Current Strips Research Articles

A new practical design of a merged APPLE-Knot undulator for High Energy Photon Source

To obtain high flux and polarization adjustable synchrotron radiation with low on-axis power density, a type of pure permanent magnetic undulator called merged APPLE-Knot has been proposed. The original configuration of the merged APPLE-Knot undulator neglects the existence of knot vacancies and sets all magnets to the same size, the polarization of fundamental photons decreases dramatically as the gap increases in vertical polarization mode. To deal with this problem, a new configuration that increases the size of the merged magnets and shifts two Knot arrays respectively before merging the magnets has been proposed. However, there is a notable net kick for electrons due to the asymmetry of magnetization orientation distribution of two magnet arrays in circular polarization mode. It cannot be corrected by end magnets only, extra current strips are needed. Here, the configuration of merged APPLE-Knot with symmetrical magnetization orientation distribution proved to be a good choice as well to obtain a good performance of synchrotron radiation without extra current strips.

The MAX III storage ring

One of the primary goals of the 700 MeV MAX III synchrotron radiation source is to test and gain experience with new magnet and accelerator technology. Each magnet cell is machined out of two solid iron blocks that are then sandwiched together after coil and quadrupole installation. The MAX III ring makes extensive use of combined function magnets to obtain a compact lattice. In order to obtain flexibility in machine tuning pole face current strips are used in the main dipoles, which also contain the horizontally defocusing gradients. Commissioning finished in 2007 and MAX III is now going into user operation. Over the last year, MAX III has been characterized in order to both obtain calibrated models for operation purposes as well as evaluating the magnet technology. The characterization results will be described in this paper.

Modeling of equivalent ionospheric currents from meridian magnetometer chain data

In recent years, quantitative analysis of the magnetosphere-ionosphere coupling and electrodynamics of the polar ionosphere received much attention. Though remarkable progress has been made in this field by using a variety of magnetogram inversion techniques in order to infer the global ionospheric current distribution, there is still a need for modeling ionospheric currents locally, over a certain region, for comparison with other geophysical ground-based and satellite observations. This paper presents a simple method for estimating equivalent ionospheric currents using magnetic field observations along a meridian chain of ground-based vector magnetometers. The method can be applied in an automatic fashion to any available magnetometer chain data, for example, from the DMI Greenland west coast chain. We first describe how we separate contributions to the observed geomagnetic variations from external (ionospheric) and internal (induced) sources. We then model the ionospheric electrojet by a sequence of narrow current strips and apply the Biot-Savart law to formulate an inversion problem. Using a regularization technique, we find a stable distribution of the equivalent ionospheric currents crossing the magnetometer chain in eastward and westward direction. Simulation tests and a case study (20 March 1999) are discussed in order to illustrate properties of the solution to the inverse problem and to present a practical tool, which is accessible through the DMI World Wide Web site.

Quiet and noisy metastable voltage states in high-Tc superconductors

The interaction between the telegraph noise and background voltage fluctuations in the current induced dissipative state of high-Tc BiSrCaCuO thin films has been investigated. Experimental time records of the voltage drop across current biased thin film strips show markedly different background noise traces in the up and down telegraph states. Detailed analysis demonstrates that fluctuations around the telegraph voltage levels are due to a unique background noise process. The apparent quiet and noisy voltage states are due only to differences in the effective frequency bandwidth at which background noise is seen at distinct telegraph levels. Changes of the background noise variance ratio with changing bias current follow changes of the statistical average lifetimes of the random telegraph process.

Analysis of Black Images in Comic Strips, 1915–1995

Negative stereotypes of blacks were dominant in strips before 1955, but virtually nonexistent in 1995. Black characters in current strips are portrayed in a wider variety of occupational roles and social settings than in the past.

