Table of contents

These proceedings contain the papers presented at the Eighth International Conference on the Physics of Highly Charged Ions (HCI-96) which was held on September 23–26, 1996 in Omiya, Saitama, Japan, hosted by the Institute of Physical and Chemical Research (RIKEN). The first conference of this series was held in Stockholm, Sweden in 1982. The subject was the "Production and Physics of Highly Charged Ions". The conference has since been held every other year; in Oxford, UK (1984), Groningen, the Netherlands (1986), Grenoble, France (1988), Giessen, Germany (1990), Manhattan, Kansas, USA (1992) and Vienna, Austria (1994).

When the first conference of this series was held, various highly charged ions were available from many heavy ion accelerators, which had been constructed since the 1960's, and ion sources such as EBIS and ECRIS, which were then new facilities. Subsequently, many other experimental techniques have been developed to study or to control highly charged ions, such as ion traps, EBIT's, storage rings, high-brilliance synchrotron radiation, and so forth. Now the properties of highly charged ions themselves and their interactions with various kinds of materials can be studied systematically using ions of any element at various collision energies. These studies will result in a deeper insight into their nature as well as giving us important basic data for use in the fields closely related to atomic physics.

About 190 scientists from 18 countries registered at the HCI-96. The number of invited talks was 21 and that of contrib- uted papers 215. In these proceedings, 20 papers of invited talks and 116 papers on contributions are included. They are classified into categories of "Structure and Spectroscopy of Highly Charged Ions and Fundamental Aspects", "Highly Charged Ions in Plasmas and Strong Fields", "Interactions of Highly Charged Ions with Atoms and Ions", "Dynamic Processes Related to Molecules and Clusters", "Interactions of Highly Charged Ions with Surfaces and Solids" and "Pro- duction and Utilization of Highly Charged Ions and Experimental Methods".

The success of this HCI-96 is based on the wide-ranging experience inherited from the organizers of previous HCI conferences, the contribution of the International Advisory Committee members who decided on the invited speakers, the excellent talks by invited speakers and steering by session chairpersons as well as the considerable efforts of the chairper- sons who chose the talks and posters for "Selected Topics" and "Selected Posters", and the eager presentations and dis- cussions by all the participants. Last, but not least, we also owe much of the success of this conference to our sponsors.

The impression of the HCI-96, apart from the scientific interests, may have been further emphasized by the typhoon that attacked the Tokyo area on September 22 causing considerable confusion to flights and traffic. We hope this mischief of nature was compensated for by the half-day trip to the old city of Kawagoe, which is called small Edo (the old name of Tokyo in the period of Tokugawa Shogunate), where we also enjoyed dance and music inherited from the Edo period.

The next International Conference on the Physics of Highly Charged Ions will be organized by Prof. Paul Mokler of GSI and his colleagues. We hope we can all meet again in 1998 at Bensheim, Germany. Finally, we thank MS Kazuko Kobayashi of the Library Division, RIKEN, for her invaluable assistance in the prep- aration of this publication.

Among the relativistic atomic structure theories developed in the last two decades, two methods - multiconfiguration Dirac-Fock (MCDF) and relativistic many-body perturbation theory (RMBPT) - have extensively been applied to calculate spectroscopic properties of neutral atoms as well as highly charged ions. The strengths and weaknesses of these methods are discussed with some examples. The MCDF method is based on the shell structure familiar to atomic physicists, and hence intuitively easier to understand. On the other hand, the RMBPT method is more systematic in introducing correlation and relativistic corrections and logically simpler to include quantum electrodynamic (QED) corrections and higher order relativistic effects than the MCDF method. A recent development in extensive relativistic configuration interaction is also described.

Experimental decay rates for the spin-forbidden ns²np^k−1-nsnp^k transitions in highly ionized Be-like, B-like, Mg-like and Al-like ions have been obtained by the beam-foil technique. Results are reported for Be-like and B-like Fe²²⁺, Al-like Kr²³⁺, Y²⁶⁺ and Rh³²⁺ and Mg-like Ni¹⁶⁺, Kr²⁴⁺, Y²⁷⁺ Zr²⁸⁺, Nb²⁹⁺ and Rh³³⁺. For all ions in the Mg- and Al-like sequences the experimental oscillator strengths are larger than the theoretical predictions and, furthermore, the discrepancy tends to increase with increasing charge state. For both the Be- and B-like ions good agreement is found between theory and experiment. The experimental data presented here was obtained using the RILAC accelerator at RIKEN.

The ESR storage ring offers unique conditions for precision investigations in the field of atomic physics. In this review, special emphasis is given to the experiments which address the study of the effects of quantum electrodynamics (QED) in high-Z hydrogen-like systems, e.g. uranium. Here, due to the strong Coulomb field of the nucleus, higher-order radiative corrections can be investigated that are not accessible by experiments for low-Z ions. Since these corrections are largest for the ground-state, the experiments are discussed that are aiming at a precise determination of the ground-state transition energies in heavy hydrogen-like ions. With respect to future experimental perspectives, the deceleration capabilities of the ESR are discussed in detail as well.

A complete solution of the relativistic Coulomb problem is presented on the basis of the second-order Dirac equation. A set of fundamental solutions of the linear and squared relativistic equation is investigated. The different forms of both the ordinary and the reduced relativistic Coulomb Green functions and the wavefunctions are discussed.

The results of analytical calculations for transition probability in the He-like ions in the first order of perturbation theory of electron interaction are presented. Both nonrelativistic and relativistic expression are obtained on the base of the Coulomb Green function method. The approximation finite series are found to present wide information for electric dipole transitions for 1snl → 1sn'l' states at n ⩽ 5, l = s, p, d, n' = 2, l' = s, p.

Radiative and Auger transitions energies, decay rates, Auger branching ratios and fluorescence yields have been calculated for the Be-like (1s²3l4l') doubly excited states in Ne⁶⁺. The calculations have been performed in the intermediate coupling scheme. The main motivation of this extensive set of theoretical calculations has been to support the analysis and identification of our high resolution soft x-ray photon and Auger electron measurements following single and double electron capture in Ne⁸⁺ + He and Ne⁸⁺ + H₂ collisions. The theoretical data confirm that the Be-like (1s²3l4l') doubly excited states are strongly populated in the Ne⁶⁺ + He by double electron capture process.

Radiative and Auger transitions energies, decay rates, Auger branching ratios as well as fluorescence yields have been calculated for the Be-like (1s²4l4l') doubly excited states in Ne⁶⁺. The calculations have been performed in the intermediate coupling scheme. These extension theoretical results have been compared with our high resolution soft x-ray and Auger electron electra arising from Ne⁸⁺ + He and Ne⁸⁺ + H₂ collisions. The comparison of our experimental and data confirms that the 1s²4l4l states of the Ne⁶⁺ decay predominantly into the 1s²2pl" continuum, while the branching ratios associated with the 1s²2sl" continuum are small. This is fundamental importance for the spectroscopic analysis and collision dynamics of double electron capture processes, in particular for the Ne + H₂ collision system, where the 1s²4l4l' states are most populated.

Energies of 2s²3l, 2s2p(¹P)3l, 2s2p(³P)3l and 2p²3l states (with l = s, p, d) for B-like Na are calculated. These perturbation-theory calculations make use of a frozen-core relativistic Hartree-Fock basis sets. The calculations include Coulomb and Breit contributions from first- and second-order diagrams for both diagonal and non-diagonal matrix elements. Corrections for the frequency-dependent Breit interaction are taken into account in lowest order and corrections for the Lamb shift are also included. Contributions from three-electron diagrams are compared with those from one- and two-electron diagrams. Comparisons are made with available experimental data; we find good agreement in most cases with experimental term-splitting values in ions with small nuclear charge.

Energies of the 2s3s (¹S₀, ³S₁), 2s3p (¹P₁, ³P_J), 2s3d (¹D₂, ³D_J), 2p3s (¹P₁, ³P_J), 2p3p (¹S₀, ³S₁, ¹P₁, ¹D₂, ³P_J, ³D_J) and 2p3d (¹P₁, ¹D₂, ¹F₃, ³P_J, ³D_J, ³F_J) states of Be-like ions with nuclear charges Z = (4, 5,..., 30, 54) are determined to second order in relativistic many-body perturbation theory. Both the Coulomb interaction and the Breit interaction are included. Corrections for the frequency-dependent Breit interaction are taken into account in lowest order; corrections for the Lamb shift are also estimated and included. Comparisons with experiment and with other theoretical calculations are made. For ions with low nuclear charge, we obtain excellent agreement for the term-splitting. Results for the 2p-3d excitation energy of Xe⁺⁵⁰ also agree very well with experimental measurements.

Relative intensities of dielectronic satellite lines determined by radiative transition probabilities and autoionization rates are calculated for transitions 1s2lnl'-1s²nl', 1s2lnl'-1s²2l (n = 4-10, l = 0-3) for Li-like ions with Z = 5-54 by using the perturbation theory method (Z-expansion). Relativistic effects are taken into account by the Breit-Pauli operators. It was observed that the relative factor intensity changes very sharply with n and Z due to redistribution between contributions of relativistic and correlation effects.

The ground state energies of the lithium-like systems from ScXIX to ZnXXVIII are calculated by using the full-core plus correlation method with multiconfiguration interaction wavefunctions. Relativistic and mass-polarization effects on the energy are evaluated perturbatively as the first-order corrections. The QED correction is also included. The predicted ionization potentials in this work are compared with the existing experimental data in the literature. The variation of the relativistic effect with the effective nuclear charge along this isoelectronic sequence is quantitatively discussed.

