Presence Of Transverse Magnetic Field Research Articles

Consistency of splitting frequency difference with longtudinal modes spacing variation in Zeeman dual-frequency laser

Phase anisotropy in laser resonant cavity will bring about an influence on laser frequency and polarization, such as laser frequency splitting, of which the frequency difference is determined by their introduced phase retardation. For a helium-neon laser with a small phase retardation in the cavity, the two split modes are very close to each other whose burned holes are overlapped. Then only one mode oscillates while the other is always in lock-in state due to strong mode competition, which forms hidden frequency split. Meanwhile the spacing between adjacent longitudinal modes deviates from original value and produces a certain variation equal to twice the hidden splitting frequency difference. As a result the longitudinal modes spacing variation is dominated by the phase retardation. On the other hand, by applying transverse magnetic field to a laser tube along the polarization direction, the neon atoms will undergo transverse Zeeman effect and be divided into two groups to provide the gain for polarized light beams parallel to the magnetic field and perpendicular to the magnetic field respectively. Then the laser mode competition is greatly weakened so that the two split modes can oscillate simultaneously to obtain the frequency difference. In order to make profound study of the consistency between longitudinal mode spacing variation and splitting mode frequency difference in the presence of transverse magnetic field, the samples of tilted quartz plate or half wave plate is placed into laser cavity to produce phase retardation. By the two mentioned methods, the splitting frequency difference varying with phase retardation of samples is deduced to make a comparison. Two measurements show that the average relative deviation is less than 1%, while the experimental results accord with theoretical analyses quite well. In this way splitting frequency difference of Zeeman dual-frequency laser can be determined accurately, and a new method to measure the phase retardation of half wave plate is provided.

Numerical analysis of Richtmyer–Meshkov instability of circular density interface in presence of transverse magnetic field

Richtmyer–Meshkov instability (RMI) caused by the interaction of a shock wave and a density interface in the presence of a transverse magnetic field is investigated numerically using the ideal compressible magneto-hydro-dynamic (MHD) equations. The MHD equations are solved with the corner transport upwind + constrained transport algorithm that guarantees the divergence-free constraint on the magnetic field. The numerical results clearly capture the evolution of the density interface induced by the RMI for both HD and MHD situations, which are in good agreement with the previous experimental and numerical results. Moreover, current numerical results reveal a potential stabilizing mechanism of the flow instability by the transverse magnetic field: it is found that the magnetic tension produces a torque on the interface fluid, which is opposite to the torque driven by the velocity shear; therefore, the Kelvin–Helmholtz instability on the density interface caused by the velocity shear is effectively suppressed. In addition, detailed information about the magnetic strength, magnetic energy, magnetic tension, and vorticity on the density interface is also quantitatively analyzed, and the results suggest that the RMI is quite an efficient mechanism for the amplification of the magnetic field, which, in turn, enhances the suppression of the flow instability.

Experimental and numerical investigation on the asymmetry of the current density extracted through a plasma meniscus in negative ion accelerator

In multi-beamlet negative ion accelerators for neutral beam injectors, the transverse magnetic field necessary for suppressing the co-extracted electrons induces a deflection of the negative ion beamlets that must be corrected. For the design, particle-tracing simulation codes are used to compute ion trajectories and optical properties of the beamlets in the acceleration stage. In these codes, uniform boundary conditions are normally assumed for the ion current density distribution at the surface (called meniscus), where negative ions are extracted from the plasma and form beamlets, which are accelerated across the apertures of the accelerator grids. Recently, experimental campaigns dedicated to the accurate measurement of the beamlet deflection in the acceleration phase revealed higher deflection than foreseen by simulations. In this work, we demonstrate that an agreement with the experimental data can be obtained by incorporating in the numerical simulations a non-radially symmetric distribution of the ion current density extracted across the meniscus surface. In the first part, the asymmetry of the ion current density at the meniscus is studied in an empirical way, by analysing and fitting the experimental results obtained with different operating parameters. In the second part, we show that the ion current asymmetry estimated by this procedure is well consistent with the flow pattern of H− ions calculated in the meniscus zone using a detailed particle in cell (PIC) model of the ion source in the presence of transverse magnetic field.

