Influence Of Axial Magnetic Field Research Articles

Influence of axial magnetic field on angular distribution of charge and energy of laser produced slow and fast tungsten ion groups

Here effect of magnetic field on the angular distribution of laser produced tungsten (W) ions is reported. Plasma plume was generated by irradiating surface of W target, placed inside a vacuum chamber under magnetic field of 0.23 T, by nanosecond pulsed laser beam. Angular distribution of W ion flux was measured with the help of an ion collector (IC) and explained under the framework of Anisimov model. Magnetic field clearly split the ion signals temporally into comparable fast and slow ion components and enhanced the intensity of fast ion group significantly. Enhancement of ion charge state with B was confirmed by Ion energy analyser (IEA). Theoretical fitting of bimodal ion signal suggested the existence of thermal and non-thermal component of nanosecond laser produced plasma. With magnetic field, a two fold increase in total charge of the fast ion component was observed. Magnetic field effect on ion energy was also investigated. The optical emission spectrum of W plasma was also recorded, and plasma parameters were measured in both the absence and presence of magnetic field. The rise of electron temperature and number density in presence of B confirmed the heating of W plasma by magnetic field.

Experimental investigation on the evolution of vacuum arc in the quench protection switch based on forced current zero

In this paper, the evolution of vacuum arc under different conditions in the quench protection switch (QPS) based on forced current zero was investigated experimentally and analyzed quantitatively. Experiments were conducted with cup-shaped axial magnetic field (AMF) contacts in a demountable vacuum chamber. Images of the arc column were photographed through the observation window with a high-speed digital camera with exposure time of 2 μs. Arc appearance was analyzed quantitatively through digital image processing. Quantified arc appearance and arc voltage characteristics indicated that the high-current vacuum arc evolution in the QPS could be divided into four stages: arc formation stage, arc column merging stage, diffusing stage, and fast extinguishing stage. The influence of AMF on the evolution of high-current vacuum arc in the diffusing stage was also studied. Experiment results indicated that the vacuum arc at relatively low current had a simpler evolution process and the arc column merging had less correlation with voltage stability. It was found that the vacuum arc with a long gap distance developed faster and the time required to enter the stable burning state was shorter. In addition, the vacuum arc with long arcing time tended to constrict again, which is not beneficial to current interruption.

Linear Stability of Magneto Viscoelastic Walter’s B ′ Type with Heat and Mass Transfer

In this paper, the couple influence of axial magnetic field and the heat and mass transfer on two rotating cylinders of Walter’s B ′ viscoelastic fluids by using the potential flow theory of viscoelastic fluid has been investigated. The normal mode method is used to compute the growth rate of disturbance. The influence of gravity is ignored at the interface, while the effect of surface tension is present in the analysis. The effect of the parameters on the stability is studied. It is found that the rotation of the inner cylinder induces stability. Furthermore, the viscoelastic ratio of fluids has a stabilizing influence. The heat and mass transfer, magnetic permeability ratio, and Ohnesorge number have a stabilized influence, while viscosity ratio of fluids, density ratio of fluids, and axial magnetic field have destabilizing influence on the considered system.

Influence of Axial Magnetic Field on Angular Distribution of Charge and Energy of Laser Produced Slow and Fast Tungsten Ion Groups

Influence of Axial Magnetic Field on Angular Distribution of Charge and Energy of Laser Produced Slow and Fast Tungsten Ion Groups

CFD analysis of Joule heating effect in a confined axi-symmetric swilling flow under the influence of axial magnetic field

The effect of axial magnetic field along with axial temperature gradient, in a confined cylindrical cavity packed with incompressible electrical conducting fluid having a top rotating lid, has been investigated. Due to the presence of axial magnetic field, Joule heating effect is considered in this study. The governing parameters ranges are as follows: [Formula: see text], [Formula: see text] at Re[Formula: see text]1000, Pr[Formula: see text]0.015. It is found that the internal heat generation due to Joule heating in mixed convection is governed by interaction parameter and temperature gradient. However, the Joule heating effect has very less effect on primary flow in comparison to the secondary flow along the meridional plane.

