Effects of an Applied Magnetic Field on Directional Solidification of Off-Eutectic Bi-Mn Alloys

1986 ◽  
Vol 87 ◽  
Author(s):  
J. L. Decarlo ◽  
R. G. Pirich
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Directional Solidification ◽  
Applied Magnetic Field ◽  
Transverse Magnetic ◽  
Chemical Analyses ◽  
Directionally Solidified ◽  
Solutal Convection ◽  
The Magnetic Field

AbstractOff-eutectic compositions of Bi-Mn were directionally solidified in applied transverse magnetic fields up to 3 kG to determine the effects odn thermal and solutal convection. For Bi-rich compositions, the magnetic field appeared to increase mixing as determined from thermal, morphological, chemical and magnetic analyses. For Mn-rich compositions morphological and chemical analyses suggest some reduction in mixing due to application of the magnetic field. Conductivity gradients in the melt are suggested as a possible mechanism for the observed results.

Numerical investigation of a plasma beam entering transverse magnetic fields

1989 ◽  
Vol 42 (1) ◽  
pp. 91-110 ◽  
Author(s):  
J. Koga ◽  
J. L. Geary ◽  
T. Fujinami ◽  
B. S. Newberger ◽  
T. Tajima ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Transverse Magnetic ◽  
Beam Momentum ◽  
Injection Velocity ◽  
Electron Mass ◽  
Particle In Cell ◽  
Plasma Beam ◽  
Beam Injection ◽  
The Magnetic Field

We study plasma-beam injection into transverse magnetic fields using both electrostatic and electromagnetic particle-in-cell (PIC) codes. In the case of small beam momentum or energy (low drift kinetic β) we study both large- and small-ion-gyroradius beams. Large-ion-gyroradius beams with a large dielectric constant ε ≫ (M/m)½ are found to propagate across the magnetic field via E × B drifts at nearly the initial injection velocity, where and M/m is the ion-to-electron mass ratio. Beam degradation and undulations are observed, in agreement with previous experimental and analytical results. When ε is of order (M/m)½ the plasma beam propagates across field lines at only half its initial velocity and loses its coherent structure. When ε is much less than (M/m)½ the beam particles decouple at the magnetic field boundary, scattering the electrons and slightly deflecting the ions. For small-ion-gyroradius beam injection a flute-type instability is observed at the beam-magnetic-field interface. In the case of large beam momentum or energy (high drift kinetic β) we observe good penetration of a plasma beam by shielding the magnetic field from the interior of the beam (diamagnetism). However, we observe anomalously fast penetration of the magnetic field into the beam and find that the diffusion rate depends on the electron gyroradius of the beam.

Possible Use of Magnetic Fields in Determining Pore Geometry of Porous Media

1971 ◽  
Vol 11 (03) ◽  
pp. 223-228 ◽  
Author(s):  
C.I. Pierce ◽  
L.C. Headley ◽  
W.K. Sawyer
Keyword(s):  
Magnetic Field ◽  
Porous Media ◽  
Magnetic Fields ◽  
Transverse Magnetic Field ◽  
Field Intensity ◽  
Flow Rate ◽  
Transverse Magnetic ◽  
Conducting Fluid ◽  
Petroleum Reservoir ◽  
The Magnetic Field