Accurate wave functions obtained from using B-spline basis functions are used to calculate oscillator strengths for mS-nP, mP-nD transitions (m, n ⩽ 5) of heliumlike ions with Z = 3-10. The uncertainty of the f values is 0.01% or better for most of the transitions considered. Our results are comparable to previous best values (Kono and Hattori Phys. Rev. A30, 2093 (1984), Cann and Thakkar Phys. Rev. A46, 5397 (1992)), and some are more accurate. Based on the relativistic and QED corrections to the energy, the relativistic corrections to f values for 2¹P-1¹S and 2³P-2³S are obtained. They are in good agreement with the results of RMBPT.

Electric multipole (E1, E2, E3) and magnetic multipole (M1, M2 and M3) radiative decay rates have been calculated in the framework of the fully relativistic multiconfiguration Dirac-Fock (MCDF) approach for all the transitions involving the lowest 17 levels in highly ionized nickel-like ions. The relative magnitudes of the different contributions to the radiative decay processes of the levels are compared. It is shown that the M3 and E3 contributions become significant for the highest ionization stages.

We describe progress towards a precision measurement of the 2s Lamb shift in hydrogen-like silicon. This will use the Oxford electron beam ion trap (EBIT) as a source of highly charged ions for laser spectroscopy. We have successfully trapped silicon ions in the EBIT, and are determining the optimum operating conditions required to maximize the number of Si¹³⁺ ions. The laser system required for the experiment is currently under development; the first stage of this work involves locking a frequency-stabilized laser operating at 734 nm to a high-finesse enhancement cavity.

Using the Oxford electron beam ion trap (EBIT), we have studied a number of magnetic-dipole fine-structure transitions in highly charged argon and barium, which lie in the visible and near-UV region of the spectrum. Our wavelength measurements, with uncertainties of between 7 and 20 ppm, are the most accurate yet reported using an EBIT as a spectroscopic source of ions, and provide a useful test of atomic structure calculations for many-electron systems. The argon transitions studied are also of astrophysical interest. Finally, we present the first studies of the polarization of a visible transition from a highly charged ion trapped in an EBIT.

We report the results of laser-microwave double resonance spectroscopy of laser cooled ⁹Be⁺ ions trapped in a linear rf trap. The microwave transition frequency between the sublevels of the ⁹Be⁺ ground state hyperfine structure in a weak magnetic field was measured with a precision of 5 × 10⁻⁶. This experiment has been carried out as a first step of our project to study the hyperfine anomaly of unstable nuclear ions at INS.

As part of the RIKEN RIBF (RI beam factory) program, high-resolution x-ray spectroscopy for highly-charged radioactive isotope beams, is proposed in order to make a systematic study of the mean-square nuclear charge radii and moments of short lived radioactive isotopes far from the line of stability. To examine the feasibility of the experiment, we are now performing a test experiment using a laser beam and Li-like ion beams from RIKEN ring cyclotron. The D1 resonance line of a ¹¹B²⁺ beam was clearly observed for the first time.

Beam-foil spectra of highly charged Ne ion at energies of 0.5 and 1.0 MeV/amu were recorded in the region between 200 and 700 nm. Most of the lines are classified as transitions of high n, l levels in Ne V to Ne X, where n ranges from 5 to 11. The lines due to transition of 2s7l-2s8l' in Be-like Ne VII were found split into l-components by the perturbation of the nearby lying doubly excited 2p5l configuration to 2s8l. The identification was confirmed by decay measurements of individual lines.

Beam-foil spectra of highly charged Ar ion at energies of 1.0, 1.7 and 2.0 MeV/amu were recorded in the region between 200 and 700 nm. Most of the lines are classified as transitions of high n, l levels in Ar X to Ar XVII. Double Rydberg transitions were observed as satellite lines on the longer wavelength side of Δn = 1 transitions only in the vicinity of the foil.

The Fe VIII (Fe⁷⁺) spectrum has been investigated in the 35-200 nm wavelength region. The radiation emission following slow ion-atom collisions has been observed for the collision system Fe⁸⁺ + T (T He or Ar) at the Fe⁸⁺ energy 80keV. Twelve new transitions from different excited states in Fe VIII were identified. New energy levels of Fe VIII have been established from the transitions. The analysis was supported by Hartree-Fock calculations.

In this work, Ne-like Ar⁸⁺ ions in metastable 2p⁵3s ³P_0,2 levels from an ECR source were passed through a He gas target to populate core excited levels of Na-like Ar⁷⁺. The resulting spectra were measured and compared with those from Ar⁹⁺ passing the same He target. The population mechanism for core excited 2p⁵3p² based on one electron capture by the metastable Ar⁸⁺ levels is discussed. Our results indicate that the two electron-one photon transitions from 2p⁵3s4p is the main populating process. Also, by increasing the length of the gas target, enhancement of the intensity ratio between lines from long lived and short lived levels was observed.

Delayed spectroscopy techniques have been used to study the isoelectronic development for Al-like and Si-like intercombination line wavelengths. The ions studied range from Kr to Nb. The trend established for the quantity (E_obs - E_calc)/ζ, (E being the transition energy and ζ the effective charge), shows that the available calculated data are not useful in identifying such intercombination lines for high Z ions. In the case of the Si-like intercombination lines the difference in wavelength between experiment and calculation is around 4Å for Nb²⁷⁺ and this difference increases for higher Z ions. The line identifications were aided by recording spectra for different charge state distributions of the ions after the exciter foil. The experiments were done using ion beams from the RILAC accelerator at RIKEN.

We have performed high resolution EUV spectroscopy on the Ne⁸⁺ + H₂ system at 80 keV impact energy. New transitions have been identified. The analysis is supported by extensive theoretical calculations. A detailed picture of the decay path of the doubly excited Ne⁶⁺ states populated in double electron transfer processes is of importance for the basic understanding of the collision dynamics and for charge exchange based diagnostic techniques in fusion experiments.

We have performed high resolution EUV and Auger electron spectroscopy on the Ne⁸⁺ + He system at 80 keV impact energy. New transitions both in the Auger and the EUV spectra have been identified. The analysis is supported by extensive theoretical calculations. A detailed picture of the decay path of the doubly excited Ne⁶⁺ states populated in double electron transfer processes is of importance for the basic understanding of the collision dynamics and for charged exchange based diagnostic techniques in fusion experiments.

Recent observation of Hydrogen-like ions of Vanadium at the NIST Electron-Beam Ion Trap and measurements of Helium-like resonance line are presented. One particular feature of the current series of experiments is the possibility of absolute calibration in a near Doppler-free environment. The current approach to the possible measurement of QED effects in such a system is reviewed. There is great potential for precision measurements in the near future.

We have observed x-ray signals from He-like Ba and Ne-like W ions trapped in an Electron Beam Ion Trap (EBIT) at an electron beam energy of 19.9 keV. In the spectra, several transitions in Ne-like Ba and W ions and radiative recombination processes (RR) to n ⩾ 2 levels were observed. These atoms were seeded by the cathode and were ionized in the trap region by electron impact. We have observed dielectronic recombination processes (DR) in Ne-like Xe.

Coster-Kronig electrons from the autoionizing Rydberg states of 2 MeV/u silicon projectiles excited through a thin carbon foil were observed at zero degrees. The most prominent lines came from Si¹⁰⁺ 1s²2p(²P°_1/2) nl-1s²2sl' and 1s²2p(²P°_3/2) nl-1s²2sl' transitions, with n ranging from 9 to ~20. Other peaks and shoulders in the spectra were examined.

Combination of a spherical mirror electron energy analyzer and a time-of-flight ion spectrometer has efficiently enabled coincident measurements between energy-selected electrons and ions. Double Auger probabilities for rare gas atoms with a core hole were estimated through measurements of multi-charged ion yields coincident with a photoelectron from the core orbital. The double Auger probability for Xe with the 4d_5/2 hole is lower than that for Xe with the 4d_3/2 hole.

X-ray and UV spectra of highly charged ions have been measured from solar flares. In order to analyze these spectra we need detailed atomic data. We show the x-ray spectral analysis of solar flare spectra obtained by the Japanese satellite Yohkoh as an example of this atomic modeling. Electron temperatures are derived through the fit of the synthetic spectra to the observed SXV, Ca XIX and Fe XXV lines. From the spectra we have obtained the time dependence of the electron temperature, ion temperature, emission measure and ion abundances. Ion density ratios derived from the spectra show a time-dependent non-equilibrium ionization. We also discuss questions relating to the atomic processes.

Laser satellites, i.e. spectral lines caused by non-linear interaction of strong laser radiation with multicharged ions, are observed for the first time. Their identification are carried out by comparison of both experimental wavelengths and intensities with theoretical ones. It is shown that observation of laser satellites allows to measure directly the energies of ionic metastable states.

Dielectronic satellite spectra near the He-like resonance line W are investigated experimentally and theoretically. We propose that under certain plasma conditions the resonance line structure plays a minor role and can be mixed with the accumulation of Rydberg satellites.

Recently there has been a revival of interest in the process of elastic scattering from positive ions. First direct experimental measurements have demonstrated strong interference structure in the angular distributions, evidence that a purely Coulombic scattering analysis may be insufficient for some applications. We demonstrate the effects of including a realistic approximation to the backscattering in computing the momentum transfer cross sections, for a range of plasma types.

