摘要:

Accurate modeling of load behavior inZ‐pinch plasma radiation sources driven by high‐current generators requires the measurement of fast‐rise‐time multimegampere currents close to the load. Conventional current diagnostics mounted in inductive cavities (such as B‐dot loops and Rogowski coils) fail at small radius because of electrical breakdown produced by highdI/dt. In this paper, we describe the use of large‐signal, nanosecond‐time‐resolution lithium niobate piezoelectric stress gauges to directly measure the magnetic pressureB2/2&mgr;0=&mgr;0I2/8&pgr;2r2generated at radiusrby a currentIflowing in a radial transmission line. Current measurements have been performed at radiusr=2.54×10−2m on Sandia National Laboratories’ Proto‐II (10 TW) and SATURN (30 TW) gas puffZ‐pinch experiments with maximum currents of 10.1 MA anddI/dtto 2.1×1014A/s. Comparisons with Faraday rotation and B‐dot current diagnostic measurements at large radius are presented. Bremsstrahlung noise problems unique to the SATURN gas puff source are discussed. For a Y‐cut lithium niobate stress gauge on a pure tungsten electrode, current densities up toI/2&pgr;r=78 MA/m can be measured before the electrode yield strength and the piezoelectric operating stress limit are exceeded. Above the Hugoniot elastic limit of the electrode material, the dynamic range and accuracy of the diagnostic are greatly reduced, but it appears that the technique can be extended to higher current densities using an X‐cut quartz piezoelectric element and a tungsten‐sapphire electrode impedance stack.

ISSN:0021-8979    

DOI:10.1063/1.347077

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Inverse Cˇerenkov acceleration (ICA) is a novel approach to electron acceleration involving the interaction of laser light with a polarizable gaseous medium. This technique may achieve very high acceleration gradients and tends to be best suited for the role as an energy booster for electrons of GeV energy or higher. A generic optimization study of ICA is performed to identify the desired properties of the ideal gaseous medium, in particular a medium in which the laser light frequency is near a resonance of the medium. Several factors that can limit the effectiveness of the interaction are taken into account. It appears that acceleration gradients exceeding 1 GeV/m are possible at low gas pressures that minimize problems with electron‐beam emittance growth.

ISSN:0021-8979    

DOI:10.1063/1.347195

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Elastic differential and total cross sections were computed for 10 eV to 1 keV electrons scattered from bound silicon and germanium atoms using the method of partial waves. The effects of including combinations of static, polarization, and exchange potentials in the optical potential for partial wave analysis were investigated. A parameterization of our total cross section results is also provided in terms of the screened Rutherford cross section.

ISSN:0021-8979    

DOI:10.1063/1.347078

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The potential of the wake‐field produced by a bunch of relativistic charged particles passing through a pill‐box cavity is expressed by using Floquet’s theorem, and an obvious requirement that the energy gain over all acceleration cavity of many pill boxes must be proportional to the number of pill boxes, based on the previous modal approach (BWW theory). It is found that the wake‐field is consisted of two classes of modes: the longitudinal modes which are independent of the aperture and the pill‐box gap, the hybrid (pill‐box) modes which are dependent of the pill‐box gap. The wake field is predominated by the fundamental longitudinal mode whose wavelength is on the order of the effective diameter of the cavity, and its magnitude is inversely proportional to the cross sectional area of the cavity for practical cavities with small apertures. Both longitudinal and transverse wake fields due to the longitudinal modes in an elliptical pill box cavity are expressed analytically in a closed series form by solving exactly the longitudinal eigenmode equation in the elliptical cylindrical coordinates in terms of Mathieu functions. It is found that both longitudinal and transverse wake fields whose amplitudes per driving charge are greater than 100 MV/m/&mgr;C can be generated in an elliptical cavity.