Abstract Simplified models, consisting of single, circular channels and channels of different length and diameter in series and parallel combinations, are used in conjunction with the equations of Poiseuille and Hartmann to demonstrate the dependence of the rate of flow of mercury in the models on channel dimensions when the models are subjected to transverse magnetic fields. Experimental tests conducted on mercury-saturated, glass-bead packs and a natural rock sample show that a magnetic field applied transversely to the direction of flow retards flow rate. The magnitude of the magnetic effect increased with increasing bead size and field intensity. Results of this work suggest that magnetic fields have potential in the study of the internal geometry of flow channels in porous media. Introduction The purpose of this work is to determine qualitatively by theoretical and experimental considerations whether or not a magnetic method has potential in the study of the basic properties of rock. The nature of the solid surface and the geometry of the pore network in petroleum-bearing rock plays an important role in the flow behavior of fluids in a petroleum reservoir. Hence, any technique of study that would provide new and additional information on the rock matrix would contribute to a better understanding of petroleum reservoir performance. One such technique appearing to offer performance. One such technique appearing to offer promise is in the area of magnetohydrodynamics. promise is in the area of magnetohydrodynamics. While much research, both theoretical and experimental, has been devoted to the problems concerned with the flow of conducting fluids in transverse magnetic fields in single channels, very little information has been published regarding the behavior of conducting liquids in porous media under the influence of a transverse magnetic field. Perhaps this dearth of information can be attributed Perhaps this dearth of information can be attributed to two main causes:the pores and pore connections are generally so small that intense magnetic fields are required to produce Hartmann numbers of sufficient magnitude to exert appreciable influence on flow rate, andthe extreme complexity of the channel systems in porous media render them intractable to theoretical analysis unless numerous assumptions are made to simplify network geometry. When a conducting fluid moves in a channel in a transverse magnetic field, a force is exerted on the fluid which retards its flow. The magnitude of flow-rate retardation increases with increasing field intensity, channel dimensions and channel-wall conductivity. These magnetohydrodynamic phenomena and theory have been described and developed by various investigators. Since a petroleum reservoir rock is an interconnected network of pores and channels within a rock framework, one would anticipate that the geometry of the network would exert some influence on the magnitude of the effect of a transverse magnetic field on the rate of flow of a conducting fluid therein. The purpose of this work is to demonstrate through the use of simple models and experimental data that the magnetic field effect on flow rate has potential for use in determining size and size potential for use in determining size and size distribution of pores in porous materials. THEORY Electromagnetic induction in liquids is not completely defined, and the complexities involved in many cases appear to defy true analytical expression. However, by applying some simplifying assumptions, these cases may be made tractable to solution to provide qualitative indication of system behavior. The following analysis was conducted in conjunction with laboratory tests to determine if magnet ohydrodynamics has possible potential as a tool for studying the internal geometry of porous systems. When a conducting liquid moves in a channel in a transverse magnetic field, an emf is developed in the channel normal to both the channel axis and the magnetic field. This emf causes circulating currents to flow in the liquid as shown in Fig. 1. SPEJ P. 223

scholarly journals Магнитоиндуцированные переходы в спектральной окрестности D-=SUB=-2-=/SUB=--линии атомов Cs: гигантский рост вероятностей переходов и различное асимптотическое поведение в растущем поперечном магнитном поле

2020 ◽  
Vol 128 (12) ◽  
pp. 1806
Author(s):  
А. Саргсян ◽  
А. Тоноян ◽  
Т.А. Вартанян ◽  
Д. Саркисян
Keyword(s):  
Magnetic Field ◽  
Applied Magnetic Field ◽  
Transition Probabilities ◽  
Theoretical Calculations ◽  
Transverse Magnetic ◽  
Strong Magnetic Fields ◽  
Small Width ◽  
Atomic Lines ◽  
The Magnetic Field ◽  
Good Agreement

Two types of magnetically induced transitions (MI transitions) in cesium atoms have been studied experimentally and theoretically. In the absence of a magnetic field MI, transitions are forbidden. As the magnetic field increases, the probabilities of MI transitions grow rapidly and can exceed the probabilities of transitions allowed in the absence of a magnetic field. The asymptotic behavior of the probabilities of MI transitions in strong magnetic fields is different. In the case of magnetically-induced transitions of the first type (MI1), with an increase in the applied magnetic field, the probability of these transitions increases enormously, and with a further increase in the magnetic field, the probabilities of these transitions tend to a constant value. In the case of magnetically induced transitions of the second type (MI2), with an increase in the applied magnetic field, there is also a giant increase in the probability of these transitions; however, with a further increase in the field, the probabilities of these transitions again tend to zero. It is shown that measuring the second derivative (SD) of the absorption spectra of Cs vapors enclosed in a nanocell with a thickness of L = 426 nm, corresponding to half the wavelength of the D2 line of cesium λ = 852 nm, allows one to perform Doppler-free spectroscopy. The small width of atomic lines and the linearity of the SD signal response in accordance with the transition probabilities make it possible to study individual atomic transitions in an external transverse magnetic field with an inductance of 0.5 to 5.3 kG. In particular, four MI transitions were investigated: two MI1 and two MI2. The theoretical calculations are in good agreement with the experimental results

scholarly journals The effects of a magnetic field on the morphologies of nickel and copper deposits: The concept of "effective overpotential"

