摘要:

We prepare hysteresis model that reproduces smooth hysteresis curves including minor loops from several experimental hysteresis loops. In this model, the distribution of susceptibility on theM‐Hplane obtained from the experimental hysteresis loops is used. The hysteresis loop in the demagnetizing process is computed with this model, and found to converge on the original point of theM‐Hcoordinates. The computed hysteresis curves including minor loops agree well with the experimental results. In addition, the present hysteresis model is used for a numerical analysis of magnetic fields with the spatial network method. In this simulation, the magnetization and magnetic fields inside and outside an infinite magnetic cylinder in an external pulse field are obtained. The results are in fair agreement with theoretical results.

ISSN:0021-8979    

DOI:10.1063/1.352419

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The Fermi integrals of half orders are important in the simulation of semiconductor transport processes. Several of these integrals (−1/2, 1/2, 3/2, 5/2) have been recently retabulated since the 1938 study by McDougall and Stoner [Phil. Trans. Roy. Soc. A237, 67 (1938)], but the derivatives were not re‐evaluated. The original integral values were calculated without the aid of high speed computers by using approximate series evaluation and tabulations of exponentials and zeta functions. In addition, a discrepancy was found in the literature since the original study in 1938. The second derivative ofF1/2has been mistakenly represented as being proportional to a Fermi integral of another order. This article tabulates the half order Fermi integrals from −1/2 to 5/2 over the reduced energy range −5 to 20 in 0.25 increments. The first two derivatives ofF−1/2are also calculated by numerical integration and tabulated to aid in interpolation. It is shown that the second derivative ofF1/2is not proportional to another Fermi integral. A suitable interpolation scheme is proposed to calculate the values of the Fermi integrals of various order to high accuracy over the total reduced energy range.

ISSN:0021-8979    

DOI:10.1063/1.352420

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Beam‐profile reflectometry is a new technique for measuring the thickness and optical constants of dielectric, semiconducting, and thin metal films. The technique consists of measuring the intensity profile of a highly focused beam reflected from the sample. By using a linearly polarized light source and a tightly focussed beam, theS‐ andP‐polarization reflectivities of the film are simultaneously obtained over a wide range of angles. The focusing also provides a submicrometer spot, thus allowing these measurements to be performed in very small geometries. How the information present in the reflectivity profiles can reveal information about as many as three unknown film parameters simultaneously is described, and results from film samples for which the multiparameter fitting capability was essential to the success of the measurement are also presented.

ISSN:0021-8979    

DOI:10.1063/1.352421

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The brightness of nanometer‐sized field‐emission‐electron sources have been measured experimentally. Ultrasharp tungsten (111) single‐crystal tips were fabricatedinsituusing Ne sputtering and field evaporation, and monitored using field ion microscopy. The average brightness of single‐atom‐terminated nanotips was found to be 3.3×108A cm−2 sr−1at 470 V, or 7.7×1010A cm−2sr−1when extrapolated to 100 kV. These results show an improvement of about two orders of magnitude in source brightness over existing cold field‐emission‐electron sources, and produce a beam with greater particle flux per unit energy than those obtainable using current synchrotron/wiggler/undulator devices.

ISSN:0021-8979    

DOI:10.1063/1.352371

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

In this article we discuss the betatron equations of motion for ane‐beam propagating in a linearly polarized undulator. We include the magnetic field multipolar contributions and go beyond the usual harmonic approximation. The equations of motion are derived with the inclusion of anharmonic and transverse motion coupling terms. The single particle motion as well as the beam dynamics are carefully examined.

ISSN:0021-8979    

DOI:10.1063/1.352372

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The relativistic multiresonator magnetron is analyzed in full cylindrical geometry, using the two‐dimensional particle‐in‐cell simulation codemagic. Detailed comparisons are made between the simulation results and the classic experiments by Palevsky and Bekefi for the relativistic A6 magnetron configuration [Phys. Fluids22, 986 (1979)]. The computer simulations show the same dependence of microwave power on axial magnetic field as measured in the experiment. It is found that the electron flow in the preoscillation regime differs substantially from ideal Brillouin flow, and that the nonlinear regime is characterized by large‐amplitude spoke formation. By analyzing a class of relativistic magnetrons for a wide range of operating voltage and axial magnetic field, it is found that the optimal microwave power exhibits an approximately cubic dependence on the applied diode voltage. Moreover, the simulations indicate that relativistic magnetrons with small aspect ratio oscillate predominantly in the &pgr; mode, whereas magnetrons with large aspect ratio can oscillate in various modes which depend upon the system parameters. Finally, it is shown that a finite power‐supply impedance can strongly modify the resonance condition, thereby significantly degrading the magnetron performance.

