Measurement of the transverse kinetic energies of argon recoil ions produced in 120 MeV -Ar collisions

Measurements were carried out to deduce the transverse kinetic energies of highly charged argon recoil ions produced in single collisions of 120 MeV ions with argon atoms in which the post collision charge states of the projectiles were not determined. A time of flight spectrometer was designed and fabricated to detect the charge states of recoils. Experimental procedures for optimizing the spectrometer for extraction, transmission and detection of recoils are described. A simple approach for determining the transverse kinetic energy of the recoil ions from FWHM of the peaks is reported. This method is shown to be independent of the choice of collision partners and requires only the knowledge of the physical values of “optimized parameters” of time-of-flight spectrometer used in the experiment. The transverse kinetic energy of the recoil ions determined from the present approach is found to vary from 0.03 eV for to 4.02 eV for Ar¹⁰⁺. These values are compared with the results reported by earlier workers and are shown to follow a q²-behaviour up to a charge state q =8+ of the recoil ions. Received: 5 February 1998 / Revised: 8 June 1998 / Accepted: 11 June 1998     

The contribution ofK-electron capture for the production of highly charged Ne recoil ions by 156 MeV bromine impact

The recoil ion production cross sections in 2MeV/amu Br ⁿ⁺+Ne⁰→Br ^n′++Ne ^q+ were measured using a projectile ion — recoil ion coincidence technique where the final charge states of both collisions partners were detected simultaneously. Multiple ionization was found to be the dominant process for the production of low charge state recoil ions whereas the production of highly charged recoil ions is accompanied by electron capture from the Nek-shell. The derived ratio of single to double Ne-k electron capture probabilities indicates deviations from a binomial statistics distribution.     

Multiple ionization of atoms and the energy of recoil ions in collisions with fast,multiply charged ions

On the basis of the sudden perturbation approximation and the model of independent electrons, simple analytical expressions are obtained for the cross sections of multiple ionization of atoms and the average energies of recoil ions in collisions between atoms and fast, multiply charged ions in the range of parameters in which the Born approximation is inapplicable. An expression for the energy distribution function of recoil ions is also obtained.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 111–116, April, 1996.     

Observation of MeV ions in long-pulse, large-scale laser-produced plasmas

A new approach for investigation of the generation of fast ions and hot electrons inside the same plasma volume in laser-produced plasmas is proposed. It is based on the spectroscopic observation of line radiation from singly and doubly excited levels with simultaneous high spectral and spatial resolution. The experimental results demonstrate the observation of fast ions from highly charged target material inside the plasma volume and suggest that the generally accepted scaling relations are seriously invalid under certain conditions. Even at rather modest intensities ions with energies of several MeV are observed. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 4, 262–267 (25 August 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Spectral and angular distribution of slow electrons emitted by hydrogen atoms in collisions with fast highly charged ions

The ionization of hydrogen atoms with the emission of slow electrons in collisions with fast highly charged ions is considered. Analytical expressions are obtained for the singly and doubly differential ionization cross sections and for a quantity which characterizes the angular asymmetry in the escape of slow electrons. A unique feature of the momentum balance for collisions that lead to the emission of slow electrons is discussed. Zh. Tekh. Fiz. 67, 13–18 (July 1997)     

Preparing a laser cooled plasma for stopping highly charged ions

We present a new cooling scheme for the preparation of highly charged ions for future in-trap precision experiments. A plasma of laser cooled ²⁴Mg⁺ ions trapped in a 3D harmonic confinement potential is used as a stopping medium for the highly charged ions. We focus on the dynamic evolution of the plasma, determining suitable cooling conditions for fast recooling of the ²⁴Mg⁺ ions. The results of a realistic parallel simulation of the complete stopping process presented here indicate that a small, constant detuning of the laser frequency is sufficient for subsequent recooling of the plasma, thus maintaining the stability of the plasma.     

Simulating the stopping dynamics of highly charged ions in an ultra-cold, strongly coupled plasma

We introduce a method for stopping highly charged ions (HCIs) in a laser-cooled one-component plasma (OCP) of ²⁴Mg⁺ ions and present results on stopping times derived from realistic molecular dynamics simulations of the complete stopping process. This stopping scheme can provide ultra-cold highly charged ions for future in-trap precision mass measurements. The choice of an ultra-cold ion plasma as a stopping medium is governed by the almost negligible charge exchange of the HCI with the laser-cooled ions and the very low temperatures which can be reached. In our analysis we focus on the stability and fast recooling of the plasma – two features essential for the experimental realization of this stopping scheme.      