ISSN:0021-8979    

DOI:10.1063/1.347079

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Scattering of an obliquely incident electromagnetic wave by an arbitrary configuration of parallel, nonoverlapping infinite cylinders is considered in this study. The incident wave is plane polarized with either of the field vectors parallel to the axes of the cylinders. The solution to the scalar wave equations is obtained by using the boundary value method. The total wave potentials in the vicinity of a cylinder is constructed by including the contributions from the primary incident wave and the scattered waves from all the cylinders. Expressions for the coefficients of the scattered wave potentials are obtained in terms of those for independent scattering. Numerical results are presented to illustrate the effect of dependent scattering by an assembly of cylinders.

ISSN:0021-8979    

DOI:10.1063/1.347080

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Finite radius electron‐beam transport in a linear wiggler free‐electron laser with a guide magnetic field is investigated. The addition of a guide magnetic field improves the beam confinement, but also leads to a detrimental drift in the direction transverse to the wiggler magnetic field. The introduction of a rotational transformation of the wiggler magnetic field is proposed to further improve the beam confinement. It is shown that the transformation results in a stable, uniform, solid body rotation of the beam provided (a) the guide field is larger than the amplitude of the wiggler field, (b) the electron drift velocity is much smaller than the rotation speed of the wiggler field as seen by the beam, and (c) the wiggler field rotates in the direction opposite to the direction of the electron gyromotion in the guide field. Theoretical predictions of the improvement of the radial beam transport with the introduction of the rotation of the wiggler field are confirmed in numerical simulations.

ISSN:0021-8979    

DOI:10.1063/1.347081

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Several silicon‐on‐insulator guided‐wave structures have been analyzed as potential electro‐optic waveguide modulators using thepisces‐iitwo‐dimensional (2D) device simulation program. From the electron and hole concentration data, the 2D refractive index profile is obtained. The profile is then spatially averaged with respect to a 2D cosine representation of the guided‐waveEfield to obtain the effective modal index changes at 1.3 and 1.55 &mgr;m. The channel‐waveguide devices studied include the metal‐oxide‐semiconductor (MOS) diode, and the one or two‐gate metal‐oxide‐semiconductor field‐effect transistor (MOSFET) with single‐or double‐transverse injection. The single‐gate double‐injection MOSFET modulator offers the most promise with 10−3refractive index changes possible, changes comparable in size to the Pockels effect in LiNbO3or GaAs.

ISSN:0021-8979    

DOI:10.1063/1.347082

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

An efficient computational approach based on the path integral concept is described to solve nonlinear pulse propagation dynamics in realistic optical fibers. As model equations which can predict the propagation, we consider the perturbed (scalar) and the coupled (vectorial) nonlinear Schro¨dinger equations for monomode and birefringent fibers, respectively. With the equivalence between path integration and Fresnel transform, an efficient algorithm can be employed which has been developed for use in the field of wave signal processing of holographic data. After ensuring the validity of the method through the application to canonical soliton problems, results are shown for nonlinear pulse propagation under realistic conditions.

ISSN:0021-8979    

DOI:10.1063/1.347083

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A model for a continuous‐wave (CW) iodine laser has been developed and compared with the experimental results obtained from a solar‐simulator‐pumped CW iodine laser. The agreement between the calculated laser power output and the experimental results is generally good for various laser parameters even when the model includes only prominent rate coefficients. The flow velocity dependence of the output power shows that the CW iodine laser cannot be achieved with a flow velocity below 1 m/s for the present solar‐simulator‐pumped CW iodine laser system.

ISSN:0021-8979    

DOI:10.1063/1.347084

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Phase matched noncollinear second harmonic generations (SHGs) are observed in 2‐methyl‐4‐nitroaniline (MNA) single‐crystal film waveguides. The phase matching condition is obtained by the cross point of the mode dispersion curves for the MNA waveguide. Theoretical analysis of the SHG conversion efficiency shows that the maximum efficiency is given by the conversion between the fundamental 1st mode and the SH 3rd mode. The experimental efficiency at this conversion is obtained to be 0.10% in the waveguide.

ISSN:0021-8979    

DOI:10.1063/1.347085

出版商:AIP    

年代:1990

数据来源: AIP