The electron capture processes in collision of highly charged ions with neutral atoms in a strong magnetic field are investigated in the case of arbitrary field direction. A semiclassical molecular-orbital close-coupling method is employed. The phase factors arising from the electron translation factor and the gauge transformation are included. We apply this method to the singlet (B⁴⁺ + H) system which have been investigated previously by us only for the field direction being along with the incident velocity vector. The total cross section averaged over field direction increases with field strength. When the field direction is perpendicular to the collision plane, the field effects become maximum.

Close-coupling equations for transition amplitudes are obtained with the help of the non-stationary continuum distorted wavefunctions. These functions include the influence of the electron-atomic-core interaction and can be considered as a generalization of the Volkov-Keldysh states. The tunneling limit in the problem of ionization of atoms by electromagnetic fields is calculated.

Cooler-storage ring facilities offer unique experimental possibilities for studies of electron-ion recombination processes at low relative energies by employing the electron cooler as a target. Through the use of an adiabatically expanded electron beam in the cooler of CRYRING, collisions down to 10⁻⁴ eV relative energies were measured with highly charged ions stored in the ring at around 15 MeV/amu energies. Examples of recombination measurements for C⁴⁺ and Ar¹⁵⁺ ions at an energy resolution of as low as 10⁻² eV FWHM are presented and compared with calculations of the energies and resonance strength for dielectronic recombination using multiconfiguration Breit-Pauli approximations. They agree in spectral shape and absolute cross section but show some deviation for lower n in the Rydberg series.

A crossed-beams energy-loss spectrometer has been used to investigate angular distributions for electron scattering from N^q+ ions, q = 1-3, at a collision energy of 10 eV. Results are compared with the predictions of a partial waves calculation based on a semi-empirical potential, and with the classical Rutherford formula.

A crossed-beams energy-loss spectrometer has been used to study, for the first time, angular distributions for the superelastic scattering of an electron from a positive ion. It is often a distinct disadvantage for collision studies that ECR sources tend to produce ions in a mixture of ground and metastable levels. We have however used this to our advantage to study superelastic scattering from metastables, observing energy gain spectra using an electrostatic hemispherical analyser fitted with a position sensitive detector. First results are presented for Ar³⁺ ions, with observation of the 3s²3p³²D° metastable state at 2.61 eV above the ground 3s²3p^{3 4}S° level.

In an animated crossed-beams experiment the following absolute cross sections σ_{q, q+n} for single (n = 1), double (n = 2), triple (n = 3) and quadruple (n = 4) ionization have been measured for the reaction e + Ti^q+ → Ti^(q+n)+ + (n + 1)e

σ_5,6 (n = 1); σ_2,4 (n = 2); σ_2,5 (n = 3); σ_2,6 (n = 4).

The measurements have been performed in an energy range from threshold up to 1 keV, partly to 6 keV.

The cross section for single ionization of ions in charge state q = 5 shows both contributions below the ground state threshold caused by the ionization of ions in excited, metastable states in the parent ion beam as well as from excitation-autoionization processes. The cross section is described well by distorted-wave calculations.

The cross sections for multiple ionization show considerable contributions from inner shell processes. Semiempirical formulae are in reasonable agreement with the experimental data.

Absolute electron impact ionization cross sections of hydrogen-like ions B⁴⁺, C⁵⁺, N⁶⁺ and O⁷⁺ have been measured at electron energies from below threshold up to about 6 keV using the crossed-beams technique. The cross sections are in good agreement with several theories and are compared with other available cross section data. The scaling behaviour of the cross sections along the hydrogen isoelectronic sequence is discussed.

Excitations of Na-like ions (Al²⁺, Si³⁺, S⁵⁺ and Ca⁹⁺) by electron impact are studied theoretically using the R-matrix method. Integral and differential cross sections are obtained for the transitions from the ground state (3s) to the 3p, 3d, 4s, 4p and 4d excited states, allowing for coupling between the lowest eleven states. The asymmetry parameter A, which describes the forward-backward asymmetry of the differential cross section is calculated also. The resulting A indicates that the backward scattering dominates in the transition 3s → 3p at low incident energy, increasingly with the ionic charge.

Formation of positronium atoms in ground state in collisions of high velocity positrons impacting on highly charged hydrogenic atoms (ions) also in ground state is theoretically studied. Differential and total cross sections are obtained by using a distorted wave model derived from a quantum three-body formalism. Scaling laws for differential and total cross sections valid at high impact energies are presented.

Using a photon-ion merged-beam technique, we studied the photoionization of multiply charged Xe^q+ (q = 1-3) ions in the 4d excitation region (50-140 eV). Relative yield spectra of photoions created by single (q → q + 1) and double (q → q + 2) photoionization were measured as a function of photon energy. A broad "4d giant resonance" peak with some preceding discrete peaks appears in each total ion spectrum. The intensities of discrete peaks observed at around 4d ionization threshold strongly depend on the target charge state. Those for Xe³⁺ target are very strong, whereas those for Xe⁺ are weak. Peaks due to 4d → 5p transition, which cannot occur in the neutral Xe case, has also been observed for each ion-target. The experimental spectrum for Xe⁺ has been analyzed by a multiconfiguration Dirac-Fock calculation. This calculation shows that results observed may be explained in terms of the correlation of valence and excited orbitals, and the effect of 4f-orbital collapse, of which the degree varies strongly with the change of the effective nuclear charge.

In the present report a development of the nonstationary Volkov-Keldysh approach is described. Two electron rearrangement mechanisms are analyzed in the following regions of collision velocities v similar q^1/2 and v similar q (q is the projectile ion charge). Analytical behavior of transition amplitudes and cross sections is established for the limiting case of large q >> 1. Calculations are in good agreement with experimental data for absolute cross sections as well as for the ratio of double to single ionization in the range of q = 2 ÷ 90.

The recently developed channel-distorted 2-centre (D2C) approximation remains to be evaluated in exact form but two different approximation schemes that lead to computable forms have been identified. In one of these schemes the ionization amplitude is expressed as a product of three factors with distinct characteristics. The first term is the off-energy-shell amplitude for electron scattering in the field of the approaching ion and represents a pure projectile property. The second term is the inelastic form factor and represents a pure target property. The third term represents a residue of a renormalization factor due to long-range and off-shell aspects of the considered interactions and is manifestly of three-body character. The second scheme is more accurate than the first but less transparent from a physical point of view and restricted by additional conditions on the form of the channel potential. It is shown that final-state interaction and channel distortion are very essential elements of the theory and various characteristic features in the ionization spectrum are discussed. Finally, we identify the popular CDW-EIS theory as a special case of the D2C theory and solve an outstanding question about the applicability of the CDW formulation.

Collision processes of multiply-charged ions with atomic hydrogen are studied by the triple-center coupled-channel (cc) method in addition to the conventional two-center cc method. Each basis function for the scattering equations is further expanded as a linear combination of the Gaussian-type orbitals (GTO). The third center is located at the saddle point of the potential between the two nuclei and the basis functions on it are chosen to be the eigenstates of united atoms. The triple-center cc method improves the overestimated ionization cross sections of the two-center cc calculations at intermediate energies. As the ionic charge increases, the difference between the triple-and the two-center cc cross sections becomes smaller. The overestimation of the two-center cc ionization cross sections is due to the overcompleteness of pseudocontinuum states attached to both the centers and the effect of the overcompleteness becomes smaller as the asymmetry of the system becomes larger.

We present an extensive study of double electron capture processes in slow collisions of bare ions from C⁶⁺ to Al¹³⁺ with gases from He to Xe and metallic vapour (strontium, barium, zinc) targets. The Stabilized Double Capture (S.D.C.) process, in which two electrons are captured and stabilized on the projectile, has been studied by measuring the radiative stabilization ratio R²_s(R²_s = σ_S.D.C./(σ_S.D.C. + σ_A.D.C.); σ_S.D.C. and σ_A.D.C. stand for the S.D.C. and Autoionized Double Capture cross sections) and by using optical spectroscopy of Rydberg transitions. We found that the population of asymmetrical configurations (n, n' » n) is responsible for high radiative stabilization ratios. The population of these configurations is due to Auto-transfer into Rydberg state (A.T.R.) and Transfer excitation (T.E.) processes. In the case of F⁹⁺ + Ne collision system, the n' distribution of excited Rydberg states has been deduced from a precise analysis of the light emitted by Rydberg transitions. The distribution is compared with a theoretical distribution issued from the A.T.R. model. We also measured the stabilization ratio for higher charge state ions Ar¹⁴⁺, Ar¹⁶⁺, Ar¹⁷⁺, Kr¹⁸⁺, Xe²⁵⁺, Xe²⁷⁺ on strontium and rare gas collisions and observed a slight enhancement of R²_s values for higher charge states. The observation of high Rydberg transitions for Xe²⁷⁺ on Xe collision shows that the radiative stabilization process is also explained by a population of asymmetrical configuration issued from A.T.R. and T.E. processes.

Atoms in a Rydberg state should be exceptional targets for a strongly-enhanced electron-capture process in collisions with multicharged ions since a quadratic increase of the cross section is expected when the binding energy of the target electron decreases. Simultaneously, because of the quasi-resonance of the capture process, very high orbitals should be populated. Laser excitation of the target atom to a Rydberg state, combined with a new detector based on field ionization and energy spectrometry, has made it possible to detect very high Kr^7+*(n) Rydberg states after single electron capture. A wide n distribution, up to n ≈ 100, of the capture cross section has been observed. Several collision systems composed of a Kr⁸⁺ projectile and a well-defined Rydberg state Rb*(n_ip) of the target atom have been investigated with various kinetic energies and various initial n_ip states (15 < n_i < 25). The production of doubly excited Kr^6+**(n_o, n) ions, after a two-electron capture has been investigated as well, and can be explained by two successive collisions with Rb(5s) and Rb*(n_ip) atoms, leading to n_o = 10 and a wide distribution of n states.