Three Dimensional Couette Flow of Dusty Fluid through a Porous Plate in the Presence of Transverse Magnetic Field

Three Dimensional Couette Flow of Dusty Fluid through a Porous Plate in the Presence of Transverse Magnetic Field

Magneto‐hydrodynamics natural convection flows of viscous carbon nanotubes nanofluids with generalized Fourier's law in a vertical cylinder

In this article, we consider the natural (free) convection flows of viscous carbon nanotubes nanofluids in the presence of transverse magnetic field in a vertical cylinder. The fractional derivative is introduced by means of generalized Fourier's law (Caputo–Fabrizio and Atangana–Baleanu fractional derivatives) in the thermal equation. The solutions of the equations are found by means of the Laplace and finite Hankel transforms, which satisfied all imposed initial and boundary conditions. The effects of fractional and physical parameters are graphically underlined.

Analysis and control of shear flow over a rotating plate in the presence of magnetic field

AbstractShear flow of an incompressible viscous electrically conducting fluid past a uniformly rotating infinite impermeable flat plate in the presence of transverse magnetic field is investigated. The flow is assumed to be governed by Navier‐Stokes equations augmented with an applied magnetic field. Solutions of the corresponding equations are analyzed. It is noted that due to shear flow over a rotating plate, the problem has no axisymmetric solutions. But it is interesting to note that this problem has no unique solution for the secondary velocity components. It is remarkable to note that Navier‐Stokes equations for this problem admit a one parameter family of solutions. Inside the boundary layer, the momentum transfer of the outer shear flow is dominated by the pressure gradient. The secondary velocity component along x‐axis is a linear combination of velocity due to shear and translation. However, it is noted that the contribution from the shear dominates. It is observed that the primary and secondary velocity components can be controlled by the applied magnetic field. It is also found that the torque exerted by the fluid on the plate is influenced by the applied magnetic field but independent of the shear in the external flow.

Free surface film flow of an unsteady second grade fluid over a stretching sheet with surface tension linearly varies with temperature

In this investigation, the work of Noor and Hashim (2010) is explored in a more advance form by considering the effectiveness of the second grade boundary layer equations with the adjust of pressure term in the presence of transverse magnetic field. The conducted unsteady momentum equations in xy-plane attached with energy equation are shifted into a group of two ODEs involving the important physical parameters, having effective results for the constructive progress. These parameters are second grade non-dimensional parameter, surface tension parameter(thermocapillary number), temperature Grashof number, sheet thickness, magnetic parameter(Hartmann number), Prandtl number and non-dimensional parameter of unsteadiness. The same system give local free surface temperature, heat transfer(heat flux) normal to the flow surface and local surface skin friction. All observations are possible by the use of Homotopy Analysis Method called HAM. Graphs and Tables are made to see the physical properties of the fluid flow by varying arbitrary parameters. Error analysis is a part of this study which define the validity of the HAM method. Further, comparison of the methods(HAM and BVP4C) are done in a table for the validity of the solution.

Model for electroluminescence in single-walled carbon nanotube field effect transistor under transverse magnetic field

Electroluminescence spectrum and radiative recombination rate of short channel single-walled carbon nanotube field effect transistor in presence of transverse magnetic field is calculated by using non-equilibrium Green’s function method. Significant enhancement in radiative recombination rate and red shift in electroluminescence spectrum are observed with increase in the strength of magnetic field. The band gap suppression estimated from energy position resolved local density of states calculation plays a dominant role in transport mechanism under the influence of external magnetic field. The tuning of electroluminescence spectrum of single-walled carbon nanotube by transverse magnetic field can be employed as nanoscale optical source in next generation optoelectronic and photonic devices.

