Effect Of Axial Magnetic Field Research Articles

Experimental investigation on the characteristic and voltage of low-current vacuum arc in vacuum OLTC

Due to vacuum interrupter's excellent interruption performance, an increasing number of on-load tap-changers (OLTCs) have chosen it as a load changeover switch in recent years. The stability of the arcing process is crucial for the interruption since the vacuum interrupter in OLTC must break current frequently with the requirement of long electrical life. In this paper, experiments on butt contacts and axial magnetic field (AMF) contacts applied in OLTC were carried out in a demountable vacuum chamber, and the arcing process was investigated by a high-speed camera. Investigations were conducted on the effects of opening speed, opening phase, current amplitude, and AMF on arc characteristics, e.g., arc expansion and arc voltage. The experiment findings demonstrated that expansion and instability of arc increased with higher opening speed, number of cathode spots moving to the inclined surface decreased with shorter arcing time, and that cathode spots' propensity to form group cathode spots increased with higher current. AMF lessened the impact of high opening speed and high current on the arcing process. The investigation carried out in this paper helps to better understand the characteristics of arc evolution and the influence of some key factors, which may serve as a guide for improving the design and vacuum arc control of vacuum OLTCs.

Effect of a dynamic axial magnetic field on a preconditioned single-wire Z-pinch

In this study, the effect and mechanism of a dynamic axial magnetic field on a preconditioned single-wire Z-pinch were investigated experimentally and theoretically. Optical diagnostic methods, including shadowgraphy, interferometry, Faraday rotation, and Thomson scattering, have been used to measure the parameters of magnetized plasmas. Compression of the azimuthal and axial magnetic fields was observed, and the suppression of the plasma instability was recorded and analyzed. The results showed that an external axial magnetic field could reduce the plasma instability and non-uniformity, but prolong the implosion time and weaken the compression ratio. In the implosion process with an axial magnetic field, the plasma rotated at a speed similar to that of imploding, which could be regarded as a stabilization method. A simplified model of the diffusion and compression processes of a dynamic axial magnetic field was developed to investigate the conditions for maximizing the amplitude of the axial magnetic field. Subsequently, the snowplow model was used to calculate the effect of axial magnetic fields on the implosion process and energy conversion.

Overlapping of linear optical spectra in metallic carbon nanotubes, Controlled by applied axial magnetic field and uniaxial strain

The excitons and absorption spectra of M11 and M22 transitions in metallic carbon nanotubes were calculated by the tight-binding model, under the combined effect of axial magnetic field and uniaxial strain. It is interesting to find that the separated absorption peaks induced by axial magnetic field will meet each other when the uniaxial strain is applied. At the same axial magnetic field, the first overlapping point is appeared for Mii−−2 and Mii+−1 exciton with small uniaxial strain, and the biggest uniaxial strain is needed for Mii−−1 and Mii+−2 exciton. When we change the magnitude of the axial magnetic field, the overlapping point displays different variation trend for four separate excitons. This overlapping phenomenon is also occurred for other metallic tubes: with bigger diameter, smaller uniaxial strain is needed. More important is that an useful tool is offered to regulate the optical properties of carbon nanotubes by applying simultaneously the axial magnetic field and uniaxial strain.

Effects of axial magnetic field on Fe-Ni interface macrosegregation of 9%Ni steel welds filled with Ni-based alloy

For the 9%Ni steel joint filled with nickel-based alloy, macrosegregation and wide partial mixing zone (PMZ) at Fe-Ni interface are critical factors to determine the cryogenic toughness. The pulsed gas metal arc welding (GMAW) assisted by the alternating axial magnetic field (AMF) is proposed to improve interface morphology and composition gradient. The welding without AMF assistance and with different AMF intensity are compared. The Lorentz force on arc and droplet caused by the alternating AMF is conductive to the stable transfer of viscous nickel-based alloy. The results show that AMF is effective to suppress the macrosegregation of Fe-Ni interface resulted from the temperature difference of melting point between base metal and filler metal. The temperature and flow speed of molten pool edge is enhanced by the stirring effect of AMF. The amount of filler metal in the PMZ of base metal increases. The melting point of mixing metal in PMZ decreases. Under the action of AMF, more PMZ is stripped from base metal. The PMZ continues to mix with liquid metal after entering the molten pool, instead of solidifying inside molten pool. After the alternating 12 mT AMF was applied, the cryogenic impact absorbed energy of fusion line increased from 0.85 J/mm2 to 1.29 J/mm2.

