High-energy radiation generated during electric explosion of a conductor in a longitudinal magnetic field

Our recent experiments [1] with the electric explosion of conductors in vacuum with an applied strong longitudinal magnetic field showed that this process was accompanied by radiation capable of penetrating through metal layers of considerable thickness. The high intensity of this radiation allowed it to be reliably detected outside the vacuum chamber using a photographic film with an amplifying luminescent (ZnS) screen situated in a paper envelope at a distance above 3 m from the region of explosion. In the same series of experiments, it was established that elements of the setup situated in the vicinity of the explosion exhibited residual radioactivity. This radioactivity was manifested, in particular, by flare spots on a photographic film in contact with an amplifying phosphor screen contained in a paper cassette that was placed inside the solenoid gap upon the discharge. No such explosion-induced radioactivity was observed in analogous experiments performed without an applied magnetic field. This paper presents the first results of investigations of the induced radioactivity, in which the activation detector was a gold ring situated at a distance of about 0.2 m from the axis of the exploding conductor.     

Jet emission from a capillary in a strong electric field

The phenomenon of multiple jet formation during a liquid efflux from a capillary in a strong electric field is considered. Conditions for the simultaneous emission of an arbitrary number of jets have been experimentally determined.     

Optical emission from laser-induced breakdown plasma of solid and liquid samples in the presence of a magnetic field

The optical properties of laser-induced plasma generated firm solid (Al alloy) and liquid (Mn, Cr, Mg, or Ti solutions) samples expanded across an external, steady magnetic field have been studied by atomic-emission spectroscopy. Various line emissions obtained from the constituents of the Al alloy and of the aqueous solution show an enhancement in intensity in the presence of an approximately 5-kG magnetic field. The enhancement of the signal was nearly a factor of 2 for the minor constituents of the solid samples and a factor of 1.5 for the elements in liquid phase. Temporal evolution of the emission from the solid sample showed maximum enhancement in emission intensity at 3-10-micros time delay after plasma formation in the laser energy range 10-50 mJ. However, for the liquid sample the maximum signal was for a gate delay of 3-25 micros the energy range 50-200 mJ. This enhancement in the emission intensity was found to be due to an increase in effective density of the plasma as a result of magnetic confinement when the plasma cooled after expansion. This enhanced emission was due to an increase in the rate of radiative recombination in the plasma.     

Computation of the magnetic field in massive conductor systems

Some analytical expressions are reported for the calculation of the magnetic induction and the vector potential in iron-free media due to slab-shaped elements in which a current flows uniformly or linearly distributed in one direction. It is seen that no matter what current distribution functions and conductor geometries are considered, they can be approximated by a series of slabs in which the current distributions are represented by a sum of linear and constant distributions. The algorithms can also be used to calculate the magnetic field in more complicated geometries and to evaluate the self- and mutual-inductance coefficients in systems with massive conductors     

A simple diagnostic method for plasma jet in strong magnetic field

An experimental study was carried out to examine the effect of strong magnetic field on the characteristics of argon plasma jet. An approximate expression was introduced to the distribution of emission line intensity and the color intensity. The distribution of the emission intensity was compared to that of the color intensity. The modified profiles of the spectral intensity agree well with those of the color intensity. The two-point analysis, that is, a calculation method with only two selected wavelengths in Boltzmann plots, was selected in the evaluation of excitation temperature because the calculation becomes significantly simple. The lateral distribution of excitation temperature obtained from the modified intensity becomes more accurate than that without the approximation. The radial distributions of excitation temperature based on the Abel inversion can be determined by the present approximation. It is found that the simple diagnostic method can utilize for understanding the characteristics on plasma jet.     