Similarity solutions for cylindrical shock wave in rotating ideal gas with or without magnetic field using Lie group theoretic method

The propagation of a cylindrical shock wave in rotating ideal gas under adiabatic flow condition is investigated using Lie group of transformation method. Both the cases of shock without magnetic field and under the influence of axial magnetic field are considered separately. The density and azimuthal fluid velocity in the case of shock without magnetic field and density, azimuthal fluid velocity and axial magnetic field in the case of shock under the influence of magnetic field are assumed to be varying in the undisturbed medium. The arbitrary constants appearing in the expressions for the infinitesimals of the local Lie group of transformations bring about two different cases of solutions, i.e. with a power law and exponential law shock paths. Exact solutions are obtained in the case of power law shock path for both the cases of cylindrical shock with and without magnetic field. It is not possible to obtain the exact solution in the case of exponential law shock path. In this case, the numerical solutions can be obtained by using the respective boundary conditions. Distribution of gasdynamical and magnetogasdynamical flow quantities are illustrated through figures.

Blast waves in a non-ideal self-gravitating gas with magnetic field

The propagation of the blast wave in self-gravitating non-ideal gas under the influence of axial magnetic field is investigated. The magnetic pressure and density are considered to be varying according to the power law. The approximate analytical solutions are obtained by expanding the flow variables in the form of power series using Sakurai’s technique. The zeroth- and first-order approximate solutions of self-gravitating non-ideal gas with magnetic field are discussed in detail. Solutions for zeroth-order approximation are constructed in analytical form. The effect of the flow parameters, namely parameter of non-idealness, adiabatic exponent, ambient density variation exponent and gravitational parameter on the flow variables, is discussed in detail. The results obtained in this work are compared with the results obtained by Sakurai and Nath, which are in good agreement

Trajectories in relativistic electron beam with elliptical cross section under the effects of self-fields, axial, planar and helical wiggler magnetic fields

The influence of axial magnetic field and self-fields in the electron gas column and electron beam with elliptical cross section is investigated. Further effects of cross section demotions and beam velocity on the electron rotating frequency are studied. It is shown that there are two solutions of fast and slow for electron rotating frequency. The obtained results are graphically presented. Besides the effects of axial magnetic field, self-fields, both planar wiggler magnetic field (PWMF) and helical wiggler magnetic field (HWMF) on trajectories of relativistic electron beam with elliptical cross section are investigated. By solving the motion equation for an electron in the considered fields, two equations for the average axial velocity and the function Φ are calculated. The effects of elliptical cross section demotions and elliptical electron beam density are studied. The effects of cross-section demotions and elliptical electron beam density are graphically investigated and so the results are compared for elliptical and circular electron beams. It is shown that with decreasing of value of electron beam density transverse velocity of electron increases about .

Similarity solutions for magnetogasdynamic cylindrical shock wave in rotating ideal gas using Lie Group theoretic method: Isothermal flow

The propagation of cylindrical shock wave under the influence of axial magnetic field in rotating medium under isothermal flow condition is investigated. The density, magnetic field and azimuthal and axial components of fluid velocity are assumed to be varying in the undisturbed medium. The arbitrary constants appearing in the expressions for infinitesimals of the Local Lie group of transformations bring about three different cases of solutions, i.e. with power law shock path, exponential law shock path and a particular case of power law shock path. Numerical solutions are obtained in the cases of power law and exponential law shock paths. Distribution of gasdynamical quantities are discussed through figures. The effects of variation in values of Alfven-Mach number [Formula: see text], ambient azimuthal velocity index [Formula: see text] and ambient density index [Formula: see text] are studied on flow variables and on shock strength. The numerical integration is done using software Mathematica. It is obtained that magnetic field has a decaying effect on shock strength. Also, increase in value of ambient density or ambient azimuthal velocity variation index in the case of power law shock path and increase in value of ambient density variation index in case of exponential law shock path have the decaying effect on shock strength.

