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Betatrons have the advantages of small size, lightweight, and simple operation. They are widely used in non-destructive testing, cargo, and vehicle safety inspection systems. Magnetic field distribution is an essential parameter of betatrons and has been investigated via experimental methods. Recently, simulations have been performed for the magnetic field distribution generated by different magnetic pole parameters. In this study, the finite element method is employed to simulate the magnetic field distribution. The effects of the different magnetic end face opening angles, pole protrusion sizes, number of central magnetic pads, and magnetic pole bottom width on the magnetic field distribution are simulated. Based on the simulation results, magnetic poles are developed, and the magnetic field distribution is measured by a gauss meter. The relative error of the measured and simulated equilibrium orbit is 2.1 %, and the relative error of the magnetic field decay index is 3.3 %. The magnetic field distribution can satisfy the essential conditions that the magnetic field at equilibrium orbit of the betatron is equal to half of the average magnetic field within equilibrium orbit and the magnetic field decay index is greater than 0 and less than 1. The results show that the finite element simulation method and established model have high reliability and effectively improve the design accuracy of magnetic poles. [ABSTRACT FROM AUTHOR]

This paper presents a novel rectangular voice coil motor (VCM) used in ultra-precision motion stage. The new analytical model of magnetic field is proposed to calculate the Lorentz force, this analytical model indicates that Lorentz force will change when coil of the VCM moves in the permanent magnet air gap. The result of finite element analysis and experiment are used to verify this analytical model. This method offers a theoretical basis for the design and optimization of the VCM. [ABSTRACT FROM AUTHOR]

A two-dimensional axisymmetric particle-in-cell code with Monte Carlo collision conditions has been used to study particle energy transfer in plasmas and conversion in applied magnetic and electric fields appropriate to coaxial acceleration. The research incorporates a computation scheme with: a model of single particle magnetic interactions; a model of single particle interactions in electric and magnetic fields; and a model of multi-particle collisional interactions in order to understand the energy transfer processes and conversion mechanisms of charged plasma particles. This approach predicts electron and ion motions along with their energy variations for physical conditions that occur in the related models; the results allow comparison with experimental data for magnetic field strengths of 0.01-0.05 T and electrode voltages of 22.0-32.0 V. With the incorporation of magnetic and electric field effects on charged particles, the multi-particle model includes electron-neutral ionization collisions, ion-neutral charge exchange collisions, and electron-ion Coulomb collisions. This research presents a new approach to achieve an underlying understanding of the plasma energy transfer and conversion in the external electric and magnetic fields that is not possible using magnetohydrodynamics continuum representations. Results indicate the following innovative conclusions: (1) Radial and azimuthal energies of magnetized electrons are converted into an axial electron energy component in the diverging magnetic field, and the azimuthal kinetic energy of unmagnetized ions is converted into axial and radial components. (2) In electric and magnetic fields, electric field energy is primarily converted into axial kinetic energy of magnetized electrons by the energy transformation effects of magnetic fields, and for unmagnetized ions, the radial kinetic energy component dominates in the conversion of electric field energy. (3) For the collisional plasma, electron kinetic energy tends to increase (or decrease) to a terminal value since electrons lose energy in collisions then gain energy again from the field. Ions acquire most energy directly from the electric field, although part of the electric field energy arrives to the ions by collisions. Further, the ion axial energy component dominates the total ion energy. The collision processes are found to be integral and essential for the conversion of the plasma non-directed energy gain to be converted into the resultant axial energy, the magnitudes of which are found to be in agreement with experimental results. [ABSTRACT FROM AUTHOR]

Three-dimensional simulations of the expansion of plasma injected into a dipole magnetic field are conducted with a kinetic ion, massless fluid electron (hybrid) electromagnetic code. Two different types of magnetic field expansions are considered, i.e., high-density plasma is injected into a dipole magnetic field with or without a background magnetic field. It is found that the existence of the background magnetic field not only changes the particle distribution, but also significantly changes the extent of magnetic field inflation. The effects of plasma injection velocity on magnetic field inflation are also studied in this paper. It is shown that the higher the injection velocity, the larger the size of the inflated magnetic bubble. For the lower injection velocity, the gyroradii of the injected particles to the dipole field scale length are small so that the particles are trapped in the dipole field. [ABSTRACT FROM AUTHOR]

Silver nanocrystals with tetrahedral shapes and {111} faces have been synthesized by the light-driven growth method in an aqueous solution. The nanocrystals of Tdsymmetry were formed under the effect of tartrate and citrate as the structural-directing reagents at the appropriate stages of reaction. Further, the nanocrystals may be assembled through electrostatic interaction to develop large-scale particle surfaces with sharp vertexes, which can generate strong localized electromagnetic field for surface-enhanced Raman scattering (SERS) studies. Benzenethiol was used as the probe to evaluate their SERS enhancement, and enhancement factors of up to 10 6are reached. As a kind of promising material, these novel nanocrystals will be applied in surface enhanced spectroscopy and plasmonics field. [ABSTRACT FROM AUTHOR]