ASACUSA: atomic spectroscopy and collisions using slow antiprotons

The ASACUSA experiment [1] was approved last year for the Antiproton Decelerator at CERN. Its aim is to study basic atomic processes of slow antiprotons: stopping power and ionization in low-pressure gases, Coulomb capture of antiprotons and to make laser spectroscopy of antiprotonic transitions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Development and application of the intense slow positron beam at IHEP

This paper describes the development and application of an intense slow positron beam at IHEP with regard to its two main components. The Variable-Energy Positron Lifetime Spectroscopy (VEPLS) based on the pulsing system consisting of a chopper, a prebuncher and a buncher has been constructed in order to meet the needs of materials science development. At present, the time resolution of the VEPLS can easily reach about 386ps with a peak-to-background ratio of about 600:1. A plugged-in ²²Na positron source section for adjusting the newly built experimental station and for increasing the beam operation efficiency has been constructed. A slow positron beam with an intensity of 2.5×10⁵e⁺/s and the beam profile whose diameter is 10mm has been obtained; the moderation efficiency of the tungsten mesh moderator reaches 5.1×10^－4 as calculated with an original positron source activity of 52mCi.     

Development and application of the intense slow positron beam at IHEP

This paper describes the development and application of an intense slow positron beam at IHEP with regard to its two main components.The Variable-Energy Positron Lifetime Spectroscopy (VEPLS) based on the pulsing system consisting of a chopper,a prebuncher and a buncher has been constructed in order to meet the needs of materials science development.At present,the time resolution of the VEPLS can easily reach about 386 ps with a peak-to-background ratio of about 600:1.A plugged-in 22Na positron source section for adjusting the newly built experimental station and for increasing the beam operation efficiency has been constructed.A slow positron beam with an intensity of 2.5x105 e+/s and the beam profile whose diameter is 10 mm has been obtained;the moderation efficiency of the tungsten mesh moderator reaches 5.1x 10-4 as calculated with an original positron source activity of 52 mCi.     

Probing the quantum vacuum with ultra intense laser pulses

This article presents 1) The theoretical background of strong field physics along with vacuum structure and stability; 2) The instrumental developments in the area of pulsed lasers and considers the physics case for the construction of ultra-intense laser facilities; and 3) The applied and fundamental uses of ultra-intense lasers.     

Many body modes of antiproton annihilation tested with antiproton production

We study the inclusive (y,¯ p) and (p,p) reactions in nuclei and check the sensitivity to the¯p annihilation mechanisms. We find that including the many body annihilation mechanisms in nuclei reduces appreciably the cross section of these reactions with respect to the evaluation considering only the one body mechanism of¯p annihilation. This shows that the¯p production reactions are more sensitive to¯p annihilation than the direct¯p annihilation reactions and makes the production experiments very useful tools to investigate the complex mechanisms of¯p annihilation in nuclei.     

An intense, slow and cold beam of metastable Ne(3s) 3 P 2 atoms

We employ laser cooling to intensify and cool an atomic beam of metastable Ne(3 s) atoms. Using several collimators, a slower and a compressor we achieve a ²⁰Ne^* flux of 6×10 ¹⁰ atoms/s in an 0.7 mm diameter beam traveling at 100 m/s, and having longitudinal and transverse temperatures of 25 mK and 300μK, respectively. This constitutes the highest flux in a concentrated beam achieved to date with metastable rare gas atoms. We characterize the action of the various cooling stages in terms of their influence on the flux, diameter and divergence of the atomic beam. The brightness and brilliance achieved are 2.1 ×10 ²¹ s^-1m^-2sr^-1 and 5.0 ×10 ²² s^-1m^-2sr^-1, respectively, comparable to the highest values reported for alkali-metal beams. Bright beams of the ²¹Ne and ²²Ne isotopes have also been created. Received 22 June 2001     

Fundamental studies of intense heavy-ion beam interaction with solid targets

Intense (10/sup 11/ particles/1 /spl mu/s /spl sim/300 MeV/u) heavy ion beams are generated in the heavy-ion synchrotron (SIS) of the GSI-Darmstadt facility. Large volumes of strongly coupled plasmas are produced by heavy ion beam interaction with solid targets, with plasma densities close to the solid state, pressures of about 100 kbar, and temperatures of up to 1 eV, with relevance for equation of state (EOS) of matter, astrophysics, and low-entropy shock compression of solids. The plasmas created by ion beam interaction with metallic converters and cryogenic crystals were studied by backlighting shadowgraphy and by time-resolved spectroscopy in the visible and vacuum ultraviolet ranges. Low entropy weak shock waves induced by the ion beams in the metal-plexiglass multilayered targets were visualized by time resolved schlieren measurements, revealing induced multiple shockwaves with pressures higher than 15 kbar in a plexiglass window and propagation velocities up to 35% higher than the speed of sound in plexiglass at room temperature. To get an insight into the plasma dynamics, both types of experiments are simulated by the BIG-2 two-dimensional hydrodynamic code.     

