Thermal processes at the anode during an intense pulsed discharge

The thermal processes during the initial and subsequent stages of the pulse are discussed on the basis of an account of surface evaporation and all the heat sources acting at the anode.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 15, No. 6, pp. 1000–1008, December, 1968.     

A cooled,intense polarized hydrogen atomic beam for the ETH polarized ion source

A slow (35 K) atomic beam with I⩾10¹⁷ atoms s⁻¹ and n_H∼2×10¹² atoms cm⁻³ has been developed. On the ETH polarized ion source, DC intensities of 0.4 mA for positive and 16 μA for negative ions have been observed.     

Influence of a static magnetic field on the detected atomic velocity distribution in an optically pumped cesium beam frequency standard

Irregularities of the microwave Ramsey patterns in an optically pumped cesium atomic beam frequency standards with a sharp angle incidence detecting laser beam have been diagnosed. They arise from a separated two-peak detected velocity distribution, which is caused by static magnetic fields. Experimentally measured results and theoretical analysis of this phenomenon are presented in this paper.     

Wigner distribution function of an Airy beam

We study the Wigner distribution function (WDF) of an Airy beam. The analytical expression of the WDF of an Airy beam is obtained. Numerical and graphical results of the WDF of an Airy beam provide an intuitive picture to explain the intriguing features of an Airy beam, such as weak diffraction, curved propagation, and self-healing. Our results confirm that these novel properties of an Airy beam are attributed to the continuum of sideways contributions to the field.     

Multiple hot images from an obscuration in an intense laser beam through cascaded Kerr medium disks

We present a theoretical investigation on the formation of hot images in an intense laser beam through cascaded Kerr medium disks, to disclose the distribution and intensity of hot images in high-power disk amplifiers. It is shown that multiple hot images from an obscuration may be formed, instead of one hot image as reported previously in the literature. This gives a clear explanation for the curious damage pattern of hot images, namely, damage sites appearing on alternating optics in periodic trains. Further analysis demonstrates that the distribution and intensity of hot images depend closely on the number of Kerr medium disks, the distance from the obscuration to the front of the first disk downstream, the space between two neighboring disks, and the thickness and B integral of each disk. Moreover, we take two cascaded Kerr medium disks for example to detail multiple hot images from an obscuration and confirm the theoretical results by numerical simulations.     

Ionization of a polarized hydrogen atomic beam in an ECR discharge

The production of an intense beam of polarized hydrogen ions with an ECR ionizer has been investigated. A deuteron tensor polarization of up to 85% of the theoretical value has been observed. The intensity is significantly improved compared to an electron beam ionizer.     

Hamiltonian dynamic analysis of an axially translating beam featuring time-variant velocity

A dynamic analysis is presented for an axially translating cantilever beam simulating the spacecraft antenna featuring time-variant velocity. The extended Hamilton’s principle is employed to formulate the governing partial differential equations of motion for an axially translating Bernoulli–Euler beam. Further, the assumed modes method and the separation of variables are utilized to solve the resulting equation of motion. Attention is focused on assessing the coupling effects between the axial translation motion and the flexural deformation during the beam extension or retraction operations upon the vibratory motion of a beam with an arbitrarily varying length under a prescribed time-variant velocity field. A number of numerical simulations are also presented to illustrate the qualitative features of the underlying mechanical vibration of an axially extending or contracting flexible beam. In general, the transverse beam vibration is stabilized during extension and unstabilized during retraction. The axial acceleration of a translating beam does not affect the transverse vibratory system stabilization.     

Temperature distribution in a sample with second-phase microinclusions during irradiation by a low-energy high-current pulsed electron beam

Using the methods of numerical integration, a temperature field has been calculated that arose in the surface layer of titanium nickelide target with NiTi₂ intermetallic inclusions during irradiation by a lowenergy high-current electron beam with a duration of the order of a microsecond. The calculated temperature field has been compared with that obtained previously for a target of stainless steel 316L containing MnS inclusions. It has been found that, as in the case of stainless steel, the regions of inclusions are overheated. However, the temperature increase for NiTi₂ (12 K) is significantly lower than in the case of stainless steel 316L (283 K). The dynamics of melting of these systems are also considerably different.     