The third particle in deep inelastic collisions

Angular correlations between charged reaction products have been measured for the reaction¹⁴N+²⁷A1 at 70 and 100 MeV. Light particle evaporation from the heavy recoil is shown to be the dominant process. In addition, however fast alphas are observed for all reaction channels. From the three-body kinematics we conclude that these alphas are emitted from the contact zone between the two heavy ions. A comparison of the results forE _Lab=70 and 100 MeV excludes an explanation of this process by the recently suggested “Piston” or “hot-spot” models.     

Neutralization of H− ions in collisions with fast, multiply charged ions

The neutralization of H⁻ ions in collisions with fast, multiply charged ions is considered in the parameter region where the Born approximation applies. An analytical formula is obtained for the H⁻ neutralization cross section in such collisions. Zh. Tekh. Fiz. 69, 1–4 (July 1999)     

Charge distribution of the daughter atom in α decay of 210Po

The evaporation model developed by Russek and collaborators for multiple ionization of outer-shell electrons in ion-atom collisions has been applied to the charge distribution of the daughter atom produced by α decay of ²¹⁰Po. The calculated result indicates that most of the daughter atoms are positively charged ions with a mean charge of + 1.41. The other ionization mechanisms, the recoil effect and the shake-off effect, are also considered. In comparison with the recent experimental results, it is shown that the evaporation model predicts more adequately than the recoil effect and the shake-off effect.     

C3+与Ne碰撞过程纯电离绝对截面的测量和研究

介绍了离子-原子碰撞过程中双微分绝对截面的计算方法.利用符合技术测量了中能区C³⁺+Ne碰撞系统的纯电离微分绝对截面. 将实验结果与多体经典蒙特卡罗方法计算结果进行对比后发现，纯电离截面随入射能量变化的趋势基本一致，对理论与实验产生差异的原因作了分析. 对多重电离的电离机制分析表明：高价态的反冲离子主要来自于俄歇贡献；随着入射能量的升高，电子-电子间的库仑作用也逐渐显现. 此实验方法可以用于相同实验装置上的各种反应出射道的绝对截面测量，入射离子种类及入射离子能量范围将得到拓展. 关键词： 离子-原子碰撞 绝对截面 纯电离     

Ionization of hydrogen and helium atoms by highly charged fast ions in collisions with small momentum transfer

Ionization of hydrogen and helium atoms is studied for the case of “soft” collisions with highly charged fast ions with v≲Z≪v² and v≫v ₀, where Z is the ion charge, v is the collision velocity, and v ₀∼1 is the characteristic velocity of the electron in the ground state of the atom. Analytical expressions are derived for the singly and doubly differential cross section for ionization of a hydrogen atom accompanied by the ejection of a slow electron v _e≲v ₀, where v _e is the velocity of the ejected electron with respect to the recoil ion). The results are generalized to the case of single ionization of helium. It is shown that soft collisions provide the main contribution to the hydrogen ionization cross section and for all practical purposes determine the cross section for single ionization of helium. The asymmetry in the angular distribution of the ejected slow electrons and the properties of momentum exchange in such collisions are discussed. Finally, a formula for the cross section for single ionization of helium is proposed. Zh. éksp. Teor. Fiz. 112, 1966–1977 (December 1997)     

On the chemical sputtering of oxygen-exposed molybdenum

The sputtering of oxygen-exposed molybdenum was studied by means of mass analysis of emitted neutral and charged particles. The irradiation was performed with 8 keV Ar⁺ ions at temperatures of 25° and 485°C. It was found that the enhanced sputtering yield at elevated temperature during oxygen exposure is due to beam-induced desorption of MoO₂ and cascade sputtering of MoO. At this temperature considerable oxygen incorporation also takes place owing to recoil mixing and diffusion.EURATOM Association     

On the behavior of an analytical form of the stopping cross-section <Emphasis Type="Italic">or</Emphasis> how sharp can a Bragg peak be made?

An analysis is made of the Bragg peak in the stopping power of fast ions, with the intension of determining how to shape the dose-depth curve for fast ions impinging on materials. We find the use of highly charged projectiles is very effective for narrowing the peak.     

