磁场调控型离子源的设计与实验

磁场调控型离子源在离子源等离子体扩散空间中引入轴向强脉冲磁场,磁场起两方面的作用,一是形成潘宁放电效应,使原子、气体分子碰撞电离效率增加;二是在脉冲强磁场的作用下,强轴向磁场将质量较轻的离子约束在轴线上,对质量较重的金属离子约束能力较弱,导致其在等离子体膨胀引出通道中碰壁损失,能够提升引出轻离子的比例。开展了磁场调控的离子源放电结构、强脉冲螺线管磁场以及引出束流光学结构的设计;测量分析了引出离子流强和离子打靶束斑形貌。研究结果表明,强轴向磁场通过等离子体对混合离子成分的筛选作用,可有效提高引出离子流强中的轻离子成分比例。     

Correlation between the energy of the ion scattered from the metal surface and its melting heat

A physical experiment and computer simulation of scattering of low-energy Cs⁺ ions from the surfaces of heavy and light metals are discussed. The presented experimental and calculated data confirm the influence of the interatomic bond of a target on the scattered ion energy. Correlation between the scattered ion energy and the melting heat of a scattering target is established.     

On excitation and loss of an electron by incident ions in relativistic collisions with atoms

The excitation and loss of an electron by ions in relativistic collisions with atoms are studied in first-order perturbation theory. General expressions are obtained for the cross sections for the excitation and loss of an electron. In the limit of nonrelativistic collision velocities these expressions pass into the well-known nonrelativistic results. It is shown that, in contradistinction to the nonrelativistic collisions, in ultrarelativistic collisions the screening of the nucleus of the target atom by the atomic electrons is very important for excitation and loss of an electron by ions even for collisions of heavy ions with light atoms. Our computational results for the cross section for electron loss are in good agreement with existing experimental data.     

On the ion drift in gas mixtures

The features of the velocity distribution function of ions during their drift in a mixture of different gases are analyzed. Examples of drift of heavy ions in light gas, a mixture of two gases with equal concentrations, and drift of light ions in heavy gas are considered. It was shown that the transition to discharge in mixtures of different gases allows the formation of an ion flux with characteristics unattainable for discharge in single-component gas under typical conditions under which experiments with dust structures in plasma are performed.     

Theory of laser acceleration of light-ion beams from interaction of ultrahigh-intensity lasers with layered targets

Experiments at the LANL Trident facility demonstrated the production of monoenergetic ion beams from the interaction of an ultraintense laser with a target comprising a heavy ion substrate and thin layer of light ions. An analytic model is obtained that predicts how the mean energy and quality of monoenergetic ion beams and the energy of substrate ions vary with substrate material and light-ion layer composition and thickness. Dimensionless parameters controlling the dynamics are derived and the model is validated with particle-in-cell simulations and experimental data.     

Energy spectra of light ions backscattered from random solids

A scheme for the calculation of energy spectra of ions backscatterred from random solids is proposed for the energy region where multiple collisions dominate. Calculations are performed for light ion bombardment of heavy targets, which is a case of special interest for the plasma-well interaction in fusion reactors. Examples of spectra obtained for protons incident on a Cu target are presented. A maximum in the spectra is found in accordance with measurements. The position of the maximum seems to vary slowly with the initial ion energy.     

Intense ion beams for inertial confinement fusion

Intense beams of light and heavy ions are being studied as inertial confinement fusion (ICF) drivers for high yield and energy. Heavy and light ions have common interests in beam transport, targets, and alternative accelerators. Self-pinched transport is being jointly studied. This article reviews the development of intense ion beams for ICF. Light-ion drivers are highlighted because they are compact, modular, efficient and low cost. Issues facing light ions are: (1) decreasing beam divergence; (2) increasing beam brightness; and (3) demonstrating self-pinched transport. Applied-B ion diodes are favored because of efficiency, beam brightness, perceived scalability, achievable focal intensity, and multistage capability. A light-ion concept addressing these issues uses: (1) an injector divergence of ⩽24 mrad at 9 MeV; (2) two-stage acceleration to reduce divergence to ⩽12 mrad at 35 MeV; and (3) self-pinched transport accepting divergences up to 12 mrad. Substantial progress in ion-driven target physics and repetitive ion diode technology is also presented. Z-pinch drivers are being pursued as the shortest pulsed power path to target physics experiments and high-yield fusion. However, light ions remain the pulsed power ICF driver of choice for high-yield fusion energy applications that require driver standoff and repetitive operation     

Experimental set-up for irradiation of solid H2 and D2 with charged particles of keV energies

