Table of contents

This issue contains papers presented at the 15th International Conference on the Physics of Highly Charged Ions, HCI2010. The conference was held at Fudan University, Shanghai, 29 August–3 September 2010. HCI is a biannual conference series going back to the very first conference held in Stockholm, Sweden in 1982. Previous editions in this millennium were held in Berkeley, USA, 2000; Caen, France, 2002; Vilnius, Lithuania, 2004; Belfast, UK, 2006, and Tokyo, Japan, 2008.

The physics of highly charged ions, HCIs, is of great interest due to their key role in testing quantum electrodynamics in strong fields, and possible testing of parity non-conservation. However, HCIs also play crucial roles in the physics of hot plasmas, for example those produced in tokamak fusion devices and in inertial confinement fusion experiments. Much of the diagnostics of matter under such extreme environments relies very heavily on high quality atomic data of HCIs. The field of x-ray astronomy hinges almost entirely on the use of spectral lines from HCIs to provide information from distant astrophysical plasmas and objects. Given these fundamental interests and the current rapid developments in fusion and x-ray astronomy, it is clear that the physics of HCIs is a rich area of research with strong and important connections to many important subfields of physics. New application areas of HCI physics are also under development: two examples are (a) to provide 13.5 nm—and later half of this wavelength—radiation for lithography and (b) applications in medical research. The need for high quality atomic data of HCIs is as important now as it has ever been.

HCI2010 was attended by over 200 scientists from around 20 countries; see the following table. Over 70 of the participants were students, which is very encouraging for the future of HCI related physics. The academic programme was organized based on the suggestions from the International Advisory Board, and consisted of six review lectures, nine progress reports, one local report and 21 selected talks.

The proceedings could never have been published without the diligent work of the referees and we are very grateful for their help. The order of the 69 articles follows the five classic subfields of the HCI conference:

• Fundamental aspects, structure and spectroscopy

• Collisions with electrons, ions, atoms and molecules

• Interactions with clusters, surfaces and solids

• Interactions with photons, plasmas and strong field processes

• Production, experimental developments and applications.

The day before the official opening of HCI2010, Sunday 29 August, we welcomed the conference delegates with a reception held at the Guanghua (Fudan twin towers) 15th floor 'sky bar' restaurant. Two poster sessions were arranged for the contributed papers on the afternoons of 30 and 31 August. After a visit to the Shanghai Synchrotron Radiation Facility on the afternoon of Wednesday 1 September we enjoyed a conference dinner at the Shanghai Sea Palace restaurant. Throughout the dinner we were entertained with traditional Chinese music by members of Fudan University's folk music group. A visit to the Shanghai 2010 World Expo, the largest World Expo in history (so far), was arranged for the Thursday afternoon. Finally the conference came to a close at lunchtime on Friday 3 September. It was a very successful conference due to the contributions of all the participants, the International Advisory Committee and the Local Organization Committee. We would like to thank them all.

The next edition of the HCI conference series will be held at the University of Heidelberg, Germany in 2012, under the Chairmanship of Professors Thomas Stoehlker and Joachim Ullrich. We wish them all the best with their plans and look forward to meeting you all again in 2012.

Committees, Exhibitors and Sponsors

HCI2010 International Advisory Committee

F Aumayr (Austria) T Azuma (Japan) P Beiersdorfer (USA) J Burgdoerfer (Austria) A Cassimi (France) H Cederquist (Sweden) J Costello (Ireland) F Currell (UK) R Hoekstra (Holland) X Ma (China) F Martín (Spain) A Mueller (German) N Nakamura (Japan) M Pajek (Poland) R Rivarola (Argentina) Z Rudzikas (Lithuania) V Shabaev (Russia) R Schuch (Sweden) T Stoehlker (Germany) J Tanis (USA) L Tribedi (India) K Tokési (Hungary) J Ullrich (Germany) D Vernhet (France) Y Zou (China) T Zouros (Greece)

HCI2010 Local Organizing Committee

Co-chairs: Yaming Zou and Roger Hutton (Fudan university) Secretaries: Baoren Wei and Yunqing Fu (Fudan University) Treasurers: Xiuqing Xu and Daoli Xu (Shanghai Nuclear Society)

Members

Chongyang Chen (Shanghai) Jianmin Yuan (Changsha) Jun Yan (Beijing) Chenzhong Dong (Lanzhou) Xiaohong Cai (Lanzhou) Xinwen Ma (Lanzhou) Xuru Duan (Sichuan) Baohan Zhang (Sichuan)

Exhibitors

Andor Technology andor.com Shanghai Kelin Technology Development Co. Ltd chnkelin.com Varian Inc. varianinc.com

Sponsors

Natural Science Foundation of China International Union of Pure and Applied Physics (IUPAP) Fudan University

In this paper, we discuss the radioactive decay of highly charged ions. There are several motivations for performing this kind of research. One of them is that stellar nucleosynthesis proceeds at high temperatures and therefore the involved atoms are highly ionized. Highly charged ions also offer the possibility of addressing the decay of well-defined quantum-mechanical systems such as, for example, one-electron ions, where all the interactions with other electrons are excluded. These studies can be performed solely at ion storage rings or ion traps, where the high atomic charge states can be preserved for extended periods of time. Although we have focused on experiments conducted at the storage ring ESR of GSI, we have tried to describe the general requirements for such experiments.