Numerical and experimental investigation of the removal of Fe impurity during different DS process under axial magnetic field

The effects of axial magnetic field on the different directional solidification (DS) process were studied by using a transient numerical model of heat and mass transfer and corresponding experiments. The shape of melt-crystal (m-c) interface, melt flow morphology, thermal stress and Fe impurity concentration in the crystal for different DS process have been studied. The simulation results indicate that axial magnetic field provided a slight convex m-c interface shape, better flow pattern, lower thermal stress as well as lower Fe impurity concentration throughout the entire DS process. To further verify the simulation results, multi-crystalline silicon (mc-Si) ingots were prepared and testing were carried out. The experimental results are in good agreement with the simulation results. The experimental results show that a slight convex m-c interface shape was obtained, and the Fe impurity concentration in the middle area of the ingot was lower and higher minority carrier lifetime could be achieved by using the axial magnetic field.

Converging strong shock wave from a cylindrical piston in a Van der Waals magnetogasdynamics with dust particles

In this study, by using the perturbation series approach, a global solution to the implosion problem is obtained for a quasi-linear hyperbolic system of partial differential equations (PDEs) describing a problem of strong converging cylindrical shock waves collapsing at the axis of symmetry in a Van der Waals dusty gas under the effect of axial magnetic field. This global solution provides the results of Guderley’s local self-similar solution which is valid only in the neighborhood of the axis of implosion. The similarity exponents and corresponding amplitudes are obtained in the neighborhood of the shock collapse. In addition, the values of leading similarity exponents are compared with the results obtained by Whitham’s method. The shock trajectory and flow variables (i.e., density, velocity, pressure and magnetic pressure) have been drawn for different values of the relative specific heat, the mass concentration of dust particles, the ratio of the density of solid particles to the initial density of the gas, Van der Waals excluded volume and shock Cowling number.

Investigation of electron acceleration in vacuum by a radially polarized laser pulse in the presence of helical wiggler field and axial magnetic field guiding

In this paper, electron acceleration by a radially polarized laser pulse in the presence of helical wiggler magnetic field and axial magnetic field has been studied. The governing equations on electron dynamics in the presence of these electric and magnetic fields were solved by the fourth order Runge-Kuta method. The effect of axial magnetic field and electron injection angle on energy gained by the electron was investigated. Numerical studies have shown that the final energy of an electron depends on the value of the magnetic field and the injection angle. It was seen that by applying a magnetic field of about 0.2 and the injection angle of about 11 degrees, the electron can gain final energy of about 3.8 GeV, which is 40 percent more than the case of zero degrees injection angle and the absence of external magnetic field.

Numerical investigation on the effect of axial magnetic field on metallurgical quality of ingots during vacuum arc remelting process

The electromagnetic stirring force generated by the axial magnetic field (AMF) interacting with the process current greatly affects the solidification process and consequently the metallurgical quality of ingots, but there are few studies about the effect of AMF on the multi-physics field involving solute transport during VAR process. Based on this, a three-dimensional full-size transient model has been developed to investigate the role of AMF on the metallurgical quality evaluated by the segregation defect and solidification quality in this paper. All essential considerations of the fluid flow, heat transfer and solute transport are incorporated in the model. Both the local solidification time (LST) and secondary dendrite arm spacing (SDAS) are adopted as indexes to characterize the solidification quality. The results show that the stirring force caused by the AMF greatly promotes the downward heat transfer and thus leads to deeper molten pool. The final value of volume-averaged segregation extent is greatly reduced by 24.13% as the AMF intensity increases from 0 to 50 G, while the difference of this value between 50 G and 100 G is only 1.96%. The volume-averaged values of the LST and SDAS are all reduced with the increase of AMF intensity, in which both values change from 1088 s to 190 μm without AMF to 890 s and 182 μm under 100 G. These results indicate that the application of AMF can significantly improve the metallurgical quality of ingots, but this effect becomes more and more limited with the increase of AMF intensity.

3D transient MHD simulation of DC breaking vacuum arc based on artificial current zero

In the vacuum DC circuit breaker based on the artificial current zero, the change of arc luminosity delays the change of current value significantly in the fast current-zero stage. This phenomenon has impacts on the breaking capacity of the DC vacuum circuit breaker. Therefore, it is necessary to study the dynamic characteristics of the arc plasma under the above condition. In this work, a 3D transient magneto-hydro-dynamic model based on the commercial cup-type axial magnetic field (AMF) contact is established to study this phenomenon. The simulation results show that the fast current-zero stage is too short for the plasma to diffuse. The changes of the physical characteristics of the arc plasma lag the change of current value. Moreover, the magnetic field hysteresis caused by the eddy current on the electrode occurs in this stage, resulting in a continuous stronger AMF. It makes the distributions of the plasma uniform, while the diffusion of the arc plasma reduced at low currents, which is detrimental to the post-arc dielectric recovery stage. In addition, in the fast current-zero stage, the AMF near the contact slot is smaller than in other areas. This indicates that the slotting is effective in suppressing eddy currents and avoiding the negative effect of excessive AMF on plasma diffusion at this stage. The simulation results are consistent with the experimental results.

