Unstable Magnetic Field Research Articles

Maser polarization simulation in the circumstellar envelope of an evolving star

An important phenomenon in a pulsing AGB (Asymptotic Giant Branch) star is the variability of its circumstellar envelope. The study of stimulated radiation called SiO maser (microwave amplification by stimulated emission of radiation) in the inner edge of the envelope shows fluctuations in polarization during the stellar pulsation period which is caused by the unstable magnetic field around the AGB star and needs to be investigated in order to understand it. We simulate the maser signal and polarization by using a computer code to describe the circumstellar envelope of the AGB star for comparison with the observations. The methods, i) Generate the energy transition of the stimulation matrix ii) Simulate the first stimulation from an electric field background iii) Convert the radiation to the frequency domain by using Fourier transform iv) Simulate the observation by amplifying radiation along a line of sight within the medium toward an observation position. At this stage, we set the tubular maser cloud with a constant magnetic field strength toward the observer. The program can simulate the maser signal and polarization, brighter when stimulating with a longer medium; the simulated polarization agrees well with expectations for this magnetic field orientation. Further works need to be carried out by testing this program with many cases to explain the obtained data from actual observations.

Bionic Magnetic Compass Algorithm Based on Radical Pair Theory

Vector magnetometers play an essential role in aerial and marine navigation due to their advantages of low cost, portability, and high sensitivity. However, the unstable magnetic field anomaly restricts the performance improvement of the magnetic compass. The existing methods have done a lot of optimization and improvement work, but the test results are less than expected in a dynamic environment. In order to solve this problem, a bionic magnetic compass algorithm based on the theory of “radical pairs” in birds was proposed. This article finds the stability convergence of the magnetic compass deviation (MCD) at the critical angle. The theoretical analysis and experiment results show that the heading accuracy at the critical angle is trustworthy. Then, the MCD distribution and the magnetic heading correction model are established. Finally, the current magnetic heading is corrected according to the angle difference between the critical angle and the current heading. The sea trial shows that compared with the traditional compensation algorithm, the reservoir environment is improved by 83.1%, and the effect in real ocean environment is improved by 30.12% and 58.49%.

Effect of magnetic fields and fertilizers on grass and onion growth on technogenic soils

The article deals with effect the use of organic (biohumus) and mineral (biochar) fertilizers based on the products of chicken vital activity on changing the fertility of technogenic sod-podzolic soils exposed to constant and unstable magnetic fields. The germination and growth dynamics of grasses and onions were investigated. The rational rate of introduction of the studied fertilizers into the technogenic soil is determined. Running (RMF) and direct (DMF) magnetic fields were applied in two ways: with fertilizers added and without fertilizers added. It has been established that the effect of preliminary magnetization of technogenic soil has a significant effect on lawn grass germination and the length of onion feathers, which are more than twice the height when exposed to the RMF, as compared with DMF. The effect of RMF on grass germination was also twice as high for DMF, when fertilizers were added. The DMF mag-netization and biohumus helps to increase the grass sprout height by 10–20%. Onion sprouts were higher in two cases: DMF and biohumus; RMF and biochar. The influence of the factor of fertilizer type has a significant effect in 30–40% of cases, whilst at a spread rate of more than 5%, significant chemical activity of biochar negatively affects the germination of both grass and onion.

Preparation of a two-state mixture of ultracold fermionic atoms with balanced population subject to the unstable magnetic field* *Project supported by the National Key Research and Development Program of China (Grant Nos. 2016YFA0301602 and 2018YFA0307601), the National Natural Science Foundation of China (Grant Nos. 12034011, 92065108, 11704234, 11804203, 11974224, 12022406, and 12004229), and the Fund for Shanxi “1331 Project” Key

We report a novel method to prepare a mixture of 40K Fermi gas having an equal population of the two ground magnetic spin states confined in an optical dipole trap, in the presence of an noisy quantization (magnetic) field. We realize the equal population mixture by applying a series of RF pulses. We observe the dependence of the population distribution between two spin states on the number of the applied RF pulses and find that the decoherence effects leading to the population fluctuations are overcome by the high number of RF pules. Our demonstrated technique can be potentially used in the precision measurement experiments with ultracold gases in noisy environments.

