Far infrared radiation generated during femtosecond laser excitation of a semiconductor surface in magnetic field

The effect of a magnetic field on the generation of electromagnetic radiation pulses in the terahertz frequency range from a semiconductor surface excited by an ultrashort laser pulse is considered within the framework of a hydrodynamic model. The appearance of a photocurrent component in the Hall direction leads to elliptic polarization of the microwave radiation and to a severalfold increase in the generation efficiency. This is consistent with the results of Monte Carlo modeling of a self-consistent field and photogenerated carrier dynamics.     

Soft X-ray emission from the plasma of a conductor exploding in a strong longitudinal magnetic field

Previous experiments with the electric explosion of conductors in a strong (50 T) longitudinal magnetic field showed the formation of a relatively low-density plasma around the central part of the explosion channel, which exhibited expansion at a velocity on the order of 10–20 km/s [1, 2]. Expansion of the plasma was accompanied by displacement of the magnetic field from the explosion channel, which was manifested by a diamagnetic signal. An analysis of the plasma energy balance is hindered by the lack of reliable data about radiative energy losses. Here, we report the first experimental results on the radiation pulse kinetics and the first estimates of the radiation energy.     

Pressure generated by the electric explosion of metal foils

We have measured the pressure generated by the electric explosion of various metal (Cu, Al, Fe, Ta, Ti, Pb, W, and brass) foils. The pressure amplitude as a function of the specific energy supplied to the exploding foil is well approximated by a linear dependence.     

Pressure waves generated by a nanosecond electric explosion of a tungsten wire in water

We have studied pressure waves generated during a nanosecond electric explosion of 70-μm-thick tungsten wires in water. The measurements were performed at a distance of 3–8 mm from the exploding conductor. In order to reduce the error caused by two-dimensional effects, we used pressure sensors with dimensions not exceeding 3 mm. The results of measurements revealed a two-component structure of the electric-explosion-induced shock wave.     

Evaluating pressure generated by the electric explosion of a foil ring in water

The pressure developed by an acoustic shock wave and the integral of action of the electric discharge formed during the electric explosion of a flat foil ring in a condensed medium are evaluated by assuming a quasi-stationary character of the process.     

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%     

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     

Calculation of electric field and force on conductor particles with a surface film

This paper applies the method of images, an analytical method, to calculate electric field on conductor particles with a surface film. The method utilizes the multipole re-expansion and appropriate fundamental solutions. Electric field is repetitively calculated so as to satisfy all the boundary conditions. The main advantage over numerical field-calculation methods is that high accuracy can be realized as neither approximation nor discretization of the particle surface or the film thickness is involved. The calculation results for arrangements of a particle chain under a uniform field show the field intensification due to the film thickness and electrical properties. We have also carried out field calculation by the boundary element method (BEM), and compared the results with the analytical ones. The results by the BEM exhibit higher error with decreasing film thickness. Force and yield stress have been calculated from the electric field and compared with experimental results. The comparison shows a good agreement for the ac field, but significant difference for the dc one.     

The longitudinal electric current in Maxwellian collisional plasma generated by a transverse electromagnetic wave

Allowance for nonlinearity leads to the appearance of the longitudinal electric current directed along a wave vector. This longitudinal current is orthogonal to the known transverse classical current at linear analysis. The kinetic Vlasov equation for collisional Maxwellian plasma is used upon the determination of the longitudinal electric current. The Bhatnagar–Gross–Krook collision integral is applied. The electron distribution function is taken from the Vlasov equation in the approximation quadratic over an electromagnetic field. The formula for the calculation of the electric current is derived. When the collision frequency tends to zero, all results for collisional plasma transfer into a corresponding known formula for collisionless plasma. The case of small wave numbers is considered. The value of the longitudinal current when the collision frequency tends to zero also transfers into the known expression for the current in collisionless plasma. The dependence of the dimensionless current on the wave number, frequency of electromagnetic field oscillations, and the collision frequency of electrons with plasma particles is studied.     

Effect of a magnetic field on ionizing electric discharge in air

We have studied the effect of an external magnetic field on the form and structure of high-voltage gas discharge used for the ionization of airflow to the degree (∼10⁻⁵) necessary for the creation of a magnetohydrodynamic (MHD) control system. The experimental setup based on a shock tube comprised a magnetic field generation system, a 2–4 μs-pulsed, high-voltage, ionizing discharge system and an expanding MHD channel with a set of electrodes oriented along and across the magnetic field. In the first series of experiments, the discharge current was closed along the magnetic field lines; in the second series, the current was closed in the transverse direction. The patterns of discharge glow at various values of the magnetic induction were monitored. It is established that the most effective configuration employs periodic pulsed ionizing discharge in the transverse direction and a system of electrodes closing the magnetic-field-induced current.     

A positive column of electric discharge in a transverse magnetic field

The influence of a transverse magnetic field on the characteristics of the positive column of electric discharge was investigated in both the diffusion and nondiffusion approximations. All solutions in the diffusion approximation were derived in analytical form. It is shown that with the enhancement of the magnetic field induction, the concentration distributions of the plasma and particle fluxes to insulated walls become nonsymmetric, the concentration maximum displaces in the direction of the magnetic force action, and the ion flux concurrent with this force may exceed substantially the ion flux in the opposite direction. The dependences of discharge parameters on the induction value are defined for helium. It is demonstrated that there is a maximum value of induction which bounds from above the range of magnetic fields, where the stationary state of the positive column is possible. In the range allowed for the stationary state, a single induction value is matched by two different modes of the positive column varying in values of the electron energy, drift speed, and electric-field strength. By means of the transverse magnetic field, it is possible to vary the electron energy within wide limits (from a few electronvolts to several hundred electronvolts).     