The angular distribution and polarization properties are reviewed for the x-ray emission from highly charged ions following dielectronic recombination (DR). Emphasis is placed on how these properties in the decay of (doubly) excited states are affected by relativity, e.g. the relativistic terms of the electron–electron interaction and the multipoles of the radiation field other than the electric-dipole (E1) component. For isolated DR resonances, it is shown that the Breit interaction, as the dominant correction to the Coulomb repulsion, may change the angular emission pattern qualitatively, from a preferred emission along the beam axis towards one that is dominant perpendicular to the beam, or vice versa. Moreover, the interference between the leading E1 and other electric and magnetic multipoles may significantly alter the angular distribution and polarization of the emitted x-rays.

We present the first clear identification and highly accurate measurement of the intra-shell transition 1s2p ³P₂→1s2s ³S₁ of He-like uranium performed via x-ray spectroscopy. The present experiment was conducted at the gas-jet target of the ESR storage ring in GSI (Darmstadt, Germany), where a Bragg spectrometer, with a bent germanium crystal, and a Ge(i) detector were mounted. Using the ESR deceleration capabilities, we performed a differential measurement between the 1s2p ³P₂→1s2s ³S₁ He-like U transition energy, at 4510 eV, and the 1s²2p ²P_3/2→1s²2s ²S_1/2 Li-like U transition energy, at 4460 eV. By a proper choice of the ion velocities, the x-ray energies from the He- and Li-like ions could be measured, in the laboratory frame, at the same photon energy. This allowed for a drastic reduction of experimental systematic uncertainties, principally due to the Doppler effect, and for a comparison with theory without the uncertainties arising from one-photon quantum electrodynamics predictions and nuclear size corrections.

Extreme ultraviolet (EUV) observations of foil-excited ion beams have been extended up to iodine (Z=53). Lines from Cu- and Zn-like ions of iodine served to calibrate the spectra. Nearby lines have the signature pattern of the intercombination line multiplet in Ga-like ions. Candidates for the two triplet–quintet intercombination lines in the Ge-like ion are proposed. Prompt and delayed spectra as well as decay curves support the proposed identifications.

The most important processes for the creation of chlorine ion excited states from the ground configurations of Cl¹⁰⁺ to Cl¹⁵⁺ ions in an electron cyclotron resonance ion source, leading to the emission of K x-ray lines, were studied. Theoretical values for inner-shell excitation and ionization cross-sections, including double KL and triple KLL ionization, transition probabilities and energies for the de-excitation processes, were calculated in the framework of the multi-configuration Dirac–Fock method. With reasonable assumptions about the electron energy distribution, a theoretical Kα x-ray spectrum was obtained, which was then compared with recent experimental data.

The oscillator strengths, line strengths and wavelengths are presented for all 1s–2p transitions in titanium ions. X-ray emission from titanium is extensively used, for example for diagnosis, in fusion experiments. The Kα 1s–2p transitions are limited to transitions from helium-like to fluorine-like ion as the 2p subshell is filled beyond fluorine. While there are two 1s–2p transitions (1s²S_1/2–2p²P_1/2 and 1s²S_1/2–2p²P_3/2) for hydrogen-like titanium, Ti²⁰⁺, the number varies depending on the number of electrons in the 2p subshell before and after the transition. For example, there are 35 1s–2p transitions giving the same number of Kα lines for carbon-like titanium, Ti¹⁶⁺. The present results are obtained from configuration interaction atomic structure calculations using the code GRASPVU, which includes relativistic effects in the Dirac–Fock approximation. The results have been benchmarked for a few ionic states. A comparison of our results with the very few transitions in the literature as well as those from other codes shows reasonable accuracy of the present results.

Theoretical concepts in the production and controlling of polarized highly charged ion beams in storage rings are investigated. A scheme for the control of the degree of ion beam polarization, based on the observation of the linear polarization of emitted x-ray photons in hyperfine quenched (HFQ) decay of excited levels of polarized He-like ions, is presented. One of the important motivations for the production of polarized ion beams is the possibility of observing the parity nonconservation (PNC) effects in HFQ transitions in He-like highly charged ions, where these effects can reach an unprecedented high value for atomic physics. The measurement of these effects requires online diagnostics of the degree of ion beam polarization. The possible schemes for such experiments as well as estimates of the magnitude of the observable PNC effects are presented.

The line-profile approach is applied to the evaluation of the electron recombination on highly charged ions within the framework of QED. Both dielectronic recombination and radiative recombination processes are considered. The interelectron interaction is taken into account partly to all orders of the QED perturbation theory. The radiative corrections to the lowest order (electron self-energy and the vacuum polarization) are also included. With this approach, the most accurate contemporary results for the electron recombination cross section on the one-electron uranium and gadolinium ions are obtained.

Experimental effort is underway at NIST to enable tests of theory with one-electron ions synthesized in circular Rydberg states from captured bare nuclei. Problematic effects that limit the accuracy of predicted energy levels for low-lying states are vanishingly small for high-angular-momentum (high-L) states; in particular, the nuclear size correction for high-L states is completely negligible for any foreseeable improvement of measurement precision. As an initial step towards realizing such states, highly charged ions are extracted from the NIST electron beam ion trap (EBIT) and steered through the electrodes of a Penning trap. The goal is to capture bare nuclei in the Penning trap for experiments to make one-electron atoms in circular Rydberg states with dipole (E1) transitions in the optical domain accessible to a frequency comb.