Optical Investigation of Excited Species Distribution in Low-Current Vacuum Discharges

It is well-known that when high currents flow through a vacuum gap, anode spots are formed on the anode surface. However, anode flare phenomena are also observed in low-current vacuum discharges. The objective of this article is to experimentally observe the spatial distribution of excited Cu atoms and ions generated from a single cathode spot (CS) and to interpret the mechanism of the anode flare at low currents (40–80 A). Optical emission spectroscopy (OES) and laser-induced fluorescence (LIF) techniques have been used for investigating low-current vacuum arc discharge confined to axial magnetic fields (AMFs). The effects of AMFs and arc currents on the axial distribution of the radiation intensity were investigated for different copper ionization states (Cu I and Cu II). The highest luminance was found near the electrodes for both excited neutral copper atoms and ions, and only weak spectral lines of excited Ni atoms were detected in the near-anode region. With increasing the external AMF, a bright “spot” appeared near the anode surface. In the visible light range, excited atoms were the main contributor to anode flare in low-current vacuum discharge. As measured by LIF, the density of copper atoms near the anode increased from 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 10^{17}$ </tex-math></inline-formula> to 14 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 10^{17}\,\,\text{m}^{-3}$ </tex-math></inline-formula> when the applied magnetic fields increased from 31 to 74 mT. The anode flare contains far more excited atoms from the cathode material than the anode material. They are the results of cathodic plasma expansion to reach the anode after charge neutralization and reflection on the anode surface. For the single CS, the observed fact that a tiny number of atoms leave the anode surface and participate in the anode flare is more likely the result of a sputtering effect rather than thermal evaporation by cathode electron stream.

Numerical Studies on the Effects of Axial Magnetic Fields and Cooling Intensities on the Macrosegregation of Directionally Solidified Ni-Based Alloys: Elimination of Thermal Convection and Stabilization of Interdendritic Liquid Flow

Numerical Studies on the Effects of Axial Magnetic Fields and Cooling Intensities on the Macrosegregation of Directionally Solidified Ni-Based Alloys: Elimination of Thermal Convection and Stabilization of Interdendritic Liquid Flow

Effects of axial magnetic field in a magnetic multipole line cusp ion source

Experiments have been performed to study the effects of axial magnetic field on plasma and ion beam parameters in a magnetic multipole line cusp ion source. Studies performed on ring cusp and Kaufmann type ion sources suggest that the axial component of magnetic field may help in improving the ion extraction current at a low discharge power. The line cusps ion sources have been used since long to produced uniform beams, however, they lack axial component of the magnetic field. These ion sources generally suffer from low efficiency possibly due the absence of axial magnetic field. In this work, an additional magnetic coil is added at various axial positions between the back-plate and the plasma grid of the multipole line cusp ion source. We have investigated the effects of axial magnetic field on the discharge efficiency and source parameters like beam current and uniformity in the multipole line cusp ion source. The beam profiles are obtained using an eleven-channel faraday cup array to estimate the effects of the axial magnetic field on beam uniformity and divergence. Initial studies suggest a reduction of beam divergence with increasing axial magnetic field. A significant rise in the beam current and the discharge current is also observed when the axial magnetic field is increased. Particle trajectory simulation using the CST-Studio suite is utilised in understanding the role of confinement of primary electrons behind the improved performance of the ion source.

Mechanism Analysis of the Effect of Axial Magnetic Field on Low Pressure Glow Discharge

The effect of axial magnetic field on glow discharge parameters at low pressure is studied in this article. First, Paschen&#x2019;s law under axial magnetic field is modified. The results show that under the same conditions, the magnetic field will increase the breakdown voltage of glow discharge. The experimental results are consistent with the theoretical analysis, but the experimental value is higher than the theoretical value. Second, the physical model of parallel field glow discharge is established, and the plasma density of glow discharge under different pressure, discharge spacing, and magnetic field is studied. The results show that the plasma density increases with the increase in magnetic field at low pressure; at high pressure, the larger the magnetic field, the smaller the plasma density. At the same position, the plasma density increases with the increase in discharge spacing in weak magnetic field, and it decreases with the increase in discharge spacing in strong magnetic field. When the surface area of the magnet is only 20&#x0025; of the surface area of the anode and cathode, the radial nonuniformity of the magnetic field makes the plasma density reach the maximum when the radial <inline-formula> <tex-math notation="LaTeX">$r =0$ </tex-math></inline-formula>.