超短超强激光等离子体物理专题编者按

强激光等离子体物理是随着激光技术的发展而快速兴起的一门交叉学科,主要研究强激光与物质相互作用形成的等离子体结构、演化及应用.其研究内容从早期纳秒激光与等离子体作用相关的惯性约束聚变物理,到近年来飞秒激光与等离子体作用的新型加速器和辐射源物理,再到当前和未来以数十至百拍瓦激光等离子体作用的量子电动力学(QED)等离子体物理,逐步得到拓展和深入.     

用于测量强流脉冲电子束的B-dot

 描述了B-dot探头测量脉冲电子束流强度和束质心位置的原理,分析了B-dot探头工作于自积分和微分模式的条件,并根据所测电子束流信号的前沿和脉冲宽度特点,确定B-dot探头工作于微分模式,设计其电感参数约为60 nH。在电子束流模拟装置上对B-dot探头的灵敏度系数和偏心曲线进行了标定,标定得到B-dot探头及测试线路的灵敏度系数为4 147 A/V。将探测器安装在神龙一号加速器上进行束测实验,多次实验结果表明该探测器可以实现电子束流强度和质心位置的准确测量。     

Plasma-wakefield acceleration of an intense positron beam

Plasma wakefields are both excited and probed by propagating an intense 28.5 GeV positron beam through a 1.4 m long lithium plasma. The main body of the beam loses energy in exciting this wakefield while positrons in the back of the same beam can be accelerated by the same wakefield as it changes sign. The scaling of energy loss with plasma density as well as the energy gain seen at the highest plasma density is in excellent agreement with simulations.     

Hollow beam formation in the intense multi-component heavy ion beam caused by beam self-field

The simulation of the hollow beam formation in the intense multi-component ion beam from ECR source is fulfilled. The influence of the helium and hydrogen beam current on the argon and calcium ions dynamics has been studied.     

Surface strain-hardening of iron alloys with an intense pulsed electron beam

Results are presented from study of surface strain-hardening and measurements of the structure of carbon (St. 45, U7A, 40Kh) and alloy (R6M5, Kh6VF) steels subjected to surface fusion by pulsed electron beams with the following parameters: electron energy 20–250 keV, pulse duration 5·10^–8–3·10^–4 sec, power density 10⁵–10⁹ W/cm³. It is shown that the microhardness of the surface of most alloys increases by a factor of 1.2–1.7 on quenched specimens and by a factor of 2.5–3.5 on unquenched specimens, depending on the regime. Microhardness increases in the surface layer due to quenching from the liquid state. An increase in electron energy from 40 to 250 keV with a pulse duration of 6·-10^–8 sec leads to a severalfold increase in the thickness of the strengthened layers and to a shift of the microhardness peak from the surface to a depth of 70 m. Here, microhardness reaches 2000 kgf/mm². This is due to an increase in the mean free path of the electrons in the metal and displacement of the energy-release maximum of the bundle deeper into the specimen.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, No. 6, pp. 38–43, June, 1985.     

Self-consistent solutions for single,intense beam polariton with linear polarization

New modes of propagation for a single, intense beam of light have been theoretically studied in the frequency region of giant two photon absorption (GTA) to excitonic molecule (EM) states. Self-consistent solutions for left and right circularly polarized (LCP and RCP respectively) components have been obtained for the polariton dispersion equations which include the ω- and k-dependent self-energy term for exciton due to the GTA process to EM. There are two types of solutions: [I] k(LCP) = k(RCP), [II] k(LCP) ≠ k(RCP). The induced branch for the former has a half of EM mass. There are experimental observations which support the existence of such new propagation modes.     