Similarity solutions using Lie group theoretic method for cylindrical shock wave in self-gravitating perfect gas with axial magnetic field: isothermal flow

Propagation of cylindrical shock wave in a self-gravitating perfect gas under the influence of axial magnetic field using Lie group of transformation method is investigated. The flow is considered to be isothermal. Density and magnetic field are assumed to be varying in the undisturbed medium. Two different cases of solutions are brought out by the arbitrary constants appearing in the expressions of infinitesimals of local Lie group of transformations. One is with a power law shock path and the other one is with an exponential law shock path. Numerical solutions are obtained for both the cases of power law and exponential law shock paths. The effects of variation in Alfven-Mach number, gravitational parameter and ambient density variation index for power law shock path and effects of variation in Alfven-Mach number, gravitational parameter and ambient magnetic field variation index on the flow variables in the case of exponential law shock path are studied. Also the effects of increase in value of gravitational parameter and in the strength of ambient magnetic field on the shock strength are investigated. The increase in value of Alfven-Mach number leads to the increase in the density ratio which infers to the decrease in shock strength.

Influence of Axial Magnetic Field on Swirling Flow and Vortex Breakdown Zones in a Cylindrical Cavity with a Rotating Lid

In this study, behavior of swirling flow under the influence of axial magnetic field in a cylindrical container with a top rotating disk has been probed. The flow is assumed to be axisymmetric for the parameters considered. The domain consists of a cylindrical cavity packed with viscous and electrically conducting metallic liquid. The qualitative effect of magnetic field is manifested in terms of torque coefficient evaluated on the rotating lid as well as the fixed end wall. Effects of the magnetic field on the zones of vortex breakdown, in the Aspect ratio (AR), Reynolds number (Re) plane, for the top rotating lid with all sides electrically insulated have been developed. Moreover, it is found that one can control the behavior of flow with help of a proper choice of the electric conducting wall.

Influence of contacts’ orientation on the AMF distribution in inter‐contact gaps of VCBs

An axial magnetic field (AMF) plays an important role in the process of vacuum arc stabilisation during the current breaking process in the vacuum circuit breakers (VCBs) of the AMF type. To minimise the contacts erosion special attention should be paid to reach a possibly high value of the AMF density (between contact plates), especially in the outer electrode region. Various contact geometries are patented all over the world to improve the AMF distribution. Nevertheless, there is an issue which is not raised in the literature as yet. It is the mutual orientation (rotation) of the moving and fixed contacts. This orientation can have an influence on the AMF distribution. The above problem is analysed here numerically using Maxwell (ANSYS) software package based on the finite element method. The own (patented) contact design is considered in the analysis mentioned. However, the beneficial influence of AMF on the arc behaviour is well known for VCB designers, the explanation of this phenomenon is described (in the literature) rather seldom and very cursorily. Therefore, a simplified model accounting for the role of AMF in vacuum arc diffusion is shortly presented at the beginning of this study.

Magnetic field assisted enhanced electron acceleration due to a chirped echelon phase modulated laser in vacuum

Electron acceleration employing chirped echelon phase modulated (EPM) linearly polarised (LP) laser pulse in vacuum under the influence of axial magnetic field has been explored. Echelon supported laser pulse with phase modulation sustains the trapping of pre-accelerated electron in the most favourable phase. Furthermore, the addition of linear frequency chirp enlarges the electron laser interaction duration. Here, application of axial magnetic field serves a critical role in boosting the electron acceleration upto larger distances in the laser propagation direction. So, few MeV electron can be expedited up to GeV energy and retains it upto longer distances due to the collective influence of the frequency chirp and phase modulation. Effect of laser initial intensity, pulse duration, beam waist and electron injection is taken into consideration and optimized for enhanced energy gain. It is observed that the electron of initial energy ˜0.5 MeV can achieve energy of ˜2.5 GeV with I∼1.38 × 1020 W/cm2 due to chirped LP EPM laser pulse in the existence of suitable axial magnetic field (˜41.7 MG) at most favourable values of electron injection angle and EPM gradient parameter.

