External Longitudinal Magnetic Field Research Articles

Numerical simulation of plasma flows in curved coaxial ducts with longitudinal magnetic field

The results of numerical researches of plasma flows in coaxial plasma accelerators ducts of a various geometry with an external longitudinal magnetic field are presented. The non-steady-state two-dimensional MHD-model of relaxation of transonic super-Alfven flows with acceleration is considered. The paper focuses on the cumulative influence of a duct geometry and longitudinal magnetic field on flow characteristics.

Enhancement of proton acceleration by a right-handed circularly polarized laser interaction with a cone target exposed to a longitudinal magnetic field

Our previous research [J. X. Gong et al. Phys. Plasmas 24, 033103 (2017)] shows that in the presence of an external longitudinal magnetic field, there is no cut-off density when a right-handed (RH-) circularly polarized (CP) laser propagates in the plasmas. In this work, the proton acceleration driven by an RH-CP laser interaction with a pre-magnetized cone target filled with a pre-formed plasma is investigated under the mechanism of target normal sheath acceleration. The strength of the external magnetic field considered in this paper is comparable to that of the incident laser. The two-dimensional particle-in-cell simulation results show that with an external longitudinal magnetic field, both the energy and yield of protons accelerated by the sheath electric field at the rear of the target are remarkably increased because of the higher coupling efficiency from RH-CP laser energy to electrons and the more efficient electron acceleration. Electrons can be converged remarkably by the external magnetic field and the divergence of protons can be controlled evidently by the collimated electrons. The maximum cut-off energy of protons with an imposed longitudinal magnetic field can be promoted to be as high as 82 MeV. Detailed simulation results show that the maximum energy of protons increases with the increasing initial external magnetic field.

Phase diagrams of the Kane-Mele-Hubbard model in the presence of an external magnetic field

We studied the Kane-Mele-Hubbard model at half filling with Zeeman magnetic field using rotationally invariant slave boson method. The competition between external magnetic field and spin orbital coupling at large Hubbard U is explored. It is found that different canted antiferromagnetic phases exist in the presence of longitudinal and transverse magnetic fields. With longitudinal external magnetic field and strong electron correlation, the z component of the local moment is preferred by the finite spin-orbital coupling.

Effect of magnetic field on the optical properties of an inhomogeneously broadened multilevel Λ-system in Rb vapor

We present a theoretical model, using density matrix approach, to study the effect of external longitudinal and transverse magnetic fields on the optical properties of an inhomogeneously broadened multilevel Λ-system using the D2 line in 85Rb and 87Rb atoms. The presence of closely spaced multiple excited states causes asymmetry in the absorption and dispersion profiles. We observe a wide EIT window with a positive slope at the line center for a stationary atom. While for a moving atom, the linewidth of EIT window reduces and positive dispersion becomes steeper. When magnetic field is applied, our calculations show multiple EIT subwindows that are significantly narrower and shallow than single EIT window. The number of EIT subwindows depend on the orientation of the magnetic field. We also obtain multiple positive dispersive regions for subluminal propagation in the medium. The anomalous dispersion exists in between two subwindows showing the superluminal light propagation. Our theoretical analysis explain the experiments performed by Wei et al. [Phys. Rev. A 72, 023806 (2005)] and Iftiquar et al. [Phys. Rev. A 79, 013808 (2009)].

Effect of external longitudinal magnetic field on arc plasma characteristics and droplet transfer during laser-MIG hybrid welding

The arc plasma behavior and droplet transfer are investigated using laser-MIG (metal insert gas) hybrid welding assisted by an external longitudinal magnetic field. The characteristic of arc plasma and droplet transfer can be recorded via combining sensing of the welding current and arc voltage with a high-speed imaging. Results indicated that the external longitudinal magnetic field had a significant impact on the arc shape, droplet formation, droplet size, and detaching. Under the magnetic field, the arc shape became a triangle gradually, and the off-axis arc and droplet gradually pointed to the axis of the filler wire. In addition, it has been found that with increasing the magnetic induction intensity, the droplet diameter and cycle time can be reduced. The mechanism of these phenomena was also further analyzed.

