Particle Simulation of a Millimeter Wave Multiwave Cerenkov Generator Producing Gigawatt Power Levels

The Multiwave Cerenkov Generator(MWCG) is investigated with a two and one half dimensional(2 1/2 D) electromagnetic relativistic Particle-in-Cell(PIC) simulation code. NonIinear beam-wave interaction is considered in the code. Deep insights into the MWCG are demonstrated by simulations. Some of the results agree with those of experiments. The radiation is generated with its dominant frequency at 35.5GHz. The power level of 3.8GW is achieved, with radiation efficiency up to 24%. The harmonics of both 71.0GHz and 106.5GHz are observed. The features of parameters dependency are presented. And reasonable explanation is put forward.     

具有谐振腔的多波切伦柯夫振荡器的粒子模拟

 设计了一种新型的多波切伦柯夫振荡器，即在第二慢波段和输出喇叭之间加一个谐振腔，并采用PIC方法模拟了器件产生微波的物理过程。结果表明这种新型器件符合普通多波切伦柯夫振荡器的基本特征，同时具有纵向尺寸短，导引磁场低，功率、效率高等优点。     

Zur Cerenkov-Strahlung von Elektronen dicht über einem Dielektrikum

The Cerenkov radiation of an electron moving parallel to a dielectric boundary is calculated usingToraldo di Francia's expansion of the electron field in a set of evanescent waves. The radiation field is composed of these waves which are refracted at the boundary. In contrast to a previous treatment of this problem byLinhart it is shown that in addition to the TM-waves TE -waves are produced of comparable energy. The angular and frequency distribution is discussed for both types of waves.     

X-band dielectric Cerenkov maser amplifier experiment

An X-band dielectric Cerenkov maser amplifier experiment is reported. The amplifier system consisted of a solid, thermionically generated electron beam propagating through a cylindrical waveguide partially filled with an annular, dielectric liner. The input signal was provided by a tunable (9-10.3 GHz) magnetron with power up to 10 kW. Electron beam voltages and currents of up to 250 kV and 100 A could be generated for 1 μs pulse durations. The system was configured to operate in the TM₀₁ mode of the dielectric-lined waveguide. In this experiment the gain of the system with respect to the length of the dielectric liner was studied at a fixed input frequency of 10.3 GHz. At electron beam parameters of 160 kV and 60 A, a power gain of 24 dB over 56 cm of interaction length was measured for an input power of 4.5 kW, corresponding to a maximum RF amplified power of 1.15 MW and 12% efficiency     

Design considerations for the gyro-peniotron oscillator

The gyro-peniotron shows great promise as a source of microwave radiation. In this paper we investigate the stability and the non-linear saturated efficiency of a gyropeniotron oscillatro with an axis encircling beam operating at the TE₂₁₁ and the TE₃₁₁ cylindrical cavity modes. Beam and cavity parameters for stable high efficiency operation are presented from a linear theory analysis of the start-oscillation condition. Using design parameters taken from the linear analysis, the strong field non-linear emission efficiencies are studied numerically. The sensitivity of the saturated efficiency to beam axial velocity and guiding center spread is also considered. The results of our modeling indicate that high efficiency (70–90%) operation of the gyro-peniotron oscillator is possible, even with large guiding center and large axial velocity spread.This work was supported by the University of California at Los Angeles under Contract 400093 through the U.S. Army Research Office Contract ARO-DAAG 29-82-K-0004.     

Thermal stimulated radiation of a dissipative Fabry-Perot etalon

The contribution of stimulated coherent radiation to the total thermal radiation of a dissipative Fabry-Perot etalon is calculated and it is shown that for sufficiently high temperatures and a sufficiently highQ of the resonator the radiation of the Fabry-Perot etalon can be predominantly a stimulated one. On the basis of thermodynamic investigation, it has been found that for the conversion efficiency of thermal energy into the energy of stimulated radiation of a two-level system , whereT _eff is a parameter characterizing the total emissivity of the system at a given frequency and¯f is the mean value of the distribution function of the photons in a given spectrum interval.The author wishes to express his gratitude to Dr. M. Trlifaj and Dr. K. Pátek for stimulating discussions.     