On the evolution of magnetic shock wave in the mixture of gas and small solid dust particles

The paper aims to analyze the evolutionary behavior of weakly nonlinear waves propagating in one-dimensional unsteady flow of perfectly conducting compressible fluid subjected to a transverse magnetic field with dust particles. The method of progressive wave approach is utilized to determine the evolution equation characterizing the propagation of wave and also obtained the condition for first wave breaking at finite time. Further, we analyze the behavior of acceleration wave propagating in the medium considered. Also, the propagation of disturbances in the form of sawtooth wave (half N-wave) is studied here. It is observed that the presence of mass fraction of solid particles (kp) and β both causes to slow down the decay process. Also, the effect of axial magnetic field is to increase the growth rate of sawtooth wave (Half N-wave) as compared to in the absence of axial magnetic field. Further, the effect of magnetic field is to slow down the decay process in the presence of mass fraction of solid particles (kp).

Research on the current-zero period of vacuum arc interruption and equivalent model of post-arc gap

In this paper, the current breaking experiments of vacuum interrupter are conducted and the waveforms of voltage and current are obtained. The results show that there is current instability phenomenon when the value of is low and the value of instability-initiation current decreases as the value of increases. The number of voltage spikes will also decrease and irregular oscillation will weaken. According to the experimental results and theoretical analysis, the ‘memory characteristic’ of plasma is proposed and a new mathematical model of post-arc initial plasma density is estabilished which will provides a new method for the calculation of the sheath growth. The equivalent circuit model of post-arc gap is established to analyze the transient recovery voltage. The equivalent parameters in the circuit are obtained by the calculation of sheath growth and plasma density and verified by comparison with measurements. Through the comparison of experimental results between the axial magnetic field (AMF) contact and the butt contact, the effects of AMF on post-arc plasma density and sheath growth are analyzed. The results show that AMF can make the post-arc plasma density higher and the sheath growth slower.

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.

Distributions of magnetic field and current in pinching plasma flows: effect of axial magnetic field

Distributions of magnetic field and current in pinching plasma flows: effect of axial magnetic field

The Influence of TMF and AMF Components on Arc Movement Characteristics in Spiral-Slot Contacts

Spiral-slot contacts produce an axial magnetic field (AMF) and the transverse magnetic field (TMF). The magnetic field between TMF contacts will affect the breaking performance of vacuum interrupters. In order to study the effect of TMF and AMF on arcing process and movement characteristics, five contacts with different TMF and AMF, but the same ratio of TMF to AMF, were designed and experimentally investigated in a demountable vacuum chamber. The arc movement phenomenon under different TMF and AMF was obtained. It was found that increasing TMF and AMF could reduce the arc jets to the outer electrode, and arc stagnation was more likely to occur in the later stage of the movement. The influence of TMF and AMF on arc movement characteristics and the utilization of contact surfaces was investigated. With the increase in TMF and AMF, the number of arc rotations increased, and the range of arc movement and the utilization of contact surface increased first and then decreased. Simulations were performed to analyze that the influence mechanism of TMF and AMF on arc movement characteristics was investigated. With the increase in TMF and AMF, the tangential force of the concentrated arc was increased, and the radial force was reduced.

Effect of axial magnetic field on TIG welding–brazing of AA6061 aluminum alloy to HSLA350 steel

External magnetic field (EMF) is favored for application in welding, due to its positive effects on joint quality. In the present study, the effect of EMF on AA6061 Al alloy/HSLA350 steel welded joints were investigated. When no EMF, coarse Al grains were formed on the welded joint. The second phase including Al–Si eutectic and large Al3FeSi slats exists in the joint fusion zone. Refinement of the Al matrix and second phases were produced as a result of the Lorentz force generated by the 380 mt EMF treatment. The joint strength with EMF treatment at welding current 60 A increased from 170 MPa (without EMF treatment) to 195 MPa and the joint ductile fracture position was on the Al alloy base material under this same condition, due to the fine grained strengthening and dispersal strengthening of the second phases, meanwhile, the intermetallic compounds (IMCs) layer at the Al/steel welding seam interface was significantly reduced.

The Effect of Axial Magnetic Field on The Breakdown Voltage of Air at Low Pressure

To add more details about the effect of the axial magnetic field on the plasma profile, the breakdown voltage of air was investigated at low pressure (9-15 Pa) in the presence of axial magnetic field (0.01-0.04T). The air was ignited by a DC voltage between two plain electrodes of aluminum separated by a distance (8.5cm). The measurements showed that the discharge voltage decreases to a minimum value, then returns to increase over the minimum with increasing the magnetic field strength, at all pressures in the range. It was also observed that a maximum decrease in the discharge voltage is obtained near the minimum of Paschen curve from the right side. The decrease in the discharge voltage was caused mainly by the effect of magnetic flux density on the diffusion of charged particles to the walls, especially on that of free electrons which were borne during the breakdown process.