A new experimental technique, high resolution recoil-ion momentum spectroscopy (COLTRIMS), has been developed to measure the transfer of energy and momentum in various atomic collision systems with high precision. In processes of electron transfer in fast ion-atom collisions, this method has been used for the measurement of cross sections which are differential in scattering angle of microradians or nanoradians for selected electronic final states. In this report, the principle of this method is reviewed briefly and some experimental results are presented for state-selective differential cross sections of one-electron capture from He atoms by highly-charged ions at MeV/u collision energies.

Recent availability of relativistic and ultrarelativistic beams of heavy ions has permitted the first controlled studies of atomic collisions at energies sufficient to measure effects of several new basic phenomena. These include measurements substantiating recently predicted finite nuclear size effects resulting in a reduction in the total electronic energy loss of heavy ions in matter, and measurements of Coulomb collisions in which electrons are excited from the Dirac negative energy continuum. Measurements of total energy loss, free electron-positron pair production, and electron capture from pair production have been recently performed using 33-TeV Pb⁸²⁺ ions from the CERN SPS accelerator in Geneva. Results of these studies are presented, along with comparisons with relevant theory.

Single- and multiple-charge changing cross sections of Ar^q+ (q = 4−9) in collisions with Ne have been measured at very low impact energies ranging from 0.0125 · q to 25 · qeV/amu, systematically. The single-charge changing cross sections have relatively weak energy dependence and their averages increase with increasing charge state of projectiles roughly in agreement with a scaling law developed by Müller and Salzborn. Multiple-charge changing cross sections strongly depend on the collision energy and have a minimum structure being in terms of the projectile charge q and the charge change. Single-charge changing cross sections are well reproduced by the multi-cross Landau-Zener calculation taking the attractive induced-dipole polarization potential into consideration.

At the previous conference, HCI94, we reported the solution of the problem on double-electron detachment in collisions of H⁻ ions with highly charged ions (HCI) at medium and large collision energies using the approach based on the non-stationary continuum-distorted-wavefunction method. At small velocities, the close-coupling based on the two-center expansion is appropriate. In the case of the "outer" electron removal, the two-center problem has the exact analytic solution in terms of the Coulomb Green's function. The "inner" electron removal is reduced to the problem of atomic hydrogen collision with the HCI. The leading process is the double-electron capture into excited ionic states followed by radiative and autoionizing decay. The cross sections of single- and double-electron detachment are calculated at collision energies from 0.5-500eV. The results are found in reasonable agreement with the experimental data available. The scaling laws are discussed.

Double differential cross sections for state-selective single-electron capture processes in Ar⁶⁺-He collisions have been measured at laboratory energies between 75 and 900 eV and scattering angles between 0 and 8°. At the lowest energy, the zero-angle spectrum shows capture into Ar⁵⁺(4p) to be the most important channel. However, as the scattering angle is increased, a second peak appears at angles ⩾2° and becomes more pronounced relative to the 4p capture channel. The energy spectra are interpreted qualitatively in terms of the reaction windows, which are calculated using the single-crossing Landau-Zener model. Total and differential cross sections are also measured and compared with available measurements and calculations.

A new apparatus employing double translational energy spectroscopy has been used to study state-selective electron capture by 4 keV beams of pure ¹S ground state and pure ³P metastable C²⁺ ions in collisions with He and H₂. In each case the main excited product channels have been unambiguously identified and their relative importance established.

We have measured the absolute multi-electron transfer cross sections and branching ratios for the decay of multiply excited Rydberg ions in slow I^q+-Xe, Ar (10 ⩽ q ⩽ 20) collisions combining the initial growth rate method with coincidence method. We report the incident ion charge dependence of transfer cross sections and branching ratios.

A method is developed that makes it possible to incorporate molecular orbital effects in the framework of the classical over-barrier model by Niehaus for many-electron transfer in slow collisions of highly charged ions with atoms. This method describes nonadiabatic transitions, for respective electrons, among discrete quantum states in a quasimolecule formed during a collision. It is applied to L-shell electrons of target Ar atoms in collisions of C⁶⁺, N⁶⁺ and O⁶⁺ ions. By further taking into account possible autoionization processes following electron transfer, we can roughly reproduce the recoil-ion charge-state distribution observed in a recent experiment. The projectile dependence is derived through the Pauli principle.

Doubly differential cross sections for single and multiple electron capture by Ne¹⁰⁺ ions colliding on He have been measured at 7.5, 15 and 30 keV by the coincident energy gain technique. The problem of the decay of multiply excited states formed during the collision is discussed for well identified processes.

We report converging evidence from two different coincidence experiments of the formation of triply excited states C³⁺(2, n, n') and Ne⁷⁺(3, n, n') with two n, n' (n and n' >> 3) Rydberg electrons. They are formed by triple electron capture in collision of C⁶⁺ and Ne¹⁰⁺ bare ions with Ar at few keV. This detailed study was triggered by measurements of surprisingly large cross sections of stabilized triple electron capture (STC) for which a full radiative decay leaves the three electrons bound to the projectile. Both the energy gains and the visible photon spectra support the interpretation in term of a large population of triply excited double Rydberg states among which some states decay without autoionization. For both systems, possible population mechanisms are discussed in term of purely atomic mechanisms occurring in the post collisional evolution of the quasi symmetrical triply excited states initially populated by the collision.

The influence of the projectile velocity on the nl-distributions and on the m_l-distributions of the Ar⁷⁺ excited states produced by electron capture during Ar⁸⁺-Li(2s) collisions have been studied experimentally by means of near UV and visible photon spectroscopy in the 0.1-1.0 keV/amu energy range (4-40 keV), and theoretically by using the classical trajectory Monte Carlo (CTMC) method. The experimental nl-distributions have been deduced from the emission cross sections of all lines corresponding to 7l'-8l and 8l'-9l transitions. The polarization rates of all these lines have been measured and compared with those obtained from CTMC calculated m_l-distributions. Electronic energy curve calculations are presented in order to discuss these results in terms of dynamical couplings.

We study electron transfer in Be⁴⁺-He collisions at 2-150keV/u. The system is described in the semiclassical close-coupling formalism. By considering only one active electron, cross sections for electron transfer could be determined for final states ranging up to the Be³⁺n = 9 states. We study also transitions from an initially excited He 2 ¹S state.

For the first time, recoil ion momentum spectroscopy has been successfully applied to study low energy, state-selective single electron capture by highly charged projectiles. The specific systems investigated are fully stripped 6.75 keV/u Ar¹⁸⁺ and 6.82 keV/u Ne¹⁰⁺ on He. Measurements of the He⁺ recoil ion longitudinal momenta are used to determine the final n-state dependence of the captured electron. Simultaneous measurement of the transverse momenta of the recoil ion yields information about the projectile scattering angle dependence of the single capture process.

We have observed polarization of emission lines for 1s²2s5g(¹G₄)-1s²2s6h(¹H₅) and 1s²2s6h(¹H₅)-1s²2s7i(¹I₆) transitions of O⁴⁺ produced by double electron capture in O⁶⁺ + He collisions in the energy range of 60-120 keV. The polarization degree was 0.2-0.23 for the 5g-6h transition and 0.28-0.33 for the 6h-7i transition. The polarization degree of the former transition with the cascading effect by the latter transition removed was estimated and found to be nearly zero with uncertainties of ±0.2. This indicates that the 7i or higher excited state ions produced by dielectronic interaction during the electron capture is aligned to the m = 0 magnetic substate, as in the case of single electron capture. The polarization degrees are almost independent of energy, in contrast to the energy dependent emission cross sections. This suggests that the production dynamics is almost the same over our energy range.

Ejected electrons from doubly-excited helium atoms, produced by double electron capture collisions of He²⁺ with Mg, Ca and Ba atoms at low energies, have been measured using zero-degree electron spectroscopy with high energy resolution. Electrons from the configurations (2lnl') (n ⩾ 2) were observed. Electron spectra from the terms of higher angular momenta are dominant in contrast to the case of ion or electron-impact excitation of neutral He.

Electron energy spectra arising from collisions between He-like ions (O⁶⁺ and N⁵⁺) and rare gas atoms (He, Ne and Ar) were measured using zero-degree Auger electron spectroscopy with high energy resolution. The electrons were ejected from doubly excited Be-like ions produced by double electron capture from the targets. Triplet states in the doubly excited systems were predominantly produced in O⁶⁺-Ne and N⁵⁺-Ar collisions.

Electron spectra ejected from doubly excited states of Be-like ions produced by two electron capture processes in O⁶⁺ + Ca, C⁴⁺ + Mg and C⁴⁺ + Ca collisions have been measured by means of high resolution zerodegree electron spectroscopy. For the O⁶⁺ + Ca collision, spectra from the 1s²4lnl' and 1s²5lnl' states are observed in addition to those from the 1s²3lnl' states in which n equals six or larger. For the C⁴⁺ + Mg and Ca collisions, spectra from the 1s²3lnl' and 1s²4lnl' states are observed. Population distributions of the states are explained as a whole using the concept of the reaction window based on the extended classical over-barrier model by Niehaus.

Photon emission following slow ion-atom collisions has been observed for the collision system He²⁺ + He. The energy of the incoming beam of helium ions was varied between 10 keV and 35 keV. In particular, the velocity dependent relative photon emission cross-sections for the 1s²¹S₀-1snp ¹P₁ (n⩽4) resonance series in neutral helium are reported and compared with theoretical results. The work has been performed at the Uppsala University ECR ion source facility.