Enhancing the electron acceleration by a circularly polarized laser interaction with a cone-target with an external longitudinal magnetic field

The propagation of left-hand (LH-) and right-hand (RH-) circularly polarized (CP) lasers and the accompanying generation of fast electrons in a magnetized cone-target with pre-formed plasmas are investigated. In this work, the strength of external magnetic field is comparable to that of the incident laser. Theoretical analyses indicate that the cut-off density of LH-CP laser is larger than that without an external magnetic field. When the external magnetic field normalized by the laser magnetic field is larger than the relativistic factor, the RH-CP laser will keep on propagating till the laser energy is depleted. The theoretical predictions are confirmed by two-dimensional particle-in-cell simulations. Simulation results show that in the presence of external longitudinal magnetic field, the energies and yields of fast electrons are greatly enhanced for RH-CP laser. Besides, the coupling efficiency of laser energy to energetic electrons for RH-CP laser is much higher than that for LH-CP laser and without external magnetic field. Furthermore, detailed simulation results perform an enhancement of the incident laser absorption with increasing external magnetic field.

A Study on Giant Magnetoimpedance Effect in VITROVAC 6025Z Micro-patterned Ribbons

In this paper, micro-patterned cobalt-based amorphous ribbons with different structures are fabricated by MEMS technology, including bonding, lithography and electroplating. The commercial amorphous ribbons (VITROVAC 6025Z) are purchased from VACUUMSHMELZE ® company. The structures of micro-patterned ribbons are designed for meander shape for different turns (one turn, two turns and three turns). The effect of external magnetic field orientation and turns on GMI ratios were studied in the frequency range of 1–40 MHz. It is found that GMI ratios almost all present negative value, which is related to the material property, namely a large coercive force. Compared with the GMI ratios obtained at transverse external magnetic field, the maximum negative GMI ratio obtained at longitudinal external magnetic field is higher. The value of −69.93% is obtained at a current frequency of 20 MHz and the magnetic field of 150 Oe. With the increase of the number of turns, the maximum positive GMI ratio increases from 0.5 % for the one turn sample to the 2.8% for the sample with three turns. The maximum nagative GMI ratio is obtained by three-turns sample. The GMI character of VITROVAC 6025Z micro-patterned ribbon is significant and the microsensor is expected to be used in biological sensing field.

Magnetization and diamagnetism of a longitudinal autosoliton in p-InSb in an external longitudinal magnetic field

It has been experimentally shown that a longitudinal thermal-diffusion autosoliton, which is generated in a nonequilibrium electron–hole plasma in p-InSb, in an external longitudinal magnetic field acquires diamagnetic properties. The results of the calculation and numerical estimates of the diamagnetism have been presented.

Asymmetric magnetoimpedance effect in CoFeSiB amorphous ribbons by combination of field and current annealing for sensor applications

The roles of applied magnetic field during the current annealing of Co68.15Fe4.35Si12.5B15 soft magnetic amorphous ribbons are studied. Samples heat treated by Joule heating effect in open air and simultaneously in the present of longitudinal external magnetic field showed asymmetric magnetoimpedance (AMI) behavior. The AMI profile can be related to the exchange bias interaction between the soft magnetic amorphous material and a harder magnetic crystalline phase formed on the surface of the ribbon. This effect stems from thermal effect, the transverse Oe field generated from the annealing current which is thickness dependent and the longitudinal external field. The single peak AMI with the field sensitivity of 101%/Oe for DC annealing current is achieved. Our results could address a simple way to achieve the AMI response toward developing high sensitive magnetic field sensors.

Electron transport estimated from electron spectra using electron spectrometer in LFEX laser target experiments

Hot electrons which are generated from targets irradiated by a high-intense laser are measured by two electron spectrometers (ESMs). However, total electron energy observed by the ESM is only less than 1%. Hot electrons are confined by self-fields due to the huge current. When an external magnetic field of several hundred Tesla is applied during the laser irradiation on targets, the ESM signals always increase. In the simulation, the same result can be obtained. The reason is that the Alfvén limit can be mitigated due to the external longitudinal magnetic field.

Generalization of the Bennett equilibrium condition for a relativistic electron beam propagating in the Ohmic plasma channel and ion focusing regime along an external magnetic field

The problem of formulating the generalization of the Bennett equilibrium condition is considered for a relativistic electron beam propagating in the Ohmic plasma channel, as well as in the ion focusing regime in the presence of an external longitudinal uniform magnetic field. We assume that the electron component of the background plasma is not completely removed from the region occupied by the beam. This equilibrium condition is derived using the mass and momentum transport equations obtained for a paraxial monoenergetic beam from the Fokker–Planck kinetic equation.

