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Journal articles on the topic 'Simulation of magnetic fields'

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Published: 30 May 2022

Last updated: 31 May 2022

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1

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

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2

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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3

Füzi, J. "Simulation of neutron motion in magnetic fields—magnetic monochromator." Measurement Science and Technology 19, no. 3 (January 30, 2008): 034013. http://dx.doi.org/10.1088/0957-0233/19/3/034013.

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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, Åke Nordlund, David Collins, Alexei Kritsuk, Michael Normal, and Sergey Ustyugov. "Magnetic Fields in Molecular Clouds." Proceedings of the International Astronomical Union 6, S271 (June 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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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 (February 11, 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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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 (October 2019): 105317. http://dx.doi.org/10.1063/1.5127919.

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8

Dilmieva, E. T., A. P. Kamantsev, V. V. Koledov, A. V. Mashirov, V. G. Shavrov, J. Cwik, and I. S. Tereshina. "Experimental simulation of a magnetic refrigeration cycle in high magnetic fields." Physics of the Solid State 58, no. 1 (January 2016): 81–85. http://dx.doi.org/10.1134/s1063783416010108.

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9

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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10

NISHIKAWA, K. I., J. NIMIEC, M. MEDVEDEV, B. ZHANG, P. HARDEE, Y. MIZUNO, Å. NORDLUND, et al. "RADIATION FROM RELATIVISTIC SHOCKS WITH TURBULENT MAGNETIC FIELDS." International Journal of Modern Physics D 19, no. 06 (June 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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11

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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12

Kim, Woong-Tae. "Effects of Magnetic Fields on Bar Substructures in Barred Galaxies." Proceedings of the International Astronomical Union 10, H16 (August 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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13

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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14

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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15

Ye, Jun-Xian, Jia-Mian Hu, Zhan Shi, Zheng Li, Yang Shen, Jing Ma, and C. W. Nan. "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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16

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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17

Amiri Roodan, Venoos, Jenifer Gómez-Pastora, Ioannis H. Karampelas, Cristina González-Fernández, Eugenio Bringas, Inmaculada Ortiz, Jeffrey J. Chalmers, Edward P. Furlani, and Mark T. Swihart. "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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18

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 (February 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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19

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 (December 2001): 112–16. http://dx.doi.org/10.1016/s0921-4526(01)00988-7.

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20

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 (July 2005): 653–58. http://dx.doi.org/10.1177/1045389x05052598.

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21

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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22

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 (July 2003): 836–47. http://dx.doi.org/10.1109/tbme.2003.813549.

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23

Fujimoto, K., K. Totsuka, Y. Uesaka, I. Saitoh, H. Fukui, F. Akagi, I. Yoshihara, Y. Nakatani, and N. Hayashi. "Computer simulation of MR response to transverse magnetic fields." IEEE Transactions on Magnetics 33, no. 3 (May 1997): 2386–91. http://dx.doi.org/10.1109/20.573862.

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24

Martinez, D., C. Plechaty, and R. Presura. "Magnetic Fields for the Laboratory Simulation of Astrophysical Objects." Astrophysics and Space Science 307, no. 1-3 (December 16, 2006): 109–14. http://dx.doi.org/10.1007/s10509-006-9275-9.

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25

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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26

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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Duţan, Ioana, Ken-Ichi Nishikawa, Yosuke Mizuno, Jacek Niemiec, Oleh Kobzar, Martin Pohl, Jose L. Gómez, et al. "Particle-in-cell Simulations of Global Relativistic Jets with Helical Magnetic Fields." Proceedings of the International Astronomical Union 12, S324 (September 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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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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Nishikawa, K. I., J. Niemiec, M. Medvedev, B. Zhang, P. Hardee, Y. Mizuno, A. Nordlund, et al. "Simulation of relativistic shocks and associated radiation from turbulent magnetic fields." Proceedings of the International Astronomical Union 6, S275 (September 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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Chen, Ping, Xiaohui Yuan, Jinshou Tian, Xing Wang, Wenlong Wen, Lehui Guo, Liping Tian, et al. "Simulation of microchannel plate photomultiplier tube in high magnetic fields." Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 936 (August 2019): 580–82. http://dx.doi.org/10.1016/j.nima.2018.10.088.