2007 ◽  
Vol 72 (8-9) ◽  
pp. 787-797 ◽  
Author(s):  
Nebojsa Nikolic
Keyword(s):  
Magnetic Field ◽  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Magnetic Fields ◽  
Applied Magnetic Field ◽  
Electrode Surface ◽  
Copper Deposits ◽  
Perpendicular Orientation ◽  
The Magnetic Field ◽  
Scanning Electron

The morphologies of nickel and copper deposits obtained without applied magnetic fields, and with both parallel and perpendicular applied magnetic fields were examined by the scanning electron microscopy (SEM) technique. Changes in the morphologies of the metals caused by the effect of the magnetic fields are explained by the concept of "effective overpotential". The morphologies of the nickel and copper deposits obtained under parallel oriented magnetic fields were similar to those obtained at some lower cathodic potentials without an applied magnetic field. The magnetic field with a perpendicular orientation to the electrode surface increased the dispersity of the nickel and copper deposits. Nickel and copper deposits obtained under this orientation of the magnetic field were similar to those obtained at some higher cathodic potentials without an applied magnetic field. .

scholarly journals The connection of fine-structure photospheric features in active regions with magnetic fields

1968 ◽  
Vol 35 ◽  
pp. 201-201
Author(s):  
N. V. Steshenko
Keyword(s):  
Magnetic Field ◽  
Fine Structure ◽  
High Resolution ◽  
Magnetic Fields ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Active Regions ◽  
Transverse Magnetic ◽  
List Type ◽  
The Magnetic Field

1.The fine structure of the proton sunspot group of July 4–8, 1966 was studied on the basis of high-resolution heliograms. The comparison of the orientation between penumbral filaments and the transverse magnetic fields (observed by A.B. Severny and T.T. Tsap) shows that the direction of the filaments coincides in general with that of the magnetic field.2.Measurements of the magnetic fields of smallest pores (1·5″-2″) showed that the pores are always connected with strong magnetic field (in average 1400 gauss), which is localized at the same small area as the pore.3.Magnetic fields of faculae are concentrated in small elements with the dimension not exceeding 1·5″-3″. Magnetic-field strength H|| of about 45% of facular granules is within the limits of photographic measuring errors (approximately 25 gauss). For a quarter of all facular granules the strength H|| is from 25–50 gauss; about 30% of facular granules have H|| > 50 gauss, and sometimes there appear faculae with field strength of about 200 gauss. The magnetic-field strength of facular granules, which are found directly above spots, is 10–20 times less than the field strength of spots. This field is 80–210 gauss only.4.All observational data mentioned above show that the appearance of the fine-structure features in active regions is directly connected with the fine structure of magnetic field of different strength and different orientation. The study of high-resolution heliograms gives additional information about the fine structure of the magnetic field.

scholarly journals Effect of transverse magnetic fields on high-harmonic generation in intense laser–solid interaction

2016 ◽  
Vol 34 (3) ◽  
pp. 545-551
Author(s):  
J. Mu ◽  
F.-Y. Li ◽  
Z.-M. Sheng ◽  
J. Zhang
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Strength ◽  
Harmonic Generation ◽  
Second Harmonic ◽  
High Harmonic ◽  
High Harmonic Generation ◽  
Transverse Magnetic ◽  
Intense Laser ◽  
The Magnetic Field

AbstractThe effect of transverse magnetic fields on surface high-harmonic generation in intense laser–solid interactions is investigated. It is shown that the longitudinal motion of electrons can be coupled with the transverse motion via the magnetic fields, which lead to even-order harmonics under normal laser incidence. The dependence of the coupling efficiency and hence even harmonic generation with preplasma scale length and magnetic field strength are presented based upon particle-in-cell simulations. When the magnetic field is parallel to the laser electric field, the spectral intensity of the second harmonic is proportional to the magnetic field strength in a wide range up to 160 MG, while the situation with the magnetic field perpendicular to the laser electric field is more complicated. The second harmonic generation due to the magnetic field also tends to increase with the plasma density scale lengths, which is different from the high-harmonic generation by the oscillating mirror mechanism. With the increase of the laser spot size from a laser wavelength λL, both the magnetic field-induced harmonics and oscillating mirror high harmonics tend to increase first and then become saturated after 3λL. The magnetic field-induced second harmonic may be used to evaluate large self-generated magnetic fields developed near the critical density region and the preplasma conditions.