A crossed beam technique incorporating time-of-flight analysis and coincidence counting of the collision products has been used to measure cross sections for O⁺, O₂⁺ and O²⁺ formation by electron capture in collisions of 5-67keV amu⁻¹ He²⁺ ions with ground state O atoms and O₂ molecules for the first time.

Recent calculations and measurements have revealed unexpected oscillations of the total cross section for excitation in low- to intermediate-energy He²⁺ + H collisions. A physical explanation of this behavior is given here stemming from analysis of classical trajectory Monte Carlo simulations, molecular orbital close coupling calculations, and solution of the time-dependent Schrödinger equation on a numerical lattice. These results indicate that the observed behavior should be characteristic of a wide range of reactions in ion-atom collisions.

Comprehensive velocity-space "snapshots" of the electron continua produced by the impact of ions on He at a projectile velocity of 1.63 a.u. have been measured for the bare projectiles of p, He, C, O and Ne. For the three highly charged ions, this velocity lies in the "ionization threshold" region where electron capture dominates the reaction. The experimental technique projects the distribution of soft continuum electrons onto a two-dimensional detector in such a way that the velocity-space distribution for all electrons with laboratory energies in the range from 0-30 eV is accurately imaged. The data show no evidence for a saddle-point feature for the highest three projectile charges.

We have measured capture- and loss-ionization cross sections differential in the projectile scattering angle for 2-MeV C³⁺ −Ar collisions. The scattering angles ranged from 0.1-1.0 mrad. The obtained differential cross sections were reproduced fairly well by a classical-trajectory Monte Carlo (nCTMC) method.

A crossed beam coincidence counting technique has been used to study Ga^q+ formation in one-electron capture by H⁺ and He²⁺ ions in single collisions with ground state Ga atoms within the energy range 35-700keV amu⁻¹. An attempt has been made to describe the measured charge state fractions F_q of Ga^q+ ions for q = 1-6 in terms of a simple model based on an independent electron description.

A method of extracting electron-ion elastic scattering cross sections from ion-atom collisions has been developed. By analyzing the binary encounter electron (BEe) production in energetic ion-atom collisions, which is due to loosely bound target electrons ionized through direct, hard collisions with the projectile ions, differential cross sections of electrons elastic scattered from highly charged ions are derived for a broad range of scattering angles. The cross sections are observed to deviate strongly from the Rutherford cross sections, and immediately yielded an electron diffraction in angular distribution of elastically scattered electrons. Experimental data are compared with a partial-wave treatment using the Hartee-Fock model.

The 3dσ-2p_3/2σ vacancy sharing ratio has been measured for Fe and Co ions on Au and Bi between 0.1-1.5 MeV/u. An almost quantitative description of the data by the hidden crossing theory, developed for one-electron two-Coulomb-center systems, has been obtained when the cores of the coupled states were approximated with effective charges inferred from the experiment.

X-rays have been detected from highly ionized swift projectiles of ⁷⁵As and ⁸⁰Se passing through thin carbon foils. The investigations have been made at two projectile energies of 55 and 80 MeV for ⁷⁵As ions and 66 and 90 MeV for ⁸⁰Se ions. The K_β/K_α ratios of the ions have been found to be almost half of the free atom values which can be attributed to the sum of the effects caused by vacancies in L and M Shells. In addition to two normal L x-ray peaks a third peak corresponding to L_REC (L-shell radiative electron capture) has been observed. All the x-ray lines show a shift towards higher energy due to perturbation of the energy levels. The relative REC cross-section between lower and higher projectile energies shows excellent agreement with the theoretical results obtained under the dipole approximation.

The double differential cross sections (DDCS) for low energy electron emission can provide stringent tests of the theoretical models for ionization in ion-atom collisions. We have measured the DDCS (d²σ/dΩ d) of soft electron emission in the ionization of H₂ bombarded by bare Carbon ions of energy 1.84 and 2.5 MeV/u. The measurements have been carried out for different emission angles (θ) and for electron energies () between 0.1 and 300eV. The angular distributions of the DDCS for electrons with fixed energies were found to peak around 70-75°. The data have been compared with CDW-EIS and FBA calculations.

Charge-state dependence for low energy projectile autoionizing transitions from 2 MeV/u S^q+ (q = 6, 11 to 13) ions on He and C-foil targets was measured using a zero-degree electron spectrometer. A series of autoionization electrons produced by the Coster-Kronig transitions of 1s²2p(²P_3/2)9l-1s²2sl' are identified in the electron energy range up to 2.5 eV for the S¹²⁺ + He collision. No characteristic lines are observed in the electron energy spectra following the S¹³⁺ ion beam excitation with He. This indicates that electron excitation and capture processes that could produce the Li- and Be-like initial configurations resulting in autoionizing Coster-Kronig transitions do not occur during collisions between S¹³⁺ ions and a He target at this collision energy. It is suggested that the electron spectra for the S¹¹⁺ projectiles show a series of autoionizing Coster-Kronig transitions of 1s²2p²7l-1s²2s2pl', 1s²2p²9l-1s²2s2pl' and 1s²2s2p9l-1s²2s²l' for S¹¹⁺ ions, in addition to 1s²2p(²P_3/2)9l-1s²2sl' transitions for S¹²⁺ ions.

The net-ionization cross sections for Ne and Xe by C⁶⁺, Ne¹⁰⁺ and Ar¹⁸⁺ ion impact are presented. These cross section data are discussed in connection with the classical-trajectory Monte Carlo (CTMC) calculations and the Born approximation.

The longitudinal momentum distributions for the recoil ion and ejected electron in single ionization of He by 3.6 MeV/amu Ni²⁴⁺ ions are presented using the continuum distorted-wave (CDW-CDW) model. The results are discussed in the context of recent continuum distorted-wave eikonal-initial state (CDW-EIS) calculations [Rodriguez et al., J. Phys. B. 28, L471 (1995)] and compared with available experimental data [Moshammer et al., Phys. Rev. Lett. 73, 3371 (1994)].

Single electron capture for intermediate and high collision energies is analyzed. Theoretical total cross sections for B⁵⁺, C⁶⁺, N⁷⁺, O⁸⁺ and F⁹⁺ projectiles impinging on H, He and H₂ targets are presented. The Continuum Distorted Wave-Eikonal Final State approximation is employed in the calculations. The theoretical results are compared with available experimental data.

The production of bound-free electron-positron pairs in relativistic heavy-ion collisions is investigated within a perturbative two-center description. We consider this process as the transfer of a negative-energy electron in the Coulomb field of the target nucleus to a bound state of the projectile. Cross sections are calculated by employing the Oppenheimer-Brinkman-Kramers (OBK) approximation incorporating exact Coulomb-Dirac wave functions. We show that this transfer-like reaction competes in magnitude with the usual excitation-type process, demonstrating that distortions due to both Coulomb centers are important in the 1 GeV/u energy range.

With heavy, highly-charged ions the electron-electron correlation is probed in the relativistic domain by Resonant Transfer and Excitation, RTE. For the studied case of initially He-like U⁹⁰⁺ ions the KLL-RTE splits into three resonance groups according to the j values of the electrons involved in the doubly-excited intermediate states. For a K to L excitation into a j = ½ state with a simultaneous capture also to a j' = ½ state, relativistic effects yield a strong cross section enhancement. The doubly excited states with jj' = 1/2-3/2 show a strong anistropy for the radiative ground state transition of the j' = 3/2 electron manifesting a pronounced non-isotropic population of the magnetic substates.

X-ray spectra have been observed for the collision system of bare C⁶⁺, Ne¹⁰⁺, Si¹⁴⁺ and Ar¹⁸⁺ ions of 75-290 MeV/u with Be and C foil targets.

The radiative electron capture into continuum states (RECC) of these projectiles is always noticeable. For 75 and 150 MeV/u Ar¹⁸⁺, we can also observe a peak due to radiative electron capture into the K-shell (K-REC) in addition to RECC. A small ridge corresponding to K-REC is discerned also for 75 MeV/u Si¹⁴⁺. These features reflect the energy and projectile charge dependence of the intensities of RECC and REC x-rays. The observed edge energies of RECC and peak energies of REC are consistent with estimated values based on energy conservation. The observed absolute intensities of these components are also compared with calculations.

In relativistic collisions between bare high-Z ions and low-Z target atoms, electron capture into the ground and excited projectile states is almost completely caused by the time-reserved photoelectric effect, i.e. radiative electron capture. A study of the REC process into bare high-Z can therefore be utilized for the investigation of the photoelectric effect. In this paper we present data for the inverse of the two-step photo-ionization process, which were obtained by measuring the angular distribution of the Lyα₁ (2p_3/2 → 1s_1/2) de-excitation photons induced by REC into the 2p_3/2 state of initially bare high-Z ions. The anisotropic emission, revealed by the experiments, demonstrates that the population of the magnetic substates by REC in fast collisions deviates strongly from the statistical one, and that it must lead to a strongly polarized Lyα₁-radiation.

Covariance mapping is used to study the dissociation dynamics of highly-charged triatomic molecules possessing linear (CS₂) and bent (NO₂) equilibrium geometries, and linear carbon clusters. An intense picosecond laser is utilized to produce these highly-charged species. The measured values of kinetic energy release when such ions dissociate are very much less than those measured in single-photon and electron-impact experiments. This reduction is likely to be a manifestation of the extent to which molecular potential energy surfaces are "flattened" by the action of the intense, linearly polarized laser radiation, akin to the bond-softening process that has been observed in the case of diatomic molecules. Our observations indicate that distortion of molecular potential energy surfaces may be the dominating feature in interactions between intense fields and linear molecules; the dynamics in the case of molecules possessing nonlinear geometries is much more complex and vector correlations appear to also play an important role.

