Energy loss of light ions with allowance for the presence of metastable particles in the ion beam

The change in the average ion charge due to the presence of particles in metastable states in beams of helium-like ions has been studied. The charge distributions and average charges have been calculated for ions with nuclear charges Z = 3?7 and a velocity of 3.65 au in nitrogen. The previously obtained data on the cross sections of loss and capture of electrons by metastable ions and ions in the ground state were used in the calculations. It is shown that the presence of metastable particles in ion beams leads to an increase in the average charge and energy loss for all considered ions.     

Ein ionenoptisches System zur Dämpfung transversaler Schwingungen in Strahlen schwerer Ionen

An ion-optical system of new type capable to reduce the divergency of heavy ion beams is proposed. The action of this system is based on the difference of mean charge of heavy ions in gas and in condensed matter. The beam is split into two parts of different mean charge and merged by unification of the mean charge alternately by local application of the different charge exchange media. Considering the beam to be bound to an axis by a series of identical coaxial lenses the ions will oscillate around the axis. Since one part of the beam remains unaffected by charge exchange processes on the average the particles of the other part are forced to increase their charges at positions near to the center line and to reduce their charges at positions of maximum elongation. This process will absorb oscillation energy from the beam. Also, the coordinates of the particles of the second part of the beam move differently in phase space while the particles are in higher charge states: the coordinates are shifted into the phase space domain occupied by the coordinates of the particles of the first part of the beam thus yielding an overall reduction of beam divergency.     

Specific features of the excitation spectrum of helium II in a plasma initiated by an electron beam

The emission of a low-pressure helium plasma (P≤2 Torr) initiated by a monochromatic electron beam is investigated. It is found that an increase in the current leads to a drastic increase in the rate of charge exchange of doubly charged helium ions. The assumption is made that inelastic collisions of He⁺⁺ ions with metastable helium atoms provide the main channel of charge exchange of these ions due to the reaction He⁺⁺+Hem→ He⁺*+He ₀ ⁺ .     

Registration of accelerated multiply charged ions from the cathode jet of a vacuum discharge

The parameters of Cuⁿ⁺ and Taⁿ⁺ ions from the plasma of a vacuum spark with a voltage up to 2.5 kV and a current rise rate up to 2 × 10¹⁰ A/s are studied using the time-of-flight method. At the initial stage of the discharge, bursts of beams of accelerated multiply charged ions from the cathode flame have been detected. It is established that the charge state distribution and energy of a beam are controlled by the initial voltage U ₀ of the capacitor. Upon an increase in this voltage, the average charge of copper ions attains the value +9, and the average charge of tantalum ions can be as high as +20, while the energy attains values of 150 and 350 keV, respectively. It is found that the average energy of ions with charge Z increases in proportion to the charge and is close to the energy eZU ₀ which would have been acquired by ions accelerated in the electric field of the discharge gap.     

Metastable states of dust plasma

The free energy of three-component dust plasma has been calculated analytically based on the spherical model of an elementary electroneutral volume. It has been shown that metastable states of dust particles, ions, and simultaneously all plasma particles can exist for finite interparticle distances. These states can be attained due to spatial correlation of electrons, while some states can be attained due to the correlation of ions. A large charge of dust particles, high electron temperature, and a small fraction of the charge of the electrons compared to the total absolute charge of the plasma particles are important conditions for the existence of metastable states. A possible connection between the existence of metastable states of particles in the plasma and their agglomeration has been analyzed.     

Peculiarities in the cross sections of electron capture by phosphorus ions

The effect of decreasing the cross sections of electron capture by phosphorus (P⁵⁺) ions penetrating through gaseous media has been revealed experimentally. This effect is a violation of the known uniform dependence between the electron-capture cross section and the ion charge. Such an anomaly was not observed in measurements performed with argon ions under the same conditions. A possible reason of decreasing the cross sections of electron capture by P⁵⁺ ions may be autoionization of excited P⁴⁺ ions. The latter are formed during electron capture into excited states by metastable particles of a beam of P⁵⁺ ions.     