Investigation of a nanostrip patch antenna in optical frequencies

This is the first report and investigation of a patch antenna in optical frequency range. Variety of plasmonic nanoantenna reported so far is good at enhancing the local field intensity of light by orders of magnitude. However, their far-field radiation efficiency is very poor. The proposed patch antenna emits a directional beam with high efficacy in addition to enhancing the intensity of near field. The nano-patch antenna (NPA) consists of a square patch of gold film of dimension 480 nm², placed on a substrate of dielectric constant \( \varepsilon_{\text{r}} \)  = 3.9 and thickness 150 nm with a ground plane of gold film of dimension 1,080 nm². The NPA resonates at 210 THz and has gain nearly 2 dB and radiation efficiency 45.18 %. The NPA might be useful in variety of applications such as optical communication, nano-photonics, biosensing, and spectroscopy.     

Precipitation of radiation belt electrons by magnetospherically reflected (MR) whistlers

We use a test particle simulation model based on gyro-averaged equations of motion to study the influence of oblique magnetospherically reflected (MR) whistlers on the near-loss-cone distribution function of radiation belt electrons. We find that MR whistlers originating in lightning can resonantly interact with radiation belt electrons over a broad range of L-shells and precipitate higher energy electrons from lower L-shells. Electrons in the energy range of 1–2.6 MeV are precipitated from L=2, whereas from L=4 the precipitated electron energy range is 150–220 keV. The precipitated differential electron flux due to this interaction is higher for higher L-shells, and the maximum value ranges from at at L=4. The lifetimes of radiation belt electrons in a given magnetic flux tube around the L-shell on which the interaction takes place are found to be of the order of several days, comparable to lifetimes corresponding to electron loss induced by hiss, which was heretofore assumed to be the dominant loss mechanism [1]. The minimum electron lifetimes vary from 2.47 days for E=1.11 MeV electrons at L=2 to 4.64 days for E=173 keV electrons at L=4.LOLA Research Center, Belgrade, Yugoslavia. STAR Laboratory, Stanford University, Stanford, California. Published in Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 6, pp. 727–740, June, 1994.     

Spectrum of stationary electromagnetic radiation in a static gravitational field

From the equation of continuity, an equation is derived for the change in the spectrum of radiation stationary in a static gravitational field, as measured by local observers in their proper frame. It is shown that an isotropic solution always exists in which the energy density per unit frequency interval is ³ times an arbitrary function of .     

The equation of motion and gravitational radiation of an ideal fluid sphere moving in a gravitational background

On the basis of an approximation method developed in a previous paper the motion of an ideal fluid sphere in a weak gravitational background is investigated. The sphere is assumed to be small in the sense that its radius is small compared with the change of the background . Furthermore the deformations of the sphere when accelerated by the background are assumed to be small compared with the extension of the sphere in the absence of acceleration. In the lowest mixed order (mixed of the background and the retarded potentials of the sphere in lowest order) the equation of motion is yielded by integrating Einstein's conservation law of energy and momentum over the world-tube of the sphere. One obtains an equation of motion for the center of the sphere that is identical with the geodesic line linearized in . In the case of a static background of a localized matter distribution it is shown that Einstein's energy-momentum complex formed with the retarded potentials from the accelerated motion of the sphere in lowest order (lowest mixed order) leads to an outgoing radiation of gravitational energy. All radiation terms can be expressed in terms of the background and the world-line of the center of the sphere.     

Energy Levels of Interacting Fields in a Box

We study the influence of boundary conditions on energy levels of interacting fields in a box and discuss some consequences when we hange the size of the box. In order to do this we calculate the energy levels of bound states of a scalar massive field nteracting with another scalar field through the Lagrangian = > in a one-dimensional box on which we impose Dirichlet boundary conditions. We find that the gap between the bound states changes with the size of the box in a nontrivial way. For the case where the masses of the two fields are equal and for large box the energy levels of Dashen-Hasslacher-Neveu (DHN model) are recovered and we have a kind of boson condensate for the ground state. Below a critical box size the ground-state level splits, which we interpret as particle-antiparticle production under small perturbations of box size. Below other critical sizes, and , of the box, the ground state and firstexcited state merge in the continuum part of the spectrum.     

Zero Energy Modes of Massless Fermions in S3R Spacetime

The Dirac-type equation on topology is worked out and the complete set of solutions in the particular physical case of the zero-energy modes of the massless field quanta is derived. Unlike the Minkowskian case, the 1/2fermionic vacua on the manifold is made of nontrivial static modes of defined chirality.     

The Cerenkov Maser at Millimeter Wavelengths

The dispersion relation for the transverse magnetic modes (TMon,) of a partially filled, dielectric-lined, cylindrical waveguide driven by a cold relativistic electron beam is derived. The effect of a gap between the electron beam and the dielectric liner is included. The dispersion relation is then used to calculate the growth rate for the Cerenkov instability in the collective tenuous beam limit. Expressions are developed for the minimum current necessary for oscillation threshold and for the power output of the Cerenkov maser in the collective regime.     