Experimental studies of collisions between highly charged ions and molecules have been carried out using the coincidence time of flight technique at high and low collision velocities. We have studied ionization of the target molecule and electron capture caused by ion impact. In general the trends are similar for molecular and atomic targets, and thus one can use the knowledge about one kind of target to help understand the other. Twoelectron processes, like ionization-excitation and double-ionization, become almost as important as single-electron processes in collisions between highly charged ions and two-electron targets. It is shown that in collisions between highly charged ions and molecules the high energy tail of the distribution of kinetic energy released in the dissociation into ion-pairs is associated with one or two electrons in highly excited states.

During collisions between slow highly charged ions and neutral atoms or molecules, a lot of electrons can be transferred into multiply excited levels of the highly charged ions, and finally the product ions are stabilized by ejection of electrons (autoionization decay) or photons (radiative decay).

The ratios of the radiative decay to the autoionization decay after double-electron transfer processes in slow I^q+ (q = 8 ÷ 23) + CO collisions have been measured by using the coincidence method. It was found that these ratios increase (from 2% up to about 10%) as the charge of the projectile ions increases. A model which explains such a feature is proposed. Based upon the model we have calculated the theoretical rediative/autoionization decay ratios, using the Cowan code, and compared them with the measured results.

We investigate fragmentation of CO molecules by collisions of He²⁺ ions at energies between 2 and 11 keV/amu by means of a reflectron time-of-flight (TOF) spectrometer. The kinetic-energy-release (KER) in the center of mass system of the molecule can be determined from the flight times of these particles. Different dissociation processes leading to different amounts of released energy and different fragments can be identified. The KER differs from the one expected from the pure Coulomb repulsion of two point charges, starting at the CO equilibrium distance and depended strongly on the collision energy. This will be discussed in terms of the classical overbarrier model. Furthermore, there is a strong influence of the projectile type on the KER. A feature of the experiments, namely the strong dependence of the KER on the projectile kinetic energy, is not yet fully understood.

Collisions between 32.2, 130.5 and 570.5 keV Ar¹¹⁺ ions and CO molecules have been studied using the Macdonald Laboratory CRYEBIS. Coincidence time of flight was used to detect all recoil ions originating from each molecule and a position sensitive detector was used to determine final projectile charge states. Single-and double-electron capture cross-sections are much larger than those for ionization at these collision energies. The dominant recoil channel associated with the Ar¹⁰⁺ final charge state is the CO⁺ molecular ion. The main ion-pair channel is the C⁺ + O⁺ dissociation of CO²⁺ while the relative yields of higher charge states of the transient CO^q+ fall off rapidly. The dissociated ions corresponding to charge states up to CO⁴⁺ were detected in coincidence with Ar¹⁰⁺ (and Ar⁹⁺), indicating that multielectron capture followed by autoionization occurs.

We have determined the absolute cross sections for one electron capture and total electron capture between slow, highly charged ions and multi-electron molecule targets (H₂, N₂, CO, CO₂, CH₄) under single collision conditions. It is found that the cross sections increase as the charge of the projectile ions increases and as the ionization potential of the target molecules decreases, as previously observed in rare gas targets. Furthermore, we have found that a scaling law previously proposed for atoms, which is based on the extended classical over barrier model, can also reproduce our data for molecular targets.

In collisions with Ar^q+ ions (q = 6-11) at 3-10 · q keV we produced SF_n^+,2+ molecular ions, n = 1-5. Since even the singly charged SF₆⁺ ion is unstable all collisions lead to dissociation with a large number of dissociation channels. We observed an alternating structure in the mass spectra of the singly and doubly charged molecular ions SF_n⁺ and SF_n²⁺. The cations SF_n⁺ are more stable for an odd number of fluorine atoms (n = 3,5) and the dications SF_n²⁺ are more stable if the number of F atoms is even (n = 2,4).

We investigated the single electron capture and the transfer ionization in the system Kr¹³⁺/BF₃ at 26.8 keV. The following results are obtained for Kr¹²⁺ ions scattered at 0°: 60% of the Kr¹²⁺ ions result from pure single electron capture and 40% result from transfer ionisation. The BF₃⁺ molecular ion dissociates with large probability into BF₂⁺ + F or BF⁺ +2F. The mean kinetic energies of the molecular fragments are determined and discussed with respect to the mechanism of the fragmentation process.

Total charge transfer cross sections σ_{6, 6-i} (i = 1-4) and σ_{8, 8-i} (i = 1-6) have been measured in the energy range of 0.3-3.8 · q keV. Two different methods based on the crossed beam technique were used to determine the cross sections. One method is based on a retarding field analysis of the ion beam flux after the collision. The other method uses a coincidence technique in order to determine both, the dissociative part of the reaction and the total cross section. In the observed energy range all measured total cross sections have no significant energy dependence and both methods give the same results. The mean values of the cross sections are σ_{6, 5} = (32 ± 7) · 10⁻¹⁶ cm², σ_{6, 4} = (8.4 ± 1.6) · 10⁻¹⁶ cm², σ_{6, 3} = (8.4 ± 1.3) · 10⁻¹⁶ cm² and σ_{6, 2} = (1.3 ± 0.2) · 10⁻¹⁶ cm². In the system Ar⁸⁺/N₂ the cross sections for the capture of i = 1, 2,..., 5 electrons amount to σ_{8, 8-i} = (132, 38, 17, 13, 3.8) · 10⁻¹⁶ cm², respectively.

A new experimental set-up has been built allowing, for the first time, the complete collection, event by event, of all fragments resulting from the dissociation of C₅^Q+ clusters (Q = 1 → 4). These ionized species were created either by dissociative excitation (Q = 1) or ionization (Q = 2, 3, 4 for single, double and triple ionization respectively) of incident 10 MeV C₅⁺ ions colliding with an He target. The fragmentation pattern of C₅⁺ is found to be radically different from the one observed in photoexcitation or in low velocity collisions. Results concerning the fragmentation of C₅^Q+ clusters with Q ⩾ 2, for which no data existed up to now, exhibit a large variety in the possible fragmentation channels.

Capture, single, double and triple ionization cross sections of 10 MeV C₅⁺ clusters colliding with He atoms have been measured. This was achieved thanks to a new experimental set-up allowing for a complete collection and unambiguous identification of all the fragments emitted by the dissociative C₅^Q+ species (Q = 0 → 4). We use these results, together with similar cross sections obtained with identical velocity atomic projectiles (2 MeV C⁺ → He system), for testing a cluster-atom collision model based on a representation of the clusters in terms of independent atoms. Ionization is qualitatively and quantitatively accounted for by the model, but capture not.

We report experiments concerning collisions of slow Ar⁸⁺ ions on a gaseous C₆₀ target. We measured recoil ion mass spectra in coincidence with the final charge state analysed projectiles Ar⁷⁺, Ar⁶⁺, Ar⁵⁺ and Ar⁴⁺ successively and we were able to establish correlation between low energy fragments produced by break up of molecular C₆₀^r+ ions. We also measured the relative cross sections of multicaptured processes, especially the stabilization ratio of two electrons in double capture process which has been found R_s² = 5%. The r-electron capture cross sections for r = 1-5 are compared with predictions of the C.B.M. barrier model.

Collision-induced fragmentation of C₆₀ by 1-4 MeV Si^1-4+ ions has been studied using a time-of-flight technique, and initial kinetic energies of fragment ions were deduced from the peak profile analysis. The kinetic energies of the small clusters decrease with increasing cluster size in the range 1-10 eV, while those of the large fragments are nearly constant values of about 0.05 eV. The results indicate that the process is dominated by hard inelastic collisions such as collective-excitation or inner-shell excitation leading to the formation of highly unstable states followed by multi-fragmentation.

Highly charged ions provide a unique way to prepare metal clusters in such high charged states that it has opened the possibility to undertake detailed investigations of the dynamics of strong Coulomb instabilities and subsequent fragmentation of charged conducting microclusters. Experimentally, a neutral atomic cluster beam is intersected by a low velocity HCI beam (Xe³⁰⁺, Xe²⁰⁺, Ar¹¹⁺, Ar⁸⁺, Ar³⁺, and O⁵⁺) and resulting charged cluster fragments are analysed. We have selected some new experimental data that bear evidence of the efficiency of the method and of the existence of an as yet unobserved fragmentation regime.

The interaction of slow highly-charged ions with surfaces is studied using thin Al₂O₃ and Ni microcapillary foils as targets as well as flat metal plates. The former provides information on hollow atoms (ions) in the first generation (i.e., above surface). In contrast, the latter is suitable to investigate those in the second generation (i.e., at or below surface). About 1% of 2.1 keV/u N⁶⁺ ions transmitted through the microcapillary are found to capture at least one electron, which is consistent with the prediction of the classical over-barrier model. The charge state distribution is found to be a very weak function of the exiting charge, which is quite different from that transmitted through a thin foil or that specularly reflected from a surface. N and Ne K x-rays emitted from the downstream of the target show that ~1% of the charge changed ions are in extremely stabilized states with lifetimes of ~ns keeping an innershell orbital open. Further, the relaxation dynamics of hollow atoms in the second generation are studied through measurements of L-X-rays from Ar ions as a function of L-shell hole numbers.

