Axisymmetric Beam Research Articles

Nonlocality of microwave-induced variations in the intensity of the visible continuum from a medium-pressure cesium-xenon dc discharge

A violation of the local relation between the visible continuum (VC) emissivity and the millimeter wave (MMW) intensity was observed in the experiments on imaging of MMW beams with subcentimeter width using the VC from a slab of the positive column (PC) of a medium-pressure cesium-xenon (Cs-Xe) dc discharge. The spatial distribution of the microwave-induced variation in the VC emissivity of the plasma slab was modeled. For this, perturbations of the electron temperature and density in a slab of the PC of a Cs-Xe discharge affected by an MMW beam were calculated. The relation between the spatial distributions of the VC brightness perturbation and the MMW intensity has been obtained. Good agreement between the results of the experiments and the modeling is demonstrated. The line spread function of a two-dimensional (2D) plasma sensor for MMWs is found, and its width is shown to be equal to 2 mm. We proved that the nonlocality of microwave-induced variations in the intensity of the VC from the PC, as well as the spatial resolution of the plasma technique of MMW imaging, are primarily determined by the influence of the electron heat conduction. Along with the electron heat conduction, the nonlocality of the electron temperature variation is caused by the influence of the hydrodynamic flux of electron enthalpy, diffusion and thermodiffusion fluxes of electrons, and also spatial inhomogeneity of the electron heating by a dc electric field, which results from a microwave-induced variation in plasma conductivity. These factors are responsible for the axial asymmetry of the images of the axisymmetric MMW beams.

環状すきま流を受ける軸対称弾性梁のアクティブ制振手法の基礎検討

Flow-induced vibration occurs in the structures subjected to annular flow such as elastic beam in the narrow passage. Once the vibration occurs, the vibration becomes larger. In this paper, active vibration control of the axisymmetric elastic beam subjected to annular flow is investigated. Fluid-structure coupled equations based on the Euler-Bernoulli type partial differential equation and Navier-Stokes equation are derived including control terms. In this paper, two kinds of control methods using piezoelectric actuator and air pressured actuator are proposed. Applying the optimal control law to the coupled system, the unstable behavior is stabilized. Simulation studies are performed to investigate the efficiency of the proposed control methods and the effects of the actuator position on control performance.

Evidence cross-validation and Bayesian inference of MAST plasma equilibria

In this paper, current profiles for plasma discharges on the mega-ampere spherical tokamak are directly calculated from pickup coil, flux loop, and motional-Stark effect observations via methods based in the statistical theory of Bayesian analysis. By representing toroidal plasma current as a series of axisymmetric current beams with rectangular cross-section and inferring the current for each one of these beams, flux-surface geometry and q-profiles are subsequently calculated by elementary application of Biot-Savart’s law. The use of this plasma model in the context of Bayesian analysis was pioneered by Svensson and Werner on the joint-European tokamak [Svensson and Werner,Plasma Phys. Controlled Fusion 50(8), 085002 (2008)]. In this framework, linear forward models are used to generate diagnostic predictions, and the probability distribution for the currents in the collection of plasma beams was subsequently calculated directly via application of Bayes’ formula. In this work, we introduce a new diagnostic technique to identify and remove outlier observations associated with diagnostics falling out of calibration or suffering from an unidentified malfunction. These modifications enable a good agreement between Bayesian inference of the last-closed flux-surface with other corroborating data, such as that from force balance considerations using EFIT++ [Appel et al., "A unified approach to equilibrium reconstruction" Proceedings of the 33rd EPS Conference on Plasma Physics (Rome, Italy, 2006)]. In addition, this analysis also yields errors on the plasma current profile and flux-surface geometry as well as directly predicting the Shafranov shift of the plasma core.

Subwavelength dark hollow focus of spirally polarized axisymmetric Bessel-modulated Gaussian beam

Dark hollow focus plays an important role in many optical systems. In this paper, dark hollow focal shaping of spirally polarized axisymmetric Bessel-modulated Gaussian beam is investigated by vector diffraction theory in detail. Results show that the dark hollow focus can be altered considerably by beam parameter and spiral parameter that indicates polarization spiral degree. One dark hollow focus and two dark hollow foci pattern may occur for certain spiral parameter, and the transverse size of dark hollow focus can be less than the diffraction limit size of bright focus. In addition, there may also appear two triangle dark hollow foci that are connected by one dark line focus.

A Simplified Design Method on Steel Beam Strengthened with CFRP

This paper explores the issue how to improve utilization ratio of CFRP strengthening steel structure in allusion to the diseconomy of steel structure strengthened with CFRP. An experiment including six single axisymmetric steel beams was carried out to study ultimate capacity of single axisymmetric steel beam strengthened with CFRP sheets. These samples were divided into three groups, and each group included two samples strengthened with one and two layers of CFRP sheets respectively. The experimental results show that single axisymmetric steel beam strengthened with CFRP is advantageous over biaxial symmetrical steel beam because the former has superior material utilization ratio. On the basis of the experimental results, a simplified analytical model is put forward for prediction of capacity and material utilization ratio. In the proposed approach, ultimate capacity formula is established and an index named material utilization ratio is suggested to study how to enhance CFRP utilization ratio. The analytical calculation results state clearly that steel beam strengthened with enough CFRP is favorable in improving capacity and material utilization and owns optimal utilization ratio. Above all, the proposed approach is convenient and accurate enough for practical application in material utilization assessmetn and capacity design.

