Effect of electron magnetic trapping in a plasma immersion ion implantation system

In this work we describe a two-dimensional computer simulation of magnetic field enhanced plasma immersion implantation system. Negative bias voltage of 10.0 kV is applied to a cylindrical target located on the axis of a grounded vacuum chamber filled with uniform nitrogen plasma. A pair of external coils creates a static magnetic field with main vector component along the axial direction. Thus, a system of crossed E×B field is generated inside the vessel forcing plasma electrons to rotate in azimuthal direction. In addition, the axial variation of the magnetic field intensity produces magnetic mirror effect that enables axial particle confinement. It is found that high-density plasma regions are formed around the target due to intense background gas ionization by the trapped electrons. Effect of the magnetic field on the sheath dynamics and the implantation current density of the PIII system is investigated. By changing the magnetic field axial profile (varying coils separation) an enhancement of about 30% of the retained dose can be achieved. The results of the simulation show that the magnetic mirror configuration brings additional benefits to the PIII process, permitting more precise control of the implanted dose.     

Calculation of the force characteristics of a multi-coil suspension of a superconducting sphere

The theory presented in the accompanying paper [Ref. 1: Zh. Tekh. Fiz. 67(1), 3 (1997); Tech. Phys. 42, 1 (1997)] for the calculation of the magnetic field and the force characteristics of an electromagnetic suspension for a superconducting body is used to carry out specific calculations of the force characteristics of a multi-coil suspension of a superconducting sphere. Formulas are obtained for the dependence of the force and the stiffness, from which it is possible to approach the problem of the stable suspension of a superconducting sphere in the field of a system of circular currents. The problem of determining the magnetic field at the sphere is analyzed and the conditions are found for which it is less than the critical field. Zh. Tekh. Fiz. 67, 10–16 (January 1997)     

Effectiveness of the repulsion of electromagnetic coils with strength and magnetic field limitations

Mechanical power units utilizing electromagnetic interaction between coils are generally distinguished by compactness and ease of control. A coil-repulsion drive configuration is preferable for increasing the efficiency of such a device. One of the main limitations in choosing the parameters of stressed electromagnetic systems is mechanical strength. The application of superconducting coils has a number of additional limitations, for example, on the maximum magnetic field strength in the cross section of the coils. The problems of optimizing the dimensions of the electromagnetic system of a power unit consisting of two identical, coaxial, annular coils of rectangular cross section with opposing currents are investigated with allowance for strength and magnetic field limitations. Zh. Tekh. Fiz. 67, 124–127 (May 1997)     

Influence of nonuniformities of a magnetic-mirror field on the space-time characteristics of a long-pulse relativistic electron beam

An experimental investigation is made of the influence of local nonuniformities of a mirror-configuration magnetic field on oscillations of the space charge and the structure of a long-pulse relativistic electron beam. It is found that the outcome depends on the axial configuration of the nonuniformity. A nonuniformity near the cathode can substantially reduce the amplitude of the oscillations and improve the beam transport. The creation of a nonuniformity far from the cathode leads to an accelerated increase in the oscillations and causes spreading of the transverse structure of the beam. A possible explanation is given for the mechanism responsible for the influence of these local magnetic field nonuniformities assuming reflection of the cathode plasma and electron flux from the magnetic mirror, and also allowing for a jump in the drift velocity. Zh. Tekh. Fiz. 67, 83–88 (August 1997)     

Effect of a weak magnetic field on the state of structural defects and the plasticity of ionic crystals

The aim of this work is to examine the influence of a weak (on the energy scale) magnetic field on the state of dislocations and point defects in ionic crystals. It is found that complex point defects existing in a metastable state are sensitive to a magnetic field B∼1 T. The contributions are identified, and the kinetics of various types of reactions within the structural defects and between them leading to plastification of the crystals in a magnetic field are determined. The effect of light on the sensitivity of the point defects to a magnetic field is described, and the spectral characteristics of this effect are determined. A resonant effect of the combined action of a weak constant magnetic field and a high-frequency magnetic field on the dislocation mobility is found to occur when these fields satisfy the conditions of electron paramagnetic resonance. Zh. éksp. Teor. Fiz. 115, 605–623 (February 1999)     

Effect of unstable MHD modes on the confinement of a stellarator plasma

The results of an experimental study of the influence of unstable MHD modes on plasma confinement in an L-2M stellarator are presented. The spectral and statistical characteristics of turbulent plasma simultaneously at both the edge and center of the plasma are investigated. It is shown that at constant power of electron-cyclotron heating of the plasma the energy content of the plasma depends strongly on the strength of the externally applied vertical magnetic field used to adjust the position of the plasma column. Appreciable degradation of plasma confinement is observed for values of the vertical field such that ideal MHD modes become unstable in the greater part of the plasma column. This in turn is due to the formation of a magnetic configuration with a magnetic “hump.” At the same time, in the edge plasma the instability of resistive-balloon modes grows, and turbulent particle transport increases. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 6, 407–412 (25 March 1999)     

Magnetic system of a superconducting separated-sector cyclotron for hadron therapy

The development of a cyclotron magnetic system based on superconducting sector magnets is discussed. The cyclotron is conceived as a booster accelerator of a source of ¹²С⁶⁺ ions with energy of 400MeV/nucleon for the purposes of hadron therapy. The results of preliminary investigations aimed at developing such a facility have been reported in our previous papers. In this paper, we consider various configurations of the booster’s magnetic system for various field levels. We also analyze the effects of the positions and shapes of superconducting coils on the magnetic field and select the optimum configuration for the cyclotron’s magnetic system.     