Enhanced production of fast multi-charged ions from plasmas formed at cleaned surface by femtosecond laser pulse

We present atomic, energy, and charge spectra of ions accelerated at the front surface of a silicon target irradiated by a high-contrast femtosecond laser pulse with an intensity of 3×10¹⁶ W/cm², which is delayed with respect to a cleaning nanosecond laser pulse of 3-J/cm² energy density. A tremendous increase in the number of fast silicon ions and a significant growth of their maximum charge in the case of the cleaned target from 5+ to 12+ have been observed. The main specific features of the atomic, energy, and charge spectra have been analyzed by means of one-dimensional hydrodynamic transient-ionization modeling. It is shown that fast highly charged silicon ions emerge from the hot plasma layer with a density a few times less than the solid one, and their charge distribution is not deteriorated during plasma expansion.This revised version was published online in August 2005 with a corrected cover date.     

Formation of relativistic positron systems by the axial channeling of positrons in ionic crystals

An analytical expression is written for the effective interaction potential of a fast charged particle with ionic crystals of the CsCl type as a function of the temperature of the medium, taking long-range order into account. A numerical analysis shows that there is a real possibility of axial superchanneling of positrons along the 〈100〉 axis of negatively charged ions in crystals with this structure. The wave function and energy spectrum of the localized state are investigated, and the possibility of the formation of metastable, two-dimensional, relativistic positron systems is analyzed. Zh. Tekh. Fiz. 68, 116–120 (April 1998)     

Exploring relativistic many-body recoil effects in highly charged ions

The relativistic recoil effect has been the object of experimental investigations using highly charged ions at the Heidelberg electron beam ion trap. Its scaling with the nuclear charge Z boosts its contribution to a measurable level in the magnetic-dipole (M1) transitions of B- and Be-like Ar ions. The isotope shifts of 36Ar versus 40Ar have been detected with sub-ppm accuracy, and the recoil effect contribution was extracted from the 1s(2)2s(2)2p 2P(1/2) - 2P(3/2) transition in Ar13+ and the 1s(2)2s2p 3P1-3P2 transition in Ar14+. The experimental isotope shifts of 0.00123(6) nm (Ar13+) and 0.00120(10) nm (Ar14+) are in agreement with our present predictions of 0.00123(5) nm (Ar13+) and 0.00122(5) nm (Ar14+) based on the total relativistic recoil operator, confirming that a thorough understanding of correlated relativistic electron dynamics is necessary even in a region of intermediate nuclear charges.     

Optical detection system for laser cooling and precision laser spectroscopy of relativistic highly charged ions at the CSRe

Laser cooling and precision laser spectroscopy experiments of relativistic highly charged ions are being prepared at the heavy-ion experimental cooler storage ring (CSRe). Optical detection of fluorescence photons, emitted from the laser-excited ions, is extremely important for both powerful methods. In this paper, we briefly report on the current status of the existing optical detectors and also on their performance during laser cooling of relativistic Li-like ¹⁶O⁵⁺ ion beams at the CSRe. In addition, we introduce the designs for our new optical detection systems, which have much higher photon detection efficiencies and can cover a much broader wavelength range. These detector systems will be used for the upcoming laser spectroscopy experiment of Li-like ¹⁶O⁵⁺ ions, as well as for future laser spectroscopy experiments with other highly charged ions.     

Laser ion source for ITEP–TWAC project

Laser ion source (LIS) is the only type of source capable of generating 10–30 mA beams of highly charged ions for the ITEP–TeraWatt (TWAC) accelerator/accumulator facility [B.Yu. Sharkov et al., Nucl. Instrum. Methods Phys. Res. A 415 20 (1998).]. The assembling stage of the new LIS based on 100 J/1 Hz master oscillator–power amplifier CO₂-laser system [Yu. Satov, et al., J. Russ. Laser Res. 25(3) 205 (2004).] is in progress at ITEP now. In the first phase, the ion beam parameters (charge state distribution, current, pulse length and emittance) will be specified for different elements and target irradiation conditions. According to the planning, the new LIS and the new high-current injector [D. Kashinsky, et al., Proceedings of the Heavy Ion Fusion Conference, Moskow (2002).] will be used to deliver the beams of highly charged ions for the ITEP–TWAC accelerator/accumulator facility.