We observed the x-ray emission of 191.7 MeV u⁻¹ Li-like uranium associated with resonant coherent excitation from 1s²2s to 1s²2p_3/2 (4459 eV) in a thin silicon crystal target. De-excitation x-rays were observed by using large-area silicon drift detectors installed inside the target vacuum chamber together with their preamplifiers. We found that the x-ray yield under the resonance condition was clearly enhanced by a factor of three compared to that under the random incidence condition.

The visible transition of a multiply charged Ba ion was observed by using an electron beam ion trap. From the dependence of the line intensity on electron beam energy, it is identified as a magnetic dipole transition between ground-state fine-structure levels (4d^9 2D_5/2–²D_3/2) of Rh-like Ba. The wavelength determined from the present experiment is compared with the existing theoretical values as well as the indirect experimental value estimated from the wavelength difference between previously reported VUV transitions 4d⁸5p–4d^9 2D_5/2 and ²D_3/2.

We present visible spectra of highly charged tungsten ions observed by using a compact electron beam ion trap. The newly observed lines and the ions responsible for them, identified by the electron energy dependence of the lines, are presented. Theoretical calculations performed for the detailed identification of the lines are also presented. Finally, the experimental and the theoretical results are compared.

Heavy few-electron ions, such as He-, Li- and Be-like ions, are ideal atomic systems to study the effects of correlation, relativity and quantum electrodynamics. Very recently, theoretical and experimental studies of these species achieved a considerable improvement in accuracy. Be-like ions are interesting because their first excited state, i.e. (1s²2s2p)³P₀, has an almost infinite lifetime (τ₀) in the absence of nuclear spin (I), as it can only decay by a two-photon E1M1 transition to the (1s²2s²)¹S₀ ground state. In addition, the energy difference between the ³P₀ and the next higher-lying ³P₁ state is expected to remain almost completely unaffected by QED effects, and should thus be dominated by the effects of correlation and relativity. Therefore, we want to determine the (1s²2s2p) ³P₀–³P₁ level splitting in Be-like krypton (⁸⁴Kr³²⁺), which has I=0, by means of laser spectroscopy at the experimental storage ring at GSI. In such an experiment, the energy splitting can be obtained with very good accuracy and can be compared with recent calculations.

Using forced evaporative cooling on stored highly charged ions (HCIs) in an electron beam ion trap, high-resolution electronic recombination spectra were obtained. Inter-shell tri-electronic recombination is reported for HCIs, mainly for C-like ions of Ar, Fe and Kr, where simultaneously with the K-shell excitation an additional L electron is excited at the resonant recombination of a free electron. Clear indications of quadru-electronic recombination are found, where besides the K electron two additional L electrons are excited simultaneously. The experimental technique is described; then the results on first- and higher-order resonant recombination processes are discussed and compared with multi-configuration Dirac–Fock calculations.

A platform for the study of highly charged ions (HCIs), the surface–foil–gas–plasma interaction at IMP Lanzhou, is introduced. Some potentially useful results obtain over the last few years on x-ray emission, ion sputtering, secondary electron emission and the nano-etching effects during HCIs' impact on surfaces, as well as the guiding effect of nano-capillaries, are reviewed. Our ongoing work on the HCI interaction with plasma is also reported.

Low-energy collision experiments of an argon dimer with Ar⁹⁺ were performed to measure branching ratios and kinetic energy release (KER) distributions for multiply ionized dimers. Two well-separated KER peaks are observed at 3.8 and 5.3 eV for the doubly ionized dimers, and are assigned to direct Coulombic dissociation and radiative electron capture followed by ionic dissociation, respectively. For the dissociation channels Ar²⁺+Ar⁺, Ar³⁺+Ar⁺ and Ar²⁺+Ar²⁺, the KER distributions show a single peak, the positions of which agree well with those expected for Coulombic dissociation. The branching ratio of asymmetric charge sharing, Ar³⁺+Ar⁺, is larger than that of symmetric charge sharing, Ar²⁺+Ar²⁺. These results represent unambiguous evidence of a strong limitation of charge mobility across the Ar dimer.

Energy-gain spectra and absolute total cross-sections have been measured for single- and double-electron capture processes in collisions of Ne⁴⁺ ions with CO₂ at laboratory impact energies between 60 and 1200 eV and scattering angles between 0° and 6° using a translational energy-gain technique. At 0° scattering angle, the dominant peak corresponds to transfer excitation into the 3d excited state of Ne³⁺ from the ground state Ne⁴⁺ (2p²³P) ion accompanied by excitation of the target product into the excited state (²Π_u) of CO₂⁺, with contributions due to capture into the excited state 3d'. There is also some contribution from an unresolved reaction at about 11.5 eV, involving capture into the 3d state. The energy dependence of cross-sections for single- and double-electron capture are also measured and found to slowly increase with increasing impact energy. The data are compared with theoretical results based on the classical over the barrier and multi-channel Landau–Zener (MCLZ) models.

In the present work, an alternative approach for the evaluation of the equilibrium degree of K-, L- and M-shell ionizations and the mean charge state for projectiles passing through various targets has been proposed. The approach is based on measured K x-ray energy shifts and line intensity ratios, and utilizes the theoretical analysis of projectile spectra using the multiconfiguration Dirac–Fock calculations.