An experimental facility was built where films of solid deuterium (and hydrogen) may be made with known thickness and irradiated with pulsed beams of electrons (up to 3 keV) and light ions (up to 10 keV). Films are made on a target plate held at 2.5–3 K. Film growth rate is calibrated with a quartz crystal film thickness monitor. The target plate, which can be heated so that films are removable by evaporation, may be used both as a calorimeter and as a beam current collector. Methods for measurement of secondary electron emission coefficients were developed, and preliminary measurements were made with electrons and hydrogen ions. For electron bombardment, the secondary electron emission coefficient of solid deuterium was much smaller than one. It was shown possible to use the set-up to study beam desorption of very thin films. Furthermore the set-up could be used for measuring the energy-reflection coefficient γ (i.e. the fraction of beam energy reflected from the target) for protons impinging on a heavy target material by using the target as a calorimeter.     

Laser Accelerated, High Quality Ion Beams

Intense beams of protons and heavy ions have been observed in ultra-intense laser-solid interaction experiments. Thereby, a considerable fraction of the laser energy is transferred to collimated beams of energetic ions (e.g. up to 50 MeV protons; 100 MeV fluorine), which makes these beams highly interesting for various applications. Experimental results indicate very short pulse duration and an excellent beam quality, leading to beam intensities in the TW range. To characterize the beam quality and its dependence on laser parameters and target conditions, we performed experiments at several high-power laser systems. We found a strong dependence on the target rear surface conditions allowing to tailor the ion beam by an appropriate target design. We also succeeded in the generation of heavy ion beams by suppressing the proton amount at the target surface. We will present recent experimental results demonstrating a transverse beam emittance far superior to accelerator-based ion beams. Finally, we will discuss the prospect of laser-accelerated ion beams as new diagnostics in laser-solid interaction experiements. Special fields of interest are proton radiography, electric field imaging, and relativistic electron transport inside the target.     

Diffraction dissociation,an important background to photon-photon collisions via heavy ion beams at LHC

The cross sections for the production of hadrons in quasi-real photon-photon collisions in proton-proton and heavy ion interactions are compared with the corresponding cross sections for central diffraction and for photon-pomeron collisions. The signatures, heavy ions or protons with only slightly changed momenta together with two large rapidity gaps and a cluster of produced hadrons in the central region, are nearly identical in all three processes. Therefore, it will be rather difficult to distinguish the reactions experimentally. It is found, that central diffraction is the dominant process in collisions of protons, light and medium-heavy ions. The photon-pomeron and photon-photon processes have quite similar cross sections in collisions of heavy ions like lead.     

Nuclear surface,mean field and isospin effects in Boltzmann master equation theory of pre-equilibrium reactions

Pre-equilibrium emission of nucleons and light charged particles is investigated in central collisions leading to the complete fusion of two heavy ions, within the Boltzmann master equation approach. Realistic nucleon momentum density distributions for both projectile and target nuclei are used and mean field effects are schematically introduced in the early stage of the reaction process. The isospin dependence of the calculation parameters is also discussed. Theoretical predictions of the spectra of the particles emitted both in symmetric and asymmetric interactions at incident energies of a few ten MeV/nucleon are in satisfactory agreement with the experimental findings.     

Depth of origin of sputtered particles under the oblique incidence of a primary ion beam

A physical model and mathematical calculations of the maximum partial depths of origin of sputtered particles versus mass, energy, and the angle of incidence of ions bombarding a one-component amorphous target are presented. Calculations reveal that the maximum depth of origin of secondary particles depends on the primary-ion incidence angle, which attains the highest value at angles of 30°–60° relative to the normal to the sample surface. When the primary beam and the target material have identical parameters, the maximum depths of origin of light secondary particles exceed those of heavy ones. Secondary particles exhibit the isotope effect. For light elements (Li, Be, and B), a heavier isotope has a larger maximum depth of origin than a lighter one. In the case of heavy elements (e.g., Mo), a lighter isotope has a greater maximum depth of origin than a heavier one.     

Coulomb explosion of a cluster with a complex ion composition

The problem of the Coulomb explosion of a homogeneous cluster with light and heavy ions has been analytically solved. The space-time and spectral distributions of accelerated ions have been obtained. The characteristics of scattered light ions are determined as functions of the atomic composition of the cluster. It has been shown that sources of monoenergetic ions can be created using the interaction of high-power ultrashort laser pulses with molecular clusters.     