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31

Wang, Lijun, Shenli Jia, Zongqian Shi, and Mingzhe Rong. "Numerical simulation of vacuum arc under different axial magnetic fields." Journal of Physics D: Applied Physics 38, no. 7 (March 18, 2005): 1034–41. http://dx.doi.org/10.1088/0022-3727/38/7/011.

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32

Thorington, C. B. "Particle simulation of electron beams with self-consistent magnetic fields." IEEE Transactions on Electron Devices 33, no. 11 (November 1986): 1883–89. http://dx.doi.org/10.1109/t-ed.1986.22839.

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33

Jobava, Roman G., Anna L. Gheonjian, Johannes Hippeli, Giorgi Chiqovani, David D. Karkashadze, Faik G. Bogdanov, Badri Khvitia, and Anna G. Bzhalava. "Simulation of Low-Frequency Magnetic Fields in Automotive EMC Problems." IEEE Transactions on Electromagnetic Compatibility 56, no. 6 (December 2014): 1420–30. http://dx.doi.org/10.1109/temc.2014.2325134.

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Baranov, V. B., D. B. Alexashov, and M. G. Lebedev. "Magnetic fields near spacecraft-explored comets: 3D MHD numerical simulation." Monthly Notices of the Royal Astronomical Society 449, no. 3 (March 31, 2015): 2268–73. http://dx.doi.org/10.1093/mnras/stv448.

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35

Jia, Shenli, Zongqian Shi, and Lijun Wang. "Vacuum arc under axial magnetic fields: experimental and simulation research." Journal of Physics D: Applied Physics 47, no. 40 (September 10, 2014): 403001. http://dx.doi.org/10.1088/0022-3727/47/40/403001.

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36

Wu, S. T., C. L. Yin, P. Mcintosh, and E. Hildner. "Magnetohydrodynamic Simulation of the Evolution of Bipolar Magnetic Regions." International Astronomical Union Colloquium 141 (1993): 98–107. http://dx.doi.org/10.1017/s0252921100028876.

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AbstractIt has been recognized that the magnetic flux observed on the solar surface appears first in low latitudes, and then this flux is gradually dispersed by super granular convective motions and meridional circulation. Theoretically, the magnetic flux transport could be explained by the interactions between magnetic fields and plasma flows on the solar surface through the theory of magnetohydrodynamics.To understand this physical scenario, a quasi-three-dimensional, time-dependent, MHD model with differential rotation, meridional flow and effective diffusion as well as cyclonic turbulence effects is developed. Numerical experiments are presented for the study of Bipolar Magnetic Regions (BMRs). When the MHD effects are ignored, our model produced the classical results (Leighton, Astrophys. J., 146, 1547, 1964). The full model’s numerical results demonstrate that the interaction between magnetic fields and plasma flow (i.e., MHD effects), observed together with differential rotation and meridional flow, gives rise to the observed complexity of the evolution of BMRs.

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37

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 (March 26, 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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38

Liu, Jianjun, Zixing Xue, Zhenhai Dong, Xiaofeng Yang, Yafeng Fu, Xiaofei Man, and Dongfang Lu. "Multiphysics Modeling Simulation and Optimization of Aerodynamic Drum Magnetic Separator." Minerals 11, no. 7 (June 25, 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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39

Machida, Mami, Takuya Akahori, Kenji Nakamura, Hiroyuki Nakanishi, and Marijke Haverkorn. "Faraday Depolarization Effects in Spiral Galaxies." Galaxies 7, no. 1 (January 12, 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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40

Narukullapati, Bharath Kumar, T. K. Bhattacharya, ANaveen Reddy, and Srikanth Gollapudi. "Modeling and simulation of Electromagnetic Fields on a Floating Aluminium." International Journal of Engineering & Technology 7, no. 4.24 (November 27, 2018): 148. http://dx.doi.org/10.14419/ijet.v7i4.24.21876.

