Strong Non-uniform Magnetic Field Research Articles

Semi-discretization and full-discretization with improved accuracy for charged-particle dynamics in a strong nonuniform magnetic field

The aim of this paper is to formulate and analyze numerical discretizations of charged-particle dynamics (CPD) in a strong nonuniform magnetic field. A strategy is firstly performed for the two dimensional CPD to construct the semi-discretization and full-discretization which have improved accuracy. This accuracy is improved in the position and in the velocity when the strength of the magnetic field becomes stronger. This is a better feature than the usual so called ``uniformly accurate methods”. To obtain this refined accuracy, some reformulations of the problem and two-scale exponential integrators are incorporated, and the improved accuracy is derived from this new procedure. Then based on the strategy given for the two dimensional case, a new class of uniformly accurate methods with simple scheme is formulated for the three dimensional CPD in maximal ordering case. All the theoretical results of the accuracy are numerically illustrated by some numerical tests.

On a large-stepsize integrator for charged-particle dynamics

Xiao and Qin (Comput Phys Commun 265:107981, 2021) recently proposed a remarkably simple modification of the Boris algorithm to compute the guiding centre of the highly oscillatory motion of a charged particle with step sizes that are much larger than the period of gyrorotations. They gave strong numerical evidence but no error analysis. This paper provides an analysis of the large-stepsize modified Boris method in a setting that has a strong non-uniform magnetic field and moderately bounded velocities, considered over a fixed finite time interval. The error analysis is based on comparing the modulated Fourier expansions of the exact and numerical solutions, for which the differential equations of the dominant terms are derived explicitly. Numerical experiments illustrate and complement the theoretical results.

Rotation of a Dust Structure in Strong Nonuniform Magnetic Field

Rotation of a Dust Structure in Strong Nonuniform Magnetic Field

Experimental investigation of liquid metal pipe flow in a strong non-uniform magnetic field

Experimental investigation of liquid metal pipe flow in a strong non-uniform magnetic field

A filtered Boris algorithm for charged-particle dynamics in a strong magnetic field

A modification of the standard Boris algorithm, called filtered Boris algorithm, is proposed for the numerical integration of the equations of motion of charged particles in a strong non-uniform magnetic field in the asymptotic scaling known as maximal ordering. With an appropriate choice of filters, second-order error bounds in the position and in the parallel velocity, and first-order error bounds in the normal velocity are obtained with respect to the scaling parameter. This also yields a second-order approximation to the guiding center motion. The proof compares the modulated Fourier expansions of the exact and the numerical solutions. Numerical experiments illustrate the error behaviour of the filtered Boris algorithm.

Взрывная кристаллизация плёнок аморфного кобальта в сильном неоднородном магнитном поле

Взрывная кристаллизация плёнок аморфного кобальта в сильном неоднородном магнитном поле

Inversion of flow and heat transfer of the paramagnetic fluid in a differentially heated cube

The present study addresses the detailed numerical analysis of the flow and heat transfer of a paramagnetic fluid inside a differentially heated cubical box and subjected to a strong non-uniform magnetic field. Two different heating scenarios are considered regarding an initial thermal stratification: unstable (heated from the bottom) and stable (heated from the top), both subjected to the same magnetic field. For a fixed value of the thermal Rayleigh number (Ra=1.4×105) integral heat transfer is measured over a range of imposed magnetic fields, 0 ≤ |b0|max ≤ 10 T. To obtain detailed insights into local wall-heat transfer and its dependency on the flow patterns generated, numerical simulations of the experimental setup are performed. A relatively good agreement between experiments and numerical simulations is obtained in predicting the integral heat transfer (with an averaged ΔNu¯<7% over the entire range of working parameters for both heating configurations). It is demonstrated that a strong convective motion can be generated under the influence of the magnetization force even for the heated-from-above situation that initially was in the pure conduction state. This magnetically assisted (heated from the bottom) and magnetically inverted (heated from the top) Rayleigh-Bénard convection produced up to 5 and 15 times more efficient heat transfer compared to the initial neutral situation, respectively.