One-electron capture reactions between doubly charged krypton ions and molecules (H₂, N₂, O₂, CO and NO) were studied using an injected-ion drift tube mass spectrometer. An energy range of 14–60 meV was studied in a center-of-mass system. The drift tube used in this experiment was cooled with liquid nitrogen, and the temperature of buffer gas, which was Kr, was measured to be about 90 K. Doubly charged ions produced in a conventional electron impact-type ion source may contain metastable states. In this work, the cross sections of ground state Kr²⁺ ions were separated from those of metastable states using variations in the ion mobilities. The cross sections of H₂ targets strongly depended on the ion states. In contrast, no ion state dependence was observed for the cross sections of O₂, CO or NO targets.

Experimental work was performed at the HI-13 tandem accelerator in the Chinese Institute of Atomic Energy (CIAE). In this experiment, L-shell x-ray production cross sections were measured for solid Ta and Au targets by 20–55 MeV O⁵⁺ and F⁵⁺ ions. The L1, Lα, Lβ and Lγ-subshell characteristic x-rays of Ta and Au were measured. The ratios σ(Lβ)/σ(Lα), σ(Lγ)/σ(Lα) and σ(Ll)/σ(Lα) of Ta and Au L-subshell production cross sections were calculated according to experimental data. The results are compared with the predictions of energy-loss Coulomb-repulsion perturbed-stationary-state relativistic theory. Fairly good agreement is obtained between the experimental and the calculated values.

The present work provides a reliable interpretation of the K^hα₁/K^hα₂ intensity ratios and an explanation of the lifetime values for K-shell hollow atoms based on an advanced theoretical analysis (using extensive multiconfiguration Dirac–Fock calculations with the inclusion of the transverse Breit interaction and quantum electrodynamics corrections). It was found that, as a result of closing the K^hα₁ de-excitation channel in the pure LS coupling scheme, the K^hα₁/K^hα₂ intensity ratio changes with the atomic number from small values (for the LS coupling limit at low Z) to about 1.5–1.6 (for the j–j coupling limit at high Z). However, closing the K^hα₁ de-excitation channel (due to the domination of the pure LS coupling for the low-Z atoms) does not enlarge the lifetimes of hollow atoms.

We have measured the differential cross-sections in F³⁺–C₆₀ collisions at low velocity (v=0.18 a.u.). Using coincidence measurements between the ejected electron number and recoil ions, we have estimated the initial charge state of C₆₀ parent ions associated with neutral outgoing projectiles to range from 4+ to 7+. We found that the formation of anions is correlated with the strong excitation of C₆₀ (average excitation energy about 160 eV). The cross-section of the production of the anion has been found to be 25 a.u. This value is in agreement with the scenario of anion formation in two steps. In the first step, F³⁺ ions are neutralized by multicollision on the C₆₀ surface. In the second step and at the exit part of the collision, the electron attachment process occurs. For the production of a stable anion, the capture of electrons on carbon must occur directly to the ground states of F⁻, giving many electron vacancies on C₆₀. This process explains the observation of strong electronic and vibronic excitations of C₆₀ leading to electron emission and multifragmentation processes.

The transmission of high-current electrons through a tapered SiO₂ capillary was investigated. The angular distribution and incident energy dependence of transmitted electrons were observed. We found that the transmitted fraction decreases with the incident energy. The transmitted electrons had significant energy loss but could not be focused by the tapered capillary.

Radiative double electron capture (RDEC) observed in collisions of bare ions with atoms is a charge exchange process during which two target electrons are captured into a bound state of the projectile and a single photon is emitted. This process can be described as a time-reversed double photoionization. In bare ions, due to the lack of spectator electrons, it is the most reliable tool for observation of electron–electron correlation in electromagnetic fields produced in ion–atom collisions. An experiment conducted at Western Michigan University, using the tandem Van de Graaff accelerator, aiming at observation of the RDEC process during O⁸⁺ + C collisions at 38 MeV, provided the first experimental evidence of this process. In this paper, an extension of the data analysis of this experiment is presented, based on Monte Carlo simulation of the generated x-ray spectra. It is shown that the total measured RDEC cross-section value exceeds the theoretical predictions by a factor of more than 20.

We have observed emission spectra in collisions of hydrogen-like oxygen and nitrogen ions with a helium target gas in the soft x-ray region using a window-less Si(Li) detector at collision energies of about 100 keV. The dominant soft x-ray emission is the 1s²–1s2p transition of helium-like ions produced by a single-electron capture reaction. We indicate that the cascades from the upper states give a large population of the 2p state, even though direct capture into the 2p state is much smaller than the 3ℓ and 4ℓ states. The intensity ratios of the 1s–2p and 1s–3p transitions are discussed, along with a comparison with the theoretical calculation.

Charge-state-specific extreme ultraviolet spectra from both tin ions and xenon ions have been recorded at Tokyo Metropolitan University. The electron cyclotron resonance source spectra were produced from charge exchange collisions between the ions and rare gas target atoms. To identify unknown spectral lines of tin and xenon, atomic structure calculations were performed for Sn¹⁴⁺–Sn¹⁷⁺ and Xe¹⁶⁺–Xe²⁰⁺ using the Hartree–Fock configuration interaction code of Cowan (1981 The Theory of Atomic Structure and Spectra (Berkeley, CA: University of California Press)). The energies of the capture states involved in the single-electron process that occurs in these slow collisions were estimated using the classical over-barrier model.