Improvement of AMF distribution in the inter-contact gap of VCB

Nowadays, many manufacturers of vacuum circuit breakers (VCB) apply the axial magnetic field (AMF) to stabilise the electric arc diffusion during current breaking process. In many papers, various designs of contacts are proposed to improve the AMF distribution between circuit breaker’s contacts. In the present paper, some methodological aspects of AMF investigations have been presented and discussed. In the beginning, a short explanation of AMF influence on arc behaviour has been presented. A simplified physical model of phenomena considered has been applied for this purpose. The above analysis indicates that special attention should be paid to reach possibly high value of the axial magnetic field density especially in the peripheral electrode region. An own laboratory stand for AMF measurements has been described. Measurement and computational results of AMF distribution have been compared. The computations have been done with a commercial software package Maxwell (Ansoft) based on the finite element method (FEM). Good convergence of the results compared indicates that AMF can be investigated in experimental as well as in theoretical way. The numerical analysis presented enabled to select the contact configuration which ensures more stable arc behaviour during the circuit breaking process. Images of arc behaviour registered with a high speed camera for a new contact construction as well as contacts known from industrial practice have been presented.

Transverse electromagnetic Hermite–Gaussian mode-driven direct laser acceleration of electron under the influence of axial magnetic field

AbstractHermite–Gaussian (HG) laser beam with transverse electromagnetic (TEM) mode indices (m, n) of distinct values (0, 1), (0, 2), (0, 3), and (0, 4) has been analyzed theoretically for direct laser acceleration (DLA) of electron under the influence of an externally applied axial magnetic field. The propagation characteristics of a TEM HG beam in vacuum control the dynamics of electron during laser–electron interaction. The applied magnetic field strengthens the $\vec v \times \vec B$ force component of the fields acting on electron for the occurrence of strong betatron resonance. An axially confined enhanced acceleration is observed due to axial magnetic field. The electron energy gain is sensitive not only to mode indices of TEM HG laser beam but also to applied magnetic field. Higher energy gain in GeV range is seen with higher mode indices in the presence of applied magnetic field. The obtained results with distinct TEM modes would be helpful in the development of better table top accelerators of diverse needs.

STUDY OF AXISYMMETRIC NATURE IN 3-D SWIRLING FLOW IN A CYLINDRICAL ANNULUS WITH A TOP ROTATING LID UNDER THE INFLUENCE OF AXIAL TEMPERATURE GRADIENT OR AXIAL MAGNETIC FIELD

The three dimensional swirling flow has been obtained by solving Navier Stokes equations, expressed in cylindrical coordinate system, using finite difference technique on a staggered grid. An explicit finite difference method using pressure correction technique, for the solution of Navier-Stokes has been implemented to solve three dimensional flows. Present study explores the 3-D axisymmetric nature of stratified swirling flow and vortex breakdown in a cylindrical annulus cavity with top rotating lid. The annulus is obtained by inserting a thin coaxial rod in cylindrical cavity. This rod may be stationary or rotating depending on the particular study. Three dimensional swirling flows in annuli have also been studied subjected to axial temperature gradient or under the influence of axial magnetic field. Influence of governing parameters Re, Ri and Ha on the overall heat transfer has been investigated through variation of the average Nusselt number with these parameters. Further, the present numerical results are shown to be in good agreement with the available benchmark solutions under the limiting conditions.

Simulation results of influence of constricted arc column on anode deformation and melting pool swirl in vacuum arcs with AMF contacts