Shock structure deformation in plasma jet caused by strong magnetic field

The shock structure deformation in a plasma jet caused by a strong magnetic field was studied using an optical method. The plasma jet images in the enclosing vacuum chamber were taken with a digital single-lens reflex camera through a viewing window. Since the relative values of the measured light intensity are known to have a strong correlation with the number density of excited atoms, the vertical distribution of light intensity can be converted to a radial distribution of excited atom density using an Abel-inversion. The results of this conversion with a magnetic field were compared in the present experiments with those without the presence of a field. It is possible to obtain a smooth radial distribution of estimated number density using an approximate line. The density along the centerline increases obviously with the magnetic field. The minimal density point around the Mach disk was moved slightly upstream with the application of the field. The density distribution inside of the jet boundary was changed considerably by the application of the strong field. The jet boundary itself was not found to be affected significantly by the field although the boundary was found to be slightly contracted to the center axis with application of the field. It has been confirmed that the density distributions are mainly affected by the magnetic field at the corresponding location.     

Superconducting cylinder in a static longitudinal magnetic field

A study of the calculation of the magnetic field forces acting on a superconducting cylinder in a longitudinal magnetic field is reported. A computation algorithm and the results of field calculation by means of the boundary integral method, taking account of the cylinder edge singularity, are presented. The method makes it possible to compute the forces pressing the cylinder with a relative error below 1%     

Two-dimensional gas of electrons in a strong magnetic field

Translated from Izmeritel'naya Tekhnika, No. 2, pp. 4–7, February, 1990.     

Low-temperature specific heat of a semiconductor in a strong magnetic field

We calculate the electronic specific heat of a semiconductor (GaAs) at very low temperatures when subjected to a magnetic field strong enough to make the electron distribution nondegenerate. The transition to nondegeneracy is characterized by a large and rapid increase in the specific heat. For large fields the value approaches that of a one-dimensional nondegenerate gas, after first exceeding this value. Zeeman splitting, even with a very smallg factor (0.32), almost doubles the maximum in the specific heat as a function of field.On leave from Centre de Recherches sur les Très Basses Températures, Grenoble, France.     

Effects of strong magnetic field on plasma immersion ion implantation of dielectric substrates

In this paper the effects of a strong magnetic field on plasma immersion ion implantation (PHI) of dielectric substrates were investigated. A plasma fluid model and finite difference schemes were used to simulate a one-dimensional system of plasma immersion ion implantation. The effect of secondary electron emission from the electrode on PHI was also taken into consideration. It was found that the magnitude and direction of the magnetic field have slight effects on sheath thickness but have considerable effects on current densities in the y and z directions which are perpendicular to the direction of the electric field (the x direction). The simulations showed that the current densities in the y and z directions increased significantly with increasing magnitude of the magnetic field at a given fixed angle, the reason being attributed to the rotational force exerted on the ions by the magnetic field. With a fixed magnetic field, increasing the angle of the magnetic field, θ, with respect to the electric field produced a continuous increase in current density in the y direction from zero to its maximum at θ = 90° but the current density in the z direction could be described as saddle-shaped being zero at both ends.     

Magnetic field effect on electron emission from plasma

The influence of external magnetic field on the significant parameters of electrons from laser induced plasma (LIP) is investigated. A Q-switched Nd:YAG laser (1064 nm, 9-14 ns, 10 mJ, 1.1 MW) is focused on annealed, 4N pure (99.99%) Silver target (2 × 2 × 0.2 cm³) for production of plasma under vacuum ∼10⁻³ torr. Temperature, density and energy measurements for electrons were made by self fabricated Langmuir probe both in the absence and presence of external magnetic field (∼1.2 T) at different positions. The signals are recorded on 200 MHz UTT 2202 digital storage oscilloscope. The results thus obtained reveal decrease in electron temperature, energy and density in presence of external magnetic field. Confinement of plasma is also observed.     

Fabrication of textured alumina by electrophoretic deposition in a strong magnetic field

Textured alumina ceramics were fabricated by electrophoretic deposition in a strong magnetic field of 10 T (Tesla) followed by sintering. Single crystalline -alumina particles dispersed in aqueous media were aligned due to their anisotropic diamagnetic susceptibility and then deposited on a cathodic substrate. The degree of crystalline orientation of the as-deposited specimen characterized by X-ray diffraction was small but highly improved by sintering in the temperature range of 1273–1873 K. Microstructural observations showed the absence of any anisotropic grain growth.     