Focal shift of cylindrical vector axisymmetric Bessel-modulated Gaussian beam with radial variance phase wavefront

Axisymmetric Bessel-modulated Gaussian beam with quadratic radial dependence (QBG beam) has attracted much attention recently. In this paper, the focal shift of the cylindrical vector QBG beam with radial variance phase wavefront is investigated theoretically by vector diffraction theory. Results show that focus shifts considerably by changing the phase parameter C that indicates the radial phase variance speed. Under condition of small beam parameter μ of cylindrical vector QBG beam, there is one focal peak that shifts far away from optical aperture on increasing C. When μ increases, there may occur two focal peaks that also shift remarkably on increasing C. And it was found that the dependence of focal shift distance on increasing phase parameter is linear. Phase parameter adjusts the focal shift distance, while, polarization angle does not affect focal shift obviously.

Analyzing X-ray pulsar profiles: geometry and beam pattern of A 0535+26

We applied a decomposition method to the energy dependent pulse profiles of the accreting binary pulsar A 0535+26, in order to identify the contribution of the two magnetic poles of the neutron star and to obtain constraints on the geometry of the system and on the beam pattern. We analyzed pulse profiles obtained from RXTE observations in the X-ray regime. Basic assumptions of the method are that the asymmetry observed in the pulse profiles is caused by non-antipodal magnetic poles and that the emission regions have axisymmetric beam patterns. Constraints on the geometry of the pulsar and a possible solution of the beam pattern are given. We interpreted the reconstructed beam pattern in terms of a geometrical model of a hollow column plus a halo of scattered radiation on the neutron star surface, which includes relativistic light deflection.

Active Control of Annular Flow-induced Vibration of Axisymmetric Elastic Beam by the Local Gap Width Control

Active Control of Annular Flow-induced Vibration of Axisymmetric Elastic Beam by the Local Gap Width Control

1014 環状すきま流れを受ける軸対称弾性梁の流動励起振動のアクティブ制振(GS-10 流体連成)

1014 環状すきま流れを受ける軸対称弾性梁の流動励起振動のアクティブ制振(GS-10 流体連成)

Transformations of spherical beam shape coefficients in generalized Lorenz–Mie theories through rotations of coordinate systems. V. Localized beam models

This paper is the fifth of a series of papers devoted to the transformation of beam shape coefficients through rotations of coordinate systems. These coefficients are required to express electromagnetic fields of laser beams in expanded forms, for use in some generalized Lorenz–Mie theories, or in other light scattering approaches such as Extended Boundary Condition Method. Part I was devoted to the general formulation. Parts II, III, IV were devoted to special cases, namely axisymmetric beams, special values of Euler angles, and plane waves respectively. The present Part V is devoted to the study of localized approximation and localized beam models, and of their behavior under the rotation of coordinate systems.

Spirally polarized axisymmetric Bessel-modulated Gaussian beam

Focusing properties of the spirally polarized axisymmetric Bessel-modulated Gaussian beam with quadratic radial dependence (QBG beam) are investigated theoretically by vector diffraction theory. Calculation results show that intensity distribution in focal region can be altered considerably by beam parameter μ and spiral parameter C that indicates polarization spiral degree. For certain real value μ, focal spot can evolve from one focal spot to one focal ring, spherical crust focal shape, then two focal rings on increasing spiral parameter C. It was found that under condition of different μ, evolution principle of focal pattern differs very remarkably on increasing C. And some novel focal shapes may appear, including rhombic shape, quadrangular shape, two-spherical crust focus shape, two-peak shape, one dark hollow focus, two dark hollow focuses pattern, triangle dark hollow focus.

Transformations of spherical beam shape coefficients in generalized Lorenz–Mie theories through rotations of coordinate systems: III. Special values of Euler angles

This paper is Part III of a series of papers devoted to the transformation of beam shape coefficients under rotations of coordinate systems. These coefficients are required for the expanded description of laser beams, particularly for use in the framework of generalized Lorenz–Mie theories. In Part I of this series of papers, we presented a general formulation for the transformation of spherical beam shape coefficients through rotations of coordinate systems, under the form of a theorem of transformation. Part II was devoted to the special case of axisymmetric beams, more particularly of on-axis axisymmetric beams. With this Part III, we investigate simplifications of the general formulation for special values of the Euler angles defining the rotation. As in Part II, one of the aims is to uncover compact forms of formulae useful to speed-up computations.