Effect of frequency-chirped laser pulses on terahertz radiation generation in magnetized plasma

The effect of frequency chirp on the generated terahertz (THz) wave by the interaction between intense laser pulses and under dense plasma in the presence of transverse magnetic field is investigated theoretically in the present model. An expression for the electron Lorentz factor coupling cyclotron motion nonlinearity is derived for static magnetic field perpendicular to the laser propagation axis. The beating lasers produce a nonlinear ponderomotive force due to their oscillatory motion. This force drives a nonlinear current, at beat frequency, which produces the THz radiation. The influence of the external magnetic field on the optimization process of THz field amplitude is investigated numerically. A linear frequency chirp increases the duration of nonlinear interaction of laser pulse with plasma electrons and hence, enforces the interaction for longer duration. The presence of magnetic field further provides the additional momentum to the THz photon to obtain a significant gain in output yield. Our numerical simulations reveal that there is a significant enhancement in the THz field strength for optimized value of the chirp parameter and magnetic field.

Analysis of MHD and heat transfer effects with variable viscosity through ductus efferentes

A novel theoretical model for unsteady, non-isothermal flow with temperature variant viscosity for the Newtonian fluid in the presence of transverse magnetic field is studied in the ductus efferentes of human male reproductive tract. Importance of cilia for the fluid transport through ductus efferente is elaborated in this study. To investigate the flow, we considered a channel and constant temperature difference is imposed between the wall of channel. A mathematical model is developed and analytical solution is achieved with the help of Adomian decomposition method (ADM) for MHD heat and fluid flow with temperature dependent viscosity. Flow is modeled by considering assumptions that Reynolds number is small, so that inertial forces are insignificant and wavelength to diameter ratio is maximum, so that pressure can be assumed uniform in the channel. Solutions are presented for the exponential dependent viscosity on temperature. Effect of different flow parameters on the axial and transverse component of velocity are analyzed graphically. Pumping characteristic due to ciliary beat from one row of cilia to another are investigated. Lastly variation of different flow parameters on the trapped bolus and pressure are examined graphically.

Impact of magnetic field on flow past cylindrical shell using cell model

The present paper concerns about finding the impact of applied transverse magnetic field on parallel cylindrical shell of magneto viscous fluid by unit cell model. The considered flow is divided into three regions, bounded fluid region, porous region and inner cavity region, where the flow in the bounded and cavity regions is governed by Stokes equation and flow in the annular porous region is governed by Brinkman’s equation in the presence of magnetic field. The boundary conditions used at the fluid–porous interface are continuity of velocity components and stress jump condition for tangential stresses together with Happel and Kuwabara boundary conditions. Expression for volumetric flow rate in the presence of transverse magnetic field is calculated, and limiting cases leads to some well-known results. The effect of Kozeny constant versus fractional void volume for varying permeability, Hartmann numbers, viscosity ratio, separation parameter and stress jump coefficient is tabulated and represented by graphs. In the limits of the motion of porous cylinder and impermeable cylinder in the cell, the numerical values of the Kozeny constant are in good agreement with the available values in the literature.

Analysis of Entropy Generation Due to MHD Natural Convective Flow in an Inclined Channel in the Presence of Magnetic Field and Heat Source Effects

The main objective of the present paper is to investigate the entropy generation in a natural convective flow of a viscous incompressible electrically conducting fluid between two infinite non-conducting inclined parallel plates channel filled with a porous medium in the presence of transverse magnetic field and heat source. The governing non-linear partial differential equations are derived and solved analytically for velocity and temperature distribution with the help of the perturbation technique and their interpretation with physical parameters are shown through graphs. Also, the skin friction coefficient and rate of heat transfer in terms of Nusselt number are discussed numerically, and their numerical values for pertained physical parameters are presented through tables. In addition, total entropy generation rate and Bejan number due to heat transfer, fluid friction, and magnetic field are also discussed and their significance with all the pertained physical parameters are conferred through graphs. The results obtained through the present study are found a good agreement with previous research. It is perceived that an increment in the strength of the magnetic field declines the velocity of the fluid and prop-ups the rate of entropy generation. The present investigation has versatile applications in industries, engineering, and medical field, such as petroleum industries, chemical industries, metallurgy sciences, and treatment of cardiovascular disease in the medical field.

