紧凑型L波段磁绝缘线振荡器的实验研究

 设计加工了一个紧凑型L波段磁绝缘线振荡器(MILO)并进行了实验研究。该MILO具有一个新型收集极和一个新型模式转换器，射频扼流腔减为一个，同时将阴极杆设计成变阻抗结构，该MILO由一台自建的600kV,8Ω，100ns加速器SPARK01驱动。在二极管电压为515～538kV, 二极管电流为58～61kA的条件下, 该MILO在实验中获得了1.76～1.78GHz， 2.2～2.5GW的TM₀₁模高功率微波辐射, 功转换效率为7.3%～7.9%。在30ns的有效电压脉宽下，实验中测得微波脉冲半高宽为15ns。实验结果与模拟结果符合得较好。     

Experimental investigation of angular dependence of photon induced L-shell X-ray emission intensity

The angular dependence of emission intensity of L shell X-rays induced by 59.57 keV photons in Pb and U is investigated by measuring the normalized intensities of the resolved L X-ray peaks at different angles varying from 40° to 120°. It is observed that while L _l and L_α X-ray peaks (originating fromJ = 3/2 state) show some anisotropic angular distribution, the emission of L_β and L_γ X-ray peaks is isotropic. The present results contradict the calculations of Co-oper and Zare (1969) that after photoionization of inner shell, the vacancy state has equal population of magnetic substates and the subsequent X-ray emission is isotropic but confirm the predictions of Fluggeet al (1972) that the atomic inner shell vacancies produced after photoionization are aligned and the x-ray emission from the filling of vacancies in state withJ ⩾ 3/2 is anisotropic.     

L波段双频磁绝缘线振荡器的实验研究

根据角向分区产生双频率高功率微波（HPM）的设计思路,开展了基于谐振腔深度角向分区模型的L波段双频磁绝缘线振荡器（BFMILO）的实验研究,建立了BFMILO的实验系统和测量系统,热测了BFMILO的辐射方向图,通过辐射场功率密度积分得到了输出微波的功率.在电子束电压约为420kV,管电流约为34kA的条件下,L波段BFMILO输出的微波频率分别为1.26GHz和1.45GHz,对应的微波功率分别为398MW和222MW.并初步得到了谐振腔深度的角向分区比例不同的BFMILO的初步实验结果.实验研究得到了 关键词： 角向分区 磁绝缘线振荡器（MILO） 双频MILO（BFMILO） 高功率微波（HPM）     

Spontaneous emission of light from a crystal

In the paper a quantum field model crystal — an infinite system of two-level atoms interacting with continuum modes of electromagnetic field — is proposed. Within the framework of this model the spontaneous transition of the crystal from a singly excited state to the ground state accompanied by emission of one photon is studied.     

X-ray emission from non-Keplerian magnetically dominated accretion disks

Summary Most accretion disk models do assume Keplerian rotation as the ?natural? one. This is not so obvious and is somewhat aprioristic, as shown by some attempts to follow different approaches. In the present work we suggest a new approach to the problem, pointing out that the disk structure is deeply related to the balance between the magnetic energy produced by dynamo action and the rotational energy associated with the accreting flow. This balance, together with the conservation laws, allows us to derive analytically the angular-velocity field, the radial velocity field and the magnetic-energy distribution inside the disk. As far as the disk X-ray emission is concerned, we adopt the point of view that the buoyancy and emergence at the disk surface of the azimuthal magnetic field generated by differential rotation gives rise to looplike structures in a hot magnetically confined corona, which is not merely overimposed, as in other models, but ?naturally? fits to the disk structure. The magnetic-energy dissipation into the coronal medium, which sustains the X-ray luminosity, is due to twisting of the magnetic loops. we give an exact analytical expression for the integrated luminosityL _x in terms of the mass of the compact object, the accretion rate, the disk size and rotational velocity, and show that in the limitr _i≪r _e (wherer _i andr _e are the inner and the outer radius of the accretion disk, respectively) it agrees fairly well with the characteristic observed values of both galactic and extragalactic strong compact sources, within the reasonable range commonly accepted for the relevant parameters. Paper presented at the 2° Convegno Nazionale di Fisica Cosmica, held at L'Aquila, 29 May–2 June 1984.     