Long-term analysis of a variational integrator for charged-particle dynamics in a strong magnetic field

The differential equations of motion of a charged particle in a strong non-uniform magnetic field have the magnetic moment as an adiabatic invariant. This quantity is nearly conserved over long time scales covering arbitrary negative powers of the small parameter, which is inversely proportional to the strength of the magnetic field. The numerical discretisation is studied for a variational integrator that is an analogue for charged-particle dynamics of the Stormer–Verlet method. This numerical integrator is shown to yield near-conservation of a modified magnetic moment and a modified energy over similarly long times. The proofs for both the continuous and the discretised equations use modulated Fourier expansions with state-dependent frequencies and eigenvectors.

Color-flavor-locked matter in a nonuniform strong magnetic field

The magnetic-color-flavor-locked quark matter is investigated in the Nambu–Jona-Lasinio model. Strong nonuniform magnetic fields are employed in order to mimic the spatial dependence of the magnetic field strength at high densities. We find that the gap solution depends strongly on the diquark coupling interaction. Based on the requirement that the parallel pressure should be an increasing function of the chemical potential, an upper limit on the central magnetic field [Formula: see text][Formula: see text]G is obtained, which increases slightly with the diquark interaction strength. Furthermore, much stronger central magnetic field could occur in the stars composed of magnetic-color-flavor matter than that of ordinary strange quark matter.

Excited States of Molecules in Strong Uniform and Nonuniform Magnetic Fields.

This paper reports an implementation of Hartree-Fock linear response with complex orbitals for computing electronic spectra of molecules in strong external magnetic fields. The implementation is completely general, allowing for spin-restricted, spin-unrestricted, and general two-component reference states. The method is applied to small molecules placed in strong uniform and nonuniform magnetic fields of astrochemical importance at the Random Phase Approximation level of theory. For uniform fields, where comparison is possible, the spectra are found to be qualitatively similar to those recently obtained with equation of motion coupled cluster theory. We also study the behavior of spin-forbidden excitations with progressive loss of spin symmetry induced by nonuniform magnetic fields. Finally, the equivalence of length and velocity gauges for oscillator strengths when using complex orbitals is investigated and found to hold numerically.

Anisotropic pressure in strange quark matter in the presence of a strong nonuniform magnetic field

Thermodynamic properties of strange quark matter (SQM) in a nonuniform magnetic field are studied within the phenomenological MIT bag model under the charge neutrality and beta equilibrium conditions, relevant to the interior of strange quark stars. The spatial dependence of the magnetic field strength is modeled by the dependence on the baryon chemical potential in the exponential and power forms. The total energy density, longitudinal and transverse pressures in magnetized SQM are found as functions of the baryon chemical potential. It is clarified that the central magnetic field strength in a strange quark star is bound from above by the critical value at which the derivative of the longitudinal pressure with respect to the baryon chemical potential vanishes first somewhere in the interior of a star under varying the central field. Above this upper bound, the instability along the magnetic field is developed in magnetized SQM. The change in the form of the dependence of the magnetic field strength on the baryon chemical potential between the exponential and power ones has a nonnegligible effect on the critical magnetic field strength while the variation of the bag pressure within the absolute stability window for magnetized SQM has a little effect on the critical field.

Magnetically Assisted Bilayer Composites for Soft Bending Actuators.

This article presents a soft pneumatic bending actuator using a magnetically assisted bilayer composite composed of silicone polymer and ferromagnetic particles. Bilayer composites were fabricated by mixing ferromagnetic particles to a prepolymer state of silicone in a mold and asymmetrically distributed them by applying a strong non-uniform magnetic field to one side of the mold during the curing process. The biased magnetic field induces sedimentation of the ferromagnetic particles toward one side of the structure. The nonhomogeneous distribution of the particles induces bending of the structure when inflated, as a result of asymmetric stiffness of the composite. The bilayer composites were then characterized with a scanning electron microscopy and thermogravimetric analysis. The bending performance and the axial expansion of the actuator were discussed for manipulation applications in soft robotics and bioengineering. The magnetically assisted manufacturing process for the soft bending actuator is a promising technique for various applications in soft robotics.