Magnetic phases and relaxation effects in fullerite C60

A highly sensitive torsional vibration technique is used to study the magnetic properties of fullerite C60 (99.98%) at temperatures of 77–300 K in dynamic and static experiments. Vibrational energy absorption peaks associated with phase transitions and realignment of the magnetic structure of the fullerite are detected at T = 152, 195, 230, and 260 K. Relaxation magnetic processes in fullerite C60 at room temperature are studied. “Spontaneous” rotation of a motionless sample of fullerite freely suspended on an elastic filament is observed when external longitudinal or transverse magnetic fields are switched on. The direction of the “spontaneous” rotation changes with time. It is proposed that these phenomena are related to relaxation processes in the rotational subsystem of C60 molecular rotators, as well as to magnetic flux trapped in the fullerite and weakly damped eddy currents induced in the sample by the applied field.

Quantum criticality of a spin-1 XY model with easy-plane single-ion anisotropy via a two-time Green function approach avoiding the Anderson–Callen decoupling

In this work we study the quantum phase transition, the phase diagram and the quantum criticality induced by the easy-plane single-ion anisotropy in a d-dimensional quantum spin-1 XY model in absence of an external longitudinal magnetic field. We employ the two-time Green function method by avoiding the Anderson–Callen decoupling of spin operators at the same sites which is of doubtful accuracy. Following the original Devlin procedure we treat exactly the higher order single-site anisotropy Green functions and use Tyablikov-like decouplings for the exchange higher order ones. The related self-consistent equations appear suitable for an analysis of the thermodynamic properties at and around second order phase transition points. Remarkably, the equivalence between the microscopic spin model and the continuous O(2)-vector model with transverse-Ising model (TIM)-like dynamics, characterized by a dynamic critical exponent z=1, emerges at low temperatures close to the quantum critical point with the single-ion anisotropy parameter D as the non-thermal control parameter. The zero-temperature critic anisotropy parameter Dc is obtained for dimensionalities d>1 as a function of the microscopic exchange coupling parameter and the related numerical data for different lattices are found to be in reasonable agreement with those obtained by means of alternative analytical and numerical methods. For d>2, and in particular for d=3, we determine the finite-temperature critical line ending in the quantum critical point and the related TIM-like shift exponent, consistently with recent renormalization group predictions. The main crossover lines between different asymptotic regimes around the quantum critical point are also estimated providing a global phase diagram and a quantum criticality very similar to the conventional ones.

The effect of external longitudinal magnetic field on laser-MIG hybrid welding

Applying the external longitudinal magnetic field to laser-metal inert gas (MIG) hybrid welding, its influence on the arc/plasma shape, motion characterization, and coupling of these two sources are researched using a high-speed camera. It is revealed that the essential effect of the external longitudinal magnetic field on laser-MIG hybrid welding arc/plasma is to make the arc and the coupling process more stable. Through analyzing the position of arc and laser-induced plasma and the mechanical model of charged particles, the energy coupling mechanics of arc and plasma under this welding condition has been proposed. The results showed that an application of a magnetic field can change the arc shape from pyramidal and static to spiral and rotational with high-speed stage and make the arc root diameter increase. It has also been found that the external longitudinal magnetic field can obviously enhance the stability of the process during laser-arc hybrid welding under the best magnetic induction intensity, which promoted efficient coupling and formed a good weld.

Comparison of the ferromagnetic Blume–Emery–Griffiths model and the AF spin-1 longitudinal Ising model at low temperature

We derive the exact Helmholtz free energy (HFE) of the standard and staggered one-dimensional Blume–Emery–Griffiths (BEG) model in the presence of an external longitudinal magnetic field. We discuss in detail the thermodynamic behavior of the ferromagnetic version of the model, which exhibits magnetic field-dependent plateaux in the z-component of its magnetization at low temperatures. We also study the behavior of its specific heat and entropy, both per site, at finite temperature. The degeneracy of the ground state, at T=0, along the lines that separate distinct phases in the phase diagram of the ferromagnetic BEG model is calculated, extending the study of the phase diagram of the spin-1 antiferromagnetic (AF) Ising model in S.M. de Souza and M.T. Thomaz, J. Magn. and Magn. Mater. 354 (2014) 205 [5]. We explore the implications of the equality of phase diagrams, at T=0, of the ferromagnetic BEG model with K|J|=−2 and of the spin-1 AF Ising model for D|J|>12.