Ionization of He targets by impact of partially stripped ions is investigated by means of an extension to the continuum distorted wave-eikonal initial state model with a particular representation of the projectile potential. Structures appearing superimposed on the binary encounter peak are interpreted in terms of coherent interference of short- and long-range contributions of the perturbative projectile potential. The case of 600 keV u⁻¹Au¹¹⁺ ions impinging on He is presented and discussed.

We investigate the electron stereo-dynamics in the multiple ionization of rare gas dimers by slow highly charged ions in terms of a three-center over-barrier model. A screening factor is introduced in the model for effective ion-core charge of a non-active atomic site in the dimer, keeping that of an active site unscreened. It is found that the screening effect is crucial for populating ion pairs with charge difference more than one, such as (Q,Q' )=(2, 0) and (3, 1). Understanding this is helpful in interpreting the result of a recent momentum imaging experiment.

In this work, a simulation calculation scheme based on a collisional radiation model and employing detailed energy levels was developed under the framework of corona approximation for low-density plasmas. Atomic data such as energy levels, radiative transition rates, Auger rates, collision excitation and ionization cross sections needed for the simulation were calculated by using the Flexible Atomic Code. In this work, the emission spectra of the first and second excited configurations of He-like Ar ions and their dielectronic and inner shell excited satellites from Li-like argon ions were studied for a low-density plasma, taking into account the influence of all satellite electrons of principal quantum number n<10. A comparison with the result of tokamak experiments under similar plasma conditions was made. Good agreement was seen for these spectra; however, the charge state balance between the He-like and Li-like Ar ions was not well modeled. A discussion of this deviation is presented.

The emission spectra in collisions of Fe^q+ (q=8–16) with He were measured in the extreme ultraviolet wavelength region at a collision energy of 20×q keV. The contribution of the double electron capture process cannot be ignored, at least in Fe^q+ (q=9–13) collisions. By comparing the emission spectra between charge exchange spectroscopy and an electron beam ion trap (EBIT) experiment, the resonance lines can be distinguished from other emission lines in the charge exchange spectra, and the charge state distribution of trapped ions can be estimated from the observed EBIT spectrum.

Spectra of highly charged ions in the extreme ultraviolet range were observed using high- and low-energy electron beam ion traps (EBITs) in Tokyo. For efficient observation, a slitless grazing incidence flat field spectrometer was specially designed for each EBIT. The present results demonstrate that the complementary use of these spectrometers enable spectroscopic studies of ions with a wide range of charge states.

The inner-shell couplings for U^q+-ions (73⩽q⩽91) moving moderately slow at ∼69 MeV u⁻¹ and bombarding thin Au targets have been investigated. Having established the definite survival probability of incoming projectile K vacancies in these targets in an earlier publication, the transfer of these vacancies to the target K-shell due to inner-shell couplings has been studied. As the system is in the quasiadiabatic collision regime for the K-shell of collision partners, advanced SCF-DFS (self-consistent field-Dirac–Fock–Slater) multielectron level diagrams have been used for interpretation. Using a simple model, the L–K shell coupling interaction distance has been estimated and compared with level diagram calculations.

In order to clarify the transmission properties of an ion beam extracted with glass capillaries into air, we measured the energy distributions of extracted protons and alpha particles using two kinds of glass capillaries. We observed the 'core' and 'halo' components in the energy spectra and obtained intensity distributions for both components as a function of the tilted angle of the glass capillary. Transmission properties of ion beams extracted with the glass capillaries have been discussed.

We present here a Monte Carlo program based on the EGS5 package for modeling the detector response of position-sensitive x-ray detectors. The program is used to estimate the polarimeter quality of two novel detector systems applied in Compton polarimetry. The validity of the underlying physical models is verified by comparing the simulation output to experimental data obtained at the experimental storage ring, ESR.

Recombination through doubly excited states that can be formed only through spin-flip of the excited electrons can give very strong contributions to the recombination rate of Be-like ions. We demonstrate this, in this paper, with the electron–ion recombination spectra of Be-like Ne⁶⁺ and Be-like Si¹⁰⁺, recently measured at the CRYRING storage ring. These resonances have significant effects on the plasma rate coefficients. We show that neglect or imprecise calculation of these resonances is responsible for large spreads observed between various theoretical results from the literature.

We have extended and generalized the modified Jain–Khare (JK) semiempirical formalism to the evaluation of partial differential and partial integral ionization cross sections for fullerenes. The differential cross sections corresponding to the production of singly, doubly and triply charged cations in the electron impact ionization of C₆₀ were evaluated at incident electron energies of 100 and 200 eV. The partial integral ionization cross sections calculated in the energy range varying from ionization thresholds to 1000 eV revealed satisfactory agreement with the available experimental and theoretical data. The ionization rate coefficients corresponding to the various cations have also been evaluated using the presently calculated ionization cross sections and Maxwell–Boltzmann energy distributions.