Die Erzeugung von negativen polarisierten Deuteriumionen aus metastabilen Deuteriumatomen im 2S 1/2-Zustand

An experimental method to produce polarized negative hydrogen ions is discussed and compared with other methods. The method makes use of the different lifetimes of the metastable 2S 1/2 state and the 2P 1/2 state of the hydrogen atom. Polarized ion beams are obtained by using a selective quenching process followed by selective ionisation. Experimental results are given for the intensity and polarization of the polarized negative ion beam of deuterons. These results were obtained as a function of the quenching-field, the magnetic field in the argon-cell and the density of argon and cesium. The yield of negative ions can be expressed by the cross sections for the different charge exchange reactions in argon. The measured tensorpolarisationP ₃₃ can be interpreted as a function of the cross sections, the argon-density and the magnetic field along the beam axis. Beams of 50 nA intensity were produced with a polarization ofP ³³=?0.250±0.006. The main advantage of this method is a low beam emittance, values of 0.7 cm rad eV^1/2 were achieved. The production of a polarized positive deuteron beam seems to be possible.     

Energy losses of beryllium ions penetrating through thin films before the attainment of charge equilibrium

The dependences between the energy losses of beryllium ions penetrating through thin organic (celluloid) films and the initial ion charge i ₀ and target thickness t are calculated. The proposed modified method is used to determine the charge fractions and average charge of an ion beam and the half-width and skewness of the charge distributions before the attainment of charge equilibrium. Calculations are performed for Be ⁱ⁺ ions with a velocity of 8 × 10⁸ cm/s (E = 0.33 MeV/nucleon).     

Multicomponent approximation for evaluation of nonequilibrium charge fractions of ions passing through thin films

A method is proposed to calculate the nonequilibrium charge fractions and mean charges of light ions, depending on film thickness. The calculated results are presented for three charge fractions of 0.75 MeV/nucleon B ion beam, passing through the organic film, and for four charge fractions of 2 MeV/nucleon Ne beam, passing through the carbon film. The dependence of energy loss on the initial charge of projectile Ne ions and target thickness in the nonequilibrium conditions is examined.     

BRing中电荷交换引起的束流损失分布模拟计算

在强流重离子加速器运行中,带电粒子与真空管道中的残余气体分子相互作用发生的电荷交换反应是影响重离子束流寿命的关键因素。这种电荷交换过程导致的束流损失将解吸出真空管壁上吸附的气体分子,进而引起真空压力的动态变化,将严重影响加速器的稳定运行和最终束流引出流强。中国科学院近代物理研究所将在广东省惠州市建造的强流重离子加速器装置（High Intensity heavy-ion AcceleratorFacility,简称HIAF）利用增强器（Booster Ring,简称BRing）提供束流流强高达2×1011 ppp的238U35+用于核物理及原子物理等实验研究。对强流重离子加速器BRing中238U35+束流发生电荷交换反应,损失一个电子成为238U36+的过程进行了追踪模拟,计算得到了U36+损失前的运动径迹和全环粒子损失位置分布,模拟结果显示U36+受到色散元件的影响,将集中损失在位于二极磁铁后的漂移节区域中。基于模拟结果,在束流损失位置处设计安装由低解吸率材料制作的准直器,优化设计后的准直效率高达95%以上;并模拟计算了有无准直器时真空压力和束流流强的变化,安装准直器后BRing的平均真空度变化小于10%,将确保BRing加速器的稳定运行。During heavy ion accelerator operation, the charge exchange effect between ions and residual gas molecules is the key factor to influence beam lifetime. The charge exchange process has ions lost on the wall and leads to a dynamical vacuum change, which will seriously affect the accelerator operation and reduce the extraction beam intensity. The Institute of Modern Physics' future project, called High Intensity heavy ion Accelerator Facility (HIAF), will be built in Huizhou city, Guangdong Province, China. The Booster Ring (BRing) will provide 2×11 ppp 238U35+ for nuclear physics experiments. This article studies the track of particle U36+ before impacting on the wall, which is the reference particle U35+ losing one electron, and gets the U36+ loss distribution along the BRing. The simulation result shows that U36+ will be influenced seriously by dispersion elements, and will be lost in the drift sections after the dipoles. Collimators made out of materials with low desorption will be installed in the particles lost positions. The collimator efficiency after optimization can be larger than 95%. It also shows BRing average pressure change and beam intensity change between collimators on and off. The result points out that the BRing average pressure change will be less than 10% with collimators on, which makes BRing operate stably.     