Anti-gravity gradient unique arc behavior in the longitudinal electric magnetic field hybrid tungsten inert gas arc welding

An external magnetic field applied in arc welding process results in electro-magnetic stirring (EMS) welding. The added longitudinal magnetic field (LMF) provides an effective method to control the arc behavior and affect the resultant welds. However, few studies have addressed arc behaviors in LMF-TIG hybrid welding, i.e., tungsten inert gas arc (TIG) hybrid welding with an external LMF; the LMF direction is the same as or parallel to the symmetric axis of welding arc. In this paper, a three dimensional (3D) multiphysics field model was established to analyze arc behavior in LMF-TIG hybrid welding. This model is formed by fluid dynamics equations coupled with Maxwell equations. The fields of temperature, velocity, and electric current field were obtained from this model through numerical simulation using the finite volume method (FVM). It was found that the arc changes from its free to strong electromagnetic field controlled status in three stages. After the applied electromagnetic field exceeds a critical value, mutation is induced in the arc resulting in an arc behavior completely different from that of the normal free arc. The arc pressure and temperature distributions shift their centers, where the peak pressure and temperature occur, from the tungsten axis. In addition, the arc exhibits negative pressure (i.e., anti-gravity gradient behavior) below the cathode and a tornado-style behavior. The arc plasma flow reverses, a circular area occurs, and a low-temperature zone forms in the center of the arc. The highest flow speed takes place on both sides of the arc symmetry axis. The unique appearance of the negative arc pressure and its formation mechanism are discussed.

Self-focusing and self-channelling of short circularly laser pulses propagating in a magnetized plasma channel

In this study, non-paraxial nonlinear propagation of a relativistic laser pulse with linear and circular polarization in a preformed plasma channel having a parabolic density profile is investigated. The circular laser spot size variation in the absence/presence of an external longitudinal magnetic field is separately analysed and the results are compared. The amplitude of oscillation is decreased in the relativistic case, but it is changed in the presence of an external field. The right-turn circular pulse behaviour is completely opposite to that of the left-turn circular pulse in the presence of an external field, because the right-turn pulse is focused later than the left-turn pulse. The effect of nonlinearities on oscillations of spot size is analysed and the nonlinear critical channel depth required for propagation of a self-trapped laser pulse is evaluated. The laser field amplitude is derived for a matched pulse and it is shown that the group velocity dispersion effect causes broadening of the pulse length.

Meander-shaped magnetoimpedance sensor for measuring inhomogeneous magnetic fringe fields of NiFe films

Magnetic fringe fields of NiFe films were measured by giant magnetoimpedance (GMI) sensor, in this work. We have observed an interesting GMI phenomenon: the impedance enhanced first and then declined due to the presence of NiFe films, it is suggested that magnetic fringe fields have strengthened the longitudinal external magnetic field. Results indicated that the GMI sensor was able to quantify the magnetized NiFe films from 1 × 5 to 5 × 5 mm2. Anyway, this study has extended the application of GMI sensor to film detection, which makes it promising in detecting the defects of soft magnetic devices.

Magnetic-field-induced quantum criticality in a planar ferromagnet with single-ion anisotropy

We analyze the effects induced by single-ion anisotropy on quantum criticality in a d-dimensional spin-3/2 planar ferromagnet. To tackle this problem we employ the two-time Green's function method, using the Tyablikov decoupling for exchange interactions and the Anderson-Callen decoupling for single-ion anisotropy. In our analysis the role of non-thermal control parameter which drives the quantum phase transition is played by a longitudinal external magnetic field. We find that the single-ion anisotropy has substantial effects on the structure of the phase diagram close to the quantum critical point.

Influence of Magneto-Thermal Treatments on Longitudinally Driven Giant Magneto-Impedance Effect in Co-Fe-Si-B Amorphous Ribbons

Co64Fe4Si14.5B14.5amorphous ribbon was fabricated by the melt-spinning technique. Soft magnetic properties of the ribbon were improved by annealing at 623K for 1 hour with a zero magnetic field, a 50mT longitudinal or transverse external magnetic field comparing with the as-quenched ribbon. The longitudinally driven giant magneto-impedance (LDGMI) effect and its field sensitivity (ξ) have been investigated in the frequency (f) range of 1kHz~1MHz. It is found that at f=51kHz, the LDGMI effect and ξ reach the largest values for the sample annealed with a longitudinal magnetic field.