Degradation in gain for a free electron laser amplifier due to electron momentum spread

A finite spread in axial momentum for the electron beam in a free electron laser amplifier is shown to decrease the small-signal gain. For millimeter and sub-millimeter wave amplifiers, where exponential growth dominates the gain, it is shown that the gain is approximately 3 db below that for a cold beam if the relative momentum spread (u/u)_1/2 = (G_o/248)^1/2 (_o/L), where G_o1 is the gain in db for the cold-beam case, _o is the magnetic wiggler period, and L is the amplifier length. Exact numerical examples are given for representative FEL amplifiers at 35 and 550 GHz.This research was sponsored by the U.S. Office of Naval Research, and by the U.S.-Israel Binational Science Foundation.     

Differential incoherent scattering of 279.2 keV photons by Zr,Sn, Ta,Pb and U

Differential incoherent scattering cross-section ratios of 279.2 keV photons by zirconium, tin, tantalum, lead and uranium elements are experimentally determined by comparing the peak areas under the degraded photon energy with that of an equivalent aluminium foil employing a high resolution 35 c.c. coaxial Ge(Li) detector. Studies have been made in single configuration in an angular range of 20° to 115°. The results are compared with theoretical values obtained from the non-relativistichfs model of Hubbell and co-workers. The cross-section ratios decrease as the atomic number increases for a given scattering angle.     

The intruder orbitals in superdeformed bands and alignment additivity of odd–odd nuclei in the region

The particle-number conserving (PNC) method for treating the cranked shell model with monopole and quadrupole pairing correlations is used to study the superdeformed (SD) bands observed in odd–odd nuclei in the A190 mass region. Spins are assigned to the levels in these bands. The microscopic mechanism of the ω evolution of the dynamic moment of inertia J⁽²⁾ for these SD bands are analyzed. In particular, the major roles of the j_15/2 neutron and i_13/2 proton orbitals played in the SD bands are investigated in detail by contributions to J⁽²⁾ from each cranked orbital and interference terms between two cranked orbitals. Additivity in the A190 mass region is investigated. The experimental evidence for additivity of alignments in ¹⁹²Tl can be reproduced by our calculations.     

Influence of angular momentum in axially symmetric potentials with octupole deformation

The chaotic classical single-particle motion in an oblate octupole deformed potential with a non-zero z-component of angular momentum Lz is investigated. The stability analysis of the trajectories shows that with increasing rotation of the system, the unstable negative curvature regions of the effective potential surface decrease, which converts the chaotic motion of the system into a regular one.     

Microwave propagation parameters in magnetic fluids

Complex dielectric permittivity and complex magnetic permeability measurements of two magnetic fluids (as microwave propagation media), in the approximate range 0.2-5GHz were performed. The two samples consisted of magnetite nanoparticles, dispersed in kerosene and in water, respectively. Based on the dielectric and magnetic measurements, the frequency (f ) dependence of the attenuation parameter, , the phase constant, , the propagation constant, , the intrinsic impedance, Z_m, the refractive index, n , the reflection coefficient, R , the wavelength, and the skin depth, , of the investigated samples were determined.     

Nonlinear microwave emission in Ba0.6K0.4BiO3 crystals near Tc

We report a detailed investigation of harmonic generation at microwave frequencies in Ba_0.6K_0.4BiO₃ crystals. Second- and third-harmonic signals are investigated as a function of temperature, external magnetic field and input power level, at temperatures close to T_c. The experimental data are discussed in the framework of a phenomenological theory, based on the two-fluid model, which assumes that the microwave and the static fields, penetrating the sample within the penetration depth, perturb the partial concentrations of the normal and condensate fluids. We show that the enhanced nonlinear effects detected near T_c in Ba_0.6K_0.4BiO₃ and YBa₂Cu₃O₇ crystals may have the same origin. However, in order to account for the experimental data of Ba_0.6K_0.4BiO₃, one needs to involve a distribution of T_c over the crystal.     

On the basic transcendental functions appearing in the dielectric tensor of a weakly relativistic Maxwellian plasma

Summary It is shown how to deduce in a straightforward way the class of transcendental functions which appear in the elements of the dielectric tensor of a weakly relativistic thermal plasma. The deduction is made directly from the second form of Trubnikov integrals and is valid for arbitrarily large values of the wave perpendicular refractive index.

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Riassunto Si mostra come sia possibile dedurre in modo molto diretto la famiglia di trascendenti che appare negli elementi della matrice dielettrica di un plasma debolmente relativistico in condizioni di equilibrio termico. Il procedimento parte direttamente dalla così detta seconda forma degli integrali di Trubnikov ed è valido per valori arbitrariamente grandi dell’indice di rifrazione perpendicolare al campo magnetico nel quale è immerso il plasma.

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Резюме Мы показываем, как вывести непосредственным образом класс трансцендентных функций, которые появляются в элементах диэлектрического тензора для слабо релятивистской плазмы в условиях теплового равновесия. Вывод проводится непосредственно из второй формы интегралов Трубникова и справедлив для произвольно больших величин показателя преломления для волны, перпендикулярной магнитному полю, в которое помещена плазма.

     

Calculation of the Effect on the Reflection of the Plane Electromagnetic Wave for Non-Magnetized Plasma with Different Electron Density Distributions

In this paper, shift operator finite-difference time-domain (SO-FDTD) method is applied for the calculation of the dispersive medium. The high efficiency and accuracy of this method is verified by calculating the reflection of the plane electromagnetic wave impinging on a non-magnetized plasma slab with different electron density distributions. The results show that the average electron density only determines overall trends of the reflection, and different distributions affect the oscillating process of the reflection. If the average electron density maintains the same, the distribution of electron density with homogenous or inhomogeneous alternation will sharply take effects on the reflection. And magnitude of alternation of electron density affects the incident frequency directly when the reflection tends to uniform.     

Quasinormal modes of a Schwarzschild black hole surrounded by free static spherically symmetric quintessence: electromagnetic perturbations

In this paper, we evaluated the quasinormal modes of electromagnetic perturbation in a Schwarzschild black hole surrounded by the static spherically symmetric quintessence by using the third-order WKB approximation when the quintessential state parameter w _q in the range of −1/3 < w _q < 0. Due to the presence of quintessence, Maxwell field damps more slowly. And when at −1 < w _q < −1/3, it is similar to the black hole solution in the ds/Ads spacetime. The appropriate boundary conditions need to be modified.