Long-Time Asymptotics of Solutions to the Cauchy Problem for the Defocusing Nonlinear Schrödinger Equation with Finite-Density Initial Data. II. Dark Solitons on Continua

For Lax-pair isospectral deformations whose associated spectrum, for given initial data, consists of the disjoint union of a finitely denumerable discrete spectrum (solitons) and a continuous spectrum (continuum), the matrix Riemann–Hilbert problem approach is used to derive the leading-order asymptotics as of solutions to the Cauchy problem for the defocusing nonlinear Schrödinger equation ( NLSE), , with finite-density initial data

The Scattering Matrix and its Meromorphic Continuation in the Stark Effect Case

Quantum scattering in the presence of a constant electric field (Stark effect) is considered. It is shown that the scattering matrix has a meromorphic continuation in the energy variable to the entire complex plane as an operator on L²(R ^n-1). The allowed potentials V form a general subclass of potentials that are short-range relative to the free Stark Hamiltonian: Roughly, the potential vanishes at infinity, and admits a decomposition , where is analytic in a sector with , and , for x₁<0 and some >0. These potentials include the Coulomb potential. The wave operators used to define the scattering matrix are the two Hilbert space wave operators.     

Millimeter-Wave HF Relativistic Electron Oscillators

A review of the experimental study of single-mode oscillators based on stimulated bremsstrahlung and Cerenkov radiation of high-current relativistic electron beams is given. Three types of Cerenkov oscillators are investigated in detail: orotrons, surface wave oscillators and a flimatron (free electron maser (FEM) based on Smith-Purcell radiation). The bremsstrahlung oscillators studied are gyrotrons with TM modes, a ubitron operating at a quasi-critical frequency and cyclotron autoresonance masers. Electrodynamic and electron methods of mode selection provide stable radiation with a reproducible space structure of radiation in all oscillators under study. The radiation power attained 50-100 MW for long and 10-30 MW for short millimeter wavelengths at the efficiency up to 5-10 percent. Various types of oscillators are compared. Promising methods for increasing power and radiation frequency are discussed.     

Investigation of radiation damage by larmor precession of112In in Ag

The temperature and magnetic field dependence of the spin rotation patterns for two isomeric states of¹¹²In in Ag have been investigated. The results obtained are consistent with a weak static electric field gradient from the radiation damage defects: . The quadrupole moment of the 6⁺ isomeric state in¹¹²In was measured: |Q(6⁺)|=0.75(15) b.     

The equation of motion and gravitational radiation of a small extended spherically symmetric mass

On the basis of an approximation method developed in a previous paper the motion of an extended small mass on a gravitational background is investigated. The mass is described by a spherically symmetric rest mass distribution with some form of rigidity; the smallness of the mass is defined by the assumption that the radius of the mass is small compared with the change of the background . The equation of motion is yielded by integrating Einstein's conservation law of energy and momentum over the world tube of the mass. In the lowest mixed order (mixed of the background and the retarded potentials of the mass in lowest order) this equation is identical with the geodesic line linearized in . In the case when the motion on a static background generated by a localized matter distribution is finite, the gravitational radiation of the mass in lowest order is given.     

Symmetries and Modular Intersections of Von Neumann Algebras

Let be von Neumann algebras acting on a Hilbert space and let be a common cyclic and separating vector. We say that have the modular intersection property with respect to if(1) -half-sided modular inclusions,(2) (If (1) holds the strong limit exists.) We show that under these conditions the modular groups of and generate a 2-dim. Lie group.This observation is the basis for obtaining group representations of Sl(2, )/Z ₂ generated by modular groups.     

Influence of a strong longitudinal static electric field on free carrier faraday effect in an n-type InSb at room temperature at submillimeter wave frequencies

The expression for free carrier Faraday rotation and for ellipticity , as the function of the applied parallel static electric field and static magnetic field for a given value of wave angular frequency and electron concentration N₀, are obtained and theoretically analyzed with the aid of one-dimensional linearized wave theory and Kane's non-parabolic isotropic dispersion law. It is shown that the maximum Faraday rotation occurs near the cyclotron resonance condition, which can be expressed as , where , , and . Here m^* and e denote the effective mass and charge of electron, respectively. _g is the forbidden bandgap of semiconductor. v₀ is the carrier drift velocity, which is a non-linear function of E₀ in high field condition. A possibility of a simple way of determining the non-linear v₀ vs E₀ characteristics of semiconductors by the measurement of Faraday rotation is also discussed.