Coil Positioning for Wireless Power Transfer System of Automatic Guided Vehicle Based on Magnetic Sensing.

As an auxiliary function of the wireless power transfer (WPT) system, coil positioning can solve the power and efficiency degradation during power transmission caused by misalignment of the magnetic coupler. In this paper, a Hall sensor array is used to measure the change of magnetic flux density. By comparing the multisensor data fusion results with the preset data obtained from the coil alignment, the real-time accurate positioning of the receiving coil can be realized. Firstly, the positioning model of the receiving coil is built and the variation of magnetic flux density with the coil misalignment is analyzed. Secondly, the arrangement of the Planar 8-direction symmetric sensor array and the positioning algorithm based on data fusion of magnetic flux density variations are proposed. In order to avoid coil positioning misalignment caused by the unstable magnetic field distribution which is actually affected by the change of mutual inductance during automatic guided vehicle (AGV) alignment, the constant current strategy of primary and secondary sides is proposed. Finally, the coil positioning experimental platform is built. The experimental results show that the coil positioning method proposed in this paper has high accuracy, and the positioning error is within 4 cm.

Plasma instability inside solenoid with laser ion source.

Using a solenoid with a laser ion source can suppress divergence of the expanding plasma; however, it has been found that the plasma becomes unstable in a certain magnetic field region. In the previous research, instability of the plasma after the solenoid was found. In this study, we investigated how the plasma instability changes inside the solenoid. A Faraday cup was placed in the solenoid, and the unstable magnetic field range was investigated. This experiment was conducted while changing the Faraday cup position from the inlet to the outlet of the solenoid. By increasing the magnetic field strength, the Faraday cup position indicating a condition triggering instability moved toward upstream in the solenoid. In addition, the instability is gradually mitigated by transporting the laser ablation plasma through the rest of the solenoid. The detailed good working range of the solenoid for the Au1+ beam was also shown.

Modeling and analysis of spoke-type permanent magnet vernier machine based on equivalent magnetic network method

In this paper, a new equivalent magnetic network(EMN) model is established for a spoke-type permanent magnet(PM) vernier(PMV) machine. Two different modeling methods are proposed for different parts of the PMV machine, considering that their magnetic field distributions are quite different. Hierarchical modeling method is proposed for the modeling of the rotor as the magnetic intensity of the rotor iron core presents gradient distribution along the radial direction. Mesh based reluctance network method is used for the modeling of flux modulation poles with irregular and unstable magnetic field distributions. Moreover, accurate PM leakage permeance calculation formulae are deduced to improve the simulation precision. The electromagnetic parameters, such as flux linkage, back electromagnetic force, electromagnetic torque and iron loss are predicted by the proposed EMN model. Finally, finite element analysis(FEA) and experimental results are given to verify the effectiveness of the proposed methods.

Understanding Space Weather: Part II: The Violent Sun

AbstractThe Sun is often racked by short-term violent events such as flares and coronal mass ejections (CMEs) but these two phenomena are often confused. Both are caused by the release of energy due to the reconnection of stressed and unstable magnetic fields. Flares bathe the solar system in electromagnetic radiation from gamma rays to radio emissions. CMEs throw billions of tons of solar plasma into interplanetary space at velocities of over 1,000 km s−1. Flares can occur without significant ejecta being spewed out from the Sun into the solar system. CMEs can occur without a significant flare being detected. The most violent and dangerous events occur when a large flare is accompanied by a major eruption. These violent events are much more common near solar maximum but can occur at any time during the solar cycle, so we are rarely completely immune to their effects. Various types of solar activity can lead to problems with electrical grids, navigation systems, and communications, and can present a hazard to astronauts, as will be discussed in future papers in this series.