Transformations of spherical beam shape coefficients in generalized Lorenz–Mie theories through rotations of coordinate systems. IV. Plane waves

This paper is the fourth of a series devoted to the transformation of beam shape coefficients through rotations of coordinate systems. These coefficients are required to express electromagnetic fields of laser beams in expanded forms, for instance for use in some generalized Lorenz–Mie theories. The main result of Part I has been the theorem of transformation of beam shape coefficients under rotations. Part II dealt with the special case of on-axis axisymmetric beams. Part III dealt with other special cases, namely when the Euler angles specifying the rotation are given some special values. The present Part IV studies another special case, namely the one of plane waves viewed as special on-axis axisymmetric beams, and can therefore be viewed as a special case of Part II. Unexpectedly, it is found that, in general, although plane waves are fairly trivial, their expansions require using non trivial beam shape coefficients, exactly as required when dealing with arbitrary shaped beams.

Transformations of spherical beam shape coefficients in generalized Lorenz–Mie theories through rotations of coordinate systems: II. Axisymmetric beams

The description of laser beams in spherical coordinates requires the introduction of expansion coefficients named beam shape coefficients, or more specifically spherical beam shape coefficients. In part I of the present series of papers, we presented a general formulation for the transformation of spherical beam shape coefficients through rotations of coordinate systems, taking the form of a theorem of transformation. The present Part II deals with the special case of axisymmetric beams, more particularly of on-axis axisymmetric beams (such as Gaussian beams in an on-axis configuration).

2D25 Active Control of Annular Flow-induced Vibration of Axisymmetric Elastic Beam by the Local Gap Width Control

Flow-induced vibration may occur in the structures such as elastic beams subjected to annular flow in the narrow passage. Once the flow-induced vibration occurs, vibration amplitude becomes larger, consequently it causes a lot of troubles such as fatigue or failure in mechanical structures. In this paper, for the purpose to avoid these troubles, the active control of vibration of an axisymmetric elastic beam subjected to annular flow is investigated. An air-pressured actuator is attached on the surface of the circular cylinder for the vibrational control. As the shape of the actuator changes by control, the gap width in narrow passage changes locally, which causes the change of the fluid pressure. Therefore, the vibration of the fluid-structure coupled system can be suppressed. The fluid-structure coupled equation based on the Euler-Bernoulli type of partial differential equation and the Navier-Stokes equations is analytically derived including control terms. By applying the optimal control law to the coupled system, the unstable behavior is stabilized. The stability of the coupled system with optimal control is investigated by eigenvalue analyses of controlled coupled equations. Numerical simulations are performed to investigate the efficiency of the proposed control method.

612 環状すきま流れを受ける軸対称弾性梁の局所すきま幅変化によるアクティブ制振(GS-10 流体関連振動)

612 環状すきま流れを受ける軸対称弾性梁の局所すきま幅変化によるアクティブ制振(GS-10 流体関連振動)

261 環状すきま流を受ける軸対称弾性梁のアクティブ制振手法の基礎検討(平行流による流体関連振動のメカニズムと計測制御,OS-22 流体関連振動・音響メカニズムと計測制御,総合テーマ「伝統を,未来へ!」)

261 環状すきま流を受ける軸対称弾性梁のアクティブ制振手法の基礎検討(平行流による流体関連振動のメカニズムと計測制御,OS-22 流体関連振動・音響メカニズムと計測制御,総合テーマ「伝統を,未来へ!」)

Helical Electron-Beam Microbunching by Harmonic Coupling in a Helical Undulator

Microbunching of a relativistic electron beam into a helix is examined analytically and in simulation. Helical microbunching is shown to occur naturally when an e beam interacts resonantly at the harmonics of the combined field of a helical magnetic undulator and an axisymmetric input laser beam. This type of interaction is proposed as a method to generate a strongly prebunched e beam for coherent emission of light with orbital angular momentum at virtually any wavelength. The results from the linear microbunching theory show excellent agreement with three-dimensional numerical simulations.

Cylindrical vector axisymmetric Bessel-modulated Gaussian beam

Focusing properties of the cylindrical vector axisymmetric Bessel-modulated Gaussian beam with quadratic radial dependence (QBG beam) in high numerical aperture system is investigated theoretically by vector diffraction theory. Results show that intensity distribution in focal region can be altered considerably by beam parameter μ and polarization angle. Polarization angle may adjust transverse intensity distribution, for instance from one focal spot to one ring shape. While μ alters axial intensity distribution remarkably, focal splitting may occur with tunable focal shift, and real value μ also may induce local intensity minimum. For certain case, with increasing imaginary value μ, transverse focal spot shrinks accompanied with higher full width half maximum of axial intensity distribution.

Using coaxial reflectors to transform multiple axisymmetric beams

A coaxial reflective optical system (CROS) is proposed for improving the spot size and combined-distance of multiple axisymmetric beams. As a reflective shaping system, the CROS can be easily designed for this aim using the method of the matrix optics. A numerical simulation of the transformed beams is presented and analyzed. The results show that multiple axisymmetric beams can be transformed to a new form with a smaller spot size and longer combined distance using the CROS. The method we proposed is simple and effectual in material processing.