This paper discusses the mechanisms governing the formation and decay of hollow atoms in front of (semi) conducting and insulating surfaces. First, the primary neutralization of the highly charged ions is treated in terms of the classical overbarrier model. Different views are presented. Then the most energetic part (the filling of the K-shell hole) of the de-excitation of hydrogenic hollow atoms is treated in terms of a balance between L-shell filling rates and KLL Auger decay rates. Special attention is focused on the influence of the electronic structure of the different targets used on the de-excitation mechanisms.

The screening of highly charged ions in metals is studied using density functional theory as applied to a static impurity in an electron gas, that represents the valence electrons of the metal. Self-consistent screening charge densities and potentials are shown to be useful when exploring the nature of the screening and can also be used to estimate time scales for neutralization and relaxation. A molecular orbital model is also used to study electron capture by the projectile from target inner shells. Several examples show that the relaxation takes place within a few femtoseconds scale. Applications of the results to interpret electron emission and energy loss data are discussed.

The total sputter yield for Au, Si, GaAs, SiO₂, MgO, LiF and NaCl bombarded with hyperthermal highly charged Ar^q+ ions (q = 1-9) has been measured. Only for alkali halides (LiF, NaCl) and to some extent for SiO₂ potential sputtering (enhancement of the sputter yield with increasing charge state of the primary ion) has been observed. All other targets showed normal collision induced sputtering. From that result it is obvious that the mechanisms for sputtering can not be explained by the Coulomb explosion model, because in this model insulators like MgO and semiconductors like Si and GaAs should also show charge state dependence of the sputtering yield. Alkali halides and SiO₂ are materials which are known for strong electron phonon coupling where electronic excitations in the valence band are localized by formation of self trapped excitons (STE) and/or self trapped holes (STH). During bombardment with highly charged ions the neutralization process in front of, at and below the surface causes the formation of STE and/or STH. Therefore the potential sputtering can be explained as a defect mediated sputtering process which is well known in electron stimulated desorption (ESD) where the decay of STH and/or STE into different colour centers leads at the end to the desorption of neutralized anions. The also created neutral cations are either evaporated (as it is the case for the alkali halides) or have to be removed by momentum transfer by the impinging projectiles. Therefore it is very likely that in the case of SiO₂ for very low impact energy mainly only oxygen is enhanced sputtered, the surface is enriched in Si and the potential sputtering effect decreases with increasing ion dose.

This work describes model SCF calculations performed to map the possible mechanism of the internal dielectronic excitation (IDE) in highly charged uranium ions approaching and entering Be surface. The IDE mechanism has been proposed by Schuch et al. to explain M shell x-ray emission in highly charged ions originally without M vacancies. We find that the accidental energy degeneracy required by the mechanism is quite frequent and can occur for several types of configurations which can be transiently populated during the deexcitation of the hollow atoms. During the studies more than 160 000 SCF calculations were performed semiautomatically by clusters of workstations.

Elastic and inelastic interaction processes of Auger electrons within a solid are simulated by using the direct Monte Carlo model, in order to understand the effect of slow secondary-electron cascade on the Auger electron emission. Calculated results show considerable importance of the electron cascade for the energy distribution of electrons emitted from the surface, as well as the total electron yield. The energy distribution broadens towards the low-energy side due to the emission of slow cascade electrons. However, the question whether the total electron yield increases or not is strongly dependent on projectile ion species and energy.

X-rays emitted from projectiles, such as N⁶⁺ and Ne⁹⁺, downstream of a Ni microcapillary target were observed. Appreciable fractions of ions were found as hollow atoms (ions) with lifetimes of similar ns.

Electron emission for impact of singly and multiply charged fullerene ions C_n^q+ (15 ⩽ n ⩽ 60; 1 ⩽ q ⩽ 5) on atomically clean polycrystalline gold has been studied at impact energies far from below threshold up to 250 eV/amu by measuring the number statistics of emitted electrons, from which accurate absolute total electron yields have been determined. In contrast to impact of atomic ions the fullerene charge q apparently has no influence on the total electron yield, i.e. no potential emission takes place. There is also no clear threshold for the electron emission which becomes measurable already around 10 eV/amu, above which it rises faster than linear with the ion impact velocity. Isotachic C_n^q+ ions cause electron yields in direct proportion to their size n, with 250 eV/amu C₆₀^q+ producing on average more than 25 electrons. These results are tentatively explained by assuming that either the fullerene ions are completey shattered at the gold surface and individual carbon atoms produce kinetic emission, or electrons originate from thermionic emission of projectiles and their fragments heated up in the surface collision.

We have measured the total secondary charged particle emission (SCPE) yields by H⁺ and H⁻ impact from some non-metallic surfaces such as oxidized Be. It is found that the SCPE yields by H⁺ impact remarkably depend on the current (flux) of the incident ions, while those by H⁻ ion impact are nearly constant. In particular, it is noted that when the current of the incident H⁺ ions exceeds a critical value, the SCPE changes from negative (electrons) to positive (ions).

Total electron yields for impact of H⁺, He⁺, He²⁺, C⁵⁺, N⁺ ÷ N⁶⁺, O⁵⁺ and O⁶⁺ on clean polycrystalline gold up to impact energies of 40 keV times the projectile charge have been determined from both the related electron number statistics and the respective ion- and ejected electron currents. The results depend on the amount of projectile potential energy deposited until close surface contact as well as on potential- and kinetic projectile energies deposited below the surface. The first contribution can be satisfactorily explained by the classical over-barrier model for potential electron emission. The second contribution results mainly from kinetic electron emission which involves nonlinear screening of the projectile-configuration dependent interaction with the metal electron gas.

The energy loss of 144keV Ar¹⁶⁺ ions in a bilayer structure of C-CaF₂ has been measured. An asymmetry in the results is found depending on which layer is passed by the ion first: the energy loss is about four times larger when the CaF₂ layer is traversed by the ion first. We interpret this as an indication of the existence of a nonequilibrium charge state of the Ar ions inside the solid in the case of the insulator.

Carbon thin film was bombarded with high charge state Xe^q+ ions, and the secondary carbon yields were measured as a function of charge state in the broad range of q = 8 to 44 at the kinetic energy of 1.0 MeV and, also, q = 44 at 175 keV. It is found that the secondary ion yields per incident ion increase with increasing q; the increase rate is remarkably high in q > 26 with the rate of q^8.5 and rather moderate in q > 31. The yield and spectra of the secondary ions are not very different for 1.0 MeV and 175 keV for Xe^q+ (q = 44) ion incidence.

Optical emissions from Al and Al₂O₃ surfaces bombarded by Ar^q+ (q = 1-9) were observed in the wavelength range from 250 nm to 750 nm. The 4s → 3p and 3d → 3p doublet transitions of Al atoms were observed. Doppler line profiles of Al (4s ²S_½ → 3p ²P_3/2: 396.15 nm) transition at 45 keV impact energy were observed for various charge state of Ar^q+. The mean velocity parallel to the surface was calculated by fitting the line profile to the Thompson-Sigmund velocity distribution for the sputtered atoms. Doppler line profiles at lower impact energy (1.84 keV) for q = 3 and q = 8 charge state were observed. No significant change for these line profiles was observed. "Coulomb explosions" at the Al₂O₃ surfaces in producing neutral excited atoms were not observed.

Energy spectra of 2-MeV C^q+ ions incident under glancing angles (3-8 mrad) on step-rich SnTe(001) surfaces are measured at various scattering angles. While the spectrum, observed at the angle of specular reflection, shows a well defined peak corresponding to the ions reflected from the surface without influence of the surface steps, the spectrum, observed at a scattering angle smaller than the specular angle, shows an extra peak of small energy loss. This extra peak is found to correspond to the ions scattered at down steps. This feature allows a direct measurement of the charge state distribution of the ions in the vicinity of the surface. The observed mean charge, 3.49 ± 0.05, in the vicinity of the surface is slightly smaller than the mean charge, 3.67 ± 0.07, for the ions observed at the specular angle. This difference can be explained in terms of velocity matching of the 2-MeV C ions and the N-shell electrons of SnTe.

The irradiation effect of high energy heavy ions in a foil has been investigated by secondary ions spectroscopy in the energy region where the electronic stopping power is dominant. We observed significant enhancement of the secondary ion yield above the threshold value of the electronic stopping power, where the irradiation effect in high T_c super conductors and metallic materials becomes remarkable.

The effects of columnar defects produced by swift heavy-ion irradiation on magnetic flux pinning were studied for the polycrystalline La_1.85Sr_0.15CuO₄. The bulk specimens were irradiated with 3.5 GeV ¹³⁶Xe³¹⁺ ions from a single direction or multi-directions in order to investigate the effects of columnar defect configuration. The magnetization hysteresis was measured with a super-conducting quantum interference device (SQUID) magnetometer, and the critical current density J_c and irreversibility line were observed. In the specimens irradiated from multi-directions, more enhancement of the critical current density and larger shifts of the irreversibility line to higher fields were observed than in the specimens irradiated from a single direction.

The behavior of a vortex system in the presence of columnar defects in a La_1.85Sr_0.15CuO₄ single crystal irradiated with swift heavy ions (3.5 GeV ¹³⁶Xe³¹⁺) is studied by measuring magnetization and AC susceptibility. The absolute value of the magnetization of the irradiated sample is significantly enhanced compared to the unirradiated one. The irreversibility line is shifted to higher temperatures as the defect density increases. It is found that for B > B_cr similar 0.5 T, ϰ" of irradiated samples exhibits double peaks, suggesting that the liquid-glass transition proceeds via two steps.