Influences of an Aluminum Covering Layer on the Performance of Cross-Like Hall Devices

This work studies the effects of an aluminum covering on the performance of cross-like Hall devices. Four different Hall sensor structures of various sizes were designed and fabricated. The sensitivity and offset of the Hall sensors, two key points impacting their performance, were characterized using a self-built measurement system. The work analyzes the influences of the aluminum covering on those two aspects of the performance. The aluminum layer covering mainly leads to an eddy-current effect in an unstable magnetic field and an additional depletion region above the active region. Those two points have influences on the sensitivity and the offset voltage, respectively. The analysis guides the designer whether to choose covering with an aluminum layer the active region of the Hall sensor as a method to reduce the flicker noise and to improve the stability of the Hall sensor. Because Hall devices, as a reference element, always suffer from a large dispersion, improving their stability is a crucial issue.

Stability of toroidal magnetic fields in stellar interiors

We present 3D MHD simulations of purely toroidal and mixed poloidal-toroidal magnetic field configurations to study the behavior of the Tayler instability. For the first time the simultaneous action of rotation and magnetic diffusion are taken into account and the effects of a poloidal field on the dynamic evolution of unstable toroidal magnetic fields is included. In the absence of diffusion, fast rotation (rotation rate compared to Alfv\'en frequency) is able to suppress the instability when the rotation and magnetic axes are aligned and when the radial field strength gradient p < 1.5. When diffusion is included, this system turns unstable for diffusion dominated and marginally diffusive dominated regions. If the magnetic and rotation axes are perpendicular to each other the stabilizing effect induced by the Coriolis force is scale dependent and decreases with increasing wavenumber. In toroidal fields with radial field gradients bigger than p > 1.5, rapid rotation does not suppress the instability but instead introduces a damping factor to the growth rate in agreement with the analytic predictions. For the mixed poloidal-toroidal fields we find an unstable axisymmetric mode, not predicted analytically, right at the stability threshold for the non-axisymmetric modes; it has been argued that an axisymmetric mode is necessary for the closure of the Tayler-Spruit dynamo loop.

Ionization and heating by X-rays and cosmic rays

High-energy radiation from the central T Tauri and protostars plays an impor- tant role in shaping protoplanetary disks and influences their evolution. Such radiation, in particular X-rays and extreme-ultraviolet (EUV) radiation, is predominantly generated in unstable stellar magnetic fields (e.g., the stellar corona), but also in accretion hot spots. Even jets may produce X-ray emission. Cosmic rays, i.e., high-energy particles either from the interstellar space or from the star itself, are of crucial importance. Both high- energy photons and particles ionize disk gas and lead to heating. Ionization and heating subsequently drive chemical networks, and the products of these processes are accessi- ble through observations of molecular line emission. Furthermore, ionization supports the magnetorotational instability and therefore drives disk accretion, while heating of the disk surface layers induces photoevaporative flows. Both processes are crucial for the dispersal of protoplanetary disks and therefore critical for the time scales of planet for- mation. This chapter introduces the basic physics of ionization and heating starting from a quantum mechanical viewpoint, then discusses relevant processes in astrophysical gases and their applications to protoplanetary disks, and finally summarizes some properties of the most important high-energy sources for protoplanetary disks.

The angular momentum transport by unstable toroidal magnetic fields

We demonstrate with a nonlinear MHD code that angular momentum can be transported due to the magnetic instability of toroidal fields under the influence of differential rotation, and that the resulting effective viscosity may be high enough to explain the almost rigid-body rotation observed in radiative stellar cores. Only stationary current-free fields and only those combinations of rotation rates and magnetic field amplitudes which provide maximal numerical values of the viscosity are considered. We find that the dimensionless ratio of the effective over molecular viscosity, $\nu_T/\nu$;, linearly grows with the Reynolds number of the rotating fluid multiplied with the square-root of the magnetic Prandtl number - which is of order unity for the considered red sub-giant KIC 7341231. For the considered interval of magnetic Reynolds numbers - which is restricted by numerical constraints of the nonlinear MHD code - there is a remarkable influence of the magnetic Prandtl number on the relative importance of the contributions of the Reynolds stress and the Maxwell stress to the total viscosity, which is magnetically dominated only for Pm $\gtrsim$ 0.5. We also find that the magnetized plasma behaves as a non-Newtonian fluid, i.e. the resulting effective viscosity depends on the shear in the rotation law. The decay time of the differential rotation thus depends on its shear and becomes longer and longer during the spin-down of a stellar core.