Asymmetry in photoelectron emission from chiral molecules induced by circularly polarized light

In photoionization of free, unoriented chiral molecules with circularly polarized radiation, a significant circular dichroism, i.e., an asymmetry in the forward-backward electron emission, has been observed in the photoelectron angular distribution. This leads also to an asymmetry in the momentum transfer to the photoions. The spectra for the left- and right-handed enantiomers of bromocamphor exhibit asymmetries up to several percent which vary as a function of orbital binding energy. This enantioselective effect can similarly occur for biomolecules with handedness, like amino acids, and may thus be a contributing factor related to the origin of the terrestrial biomolecular homochirality.     

高发射电流密度二极管实验研究

介绍了一种径向绝缘的高发射电流密度二极管的结构及其磁场系统,该二极管采用爆炸发射方式,阴极为高密度热解石墨,绝缘子为氧化铝陶瓷,并采用阴极屏蔽技术,阴极尖端处的最高场强达2.470 MV/cm。同时利用CHP01加速器实验平台对这种二极管的发射特性进行了实验研究。其输出电子束参数达到：电压600 kV、电流12 kA、脉冲宽度45 ns、脉冲重复频率100 Hz、阴极电子发射密度达17 kA/cm2。电压不稳定度小于3%,电流不稳定度小于5%。研究了在高发射电流密度下二极管重复频率稳定运行问题及引导磁场对二极管输出束流及特性阻抗的影响,结果表明：二极管输出束流随磁场增大而有所减小并趋于稳定;特性阻抗则随磁场的增大而增大,当磁场强度达到临界磁场以上时,特性阻抗也趋于稳定。     

CSRm束流径向和轴向振荡的耦合

介绍了由于磁铁的安装误差和螺线管的存在而造成的束流径向和轴向的耦合，以及耦合对束流稳定的影响。结合CSRm结构的典型参数分析得出:二极磁铁和四极磁铁在纵向角安装偏差为-0.5~0.5 mrad；有螺线管存在的情况下，工作点落在和共振线时，将导致束流不稳定而大量损失，落在差共振线时，束流稳定。通过模拟计算发现:螺线管产生的耦合远大于磁铁的纵向角安装偏差产生的耦合。     

Effect of multiple tips on light emission induced by STM from gold nanostructures

Light emission induced by scanning tunneling microscope on gold islands grown on MoS₂ surfaces has been investigated. Surface geometry and roughness show that different apexes of the same tip can modify the energy of photons emitted in the tunneling junction. Comparisons of topography and photon map are used to locate islands imaged twice and to represent approximately the tip shape used. Light emission spectroscopy on the same island with two apexes of the multiple tip reveals variations of emission properties according to the apex used, showing the importance of tip geometry in the emission process induced by tip induced plasmon modes.     

Nd L-shell x-ray emission induced by light ions

The L-shell x-ray of Nd has been obtained for 300-600 keV He²⁺ ions impacting, and compared with that produced by H⁺ and H₂⁺ ions. The threshold of projectile kinetic energy for L-shell ionization of Nd is crudely verified in the energy region of about 300-400 keV. It is found that the energy of the distinct L-subshell x-rays has a blue shift. The relative intensity ratios of Lβ_{1, 3, 4} and Lβ_{2, 15} to Lα_{1, 2} x-ray are enlarged compared to the atomic data, and they decrease with the increase of the incident energy, and increase with increasing the effective nuclear charge of the incident ions. That is interpreted by the multiple ionization of outer-shells induced by light ions.     

STM induced light from nontrivial metal structures: Local variations in emission efficiency

Scanning tunneling microscopy is performed on a gold surface which is structured on a length scale of 10–100 nm by colloidal lithography and the light emission induced by the tunneling electrons is investigated. The lithographically defined structure is reflected in a contrast in photon emission. It turns out that a major contrast mechanism depends only on the local geometry of the tunnel contact. Remarkable variations in photon images are observed, dark flat areas and bright slopes as well as the inverted case may be obtained upon imaging with different tips. A qualitative explanation for this behavior is proposed.     