Exact, closed-form field expressions for two-dimensional, traveling-wave current strips

In this paper, exact, closed-form expressions are derived for the electromagnetic fields associated with two-dimensional, traveling-wave current strips radiating into a homogeneous space. The field expressions involve incomplete Lipschitz-Hankel integrals of the Hankel form. Convergent and asymptotic series expansions for the incomplete Lipschitz-Hankel integrals allow the fields to be computed more efficiently than was previously possible using numerical integration. Two-dimensional, traveling-wave current strips are important because they appear in problems involving physical optic scattering from strips, diffraction through slits, and radiation from parallel plate waveguides. The problem of physical optic scattering from a strip is investigated in this paper. >

Analysis of two-dimensional electromagnetic scattering from nonplanar periodic surfaces using a strip current model

A method-of-moments solution is presented for the problem of two-dimensional transverse magnetic (TM) scattering of a plane wave from a nonplanar periodic surface separating two contrasting homogeneous media. The moment solution uses fictitious spatially periodic and properly modulated electric current strips to simulate the field scattered by the surface and the field penetrating the surface. The fields radiated by the current strips are represented in terms of Floquet modes, and the problem is reduced to a consideration of the fields over a single period. The simulated fields are forced to obey the continuity conditions for the tangential components of the electric and magnetic fields at a selected set of points on the interface within a single period. The procedure is simple to implement, rapidly converging, and applicable to arbitrary smooth profiles. Perfectly conducting media are treated as reduced cases of the general procedure for penetrable media. Results for sinusoidal surfaces are given and compared with available data. The efficiency of the method is demonstrated. >

Analysis of diffraction from echelette gratings, using a strip-current model

A method is presented for analyzing electromagnetic scattering from an echelette grating separating two contrasting homogeneous media and illuminated by a plane wave. The reduction of the general problem to a consideration of the fields over a suitably selected period, referred to as the unit cell, is facilitated by the Floquet theorem. The solution, in the p-polarization case (electric field parallel to the grooves), uses sets of spatially periodic and properly modulated fictitious electric-current strips to simulate the field scattered by the grating boundary surface and the field penetrated through the surface. In the s-polarization case (magnetic field parallel to the grooves), which is not examined in this paper, sets of fictitious magnetic-current strips, instead of electric ones, should be used. The fields radiated by the current strips are expressed in terms of Floquet modes and are adjusted to fit the continuity conditions for the tangential components of the electric and magnetic fields at a finite number of points on the grating surface within the unit cell. Special attention is given to the behavior of the fields at the corners. The procedure is simple to perform and is applicable to gratings of arbitrary cross section. Perfectly conducting gratings are treated as reduced cases of the general procedure. Results are given and compared with existing data. The efficiency of the suggested method is demonstrated.

Analysis of two‐dimensional electromagnetic scattering from a periodic grating of cylinders using a hybrid current model

A method of moments solution is presented for the problem of two‐dimensional electromagnetic scattering from a periodic grating composed of an infinite set of penetrable cylinders illuminated by a TM (transverse magnetic relative to the cylinder axis) plane wave. The reduction of the general problem to a consideration of the fields over a suitably selected period, referred to as the unit cell, is facilitated by the Floquet theorem. The solution then uses fictitious spatially periodic and properly modulated electric current strips to simulate the scattered field in the exterior region within the unit cell and fictitious filamentary currents to simulate the field penetrated into the cylinder enclosed within this cell. The fields radiated by the current strips are represented in terms of Floquet modes. Finally, the simulated fields are forced to obey the continuity conditions for the tangential components of the electric and magnetic fields at a selected set of points on the cylinder boundary within the unit cell. The procedure is simple to implement, rapidly converging, and is applicable to cylinders of arbitrary smooth cross section. Perfectly conducting cylinders are treated as reduced cases of the general procedure for penetrable cylinders. Results are given and compared with available data. The efficiency of the suggested method is demonstrated.

Eddy current losses due to alternating current strips

A two dimensional solution for the vector potential and eddy current loss in a plurality of conducting regions due to a plurality of current sources is presented. The solution is applicable to those problems with boundaries which may be aligned with the coordinate surfaces of an orthogonal system of separable coordinates. The vector potential solution and current sources are represented by a series of eigenfunctions and the boundary conditions for the fields are applied such that numerical techniques can be used in solving for the coefficients of the series solution and then the eddy current losses. The method is applied to the problem of currents parallel to conducting plates in rectangular coordinates and the results are compared to those of previous investigations.