Micropolar mixed convective flow with Cattaneo-Christov heat flux: Non-fourier heat conduction analysis

The purpose of this study is to investigate the impact of thermal relaxation time on the mixed convection flow of non-Newtonian micropolar fluid over a continuously stretching sheet of variable thickness in the presence of transverse magnetic field. An innovative and modified form of Fourier?s law, namely, Cattaneo-Christov heat flux is employed in the energy equation to study the characteristics of thermal relaxation time. The governing equations are transformed into ODE, using similarity transformations. Fourth order Runge-Kutta numerical method is used to solve these equations. The effects of relevant parameters such as a micro-rotation parameter, magnetic parameter, thermal relaxation parameter, Prandtl number, surface thickness parameter, and mixed convection parameter, on the physical quantities are graphically presented. Results illustrate that fluid temperature enhances with the rise of thermal relaxation parameter, but it reduces with an increase in micro-rotation parameter. The skin friction decreases with a rise in micro-rotation and micro-element parameters. However, variation in the rate of heat transfer is quite significant for small values of thermal relaxation parameter.

Mixed Convective MHD Micro-Polar Fluid Flow in a Porous Medium with Radiation Absorption

An unsteady mixed convective flow of micro-polar fluid in a porous medium has been considered in presence of transverse magnetic field, Dufour effects and radiation. Effects of radiation absorption and heat source/sink are taken into account. The Buoyancy force leads to free convection and oscillatory free stream velocity is responsible for forced convection. Partial differential equations governed by conservation principles of mass, momentum and energy are solved analytically using perturbation scheme. Effects of various parameters on the governing fluid motion are shown graphically and numerically in tabular form.

Excitation of terahertz radiation by parametric mixing of four waves in magnetized plasma

THz radiation may be excited by nonlinear mixing of two counter-propagating laser beams, having frequency difference ω1∼ω2≥2ωp, in under dense plasma. Beating laser beams exert nonlinear ponderomotive force on plasma electrons and excite a nonlinear density perturbation. The nonlinear density perturbation drives a non-resonant space charge mode which may excite a pair of plasma wave and back scattered electromagnetic terahertz wave at resonance. The presence of transverse magnetic field further enhances the growth of THz wave. The transverse magnetic field also tunes the amplitude and frequency of THz wave. The maximum growth rate of excitation process Γ∼6.22×10−6 s−1 is achieved for applied magnetic field ∼175 kG.

Laser-induced breakdown spectroscopy of aluminum plasma in the absence and presence of magnetic field.

The effect of magnetic field on laser-induced breakdown spectroscopy of aluminum (Al) plasma has been investigated. Al targets were exposed to Nd:YAG laser pulses at different irradiances ranging from 1 GWcm-2 to 2.7 GWcm-2, under argon (Ar) and neon (Ne) environments at various pressures ranging from 5torr to 760torr and at different time delays from 0.42μs to 9.58μs. All spectroscopy measurements were performed in the absence and presence of transverse magnetic field of strength 0.9 tesla. When laser irradiance is increased by keeping the pressure (10torr) and time delay constant (1.25 μs), both excitation temperature (Te) and number density (ne) increase up to certain values. The same trend is observed for Te and ne when the ambient gas pressure of Ar and Ne is increased by keeping the irradiance (1.7 GWcm-2) and time delay constant. At higher irradiances and pressures, saturation is observed, which is attributed to the self-regulating regime of plasma. In the case of time delay, both electron temperature and number density decay exponentially, which is according to the adiabatic expansion model. It is revealed that emission intensity and electron temperature are higher in the presence of magnetic field as compared to the field-free case, which is attributed to magnetic confinement, as well as the joule heating effect. Plasma plume confinement is confirmed by analytical evaluation factor β. β is an analytical factor that is the ratio of plasma pressure to magnetic pressure, i.e., β=Plasma pressureMagnetic pressure. It confirms the validity of magnetic field confinement if β is less than 1. As the evaluated values of β are less than 1 for all cases, they confirm the validity of magnetic confinement.