A new type of coherent x-ray radiation from relativistic heavy ions passing through a crystal is considered theoretically. It is shown that the intensity of the coherent x-ray radiation can be of several orders of magnitude higher than the x-ray bremsstrahlung from an electron. A possible application of the radiation to a relativistic beam monitor is also pointed out.

We have developed a parallel beam suitable for channeling experiments with relativistic heavy ions at HIMAC (Heavy Ion Medical Accelerator in Chiba). To observe channeling phenomena, we used a silicon surface barrier detector (SSD) as a sample crystal and as a detector for the energy loss in itself. Further, we measured the angular spread of the beam transmitted through the SSD by a position sensitive detector (PSD) placed downstream of the SSD. Under <110> axial and (111), (220) and (004) planar channeling conditions, we observed that the energy loss of the channeled ions in the SSD became almost a half and their angular spread was also reduced.

The SMILETRAP experimental set-up, a Penning trap mass spectrometer for highly charged ions, is described. Capture and observation of cyclotron frequencies of externally produced highly charged ions is demonstrated. Mass measurements utilizing different charge states and species to verify the consistency of the measurements are presented. A relative uncertainty <3 · 10⁻⁹ is attained in comparisons between highly charged ¹²C, ¹⁴N, ¹⁶O, ²⁰Ne and singly charged H, H₂ and H₃ ions. The current limitations and future developments are discussed.

The electron beam ion trap (EBIT), and the higher-energy Super EBIT at Lawrence Livermore National Laboratory can produce any highly charged ion. These highly charged ions are used in a variety of research programs. Recent results from four different experiments are reviewed here. K-shell ionization cross sections have been measured for the hydrogenlike ions of several elements, and L-shell ionization cross sections have been measured for uranium ions. A measurement of the ground-state hyperfine transition in hydrogenlike ¹⁶⁵Ho⁶⁶⁺ is notable because of the complete absence of Doppler shifts. A cryogenic Penning trap, injected with EBIT ions, has been used to observe a single highly charged ion as it recombines by sequential electron capture from H₂ gas. A large sputtered ion yield, suggesting a surface Coulomb explosion, has been observed from insulators bombarded with very highly charged EBIT ions.

A new Electron-Beam-Ion-Trap (EBIT) has been installed at the Max Planck Institute of Plasmaphysics Berlin branch. The experimental technique consists in producing and trapping highly charged ions inside the space charge of an electron beam and measuring the emitted x-ray radiation. During the first test phase x-ray spectra of highly charged Ba, W and Ar-ions were observed.

A new Electron Beam Ion Trap has recently been completed in Tokyo. The general features of the apparatus, design and operation are given. This paper also surveys the planned and ongoing experimental program.

We introduce the control and power supply system of the Electron Beam Ion Trap at the University of Electro-Communications, Tokyo.

A beam line for transporting highly charged ions extracted from the Tokyo Electron Beam Ion Trap is being constructed in order to study ion-surface interactions and to inject into secondary ion traps for atomic physics experiments. A basic idea for the design and a computer modeling for the extraction system are described. The results of a test experiment to detect the total number of ions extracted from the EBIT are also reported.

This article describes two data systems, primarily for use with x-ray detectors in conjunction with an Electron Beam Ion Trap (EBIT). Both systems are designed from a common viewpoint that useful information should be presented in real-time whilst as much information as possible should be stored for subsequent off-line analysis.

Because of the range of high charge states trapped in an EBIT, the Coulomb interactions can be expected to have a significant effect on ion motion. The large number of ions trapped makes a simulation involving the coordinates of each ion computationally expensive. Two ways to approximate the Coulomb interactions and also reduce the computational time are investigated.

The evolution of the ion charge state balance in an electron beam ion trap has been studied using a computer program which models the atomic processes occurring within the trap. The predictions of this modelling code have been compared with experimentally-determined charge state distributions. Results are presented here for highly charged nickel.

A small and versatile electron beam ion source with a ring permanent magnet, called micro-EBIS, has been constructed. Ne⁷⁺ and Ar⁹⁺ ions are extracted at about 20 and 70 counts per second, respectively, with 2.0 keV/ 1 mA electron beam. The detailed electron trajectry analysis suggests that a slight modification can result in better electron beam focussing and in producing higher charged ions.

A summary of recent modifications and developments of a compact ECR ion source where the magnetic field is produced by permanent magnets will be given in this paper. To improve the confinement of the plasma electrons the axial magnetic mirror ratio has been enhanced to 2.5. This results in a more efficient plasma heating at low microwave power levels and therefore ion currents up to 320 eμA could be extracted with a microwave power of less than 10 Watts. The maximum ion currents for different charge states and various gases obtained so far will be shown. Further interest arises from the fact that photons produced in an ECR plasma due to ionization and recombination processes can be used for spectroscopic applications in the VUV wavelength region between 10 and 80 nm.

A new research facility for the study of interactions of multiply-charged ions has recently been completed at the Jet Propulsion Laboratory. A 1.2 tesla/14.0 GHz Caprice-type electron-cyclotron-resonance (ECR) ion source is used to produce highly-charged ions. The JPL facility can deliver ions into three experimental stations. Two are currently in operation for (a) measurement of absolute electron collisional excitation cross sections, and (b) measurement of lifetimes and f-values of metastable levels.

Gas (ion) mixing is an effective experimental method to improve the ECR ion source operation. The addition of light ions stabilizes the plasma and increases the highly charged ion production. A theoretical study and numerical simulation have been used to show that this effect has three different mechanisms of improving highly charged ion production: reduction of the heavier ion temperature (ion cooling); increase the plasma density due to the growth of electron production rate; concentration of highly charged ions in the central region of the source.

A new apparatus which utilizes double translational energy spectroscopy (DTES) is described. This allows studies of state-selective electron capture by multiply charged ions in well defined states. This approach avoids the ambiguities inherent in the results of many previous measurements carried out with beams containing metastable ions. The considerable potential of DTES has been illustrated by measurements of one-electron capture by C²⁺ ions in collision with Ar at 4 keV.

The investigation of electron-ion collisions using highly charged heavy ions in the storage ring ESR at GSI have so far been performed by using the electron cooler. The switching between cooling and probing mode and the interaction angle limit the attainable center-of-mass energies to a few hundred eV. This limitation can be overcome by the use of a separate transverse or longitudinal target. We propose to use the high energy electron beam of an electron beam ion source and trap without the use of a focusing magnetic field (XEBIST). An electron beam of up to 100 keV will be launched from a cathode with high emission density to form a target with a transverse temperature of about 10 meV resulting from beam expansion. The total center-of-mass energy spread for typical ions like U⁹¹⁺ may be as low as 10 eV, which will give eV-range resolution at high counting rates, allowing significant tests of QED theories.

We have created new applications of experimental instrumentation for diagnostics of hot plasma and studies of interaction of multicharged ion beams with matter (atoms, ions, molecules, microstructures, surfaces, solids) based on both glass capillary devices and multilayer mirrors or crystals, where glass capillary devices provide guiding, focusing and polarization analysis of short wavelength radiation with a large bandwidth, and multilayer mirrors or crystals optical elements are used for dispersing, focusing and polarization sensitive studies of radiation within a narrow bandwidth. In particular we report here about the development and test of such optical diagnostic devices for the spectral range 0.1 nm < λ < 100 nm. This type of micro-instrumentation is very suitable also for 2D, 3D and multiparameter applications.

A new optical technique for the extreme ultraviolet (EUV) spectral region based on glass capillary converters has been tested for studies of highly charged ion collision processes, plasma diagnostics and synchrotron radiation applications. Specifically a complex glass capillary converter system has been utilized in conjunction with a high resolution 2.2m grazing incidence monochromator to record EUV (10-100 nm) projectile and target spectra following multicharged ion collisions with He, leading to an enhancement of detected EUV photon flux between 10 and 30.

The course of Electron-Beam Ion Trap (EBIT) experiments depends more and more on precision measurement. To design and test a system of absolute spectroscopy to 10-20 parts per million for such a source is a challenging task. Other design criteria include good efficiency in the 3-10 keV energy range, ability to focus a line source and high vacuum compatibility. Some difficulties are discussed. The use of a non-scanning Johann focussing spectrometer and its consequent calibration is discussed. The spectrometer has been used in a series of experiments on the NIST EBIT. The detector location is shown (both experimentally and by modelling) to provide a major systematic contribution, which can however be controlled to a suitable tolerance. Future directions are indicated.

Performance of a broad-range x-ray spectrometer composed of a twodimensional position-sensitive proportional counter (PSPC) and a flat crystal has been investigated. The 6 cm × 6 cm PSPC with 130 μm position resolution along anode wires and 2 mm wire spacing has been used. The iron Kα₁ and Kα₂ lines are clearly resolved with a "mosaic" LiF(200) crystal at a certain crystal-PSPC distance. This is interpreted as an intrinsic focussing effect due to the mosaic structure of the flat crystal.

A toroidal electrostatic analyzer with a two dimensional position sensitive electron detector has been designed and built. The analyzer is installed to the electron spectrometer for measurements of the differential excitation cross sections in electron-ion collisions. The electron position is resolved in the energy and angular dispersive directions of the analyzer by means of microchannel plates and a charge dividing collector. The analyzer has an acceptance angle of 90°, and the analyzing energy range is 20% of the central pass energy with a relative energy resolution of 1%.

An experimental apparatus with good temporal and spatial resolutions has been developed for the two dimensional detecting system of multi-fragment ions produced through the Coulomb explosion and tested with fragmented ions from N₂O generated under Ar⁸⁺ impact.