TO EVALUATION TEST OF QUALITY OF MAGNETIC FLUIDS FOR MAGNETOFLUID DEVICES

Magnetic fluid is a colloid of magnetic nanoparticles. Using of magnetic fluids in technical devices demands applying of strong non-uniform magnetic fields for a long time. One of the most widespread magnetic fluid devices are magnetic fluid seals of mobile shafts, magnetic fluid supports, bearings, acceleration and angle of inclination gauges, devices for information input in the computer and etc. These devices demand high quality of used fluids. Processes of magnetophoresis and Brownian diffusion in magnetic fluid lead to concentration of magnetic particles in the areas with higher intensity of magnetic field and increase of fluid magnetization in these areas. A local change of particles concentration in the fluid leads to variation of its physical properties. Formation of aggregates from the particles and the further stratification of magnetic fluid, up to its destruction, may be the most serious consequence of redistribution of concentration of magnetic particles. These factors lead to variation of parameters of magnetic fluid devices; cause disturbance of their normal operation and even failure. Therefore, the consistent, high quality magnetic fluids which are not subject to fast stratification in a non-uniform magnetic field are necessary for effective work of the devices. The procedure of evaluation test of quality of magnetic fluids is proposed in this paper. The test is based on studying of influence of processes of magnetophoresis and Brownian diffusion of magnetic particles in magnetic fluid on the forces acting on the volume of fluid in an external non-uniform magnetic field. The procedure is developed on the basis of analysis of magnetic force variation in time under the action of non-uniform field of permanent magnets. Methods of determination of stability of magnetic fluid, known at present, demand rather complicated equipment and laborious and complex investigations. Proposed procedure can be used as an express method for evaluation of magnetic fluid quality for usage in technical devices, and it does not need complicated equipment.

Spin-transport effects in electron systems on liquid helium surfaces

Transport phenomena are examined in electron systems on liquid helium surfaces in strong nonquantizing nonuniform magnetic fields. For applied electric fields with frequencies low enough that an equilibrium distribution of the spins along the conducting surface can develop during the wave period, the electrical resistance is determined by different current carrier scattering processes than in the uniform case. Spin nonuniformity makes electron-electron collisions efficient with respect to momentum loss, so that galvanomagnetic effects differ substantially from the Drude-Lorentz theory. A nonstationary spin-electron effect is found in a direction perpendicular to the applied electric field. The evolution of the transport properties following application of a nonuniform magnetic field is discussed.

Performance of the BGO endcap calorimeter of the CMD-3 detector

The BGO endcap calorimeter was successfully operated in the CMD-2 detector at the VEPP-2M collider. It consists of 680 BGO crystals, each with a size of 25 × 25 × 150 mm3, arranged in two identical endcaps, with a total crystal weight of 450 kg. The light readout used vacuum phototriodes. The endcap calorimeter has been upgraded to operate in the CMD-3 detector at the new collider VEPP-2000. The major part of the endcap calorimeter, the BGO crystals, remains the same. The main upgrade is the use of silicon PIN photodiodes and new electronics. The main reason to change a photosensitive device is the strong non-uniform magnetic field in the endcap calorimeter volume and reduced available space. The Hamamatsu PIN photodiode S3590-08 was chosen as an optimal solution, as it is insensitive to magnetic fields and is both compact and stable. An order of magnitude larger capacitance of silicon photodiodes requires design and produce new custom electronics. The upgrade is expected to bring an overall improvement of parameters. The endcap calorimeter has been installed in the detector and participates in data taking which started in 2010. The preliminary energy resolution is measured in the energy range 160–1000 MeV. It is better to compare to the CMD-2 detector.