Free convective flow of a couple stress fluid through a vertical porous channel in the presence of a transverse magnetic field

Nonlinear oberbeck convection of a couple stress fluid in a vertical porous channel in the presence of transverse magnetic field is investigated in this paper. Analytical solution is obtained using the perturbation technique for vanishing values of the buoyancy parameter. Numerical solution of the nonlinear governing equations is obtained using the finite difference technique to validate the results obtained from the analytical solutions. The influence of the physical parameters on the flow, such as couple stress parameter, Hartmann number, temperature parameter, porous parameter and buoyancy parameter are evaluated and presented graphically. A new approach is used to analyse the flow for strong, weak and comparable porosity cases. It is found that increase in porous parameter, couple stress parameter, Hartmann number and temperature parameters decrease the velocity considerably.Kathmandu University Journal of Science, Engineering and Technology Vol. 12, No. I, June, 2016, Page: 49-62

Unsteady MHD mixed convection along an exponentially stretching surface

Purpose This paper aims to investigate the unsteady mixed convection along an exponentially stretching surface in presence of transverse magnetic field applied at the wall and the opposing buoyancy flow. Design/methodology/approach The dimensional partial differential equations governing the flow field are transformed to non-dimensional coupled partial differential equations with the aid of suitable non-similar transformations. The resulting equations are then solved by the coalition of quasilinearization technique and the finite difference method. Findings Effects of volumetric heat source/sink, suction/blowing and other dimensionless parameters on velocity and temperature profiles are examined numerically. This investigation reveals that in presence of opposing buoyancy flow, the suction and volumetric heat source enhances the skin-friction coefficient, while the rise in the MHD increases the momentum boundary layer. Originality/value To the best of the authors’ knowledge, no such investigation has been carried out in the literature.

Interplay of non-conducting and conducting walls on magnetohydrodynamic (MHD) natural convection flow in vertical micro-channel in the presence of induced magnetic field

In this research paper, exact solution for fully developed magnetohydrodynamic (MHD) natural convection flow of viscous, incompressible, electrically conducting fluid in vertical micro-channel formed by electrically non-conducting and conducting infinite vertical parallel walls in the presence of velocity slip and temperature jump at the micro-channel walls is investigated. The influence of induced magnetic field (I.M.F) arising due to the motion of an electrically conducting fluid in the presence of transverse magnetic field is taken into consideration. Due to the presence of induced magnetic field, the momentum and induction equations are coupled. The exact solutions in dimensionless form have been obtained under relevant boundary conditions. The expressions for velocity field, the induced magnetic field, temperature field, induced current density and skin friction have been obtained. The effects of the various physical parameters appearing into the model such as rarefaction, fluid wall interaction, Hartmann number and the magnetic Prandtl number are demonstrated through graphs and table. The results indicate that, increase in Hartmann number and magnetic Prandtl number causes a pronounced reduction in volume flow rate.

A spectral relaxation method for three-dimensional MHD flow of nanofluid flow over an exponentially stretching sheet due to convective heating: an application to solar energy

The principle aim of the present investigation is to study the boundary layer analysis of nanofluid flow over a bidirectional exponentially stretching sheet in the presence of transverse magnetic field and also in convective condition. The effects of Brownian motion and thermophoretic diffusion of nanoparticle are considered from the mathematical model. Governing partial differential equations are reduced into coupled non-linear ordinary differential equations using suitable similarity transformations, further the system of equations are solved by a new spectral relaxation method. Validation of the results is achieved by comparison with emitting case from previous studies in the literature. Also, it has been shown that the convergence rate of the spectral relaxation method is significantly improved by using the method in conjunction with the successive over relaxation method. The results reveal the existence of interesting Sparrow–Gregg-type Hills for temperature distribution pertinent to some range of parametric values. Moreover the numerical data of drag coefficient, local heat and mass transfer rates are evaluated and analyzed. Effects of local Biot number on temperature and concentration profiles are qualitatively similar. Both the temperature and concentration profiles are enhanced for higher values of local Biot number.