Dogs are sensitive to small variations of the Earth’s magnetic field

IntroductionSeveral mammalian species spontaneously align their body axis with respect to the Earth’s magnetic field (MF) lines in diverse behavioral contexts. Magnetic alignment is a suitable paradigm to scan for the occurrence of magnetosensitivity across animal taxa with the heuristic potential to contribute to the understanding of the mechanism of magnetoreception and identify further functions of magnetosensation apart from navigation. With this in mind we searched for signs of magnetic alignment in dogs. We measured the direction of the body axis in 70 dogs of 37 breeds during defecation (1,893 observations) and urination (5,582 observations) over a two-year period. After complete sampling, we sorted the data according to the geomagnetic conditions prevailing during the respective sampling periods. Relative declination and intensity changes of the MF during the respective dog walks were calculated from daily magnetograms. Directional preferences of dogs under different MF conditions were analyzed and tested by means of circular statistics.ResultsDogs preferred to excrete with the body being aligned along the North–South axis under calm MF conditions. This directional behavior was abolished under unstable MF. The best predictor of the behavioral switch was the rate of change in declination, i.e., polar orientation of the MF.ConclusionsIt is for the first time that (a) magnetic sensitivity was proved in dogs, (b) a measurable, predictable behavioral reaction upon natural MF fluctuations could be unambiguously proven in a mammal, and (c) high sensitivity to small changes in polarity, rather than in intensity, of MF was identified as biologically meaningful. Our findings open new horizons in magnetoreception research. Since the MF is calm in only about 20% of the daylight period, our findings might provide an explanation why many magnetoreception experiments were hardly replicable and why directional values of records in diverse observations are frequently compromised by scatter.

Numerical simulations of the CME on 2010 April 8

AbstractWe present 3D zero-beta ideal MHD simulations of the solar flare/CME event that occurred in Active Region 11060 on 2010 April 8. The initial magnetic configurations of the two simulations are stable nonlinear force-free field and unstable magnetic field models constructed by Su et al. (2011) using the flux rope insertion method. The MHD simulations confirm that the stable model relaxes to a stable equilibrium, while the unstable model erupts as a CME. Comparisons between observations and MHD simulations of the CME are also presented.

Compensation of effect of field instability by reference deconvolution with phase reconstruction

A compensation method based on reference deconvolution is developed to obtain high-resolution NMR spectra under an unstable magnetic field. It is shown that the applicability of the original deconvolution method is limited for small fluctuation, and a process what may be called phase reconstruction is proposed to compensate large field fluctuation. We demonstrate the method using a probe with a coil that can generate a fluctuation field artificially. A high-resolution 1H NMR spectrum of ethylbenzene was obtained under the unstable field after compensation with this method.

Experimental study on the physical mechanism of coupling oscillation: a newly discovered oscillation in Hall thrusters

In order to study the physical mechanism of an oscillation newly discovered by the Harbin Institute of Technology Plasma Propulsion Lab (HPPL) in the range of hundreds of kHz to several MHz, Hall thrusters with different magnetic coils are studied by changing one of the following three parameters: discharge voltage, anode flow and coil current, directly measuring the coil current and measuring plasma oscillations related to coil current oscillation with the Langmuir probe. Experimental results indicated that in the discharge process of a Hall thruster the broadband turbulence of the Hall current causes an unstable spatial magnetic field and this field causes the magnetic circuit to resonate as an equivalent high level resistance–inductance–capacitance (RLC) network. As the response of the network, the oscillation of the coil current has a large oscillating component at the natural frequencies of the network. Also, the oscillation of coil current has an effect on the discharge process at the same time, so that they reach a self-consistent equilibrium state. As a result of such a coupling, both coil current and the discharge current exhibit their oscillating component at the natural frequencies of the magnetic circuit. It is therefore concluded that the newly discovered oscillation is caused by the coupling between the magnetic circuit and the discharge circuit.