New research of charmonium over D \bar D threshold using the antiproton beam with momentum ranging from 1 to 15 GeV/c

The spectroscopy of charmonium c $\bar c$ is discussed. It is a good testing tool for the theories of strong interactions, including: QCD in both the perturbative and non-perturbative regimes, LQCD, potential models and phenomenological models. For this purpose an elaborated analysis of the charmonium spectrum is given, and attempts to interpret recent experimental data in the above D $\bar D$ threshold region are considered. Experiments using antiproton beams take advantage of the intensive production of particle-antiparticle pairs in antiproton-proton annihilations. Experimental data from different collaborations are analyzed with special attention given to new states with hidden charm that were discovered recently. Some of these states can be interpreted as higher-laying S, P, and D wave charmonium states. But much more data on different decay modes are needed before firmer conclusions can be made. These data can be derived directly from the experiments using a high quality antiproton beam with momenta ranging from 1 to 15GeV/c.     

慢正电子束流技术在金属/合金微观缺陷研究中的应用

正电子湮没谱学技术是研究材料微观结构非常有效的一种核谱学分析方法, 主要用于获取材料内部微观结构的分布信息, 特别是微观缺陷结构及其特性等传统表征方法难以获取的微观结构信息. 近年来, 在慢正电子束流技术快速发展的基础上, 正电子湮没谱学技术在薄膜材料表面和界面微观结构的研究中得到了广泛应用. 特别是该技术对空位型缺陷的高灵敏表征能力, 使其在金属/合金材料表面微观缺陷的形成机理、缺陷结构特性及其演化行为等研究方面具有独特的优势. 针对材料内部微观缺陷的形成、演化机理以及缺陷特性的研究, 如缺陷的微观结构、化学环境、电子密度和动量分布等, 正电子湮没谱学测量方法和表征分析技术已经发展成熟. 而能量连续可调的低能正电子束流, 进一步实现了薄膜材料表面微观结构深度分布信息的实验表征. 本文综述了慢正电子束流技术应用研究的最新进展, 主要围绕北京慢正电子束流装置在金属/合金材料微观缺陷的研究中对微观缺陷特性的表征和表面微观缺陷演化行为的应用研究成果展开论述.     

强流脉冲电子束位置测量探头标定结果不确定度分析

根据探测器测量原理和标定方法、特点,分析其位置测量的不确定度主要来源于测量过程的A类不确定度、B类不确定度和最小二乘法引入的拟合不确定度,确定了各个不确定度的计算方法,得到了探测器的合成不确定度,对于应用于神龙二号直线感应加速器的电阻环和磁探测器,其合成不确定度约为0.1 mm。     

强流电子束聚焦数值模拟

采用粒子模拟（PIC）方法模拟了强流电子束在薄磁透镜中的聚焦。建立了强流电子束的聚焦模型,模拟了神龙一号加速器某次实验的结果,得到的模拟结果非常接近实验值,证明采用建立的PIC模型模拟强流束经过磁透镜时的聚焦是可信的。应用此模型模拟了电子束参数（入射半径、发射度、能散度、相位角等）对焦斑直径的影响, 结果表明：在模拟条件下,电子束平行入射时最佳束包络半径位于20.0~22.5 mm;发射度和能散度对焦斑直径的影响和理论公式吻合得较好;只有入射电子束包络半径和相位角匹配时才能得到小的焦斑直径。     

Generation of an intense low-velocity metastable-neon atomic beam

A metastable neon (1S ₅) atomic beam with a velocity of 394 m/s (373 K) and an intensity of 1.1×10¹⁵ s^–1 sr^–1 is produced with a novel construction using a dc glow discharge.     

Betatron resonance crossing during the intense beam bunching

In the process of bunching an intense beam, the betatron oscillation frequency of particles changes due to a growth in their momentum rejection (in the presence of chromaticity) and changes in the Coulomb shift. These changes lead to the intersection of nonlinear betatron resonances. A mathematical model of the dynamics of ions in the process of bunching an intense beam has been built in order to assess the influence of transverse betatron resonances on the motion of particles. This model takes into account the influence of space charge on the longitudinal and transverse oscillations of particles in the presence of one- and two-dimensional betatron resonances. An analysis of the motion of particles near the one- and two-dimensional third-order resonances is given. Results of the numerical simulation of particle losses and emittance growth in the process of bunching an intense beam in the storage ring at the Institute for Theoretical and Experimental Physics (ITEP) are presented.