Potential surface waves at the boundary of a metal with a magnetoactive plasma at finite pressure

The propagation of surface-type potential waves along the interfacial boundary of a plasma with an ideally conducting metal in an external magnetic field perpendicular to the boundary is examined. It is shown that a necessary condition for the existence of these waves in the system is a finite gas kinetic pressure. Dispersion relations for these waves and expressions for the penetration depth of the wave fields into the plasma are obtained, and they are studied numerically for various plasma parameters. The frequency region for propagation of these waves is found. It is also shown that in a nonzero external magnetic field a system of this kind has a range of frequencies in which the wave is a generalized surface wave. Zh. Tekh. Fiz. 69, 30–33 (November 1999)     

Complex magnetic susceptibility of uniaxial superparamagnetic particles in a strong static magnetic field

The magnetic relaxation of a system of single-domain ferromagnetic particles in the presence of a strong static magnetic field directed at an arbitrary angle relative to the particle anisotropy axis is investigated. A system of linear difference-differential equations for the moments (averaged spherical harmonics) is derived without recourse to the Fokker-Planck equation by averaging Gilbert’s equations with a fluctuating field. An exact solution (in terms of matrix continuous fractions) is found for this system. The relaxation times and spectra of the complex magnetic susceptibility are calculated. Fiz. Tverd. Tela (St. Petersburg) 40, 1642–1649 (September 1998)     

System of quantum wells in a parallel magnetic field

The energy spectrum and quantum states of electrons in a system of quantum wells in a strong magnetic field parallel to the heterogeneous boundaries are studied. The combined effect of the quantizing magnetic field and the potential of the system of quantum wells leads to a radical change in the electron dispersion relation owing to the appearance of one-dimensional Landau bands. The neighborhoods of the anticrossing points of the different bands correspond to an effective redistribution of the electron envelope functions, which becomes stronger as the magnetic field is raised. The character of the electron-state density in the size-quantization subbands is examined qualitatively in connection with the change in the system of isoenergy contours when a magnetic field is applied. Fiz. Tverd. Tela (St. Petersburg) 40, 1719–1723 (September 1998)     

Interference simulation in a cold collisionless moving magnetized plasma slab and (free surface of plasma slab)

Abstract

The pattern of intensity due to the interference in a cold collisionless magnetized moving plasma slab is investigated. Theoretically, it is assumed the mentioned layer has been located as a thin layer in an etalon Fabry–Perot interferometer surrounded by vacuum. The direction of external magnetic field is normal to the plasma surface and the plasma slab moves parallel with external constant magnetic field. By taking into account the relativistic considerations, the functions of transmitted intensity are presented coincident with the Airy function form in laboratory and plasma slab frames, respectively. The effects of plasma frequency, cyclotron frequency, thickness of plasma slab, and velocity of the plasma slab on band width, finesse factor, and visibility are simulated. Finally with the assumption that there are two wavelengths near together in incident electromagnetic beam the power resolution for this configuration are analyzed. All studies mentioned above have been done for S-polarized and P-polarized electromagnetic beams separately.     

Penetration of magnetic field into a long periodically modulated Josephson contact

A new approach to magnetic field profiling inside a Josephson contact is suggested. Its essence consists in analyzing continuous variation of a current configuration leading to a decrease in the Gibbs potential. With this approach, one can find a configuration into which the Meissner state turns when an external field slightly exceeds the upper boundary of the Meissner regime and trace the evolution of this configuration with increasing field. Calculations show that there exists critical value I _c of the pinning parameter in the range 0.95–1.00. This critical value separates two possible conditions of magnetic field penetration into the contact. At I > I _c, a near-boundary current configuration completely compensating for the external field inside the contact arises irrespective of the external field strength. At I < I _c, such a situation is observed only until the external field strength exceeds certain value H _max. Higher fields penetrate into the contact indefinitely deep. In nearboundary configurations, the magnetic field drops with increasing depth almost linearly. Its slope k has rational values, which remain constant within finite intervals of I. As I goes beyond a given interval, k rises stepwise and takes on another rational value. When an external magnetic field is switched on adiabatically, configurations with a maximal growth rate of the magnetic field are observed.     