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The electromagnetic field calculation for a floating aluminum disc is difficult to calculate since the equation involved does not produce a closed solution. The numerical, analytical, semi-analytical techniques that are already developed to find these magnetic fields have no proper mathematical formulation when the disc is disturbed from its coaxial position. The stabilization of disc is going to be effected when the disc moves away from its coaxial position due to a change in inductance between the disc and coils, due to change in magnetic flux linkage, etc. In this paper, a 2D FEM model is developed to determine the magnetic fields on a floatingaluminum disc when it is moved away from its coaxial position. The 3D FEM model developed is simulated in both COMSOL-Multiphysics and ANSYS-Electronics. The results obtained by simulation are compared, for accuracy, with the numerical solution developed earlier using Finite Difference method (FDM) and also discussed.

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41

Siejkowski, Hubert, Marian Soida, Katarzyna Otmianowska-Mazur, Michał Hanasz, and Dominik J. Bomans. "3D model of magnetic fields evolution in dwarf irregular galaxies." Proceedings of the International Astronomical Union 6, S274 (September 2010): 389–92. http://dx.doi.org/10.1017/s1743921311007344.

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AbstractRadio observations show that magnetic fields are present in dwarf irregular galaxies (dIrr) and its strength is comparable to that found in spiral galaxies. Slow rotation, weak shear and shallow gravitational potential are the main features of a typical dIrr galaxy. These conditions of the interstellar medium in a dIrr galaxy seem to unfavourable for amplification of the magnetic field through the dynamo process. Cosmic-ray driven dynamo is one of the galactic dynamo model, which has been successfully tested in case of the spiral galaxies. We investigate this dynamo model in the ISM of a dIrr galaxy. We study its efficiency under the influence of slow rotation, weak shear and shallow gravitational potential. Additionally, the exploding supernovae are parametrised by the frequency of star formation and its modulation, to reproduce bursts and quiescent phases. We found that even slow galactic rotation with a low shearing rate amplifies the magnetic field, and that rapid rotation with a low value of the shear enhances the efficiency of the dynamo. Our simulations have shown that a high amount of magnetic energy leaves the simulation box becoming an efficient source of intergalactic magnetic fields.

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42

Smith, K. T. "Simulating turbulent solar magnetic fields." Science 351, no. 6280 (March 24, 2016): 1411. http://dx.doi.org/10.1126/science.351.6280.1411-a.

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43

Luque, Alejandro, and Daniel Peralta-Salas. "Motion of Charged Particles in ABC Magnetic Fields." SIAM Journal on Applied Dynamical Systems 12, no. 4 (January 2013): 1889–947. http://dx.doi.org/10.1137/130915236.

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44

NISHIKAWA, K. I., J. NIEMIEC, B. ZHANG, M. MEDVEDEV, P. HARDEE, Y. MIZUNO, Å. NORDLUND, et al. "SIMULATION OF RELATIVISTIC JETS AND ASSOCIATED SELF-CONSISTENT RADIATION." International Journal of Modern Physics: Conference Series 08 (January 2012): 259–64. http://dx.doi.org/10.1142/s2010194512004680.

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Plasma instabilities are responsible not only for the onset and mediation of collisionless shocks but also for the associated acceleration of particles. We have investigated particle acceleration and shock structure associated with an unmagnetized relativistic electron-positron jet propagating into an unmagnetized electron-positron plasma. Cold jet electrons are thermalized and slowed while the ambient electrons are swept up to create a partially developed hydrodynamic-like shock structure. In the leading shock, electron density increases by a factor of about 3.5 in the simulation frame. Strong electromagnetic fields are generated in the trailing shock and provide an emission site. These magnetic fields contribute to the electrons transverse deflection and, more generally, relativistic acceleration behind the shock. We have calculated, self-consistently, the radiation from electrons accelerated in the turbulent magnetic fields. We found that the synthetic spectra depend on the Lorentz factor of the jet, its thermal temperature and strength of the generated magnetic fields. The properties of the radiation may be important for understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets in general, and supernova remnants.