For the rapid calculation of population kinetics of high-Z nonlocal thermodynamic equilibrium (NLTE) plasmas, a collisonal–radiative model based on the nonrelativistic configurations approach was developed. The required atomic data about the collisonal and radiative processes such as photoexcitation, electron-impact excitation, photoionization, electron-impact ionization and autoionzation were obtained by using a set of analytical formulae. The population kinetics were determined by solving the rate equation in the steady-state approach. As illustrative results, experimental measurements of the average ionization degree and population distribution of Xe and Au plasmas were reproduced, and overall good agreement was found. The present model provides a useful tool for modeling the population kinetics of NLTE plasmas.

Electron cyclotron resonance (ECR) ion sources produce low-energy, highly charged ions. A new 14.5 GHz ECR-based low-energy ion accelerator facility has been developed. The ion source involves a plasma chamber ('supernanogan') surrounded by permanent magnets that provide a suitable magnetic field. The entire assembly including the ion source and the analyzing magnet is mounted on a 400 kV deck. A LabVIEW-based command and control system has been developed for the beamline. In addition, wireless communication has been installed to operate the machine in high voltage. The charge state distribution of several ions (He, N₂, O₂, Ne, Ar and Xe) has been measured. For Ar and Xe, the maximum charge states measured were 16⁺ and 29⁺, respectively. A direct x-ray measurement for plasma diagnostics was also initiated.

The rate coefficient for the recombination of Au²⁰⁺ with free electrons was measured in the electron–ion collision energy range of 0–10 eV by employing the electron–ion merged-beams technique at the heavy-ion storage ring TSR of the Max-Planck-Institute for Nuclear Physics in Heidelberg, Germany. In contrast to earlier measurements with more highly charged Au²⁵⁺ (Hoffknecht et al 1998 J. Phys. B: At. Mol. Opt. Phys.31 2415), sharp dielectric recombination resonance features are observed.

The Young-type interference effect has been investigated in electron emission from molecular hydrogen in collision of 5 MeV u^{− 1} F⁹⁺ ions. The double differential cross section ratios of molecular-to-atomic hydrogen exhibits oscillatory structure, which is discussed in terms of the Young-type electron interference. We have obtained the frequencies of such oscillation for different angles. A comparative study of the frequency parameter is given with early measurements performed by other groups.

The transmission of electrons through an insulating single cylindrically shaped glass capillary of macroscopic dimensions has been investigated for electron energies from 300 to 1000 eV using a high-resolution electrostatic parallel-plate analyzer (spectrometer). The transmitted intensity decreased with increasing sample tilt angle relative to the beam direction, and had two regions: direct, where there is no interaction of the beam with the inner capillary wall, and indirect, where it does interact. From the full-width-at-half-maximum of the angular distributions, the indirect region was found to reveal a further two distinct areas of characteristics versus tilt angle with respect to elasticity/inelasticity of transmitted electrons. Electron transmission for the case of no tilt of the sample was found to be time dependent, due to charge-up of the capillary inner surface. The new results are compared with previous experimental data obtained using a 10× lower resolution spectrometer.

A joint experimental and theoretical study of low-keV H and F ions in grazing scattering on a missing row reconstructed Au(110) surface is presented. We show the influence of surface electronic corrugation and trajectory effects on energy-loss spectra. Measurements of energy losses for grazing angles scattering in surface channeling conditions for various azimuthal orientations of the crystal have been performed and discussed in semi-classical simulations, which allow us to delineate various trajectory classes that correspond to different contributions in the energy-loss spectra for various azimuthal orientations of the surface.

Highly oriented pyrolytic graphite (HOPG) samples were irradiated with a highly charged ion (HCI) Ar¹¹⁺ at a fluence of 10¹⁴ cm⁻². After irradiation, scanning electron microscopy (SEM) was used to observe the irradiated trace. During SEM measurement, an electron acceleration voltage of 0.5, 1 and 5 kV was applied to measure the samples, respectively. The irradiated contrast can be observed in the Si surface at 0.5 kV, which could not be found at 1 kV or higher. The irradiated area becomes brighter than that of the unirradiated area. When Ar¹⁺ was used to bombard the solid surface, the fluence should become of the order of 10¹⁵ cm⁻². In this case, the irradiated contrast could be observed. It means HCI is able to enhance more effectively the surface modification. Furthermore, electron spin resonance was used to measure the surface of highly oriented pyrolytic graphite (HOPG). A clear resonant peak appears in the irradiated sample, which cannot be found in the pristine sample. The phenomenon could be related to defects induced by the HCI impact.

We observed convoy electrons emitted from 416 MeV/u He-like Ar¹⁶⁺ passing through a thin Si crystal under the condition of three-dimensional resonant coherent excitation (3D-RCE). The convoy electrons, which originate from electrons released from ions into the continuum by collisions with target atoms, emerged in the forward direction and formed a cusp-shaped peak in the energy distribution. We selectively controlled the population of the ground and excited states of ions traveling through the crystal by using 3D-RCE, where the 1s electron was excited to the 2p state by a periodic crystal field. Under the resonance condition, we found an enhancement of the convoy electrons with a narrowing in the energy distribution, which reflects the electron momentum distribution of the initial bound state of the excited ions.

In this work, we employ highly charged ions to study the sputtering of positive molecular fragments from two different alkanethiol self-assembled monolayers (SAMs) on gold surfaces: undecanethiol and dodecanethiol. The SAMs are bombarded with a pulsed Ar^q+ beam (3<q<12) with kinetic energies ranging from 1 to 15 keV. The desorbed positive molecular ions were detected and analyzed from time-of-flight spectra, and thereby the masses and yields of secondary ions were obtained. The proton yields are dependent on the charge state of the incident ion. On the other hand, the positive molecular ion yields, such as C_nH_m⁺, are charge state independent. The positive molecular ion yields decay with the molecular size n.