Spatially correlated light emission from a resonant-cavity light-emitting diode

We present the angular-resolved intensity noise characteristics of a resonant-cavity light-emitting diode under quiet pumping conditions. Measurements by a sensitivity-enhanced lock-in amplifier detection scheme yielded a spatial anticorrelation between the intensity noise of the central and peripheral parts of the emitted far field. Proposals for possible explanations of this anticorrelation from a semiconductor emitter point of view and its consequences for applications in quantum optical imaging are discussed.     

碳纤维阴极发射均匀性的实验研究

 分别用自制浸渍碘化铯（CsI）针式环状碳纤维阴极和环状不锈钢阴极所产生的电子束轰击尼龙目击靶,研究碳纤维阴极发射均匀性。在碳纤维阴极电子束轰击的目击靶上得到了均匀的烧蚀痕迹,而不锈钢阴极电子束轰击的目击靶上烧蚀痕迹不均匀,表明碳纤维阴极发射电子束的均匀性优于不锈钢阴极。分析认为两阴极不同的发射机制及其所特有的材料性质和结构导致其发射电子束均匀性的差异。用光学显微镜和电子显微镜对不锈钢阴极尖端和碳纤维阴极尖端和侧面进行扫描,发现不锈钢阴极仅尖端处被烧蚀,而碳纤维阴极尖端和侧面都有烧蚀痕迹,验证了碳纤维阴极由场发射和表面闪络共同作用的发射机制的假设分析。     

Pre-equilibrium light particle emission in heavy ion induced reactions

We derive a master equation to describe the time evolution of the intrinsic state in heavy-ion collisions. It takes into account the energy supply from the relative motion due to the one-body dissipation mechanism, and the equilibration process and the particle emission due to the two-body residual interaction. We then calculate the energy spectrum and the angular distribution of the emitted protons in¹⁴N,¹⁶O andα induced reactions for various targets and incident energies. The angular distribution is calculated based on a simple phase-space consideration. The numerical results agree very well with experimental data.     

Limits on light emission from silicon

Although silicon is an indirect semiconductor, light emission from silicon is governed by the same gener- alized Planck＇s radiation law as the emission from direct semiconductors. The emission intensity is given by the absorptance of the volume in which there is a difference of the quasi Fermi energies. A difference of the Fermi energies may result h＇om the absorption of external light （photoluminescence） or from the injection of electrons and holes via selective contacts （electroluminescence）. The quantum efficiency may be larger than 0.5 for carrier densities below 10^15 cm^-3. At larger densities, non-radiative recombination, in particular Auger recombination dominates. At all carrier densities, the relation between emission intensity and difference of the quasi Fermi energies is maintained. Since this difference is equal to the voltage of a properly designed solar cell, luminescence is the key indicator of material quality for solar cells.     

Size-dependent light emission from mass-selected clusters

The emission of photons in the visible wavelength range from mass-selected Ag⁺ _n, Cu⁺ _n, Pt⁺ _n and Pd⁺ _n () clusters is observed. Photons are detected 10^-4 s after the cluster generation in a sputter source. The emission intensities display distinct variations with cluster size and material. The observations are interpreted in terms of the decay of metastable states which are excited during the high-energy sputtering process used for the generation of these clusters. Received: 28 October 1997 / Revised: 5 January 1998 / Accepted: 30 January 1998     

Spontaneous light emission from fractional-dimensional excitons

We apply the concept of fractional-dimensional excitons to study the process of light emission in quantum confined systems. We focus on a single parameter , known as the degree of dimensionality and which is related to the exciton coherence volume. We compute rates of light emission due to free excitons in GaAs/Al_xGa_1-xAs quantum wells as functions of and link them to experimental observations. The rates are compared with those of quantum well excitons embedded in a microcavity.