles. This model may provide a reference for the accurate control of magnetic separation enhanced by a coupling force field.

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