Instability of the flat surface of a magnetic fluid in a cylindrical cavity in the presence of a vertical magnetic field

The problem of a magnetic liquid which completely fills a vertical cylindrical cavity in an undeformable horizontal layer of a magnet having the same magnetic properties as the liquid is considered. The entire system is immersed in a uniform vertical magnetic field. in a linear formulation of the problem an approximate solution in the form of series is obtained for the evolution of an initial small deviation of the free surface of the liquid from its flat equilibrium shape. An experiment is performed which shows that the initially flat free surface takes on a stable domed shape as the field strength is increased (from zero) and that a further increase in the field in a certain restricted range leads to the formation of an annular corrugation. The structures observed, which are the result of the nonlinear stage in the development of the initial perturbation, are qualitatively similar to the first two modes of the solution obtained. Zh. Tekh. Fiz. 68, 23–30 (January 1998)     

Coherent repopulation of the components of a three-level quantum system in the field of a pulsed bichromatic radio frequency wave

The coherent repopulation of a quantum system consisting of three nonequidistant levels in the field of a resonant bichromatic rf wave is studied. The atoms are assumed to have an impulsive interaction with the rf wave in which the pulse duration is less than any of the relaxation times. The hyperfine structure of gas atoms and a system of atomic oscillator levels in a magnetic trap are considered as examples of such a quantum system. It is shown that in the second case, the coherent repopulation effect can be used to cool neutral atoms in magnetic traps. Zh. éksp. Teor. Fiz. 113, 1181–1192 (April 1998)     

Three-dimensional diagrams of the regions occupied by induced Anger states in a multidomain magnetic medium

The regions of existence of Anger states in an iron garnet film are plotted and investigated for the first time in a space of three controlling parameters: the frequency and amplitude of the alternating field and the magnitude of the static bias field. It is shown that the dynamic spiral domains differ significantly in their configuration and properties in different regions. A quantitative parameter involving the velocity of the domain walls and the “looseness” (sparseness) of the dynamic array of magnetic domains is introduce to characterize the favorability of conditions for the formation of spiral domains. Fiz. Tverd. Tela (St. Petersburg) 40, 1865–1870 (October 1998)     

Effect of an electric field on the bifurcation of a biaxially stretched incompressible slab rubber

This paper describes the effect of an electrical field on the bifurcation phenomenon that appears in a biaxially stretched slab of Mooney-Rivlin material (M. Mooney, J. Appl. Phys. 11, 582 (1940)) subjected to equal dead loads. The main conclusion of the analysis is that the stretch ratio at which the bifurcation phenomenon appears crucially depends on the configuration of the system rubber slab-electrodes. The theoretical foundations of the present study are based on a recent formulation on this subject carried out by Dorfmann and Ogden (A. Dorfmann, R.W. Ogden, Acta Mech. 174, 167 (2005); J. Elasticity 82, 99 (2006)).     

An investigation on the magneto-optic properties of terbium gallium garnet under high magnetic field

The superexchange interaction on a magnetic ion may be represented by an effective field H_m = $\lambda$M in some paramagnetic materials, here λ is the coefficient of effective field and M = $\chi$H_e with $\chi$ being the magnetic susceptibility and H_e being the applied field. The variation of the equivalent $\lambda_{\chi}$with the dynamic applied field is given and the crystal field-splitting levels of the excited configuration 4f⁷5d¹ of the Tb³⁺ ion are calculated in the Tb₃Ga₅O₁₂. By means of the effective field H_m and the applied field H_e, the Faraday rotation of Tb₃Ga₅O₁₂ at 6 K and 41 K, under the high magnetic field and at 0.63 μm wavelength, are presented. Our calculated results are in agreement with the experimental data.     

Distribution of the electric field and current in a turbulent conducting fluid for small magnetic Reynolds numbers

Various aspects of the influence of an external magnetic field on turbulent flow of a conducting fluid are investigated. The distributions of electric variables are determined for weak magnetic fields (both the electric field and the current have nonzero values in this case). For very strong magnetic fields it is shown that turbulent motion acquires a two-dimensional character. The emergence of an electric current component perpendicular to the flow and to the magnetic field is described in the case of a temperature-stratified medium in the presence of turbulent heat flux. Zh. éksp. Teor. Fiz. 111, 528–535 (February 1997)     

Influence of the domain structure in a magnetizing field on the high-frequency susceptibility of a ferromagnet

The high-frequency properties of a biaxial domain-containing bulk ferromagnet in an external magnetic field with a modulated amplitude are investigated on the basis of the Landau-Lifshitz equations. The components of the frequency-dependent magnetic susceptibility tensor and the dependence of the resonant frequency of the uniform pulsation modes of a stripe domain on the amplitude of the external magnetic field are determined. Fiz. Tverd. Tela (St. Petersburg) 39, 671–675 (April 1997)     

Formation and focusing of electron beams in an electron-optical system with a plasma emitter placed in a magnetic field

The configuration and strength of a magnetic field are calculated in the regions of electron generation, acceleration, and transport in the electron-optical system of the plasma electron source. A magnetic field necessary for discharge initiation and maintenance is generated with a permanent magnet placed in a discharge chamber. It is shown that the magnetic field strength and configuration in these regions can be considerably varied by appropriately choosing the materials of electrodes forming the magnetic circuit. It is found that the beam focusing can be significantly improved by producing a quasi-uniform magnetic field in the electron-optical system of the plasma electron source.