Near-field anomalous spectral behavior in diffraction of a Gaussian pulsed beam from an annular aperture

Based on the Fresnel diffraction integral and by introducing a hard-aperture function into a finite sum of complex Gaussian functions, the approximate analytical expression for the near-field spectral intensity distribution of a space-time-dependent Gaussian pulsed beam passing through an annular aperture is derived, which permits us to study the on- and off-axis spectral anomalies that are near phase singularities of the diffracted Gaussian pulsed beam in the near-field. The expressions for a circular black screen and a circular aperture are given as special cases of the general results. The relative spectral shift of a space-time-dependent Gaussian pulsed beam versus the different values of the truncation parameters and the position parameters of observation points are also studied and illustrated with numerical calculations. It is shown that the spectral switch appears near phase singularities in the near-field, and the near-field spectral behavior depends on the truncation parameters, the pulse duration tau, and the position parameter. The results of this work have potential applications in free-space information encoding and transmission.     

Propagation modes and regimes of intense laser beam in magnetized plasma

This paper presents an analytical and numerical investigation of a circularly polarized beam propagating along the static magnetic field parallel to oscillating magnetic field in plasma at relativistic intensities. In the high intensity regime, such a magnetic field is created by the pulse itself. The authors have identified three regimes of propagation taking into account the relativistic mass correction. Based on WKB and paraxial ray theory, an appropriate expression for a dielectric tensor has been evaluated in the presence of an externally applied magnetic field. The natural electromagnetic modes are circularly polarized. Consequently, extraordinary and ordinary modes propagate, which are significantly affected due to the relativistic mechanism. The regimes are characterized by dimensionless power and beamwidth, characterizing the nature of propagation as steady divergence, oscillatory divergence and self-focusing. Numerical computations are presented and discussed for typical parameters of laser plasma interaction; defined through critical parameters, namely cyclotron-to-beam frequency (Ω _c ), plasma-to-beam frequency (Ω _p ) and beam power for arbitrary large intensities.     

Space charge effects and dynamic interactions in the case of a broad and intense ion beam bombarding an insulated substrate

A small single grid ion gun system, isolated by a quartz tube, was investigated. The dependence of the potential of the floating substrates was measured, and its dependence on grid voltage and pressure was determined. This potential could be controlled by changing the parameters of the ion gun. This seems to be a new possibility for controlled deposition of insulating materials with ion beams of low energy. And it explains results which were obtained in deposition of diamond-like carbon films on insulating substrates.     

Experimental investigation of the temperature distribution in thin films heated by an electron beam

The temperature distribution in thin carbon films irradiated in an electron microscope has been measured. The experimental curve is in good agreement with the result calculated by assuming that heat is removed from the object mainly by conduction.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol.21, No.6, pp. 1084–1090, December, 1971.     

Crater-formation-induced metastable structure in an AISI D2 steel treated with a pulsed electron beam

A detailed investigation concerning the microstructure and phase formations in the crater-erupted areas formed under low energy high current pulsed electron beam bombardment has been carried out for a treated AISI D2 steel. The crater formations are initiated at carbides. Such carbide eruption events change the composition, phase selection and grain growth behaviour inside the craters. Under these extremely non-equilibrium conditions, amorphous patches and feathery type structures containing twinned nano-grains are retained.     

缓冲层对碳纳米管强流脉冲发射特性的影响

为了研究缓冲层对碳纳米管薄膜(CNTs)强流脉冲发射特性的影响,采用酞菁铁高温热解方法分别在镀镍和不镀镍硅基底上生长了碳纳米管薄膜(Ni-CNTs和Si-CNTs),镍层采用化学镀方法制备,强流脉冲发射特性采用二极结构在单脉冲下进行测试。实验发现,通过引入镍缓冲层,CNTs的强流脉冲发射能力显著增强。在峰值为～10.4 V/μm的脉冲场强下,平均开启电场强度从Si-CNTs的5.0V/μm下降到Ni-CNTs的4.3V/μm,而峰值发射电流和电流密度从Si-CNTs的70A和3.5 A/cm2升高到Ni-CNTs的162 A和8.1 A/cm2,Ni-CNTs的峰值电流比Si-CNTs提高了1.3倍。     

Numerical analysis of beam propagation in pulsed cavity ring-down spectroscopy

A numerical simulation of pulsed cavity ring-down spectroscopy (CRDS) is developed with the commercially available software package GENERAL LASER ANALYSIS AND DESIGN. The model is verified through a series of numerical experiments. Several issues of concern in CRDS are investigated, including spatial resolution, misalignment, non-Gaussian beam input, and the effect of flames inside a ring-down cavity. Suggestions for the design of pulsed CRDS instruments are provided.