The transmission of highly charged Xe and Ne ions through polycarbonate (PC) nanocapillaries with multiple holes (m-PC) was investigated at the Institute of Modern Physics (IMP) in Lanzhou. In particular, Au films were evaporated on both the front side and the back to prevent the surface from charging up. The time effect was observed and the charging up model in an insulating nanocapillary was employed to explain the phenomenon. It was found that more than 98% of the transmitted ions remained in their initial charge state. The guiding effect and the relationship between the charge state and the critical angle were also studied.

We present here coincidence measurements for two K x-rays emitted in the dielectronic recombination process of hydrogen-like krypton. We report the first observation of clear coincidence signals obtained from two Ge detectors placed in such a way that the Tokyo electron beam ion trap was between them. The doubly differential cross section is obtained by normalizing the coincidence counts to the radiative recombination x-ray counts.

The dynamics of highly charged ions in a strong laser field are investigated by solving the two-dimensional time-dependent Dirac equation. Relativistic effects are discussed for the hydrogen-like ions with nuclear charges of Z=4, 24 and 79 by considering the changes in the electron trajectory and coherent emission spectrum with changes in the frequency and intensity of the laser field. With increasing Z, the relative field strength between the ionic core and laser fields changes and this results in different characteristics of the dynamical electronic trajectory as well as the corresponding emission spectrum. For an infrared laser field of strength E=8.0 au, the tunneling ionization can hardly be seen for the hydrogen-like ions of Z=24 and only the resonant multiphoton emission spectra below the ionization threshold are predicted. The above threshold harmonics need more intense laser fields or a higher photon energy.

This paper shows photoelectron spectra produced from the irradiation of x-ray free-electron laser light pulses onto targets, with various shapes such as spheres and ellipsoids. It is found that photoelectron spectra are almost independent of shape; that is, spherically symmetric models may be available to non-spherically symmetric targets in photoelectron spectra.

We developed a simulation code for the radiation damage of clusters (pseudo-biomolecules) induced by irradiation with x-ray free electron lasers (XFEL). We evaluated the radiation damage of C₁H₁, N₁H₁ and O₁H₁ clusters induced by XFEL irradiation by using the code developed and considering the photoionization, Compton scattering, Auger decay, electron-impact ionization and electric field ionization. We found that the clusters were ionized by the XFEL irradiation at an x-ray flux of about 1×10¹⁹ photons mm⁻² at a target radius of 100 Å, and the radiation damage of the clusters increased slightly as the atomic number of the atoms in the targets increased. We found that the radiation damage of the clusters is almost independent of the pulse widths in the case of the same x-ray flux and the same target if the pulse widths are less than 10 fs.

The quadrupole photoionization of hydrogen atoms under the perturbation of plasma screening effects is investigated by the complex-coordinate rotation method. The Debye–Hückel (DH) and modified-DH potentials are adopted for describing the different features of plasmas. Comparisons of the quadrupole photoionization cross sections for these two screened potentials are made. The variation of cross sections with various Debye screening lengths is presented for illustrating the appearance of Cooper-type minima and shape resonances induced by plasma screening. The relations between the Cooper-type minima and the instability of the initial bound states are discussed.

Photoionization experiments were performed with tungsten ions using a photon–ion merged-beams setup at the Advanced Light Source. Cross-sections σ_q,q+1 for photon-induced single ionization of W^q+ ions (q=1,2,3,5) and σ_q,q+2 for photon-induced double ionization of W⁺ ions have been explored in the energy range 20–70 eV. While σ_q,q+1 for the lower charge states is dominated by broad resonance features in the range of 4f and 5p excitations, the cross-section σ_{5, 6} shows much narrower peak features. Significant contributions from initial metastable states are evident. Double ionization is substantially enhanced at energies above the threshold for single ionization of a 4f electron in W⁺.

The research in intense coherent x-ray production from free electron lasers, and investigations in interaction of laser radiation and synchrotron radiation with atoms, molecules and clusters, opens a broad opportunity for experimental measurements of x-ray scattering on the inner shells of heavy atoms and molecules. For x-ray photons, the accuracy of the dipole approximation may be not enough and retardation needs to be included. So the fully relativistic calculations are interesting in the case of x-ray scattering, especially for above-threshold photons. But such calculations require complicated relativistic expressions. This report deals with the fully relativistic photon scattering processes of H-like ions as the model of scattering on the inner shells. Simple general expressions are obtained for two-photon processes on H-like ions. Numerical calculations of analytical functions give exact results under and above a threshold.

Based on the non-relativistic theory and dipole approximation, we have developed a new program to study the interaction between a circularly polarized laser and hydrogen atoms. In this paper, we present our calculation of above-threshold ionization (ATI) rate based on the new code and compare the results with that of a pertubation theory calculation. The comparison shows that our non-perturbative calculations can produce ATI peak suppression.

We have built a new small electrostatic ion storage ring, the so-called mini-ring, in order to store ion beams for long durations (up to seconds) using a limited number of electrodes in limited space. In this paper, we demonstrate the capability of the mini-ring to store ions on a rather long time scale (100 ms) limited by collisions on the background gas. We also show that by measuring the frequency of ion motion around the ring, we can use the mini-ring as an energy analyzer to determine the energy loss of F⁻ anions produced in the double electron transfer process in 4 keV F⁺–Ar collisions.