Study of the angular and energy distributions of Na+ and K+ ions which have passed through thin copper films

The angular and energy distributions of alkaline Na⁺ and K⁺ ions which have passed through thin Cu films in different crystal states are studied. The ion energy E₀ is varied from 10 to 40 keV, and the incidence angle. ranges from 0° to 60°. The angular aperture of the detector is ～0.5°, which allows the form of the angular distribution of ions which have passed through the solid thin films as a function of the energy, the angle of primary-ion beam incidence, and the layer thickness to be studied in detail. It is shown that, in the range E₀ = 10.40 keV, the energy loss ΔE of those ions that have passed increases linearly as the energy of incident ions increases. The energy loss increases with increasing ion mass in the case of singly charged ions. The surface amorphization of single- and polycrystalline films leads to an increase (by 150–200 eV) in the energy loss caused by the diffuse propagation of ions and to loss-peak broadening. It is probable that surface amorphization is accompanied by an increase in the number of atoms experiencing multiple collisions with atoms of the film, which leads to an increase in the average energy loss by ions that have passed through films.     

Effect of beam-plasma interaction on ion transport through a cyclotron injector

The influence of collective effects associated with transverse plasma oscillations excited by a beam of negative ions on the neutralization of the space charge due to fast ions is studied. Conditions for the dynamic deneutralization of an unstable ion beam are refined. Analytic expressions for the plasma ion density distribution and for the stationary electric field in a partially neutralized beam are obtained. The equation of motion of a beam in the self-electric field and in an external magnetic field is used to determine the effect of secondary charged particles on the transport of negative ions through the injector of a cyclotron.     

Single-electron charge transfer and excitations at collisions between Bi<Superscript>4+</Superscript> ions in the kiloelectronvolt energy range

Pioneering theoretical data for single-electron charge transfer and excitations due to collisions between Bi⁴⁺ ions in the ground (6s) and metastable (6p) states are gained in the collision energy interval 5–75 keV in the center-of-mass frame. The cross sections of the processes are calculated in terms of the close-coupling method in the basis of two-electron quasi-molecular states for the Coulomb trajectory of nuclei. It is found that single-electron capture into the singlet 6s ² states of Bi³⁺ ions makes a major contribution to the charge transfer total cross section for Bi⁴⁺(6s) + Bi⁴⁺(6s) collisions (reaction 1), whereas single-electron capture into the singlet 6s6p states is the basic contributor to the total cross section in Bi⁴⁺(6s) + Bi⁴⁺(6p) collisions (reaction 2). In the collision energy interval mentioned above, the collision cross sections vary between 1.2 × 10^?17 and 1.9 × 10^?17 cm² for reaction 1 and between 3.8 × 10^?17 and 5.3 × 10^?17 cm² for reaction 2. In reaction 1, the 6s → 6p excitation cross sections vary from 0.6 × 10^?16 to 0.8 × 10^?16 cm² for the singlet channel and from 2.2 × 10^?16 to 2.8 × 10^?16 cm² for the triplet channel. The calculation results are compared with the data obtained in experiments with crossed ion beams of kiloelectronvolt energy. The fraction of metastable ions in the beams is estimated by comparing the experimental data with the weighted average theoretical results for the cross sections of reactions 1 and 2. From the data for the charge transfer cross sections, one can estimate particle losses in relativistic beams due to a change in the charge state of the ions colliding with each other in the beam because of betatron oscillations.     

PIC mode simulation of solenoid collimation channel

A new SSC(Separated Sector Cyclotron)-Linac is being designed to serve as an injector for the SSC at the HIRFL(Heavy Ion Research Facility Lanzhou).The beam intensity at the LEBT(Low Energy Beam Transport)for the heavy ions after the selection is typically low and the space charge effects are inconspicuous.The space charge effects become obvious when the beam current increases to a few hundred microamperes.The emittance growth deriving from the space charge effects may be particularly troublesome for the following linac and cyclotron.An optical system containing three solenoids has been designed for the LEBT to limit the beam emittance and to avoid the unnecessary beam loss in the cyclotron,as well as for the purpose of immunizing the LEBT emittance growth due to the space charge effects.The results of the PIC(Particle-In-Cell)mode simulation illustrate that this channel could limit the beam emittance growth and increase the beam brightness.     