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45

Xu, Wen Ting, Hai Ling Tu, Qing Chang, Qing Hua Xiao, Xiao Lin Dai, Yun Xia Liu, Zong Feng Li, Lin Chang, and Wei Da Liu. "Numerical Simulation of 300mm CZ Silicon Crystal Growth with Axial Magnetic Fields." Materials Science Forum 689 (June 2011): 179–83. http://dx.doi.org/10.4028/www.scientific.net/msf.689.179.

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We studied the optimization of 300mm CZ silicon crystal growth in 28 inch hot zone with axial magnetic field. The convex of melt-crystal interfaces toward to the crystal are observed in our simulations under different growth velocities (0.3mm/min, 0.5mm/min and 0.65mm/min). The convections in melt were illustrated under different growth rates and intensities of magnetic field. The growth rate of 0.5mm/min and axial magnetic fields intensity of 0.3T were recommended as an appropriate control condition.

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46

Segura, Javier Lopez, and Nicolas Urgoiti. "AC Magnetic sensor to measure mega-amps current and kilo-tesla magnetic fields up to gigahertz frequencies." Journal of Technological and Space Plasmas 1, no. 1 (August 12, 2020): 36–44. http://dx.doi.org/10.31281/jtsp.v1i1.13.

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An AC magnetic sensor is presented for measuring the high speed and high strength magnetic field generated in Z-pinch fusion machines. The proposed magnetic sensor provides the measurement of magnetic fields across a broadband frequency range. The simulation of magnetic probe is presented using a SPICE simulation software LTspice. The magnetic sensors are installed in a Pulsotron-3 Z-pinch machine and measured performance of the sensor are presented. This sensor also can be used to check the ignition conditions of the Z-Pinch by measuring the magnetic field generated by the output streams of large number of reacted alpha particles. The equations for measuring non-stationary magnetic field due to rapidly varying electric currents and a LTspice simulation file are provided to help the engineers to design, build, and install this kind of sensors.

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47

Guo, Zhen Gang, Li Qing Pan, Hong Mei Qiu, Xue Dan Zhao, and Li Hong Yang. "Micromagnetic Simulation of Asymmetrical CoFe Nanorings." Advanced Materials Research 538-541 (June 2012): 529–33. http://dx.doi.org/10.4028/www.scientific.net/amr.538-541.529.

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Domain wall motions and magnetization reversal processes in the nanoscale asymmetrical Co50Fe50rings have been studied using micromagnetic simulations. The results reveal that the switching fields and the plateau width of vortex state can be tuned through changing the asymmetrical parameter of magnetic nanorings. The chirality of vortex states can be easily controlled by the orientation of the applied magnetic field.

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48

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 (September 29, 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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49

Biondi, Riccardo. "Monte Carlo simulation for ultracold neutron experiments searching for neutron–mirror neutron oscillation." International Journal of Modern Physics A 33, no. 24 (August 30, 2018): 1850143. http://dx.doi.org/10.1142/s0217751x18501439.

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Neutron oscillation into mirror neutron, a sterile state exactly degenerate in mass with the neutron, could be a very rapid process, even faster than the neutron decay itself. It can be observed by comparing the neutron lose rates in an ultracold neutron trapping experiment for different experimental magnetic fields. We developed a Monte Carlo code that simulates many of the features of this kind of experiment with nonuniform magnetic fields. The aim of the simulation is to provide all necessary tools, needed for analyzing experimental results for neutron traps with different geometry and different configurations of magnetic fields. This work contains technical details on the Monte Carlo simulation used for the analysis in Ref. 46 not presented in it.

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Ueda, Hiroyuki, Yosuke Ito, Takenori Oida, Yo Taniguchi, and Tetsuo Kobayashi. "Magnetic resonance imaging simulation with spin-lock preparations to detect tiny oscillatory magnetic fields." Journal of Magnetic Resonance 324 (March 2021): 106910. http://dx.doi.org/10.1016/j.jmr.2020.106910.

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