Conductance of carbon nanotubes in a transverse electric field and an arbitrary magnetic field

The electronic and transport properties of carbon nanotubes subject to the influences of a transverse electric field and an arbitrary magnetic field are studied by the tight-binding model. The external fields would modify the energy dispersions, destroy the state degeneracy, change the symmetry characteristics, alter the energy gap, modulate the electron effective mass, and create extra band-edge states. The energy gap and the electron effective mass exhibit a rich dependence on the field strength, the magnetic field direction, and the types of carbon nanotubes. A semiconductor-metal transition would be allowed for certain field strengths and magnetic field directions. The variations of energy dispersions with the external fields will also be reflected in the conductance. Special features of the conductance, such as single-shoulder, multi-shoulder, and spike structures, are predicted.     

The influence of longitudinal magnetic field on recombination radiation of low-pressure glow discharge in hydrogen and helium

We study the influence of longitudinal magnetic field on the radiation of low-pressure glow discharges in hydrogen and helium. We conducted experiments under a pressure in a discharge chamber of 10–20 Pa and a discharge current of 10–20 mA. A 0–1600 G magnetic field influenced only the cathode parts of the discharge, negative glow, and the dark Faraday space. The electron temperature and density were measured by the two-probe method as a function of magnetic field. We studied the dependence of the intensity of radiation in the spectral lines and continuous spectrum on magnetic field induction. We discovered that, under the action of magnetic field, discharge in hydrogen and helium is compressed and its glow volume increases by a factor of 20–25. In contrast, the radiation intensity in the lines and continuous spectrum increase by a factor of 100–200. We found a strong discrepancy in the measured intensity of the continuous spectrum into spectral ranges with calculation of electron-ion recombination.     

Nonuniformity of the pressure wave formed during electric explosion of a foil

Temporal waveforms of pressure amplitude in various regions of a flat electrically exploded foil (EEF) have been measured. The results of measurements have been used to reconstruct the temporal evolution of spatial pressure profiles generated by the EEF. The measurements were performed using quartz pressure sensors arranged in various (central and peripheral) regions of the free surface of a dielectric substrate glued to the foil. The obtained data show that the electric explosion starts at the edges of a foil, which is followed by stronger pressure buildup in the central axial region of the EEF.     

Distortion of the electric field distribution induced in the brain during transcranial magnetic stimulation

In this study, the effects of various parameters, such as the geometrical head model, conductivity condition and stimulus position, on the electric field induced in the brain during transcranial magnetic stimulation are thoroughly examined. It is revealed that the distortion of the induced field causes the movement of the maximum field point and also leads to the deviation of the field focusing region from the stimulus centre. Numerical results show that the induced field distortion is primarily caused by the spatial asymmetry of the head geometry with respect to the stimulus centre and the induced field distribution is further deformed by imposing the heterogeneous conductivity condition. For verification purposes, an elaborate phantom head model has been constructed and the experimental results have been compared to the predicted fields yielding good agreement.     

Magnetic field distribution in a ferromagnetic conductor

The magnetic field distribution in a cylindrical ferromagnetic conductor is determined for the case of a direct current flowing along the axis of the cylinder and a constant external magnetic field applied in a direction transverse to the current flow. The Gauss-Seidel iteration method is employed to obtain the vector potentials for different values of current and external field with the aid of a digital computer. The magnetic fields are then calculated from the resultant vector potentials. Calculations are carried out for currentI = 1.5A, radius of the cylindera = 2mm, and external magnetic fieldB_{0} = 0to 0.6 Wb/m².     

Streamlining of a cylinder with an electric arc rotating in a magnetic field

Streamlining of a circular cylinder with a localized heat source modeling an MHD actuator in which the plasma arc channel moves along the cylinder surface under the action of the Lorentz force in a radial magnetic field is studied experimentally and simulated numerically. It is shown that the presence of a moving heat release region leads to a break in the symmetry in cylinder streamlining by the external flow and the appearance of a nonzero lift force and circulation.     

Temperature-dependent resistivity of a flat conductor and the temperature,current, and electric field patterns

Characteristic physical quantities have been determined as functions of the nonlinearity criterion and the frequency criterion for a flat conductor heated by a current having stationary and current distributions but temperature-dependent conductivity.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 29, No. 3, pp. 535–537, September, 1975.     

Analysis of open-flame electric arc in transverse magnetic field

The distribution of temperature and pressure, electromagnetic fields, and the structure of flow under the effect of an external transverse magnetic field are determined using a three-dimensional magnetogasdynamic model of a steady-state curved arc. The calculation results are consistent with the experimentally observed properties of the arc, such as stabilizing effect of current strength and the magnetogasdynamic mechanism of arc extinction.     

Heat transfer mechanism in an electric arc moving through a magnetic field

A model of an electric arc moving through a magnetic field is analyzed. Numerical estimates and universal characteristics indicate that the basic mechanism of heat removal from the arc column is the transmission of energy by the gas stream flowing inside the arc.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 23, No. 4, pp. 673–680, October, 1972.