On the ignition of a self-sustained fusion reaction in a dense DT plasma

1984 ◽  
Vol 31 (3) ◽  
pp. 381-393 ◽  
Author(s):  
M. A. Liberman ◽  
A. L. Velikovich
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Fusion Reaction ◽  
Transverse Magnetic ◽  
High Magnetic Fields ◽  
Ignition Energy ◽  
Plasma Confinement ◽  
Fuel Density ◽  
Critical Ignition ◽  
The Magnetic Field

Ignition of a self-sustained fusion reaction in a strong magnetic field is studied. The critical ignition dimensions and the threshold ignition energy are calculated as functions of the fuel density and the magnitude of the transverse magnetic field. A new method for producing ultra-high magnetic fields is proposed which provides at once heating of the fuel by induction currents and localization of the micro-explosion by the magnetic field. Simple analytic estimates show that a certain combination of inertial, magnetic and wall methods of plasma confinement may decrease the ignition energy below 100 kJ.

Stimulated emission from a He–Cd hollow-cathode discharge in a magnetic field

1978 ◽  
Vol 56 (8) ◽  
pp. 1071-1076 ◽  
Author(s):  
C. P. Cristescu ◽  
A. I. Lupaşcu ◽  
I. M. Popescu ◽  
A. M. Preda
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Transverse Magnetic Field ◽  
Hollow Cathode ◽  
Power Output ◽  
Transverse Magnetic ◽  
Stimulated Emission ◽  
Atomic Transition ◽  
Simultaneous Oscillation ◽  
The Magnetic Field

The simultaneous oscillation on the 533.7 and 537.8 nm lines of Cd II of a hollow cathode laser with internal mirrors is studied as a function of an applied transverse magnetic field. The oscillations parallel to the field and perpendicular to it show different behaviour, but both of them are suppressed by magnetic fields in excess of certain values, which are different for the two oscillations. It is shown that the observed change of the power output with the increase of the magnetic field can be understood only if the effects of the field both on the plasma and on the atomic transition are taken into account.

Positron Annihilation Rate Variation in the Presence of Electric and Magnetic Fields

1975 ◽  
Vol 53 (2) ◽  
pp. 133-139 ◽  
Author(s):  
M. P. Srivastava ◽  
P. S. Grover
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Electric Field ◽  
Positron Annihilation ◽  
Applied Magnetic Field ◽  
Noble Gases ◽  
Rate Variation ◽  
Annihilation Rate ◽  
Electric And Magnetic Fields ◽  
The Magnetic Field

The variation of the positron annihilation rate λa in noble gases He, Ne, and Ar has been studied in the presence of an external applied magnetic field, when the electric field is kept constant. It is found that λa increases as the magnetic field is increased. In the case of Ar, the dependence is quite appreciable whereas in He and Ne it is comparatively smaller.

Radio Measurements of Coronal Magnetic Fields

1994 ◽  
Vol 144 ◽  
pp. 21-28 ◽  
Author(s):  
G. B. Gelfreikh
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Active Regions ◽  
High Sensitivity ◽  
Coronal Magnetic Field ◽  
Transverse Magnetic ◽  
Radio Sources ◽  
Radio Waves ◽  
Solar Active Regions

AbstractA review of methods of measuring magnetic fields in the solar corona using spectral-polarization observations at microwaves with high spatial resolution is presented. The methods are based on the theory of thermal bremsstrahlung, thermal cyclotron emission, propagation of radio waves in quasi-transverse magnetic field and Faraday rotation of the plane of polarization. The most explicit program of measurements of magnetic fields in the atmosphere of solar active regions has been carried out using radio observations performed on the large reflector radio telescope of the Russian Academy of Sciences — RATAN-600. This proved possible due to good wavelength coverage, multichannel spectrographs observations and high sensitivity to polarization of the instrument. Besides direct measurements of the strength of the magnetic fields in some cases the peculiar parameters of radio sources, such as very steep spectra and high brightness temperatures provide some information on a very complicated local structure of the coronal magnetic field. Of special interest are the results found from combined RATAN-600 and large antennas of aperture synthesis (VLA and WSRT), the latter giving more detailed information on twodimensional structure of radio sources. The bulk of the data obtained allows us to investigate themagnetospheresof the solar active regions as the space in the solar corona where the structures and physical processes are controlled both by the photospheric/underphotospheric currents and surrounding “quiet” corona.

Sign in / Sign up

Export Citation Format

Share Document