The energy of thermal electrons in electron beam created helium discharges

We have measured the electron energy of the thermal group of electrons in both longitudinal and transverse electron beam created helium glow discharges. The measurement technique employs the ratio of intensities of spectral lines in the 2s³S?np³P He I series. Values of kT_e between 0.07 and 0.11 eV were obtained. These energies are typical of the beam-generated electric field free plasmas. The competitive loss of helium ions by recombination and by charge transfer in a He?Hg electron beam created plasma is calculated. The results are applied to the Hg⁺ laser pumping scheme using a electron beam created He?Hg plasma.     

Kinetic Description of the Stationary Band-Like Weakly Turbulent Beam Discharge Plasma in Hydrogen. I. Basic Equations — Numerical Approach — Ionization and Dissociation Budget

On the basis of the electron Boltzmann equation and of the balances for the charge carriers (e, H⁺, H₂⁺, H₃⁺), the H-atoms and the metastable H(2s)-atoms for the H/H₂-mixture the behaviour of the weakly turbulent, band-like electron-beam discharge plasma in hydrogen has been calculated taking into account the main collision and transport processes. In dependence of the normalized discharge length, the life time of the neutral particles in the band-like plasma and the electron beam generated turbulence energy density the ionization and dissociation budget and in particular the most important electron-heavy particle collision rates, which appear in the balance equation system, are investigated in the present part of our paper. In a second part the results related to the budget of the ions and the metastable atomic state will be reported and an analysis of the main processes in the balances will be made.     

Ultrahigh charging of dust particles in a nonequilibrium plasma

Charging of dust particles in a plasma with the two-temperature energy distribution of electrons has been studied. It has been shown that the dust-particle potential divided by the electron temperature decreases with increasing electron temperature in the plasma with cold ions. Owing to this behavior, the potential of the dustparticle surface increases with the electron temperature more slowly than the linear function and is lower than the electron temperature (divided by the elementary charge) for T _e > 5.5 eV in hydrogen and for T _e > 240 eV in argon. The fraction of fast electrons at which these electrons begin to contribute to the charge of dust particles has been determined. It has been shown that the charge of micron particles can reach 10⁶ elementary charges. The effect of the cold and thermal field emission on the charge of dust particles has been analyzed. The possibility of obtaining ultrahigh charges (to 10⁷ elementary charges on dust particles with a radius of 50–100 μm irradiated by a 25-keV 1-mA electron beam has been demonstrated.     

Stopping of heavy ions in plasmas at strong coupling

Standard approaches to the energy loss of ions in plasmas like the dielectric linear response or the binary collision model are strictly valid only in the regimes where the plasma is close to ideal and the coupling between projectile-ion and the plasma target is sufficiently weak. In this review we explore the stopping power in regimes where these conditions are not met. Actually relevant fields of application are heavy ion driven inertial fusion and the cooling of beams of charged particles by electrons. The conventional linear mean-field treatments are extended by many-body methods and particle simulations to account for strong correlations between the particles and for nonlinear coupling. We report the following important results in connection with the stopping at strong coupling: The energy loss of an ion scales with its charge approximately like Z^1.5, the effective screening length depends on Z and is larger than the Debye length. Slow highly charged ions are surrounded by a cloud of electrons trapped by many body collisions. Quantum effects like the wave nature of the electrons and Pauli-blocking reduce the stopping power by mollifying the effective interactions.     

Process in high energy heavy ion acceleration

A review of processes that occur in high energy heavy ion acceleration by synchrotrons and colliders and that are essential for the accelerator performance is presented. Interactions of ions with the residual gas molecules/atoms and with stripping foils that deliberately intercept the ion trajectories are described in details. These interactions limit both the beam intensity and the beam quality. The processes of electron loss and capture lie at the root of heavy ion charge exchange injection. The review pays special attention to the ion induced vacuum pressure instability which is one of the main factors limiting the beam intensity. The intrabeam scattering phenomena which restricts the average luminosity of ion colliders is discussed. Some processes in nuclear interactions of ultra-relativistic heavy ions that could be dangerous for the performance of ion colliders are represented in the last chapter. The text was submitted by the author in English.     

Effect of the capture and loss of two electrons on the charge distributions of ions

The effect of the processes of capture and loss of two electrons on the width of the equilibrium charge distribution of ions in different materials is studied. These processes increase the width of the equilibrium charge distribution in the energy region of E < 0.1 MeV/nucleon. The effect increases with decreasing ion nuclear charge and reaches 10–15% for boron ions.