In the process of vacuum arc breaking, the energy injected into the anode will cause anode melting, evaporation, and deformation, resulting in the formation of the anode melting pool. The anode activities have great influence on the arc behavior. When the arc current is large enough, even the influence of axial magnetic field is considered, the arc column still is in contraction state, which means the arc burns only on a part of the electrode. In this paper, the model of anode melting pool deformation and rotation is used, and the model includes anode melting and solidification module, magneto-hydro-dynamic module of the anode melting pool, the volume of fraction method, and the current continuity equation. In this paper, the diffuse arc area is selected as 100%, 75%, and 50%, respectively. The anode temperature and deformation, the anode melting layer thickness, and the rotational velocity of the anode melting pool are obtained. The results show that when the current is at 17.5 kA (rms) and the diffuse arc area is 100%, the anode's maximum temperature is 1477 K and the crater depth is 0.83 mm. But when the diffuse arc areas are 75% and 50%, the anode's maximum temperatures reach 1500 K and 1761 K, and the crater depths reach 1.2 mm and 3 mm, respectively. Arc contraction will lead to more serious anode deformation. A similar result is obtained when the simulation current is 12.5 kA. Under the similar situation, the simulation results in the crater depth, the residual melt layer thickness, the rotational speed of the melting pool, and the maximum temperature of the anode at current zero are in good agreement with the experimental results.

Influence of Axial Magnetic Field on Cathode Plasma Jets in High-Current Vaccum Arc

The cathode plasma jets in vacuum arc and the effect of magnetic field on them have been studied for several years and these studies are helpful to understand the arc characteristics and improve the controlling effect of magnetic field on arc plasma. In this paper, the experiments of the cup-shaped axial magnetic field (AMF) contacts were conducted in which a Helmholtz coil was introduced to generate different external imposed AMFs. It was found that the appearance of arc plasma was changed by variation of the external imposed AMF. If the composite AMF in arc column increased gradually, the obvious individual cathode plasma jets were detected, the arc constriction decreased, and the arc stability increased. Meanwhile, the inclination of cathode plasma jets was observed and the inclination direction was found to be consistent with the magnetic field vector direction which is closely related to the composite AMF. By variation of the external imposed AMF and its direction, the inclination direction of cathode plasma jets also changed. The criterion to detect obvious cathode jets in arc column is obtained that at the contact peripheral where R> 80.5% R0 (R0 is the contact radius), the AMF strength is no less than 4.5 mT/kA. It was also found that if the composite AMF in interelectrode gap points to different directions at a certain moment, it may lead to the transfer of arc column from the center to the edge of the interelectrode region and the arc instability until when the composite AMF in the interelectrode gap points to the same direction. It can be concluded that the appearance of individual cathode plasma jets can be manipulated by the variation of AMF, which is helpful to study the interaction between arc plasma and electrodes, especially the anode, and improve the interruption performance at higher current.

Influence of axial magnetic field on shape and microstructure of stainless steel laser welding joint

The morphology and microstructure of the weld joint have significant influence on mechanical properties of welded specimens. In this paper, the mechanism on how the external magnetic field affected weld profile and microstructure was discussed by applying the longitudinal steady magnetic field to laser welding for SUS301 stainless steel. The optimal and scanning electron microscopes were used to measure the shape of the cross section and observe the microstructure after welding. The results showed that the shape of the cross section and microstructure could be significantly changed using the external magnetic field. Moreover, joint shape changed distinctly with the magnetic field intensity changing. With the increasing of magnetic flux density, the weld profile of the full penetration model changed from funnel to X type; meanwhile, the bottom weld width increased by 40%. In addition, the partial fusion zone occurred, and the weld width decreased by 20% while penetration increased by 18% when magnetic flux density turned into 380 mT. As far as microstructure of weld joint was concerned, it appeared that application of axial magnetic field led to indistinct fusion line and blocky austenite in big size rather than columnar grain in the center of the cross section. This phenomenon could be explained by numerical simulation results.

Electron injection for direct acceleration to multi-GeV energy by a Gaussian laser field under the influence of axial magnetic field

Electron injected in the path of a circularly polarized Gaussian laser beam under the influence of an external axial magnetic field is shown to be accelerated with a several GeV of energy in vacuum. A small angle of injection δ with 0∘<δ<20∘ for a sideway injection of electron about the axis of propagation of laser pulse is suggested for better trapping of electron in laser field and stronger betatron resonance under the influence of axial magnetic field. Such an optimized electron injection with axial magnetic field maximizes the acceleration gradient and electron energy gain with low electron scattering.