ISSN:0021-8979    

DOI:10.1063/1.352373

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Focusing of heavy‐ion beams on an indirectly driven inertial fusion target can be achieved, in principle, under vacuum conditions in the reactor chamber. Due to performance limitations in the storage rings of the driver accelerator, a relatively large number of small emittance beams is required. We suggest that the effect of space charge can be described in terms of three distinct mechanisms: an increase of the entrance divergence angle; a current sensitivity of the focal spot; and the effect of a nonuniform distribution. The first two can be calculated by means of an envelope model. The resulting current sensitivity formula is confirmed by a computer simulation taking into account the correct Coulomb forces between interacting beamlets. We find that for propagation in vacuum the current sensitivity is considerable, in particular for charge statesZ≥1, since the spot size blow‐up scales likeZ4/A2. The effect depends on the total current in a bundle—and not the number of beamlets in it—and thus determines how many bundles have to be used. Possible cures are briefly discussed.

ISSN:0021-8979    

DOI:10.1063/1.352374

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Two‐dimensional governing equations of successively higher‐order approximations for guided electromagnetic (EM) waves in an isotropic dielectric plate surrounded by free space are deduced from the three‐dimensional Maxwell’s equations by expanding the EM vector potential in a series of trigonometric functions of a thickness coordinate in the plate and in exponentially decaying functions of a thickness coordinate in the upper and lower halves of free space. By further satisfying the continuity conditions of the EM field at the interfaces between the plate and free space, a single system of two‐dimensional governing equations is obtained. Solutions and dispersion relations are obtained from the two‐dimensional approximate equations. Dispersion curves are computed and compared with the corresponding ones obtained from the solutions of the three‐dimensional Maxwell’s equations for the transverse electric (TE) and transverse magnetic (TM) waves of the first four modes and for values of the refractive indexnˆ=1.5, 5, 15. It is shown that the agreement between the approximate and exact dispersion curves is very close for various order of TE and TM waves and for a broad range of the values ofnˆ. For bounded plates with edges in contact with free space, a uniqueness theorem for the solutions of the system of two‐dimensional equations is derived from which the specification of continuity conditions on the components of the two‐dimensionalHandEfields at the edges are established.

ISSN:0021-8979    

DOI:10.1063/1.352375

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Two‐dimensional equations for guided electromagnetic waves propagating in a dielectric plate surrounded by free space were recently derived from the three‐dimensional Maxwell’s equations. These equations are employed for the study of vibrations of circular disk dielectric resonators embedded in free space. Closed form solutions are obtained for which the continuity conditions of the tangentialEandHfields at the end faces and the lateral cylindrical surface are accommodated. It is found that the solutions represent two types of modes: (1) the modes in which the electric field is transverse to the axis of the disk [transverse electric (TE) modes] and (2) the modes in which the magnetic field is transverse to the axis of the resonator [transverse magnetic (TM) modes]. Frequency equations are solved and resonance frequencies are computed as functions of the diameter‐to‐thickness ratioa/bfor TE and TM modes. It is found that the computational results presented as &OHgr;ˆ [≡&ohgr;/(&pgr;/2b)c] vsa/bcurves are independent of the refractive indexnˆ. Hence, these curves can be conveniently applied to the dielectric disks of anynˆ. Predicted results are compared with the experimental data by Cohn [IEEE Trans. Microwave Theory Tech.MTT‐16, 218 (1968)], Chow [IEEE Trans. Microwave Theory Tech.MTT‐14, 439 (1966)], and Yee [IEEE Trans. Microwave Theory Tech.MTT‐13, 256 (1965)], and with the computational results by Chow [IEEE Trans. Microwave Theory Tech.MTT‐14, 439 (1966)] and Yee [IEEE Trans. Microwave Theory Tech.MTT‐13, 256 (1965)]. It may be seen that present predictions agree overall with different sets of experimental data and for modes of various types and order.

ISSN:0021-8979    

DOI:10.1063/1.352376

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

As part of a program to develop a repetition rate (10–20 Hz) long optical pulse (500 ns) XeCl excimer laser, a parametric study of three different modes of magnetic‐spiker circuits has been made: the switch mode, the diode mode, and the overshoot mode. A 500‐ns‐duration laser pulse was achieved using the overshoot mode and the possibility of developing a 20 Hz long‐pulse XeCl laser is discussed.

ISSN:0021-8979    

DOI:10.1063/1.352377

出版商:AIP    

年代:1993

数据来源: AIP