Elastic scattering of stored ions on background gas atoms in an electrostatic ion trap was programmed. From simulations using this program in the SIMION 8 software, the losses of trapped 1.2 keV Ar⁺ and 2.4 keV Ar²⁺ ions by elastic scattering were estimated as a function of trapping time. The background gas atoms were Ar, Ne or Kr atoms. Experimental results were reproduced well by these simulations.

A new method for determining the absolute detection efficiencies of a microchannel plate (MCP) detector is presented. This method uses a charge transfer reaction and can be applied to determine not only the detection efficiencies for ions but also those for neutral atoms. The measurements were carried out for Ar⁺ and neutral rare gas atoms (Ne, Ar, Kr and Xe) in the 0.5–4.8 keV energy range. The detection efficiencies for all species increase with increasing impact energy and approach the open area ratio of the MCP used (about 50%). The measured detection efficiencies were found to scale with the Lindhard, Scharff and Schiott formula for electronic stopping power at keV energies.

In this work, the space charge effects on electron trajectories and electron kinetic energy are studied for the case of a low-energy electron beam ion trap. The study is based on computer simulation using the commercially available Tricomp software from Field Precision.

To study the interaction between low-energy electrons and molecules, a recoil-ion and electron momentum spectrometer (RIMS) has been developed at Shanghai EBIT laboratory. As the low-energy electron source, the ELG-2 electron gun (Kimball Physics) coupled with an ultrafast pulse generator has been tested. The energy of the electron beam ranges from a few eV to 2 keV, and the pulse width of the beam is about 1 ns.

This paper contains a brief introduction to the main parameters of a micro-calorimeter designed to operate at the Shanghai electron beam ion trap. This is followed by short descriptions of some aspects of the calorimeter.

In this paper, a brief description of the progress of the Shanghai permanent magnetic electron beam ion trap is presented. Some test results regarding the electron beam current versus beam energy are presented. The electron beam width was measured and compared with our simulations, and good agreement was found.

An emittance meter for pulsed, low-energy ion beams was developed. Based on the pepperpot method, the device is compact and portable. It has been installed at the S-EBIT Laboratory at AlbaNova, Stockholm University, to measure the emittance of highly charged ions extracted from the electron beam ion trap R-EBIT and the cooling trap of the high-precision Penning trap mass spectrometer SMILETRAP II. Using a fast delay-line anode detector, the emittance and time-of-flight of the extracted ions can be measured simultaneously. In this paper, design and data processing system are described and preliminary results are presented.

A high-precision high-voltage divider with a range of 85 kV was designed for electron beam energy measurements, particularly in the Shanghai electron beam ion trap (Zhu et al 2005 Nucl. Instrum. Methods Phys. Res. B 235 509). After minimizing the uncertainties caused by temperature fluctuations, including the effect of temperature on the resistance of the resistors, the divider was calibrated from 0 to 63 kV with a precision of less than 10 parts per million (ppm). During the calibration a parallel connection method was used to simplify the measurement.

An ultrasoft x-ray and extreme ultraviolet spectrometer built and calibrated in the wavelength range of 7–60 Å is reported here. Details of the alignment of this flat field spectrometer with both a laser and a telescope are presented. The light path function rather than a standard calibration function, i.e. a polynomial function, is introduced as the fit function, which gives good agreement with the spectrometer design values and makes the calibration more reliable when extended to the region outside the points used for calibration, compared with a standard calibration function. The calibration results of a Manson ultrasoft x-ray source (model 2) with source targets of Cu, Fe and Ti are presented with all the peaks marked.

The ionization and dissociation of methane in an intense laser field (approximately 10¹³ W cm⁻²) with pulse duration of 7 ns were studied experimentally. The yields of fragment ions are plotted as a function of laser pulse energy. Singly charged ions of CH₃⁺, CH₂⁺, CH⁺, C⁺, H⁺ and H₂⁺ were observed from 6 to 20 mJ, and C²⁺ ions were observed when the laser pulse energy was above 10 mJ. However, the yields of CH₃⁺ and CH₂⁺ ions decreased when the laser pulse energy increased from 6, whereas the remaining singly charged ions of CH⁺, C⁺, H⁺ and H₂⁺ were enhanced. The kinetic energy of fragment ions, which corresponds to the excitation energy, was measured. At higher energies of the laser pulse, a molecule can absorb more photons and undergo multi-fragmentation by an emitted high-velocity atom (H atom). As far as we know, there are few or no published data of an experiment on methane irradiated by a nanosecond high-intensity laser.

Based on ray-tracing procedures/techniques, we have carried out simulations on the operation of (i) a toroidal mirror used along with a vacuum ultraviolet scanning monochromator and (ii) variable line spacing gratings such as those used in flat-field spectrometers. In case (i), a toroidal mirror was installed in the optical beam line for normal incidence spectroscopy at the Shanghai electron beam ion trap (EBIT) (Zou Y and Hutton R 2005 Phys. Scr.T120 47) based on simulation results. Case (2) yielded results that can be used in aligning flat-field spectrometers; the results of the simulations were tested by experiment and were found to be in good agreement.