Evaluation of magnetic resonance imaging issues for implantable microfabricated magnetic actuators

The mechanical robustness of microfabricated torsional magnetic actuators in withstanding the strong static fields (7 T) and time-varying field gradients (17 T/m) produced by an MR system was studied in this investigation. The static and dynamic mechanical characteristics of 30 devices were quantitatively measured before and after exposure to both strong uniform and non-uniform magnetic fields. The results showed no statistically significant change in both the static and dynamic mechanical performance, which mitigate concerns about the mechanical stability of these devices in association with MR systems under the conditions used for this assessment. The MR-induced heating was also measured in a 3-T/128-MHz MR system. The results showed a minimal increase (1.6 °C) in temperature due to the presence of the magnetic microactuator array. Finally, the size of the MR-image artifacts created by the magnetic microdevices were quantified. The signal loss caused by the devices was approximately four times greater than the size of the device.

Thermal radiation effect on flow and heat transfer of unsteady MHD micropolar fluid over vertical heated nonisothermal stretching surface using group analysis

The aim of this paper is to study the thermal radiation effects on the flow and heat transfer of an unsteady magnetohydrodynamic (MHD) micropolar fluid over a vertical heated nonisothermal stretching surface in the presence of a strong nonuniform magnetic field. The symmetries of the governing partial differential equations are de- termined by the two-parameter group method. One of the resulting systems of reduced nonlinear ordinary differential equations are solved numerically by the Chebyshev spec- tral method. The effects of various parameters on the velocity, the angular velocity, and the temperature profiles as well as the skin-friction coefficient, the wall couple stress co- efficient, and the Nusselt number are studied.

Laminar pipe flow at the entrance into transverse magnetic field

High-resolution numerical simulations are conducted to analyze transformation of a liquid metal flow in a pipe at the entrance into a transverse magnetic field. The case of laminar flow, perfectly insulating pipe walls, and Hartmann number up to 200 is considered. The simulations reveal detailed structure of velocity and electric current fields and distribution of forces with particular attention given to the flow with an M-shaped velocity profile. They also establish criteria for accurate computations of laminar magnetohydrodynamic flows in strong non-uniform magnetic fields.

Upgrade of the CMD-3 BGO Endcap Calorimeter

The BGO endcap calorimeter was successfully operated in the CMD-2 detector at the VEPP-2M collider. It consists of 680 BGO crystals each with a size of 25×25×150 mm3, arranged in two identical endcaps, with a total crystal weight of 450 kg. The light readout used vacuum phototriodes. The endcap calorimeter has now been upgraded to work in the CMD-3 detector at new collider VEPP-2000. The major part of the endcap calorimeter, the BGO crystals, remains the same. The main upgrade is the use of silicon PIN photodiodes and new electronics. Main reason to change photosensitive device is the strong non-uniform magnetic field in the endcap calorimeter volume so the vacuum photosensitive devices cannot operate in such magnetic fields. Also the available space for the endcap calorimeter space had to be reduced. The Hamamatsu PIN photodiode S3590-08 was chosen as the optimal solution, as they are insensitive to magnetic fields and are both compact and stable. An order of magnitude larger capacitance of silicon photodiodes requires design and produce new custom electronics. The upgrade is expected to bring an overall improvement of parameters. The endcap calorimeter has been installed in the detector and participates in data taking which started at 2010. The preliminary data analysis shows an improvement of the energy resolution compare to the CMD-2 detector.

An analysis of unsteady thermal convection of paramagnetic fluid in cubical enclosure under strong magnetic field gradient

The experimental studies of the flow and heat transfer of a paramagnetic fluid inside a cubical enclosure in a configuration heated from below and subjected to various strong non-uniform magnetic field gradients are presented. In contrast to the previously reported studies in literature, which observed solely laminar flow regimes, the appearance and sustenance of the periodic- and fully transient – flow motions for the very first time were investigated. This was consequence of using significantly stronger magnetic field gradient (up to 900 T2/m) than those used in previous studies (up to 200 T2/m). The fluid flow was studied at two Rayleigh numbers: 7.89·105 and 1.86·106. Non-monotonic behaviour of flow with increase of imposed magnetic field gradients was observed for both cases. Detailed analysis (Fast Fourier Transform) of temperature time series has been reported.