Laser-triggered quasi-monoenergetic ion beams at a moderate intensity and pulse duration

Plasma produced by short laser pulses from thin homogeneous foils with light and heavy ions is capable of generating quasi-monoenergetic light ions. This happens for the tail of light ions near the front of heavy ions. It was found that this effect is well pronounced for a moderate laser intensity (～10¹⁸ W/cm²) and pulse duration (～1 ps) by using a 2D particle-in-cell simulation of the laser interaction with thin CD₂ foils. Quasi-monoenergetic deuterons form a jet from the rear side of the foil with the energy ～1 MeV. The conversion efficiency to these quasi-monoenergetic ions is 10^?3.     

基于HIRFL-CSR测量丰中子重核质量的建议

丰中子重核区有大量原子核质量未知,迫切需要实验测量。我们建议,利用兰州重离子加速器研究装置HIRFL-CSR上的等时性质谱术,高精度测量204Pt等丰中子重核的质量。CSR质量测量实验中,在目标核产额尽可能高的前提下,需要每次注入都有多个离子同时储存到实验环CSRe中,才能针对逐次注入修正磁场晃动的影响,得到高精度测量结果。但在丰中子核区,当目标核产生截面非常低时,每次注入能储存到环中的离子数目太少。为了解决这个问题,我们提出了一种"混合厚度靶"的方法,在不明显改变目标核产额的情况下,显著增加同时储存在CSRe中的离子数,满足实验要求。模拟计算表明,在CSRe测量丰中子重核质量是可行的,并推荐了实验的设置。     

On a supersonic flow of ions in a light gas

The possibility of attainment of large Mach numbers is analyzed for the case of heavy ions drifting in a light gas. Under conditions typical of experiments with dust structures in plasmas, the use of the mixture of light and heavy gases is shown to make it possible to suppress the ion heating in the electric field and to form supersonic flows characterized by large Mach numbers. The drift of xenon ions in helium is considered as an example.     

4.5AGeV/c 24Mg与核乳胶碰撞中簇射粒子的赝快度分布

报道了4.5AGeV/c ²⁴Mg与核乳胶碰撞中产生的簇射粒子的赝快度分布,结果表明,分布宽度和峰值位置明显依赖于靶核尺寸.用柱模型对赝快度分布进行了分析,MonteCarlo方法计算得到的结果基本符合实验数据的走向,并重现了实验数据中的涨落现象.     

Determination of charge states of single swift heavy projectiles by high-energy delta-electrons

The effective charge state is an important particle parameter which is required for the calculation of many effects concerning the interaction between radiation and matter such as an estimate of the radial dose of swift heavy projectiles, stopping power and so on. A new method for the determination of effective charge states of heavy ions is based on the measurement of the number of high-energy delta-electrons which are ejected from a target by the penetrating ion. These electrons are detectable with a CCD-detector and their number can be correlated to the effective charge state of the projectile for known particle velocities. This method is even applicable to operation with single swift heavy ions within statistical bounds.     

Pseudorapidity Distribution of Shower Particles in 24Mg-Emulsion Collisions at 4.5A GeV/c

The pseudorapidity distribution of shower particles produced in the ²⁴Mg-emulsion collisions at 4.5A GeV/c is reported in this paper. The dependences of the distribution width and the peak position on the target size are observed.The pseudorapidity distribution of shower particles for the events with low target multiplicity (light target) is narrower than that with high target multiplicity (heavy target). The maximum probability pseudorapidity for light target is greater than that for heavy target. The experimental data is analyzed by using the cylinder model suggested by Liu et al. The Monte Carlo results based on Liu's cylinder model are approximately in agreement with the experimental tendency and fluctuation.     

Nuclear reactions triggered by laser-accelerated high-energy ions

A technique is suggested for triggering nuclear reactions by accelerating ions with a powerful ultrashort laser pulse in a plasma. The underlying idea of the suggested compact “reactor” is utilization of high-energy ions accelerated by the charge-separation electrostatic field in the direction perpendicular to the laser beam axis in a gas-filled capillary. Accelerated ions with energies of several MeV penetrating the target from the inside surface of a channel give rise to nuclear reactions which can be used to create a compact source of fast neutrons and neutrons of intermediate energies for generating various (short-and long-lived, light and heavy) isotopes, for generating gamma radiation over a broad energy range, for making sources of light ion and induced radioactivity. The yield of the corresponding nuclear reactions as a function of the laser beam parameters has been investigated. The suggested technique for triggering nuclear reactions provides a practical tool for studies of nuclear transformation on the pico-and nanosecond scales, which cannot be achieved using other methods. Zh. éksp. Teor. Fiz. 115, 2080–2090 (June 1999)