Initial stage of nematic twist-straining in strong magnetic field

The initial stage of straining of a planar-oriented nematic liquid crystal (NLC) cell in a strong magnetic field parallel to substrates is theoretically analyzed. It is pointed out that, in this case, the influence of boundaries on the development of instability is insignificant. Equations that describe the dynamics of NLC straining with allowance for flows are obtained in the framework of the Ericksen-Leslie-Parodi theory. It is established that simple wave solutions of these equations can be obtained in the given system geometry.     

Processing of non-ferromagnetic materials in strong static magnetic field

Static magnetic field processing of non-ferromagnetic materials has been of broad interest and been applied in such fields as drug delivery, colloid chemistry and engineering of materials containing particles. A ‘strong’ magnetic field refers to a ‘strong’ response from the manipulated material and can vary in definitions. The response is corresponding to a local interaction between the material and the local magnetic field, being influenced by the magnetic susceptibilities of the material and the surrounding/coated medium. By carefully designing the medium, a significantly ‘strong’ response from a weakly magnetic material can even be generated by a traditional magnet, i.e. magnetic flux density ∼0.01 T. Therefore, the ability to manipulate materials by using a magnetic field depends critically on the understanding of the principles of the magnetic properties of materials and their magnetic responses. This paper provides a critical discussion on the principles including magnetic field effect thermodynamics, magnetic energy, magnetic anisotropy and different magnetic forces during ’strong’ magnetic field processing of weakly magnetic materials (focusing on metallic materials). A series of case studies and the related magnetic field effect are subsequently integrated and discussed. Overall this review aims to provide a better understanding and efficient overview on the phenomenon principles in the field of magnetic field processing.     

Acoustic emission in a composite copper NbTi conductor

Acoustic emission generated in a composite copper multifilamentary NbTi conductor has been measured. Its source appears to be dissipation associated with the Lorentz force induced flux motions. It is demonstrated that acoustic emmision transducers can be used to detect a superconducting-to-normal transition.     

Dynamics of the magnetic field transport in a plasma opening switch

It is shown that the process of magnetic field penetration into the plasma bridge in a plasma opening switch is determined by the field diffusion near the magnetic piston, followed by the convective transport of magnetic field in the bridge. This transport is due to the field being “frozen in” to the flow of plasma behind the front of a shock wave, which is formed in the plasma accelerated by the magnetic field pressure.     

Organization of gold nanorods on a substrate using a strong magnetic field

The effects of magnetic processing on the organization of gold nanorods (AuNRs)/poly(styrenesulfonate) (PSS) composites using a strong magnetic field were examined by absorption spectra corresponding to surface plasmon on a glass plate and TEM images. The results in the absorption spectra and the TEM images showed that the side-to-side aggregation of AuNRs/PSS composites formed in the presence of a magnetic field directed horizontally to the surface of the sample. In the absence of the magnetic field, side-to-side AuNRs/PSS aggregates were not observed. The effects of magnetic processing are attributed to the induced magnetic dipoles of the AuNRs.     

The longitudinal electrical conductivity of metal-matrix composites at cryogenic temperature in the presence of a longitudinal magnetic field

We solve the Boltzmann equation in the relaxation time approximation with parallel E and B fields parallel to the continuous fibres reinforcing a metal matrix. It is shown that this solution is identical to that described by us elsewhere, except for the addition of the cyclotron frequency. The addition of the cyclotron frequency term shows that the electrons follow helical paths as they drift down the composite. The boundary considered is either the external or the internal surface of a cylinder representing the fibre. To apply this solution to metal-matrix composite materials we assumed that the cylindrical fibres are non-conducting cylinders in a matrix of pure crystalline metal. The electron mean free path is never greater than half the fibre separation distance. In a companion paper we discuss the application of this solution to metal-matrix composites.