Compensation of instabilities in magnetic Taylor-Couette flow

The axisymmetric linear stability of the Taylor-Couette flow with an azimuthal magnetic field is considered. It is shown that a flow with the combination of a linearly unstable rotation and a linearly unstable azimuthal magnetic field can be linearly stable. The flow stabilization takes place for both ideal and dissipative flows. For dissipative flow the stabilization exists only for a combination of counter-rotating cylinders and a counterdirecting azimuthal magnetic field on cylinders. The effect can be important for the problem of a plasma confinement by the magnetic field.

Rotational stabilization of pinch instabilities in Taylor-Couette flow

The axisymmetric linear stability of dissipative Taylor-Couette flow with an azimuthal magnetic field is considered. The magnetic field can be unstable without a rotation. This is the well-known pinch type instability. The stable rotation stabilizes the unstable azimuthal magnetic field. The dissipative flow stability can be classified according to Michael's stability condition for an ideal flow. The dissipative effects stabilize the flow and an ideally unstable flow becomes really unstable only when both the angular velocity and the magnetic field exceed some critical values.

Pinch instabilities in Taylor-Couette flow

The linear stability of the dissipative Taylor-Couette flow with an azimuthal magnetic field is considered. Unlike ideal flows, the magnetic field is a fixed function of a radius with two parameters only: a ratio of inner to outer cylinder radii, eta, and a ratio of the magnetic field values on outer and inner cylinders, muB. The magnetic field with 0<muB<1/eta stabilizes the flow and is called a stable magnetic field. The current free magnetic field (muB=eta) is the stable magnetic field. The unstable magnetic field, which value (or Hartmann number) exceeds some critical value, destabilizes every flow including flows which are stable without the magnetic field. This instability survives even without rotation. The unstable modes are located into some interval of the axial wave numbers for the flow stable without magnetic field. The interval length is zero for a critical Hartmann number and increases with an increasing Hartmann number. The critical Hartmann numbers and length of the unstable axial wave number intervals are the same for every rotation law. There are the critical Hartmann numbers for m=0 sausage and m=1 kink modes only. The sausage mode is the most unstable mode close to Ha=0 point and the kink mode is the most unstable mode close to the critical Hartmann number. The transition from the sausage instability to the kink instability depends on the Prandtl number Pm and this happens close to one-half of the critical Hartmann number for Pm=1 and close to the critical Hartmann number for Pm=10(-5). The critical Hartmann numbers are smaller for kink modes. The flow stability does not depend on magnetic Prandtl numbers for m=0 mode. The same is true for critical Hartmann numbers for both m=0 and m=1 modes. The typical value of the magnetic field destabilizing the liquid metal Taylor-Couette flow is approximately 10(2) G.

Taylor-Couette flow stability with toroidal magnetic field

The linear stability of the dissipative Taylor-Couette flow with imposed azimuthal magnetic field is considered. Unlike to ideal flow, the magnetic field is fixed function of radius with two parameters only: a ratio of inner to outer cylinder radii and a ratio of the magnetic field values on outer and inner cylinders. The magnetic field with boundary values ratio greater than zero and smaller than inverse radii ratio always stabilizes the flow and called stable magnetic field below. The current free magnetic field is the stable magnetic field. The unstable magnetic field destabilizes every flow if the magnetic field (or Hartmann number) exceeds some critical value. This instability survives even without rotation (for zero Reynolds number). For the stable without the magnetic field flow, the unstable modes are located into some interval of the vertical wave numbers. The interval length is zero for critical Hartmann number and increases with increasing Hartmann number. The critical Hartmann numbers and the length of the unstable vertical wave numbers interval is the same for every rotation law. There are the critical Hartmann numbers for m = 0 sausage and m = 1 kink modes only. The critical Hartmann numbers are smaller for kink mode and this mode is the most unstable mode like to the pinch instability case. The flow stability do not depend on the magnetic Prandtl number for m = 0 mode. The same is true for critical Hartmann numbers for m = 0 and m = 1 modes. The typical value of the magnetic field destabilizing the liquid metal Taylor-Couette flow is order of 100 Gauss.