Multiple ionization in fast ion-atom collisions: simultaneous measurement of recoil momentum and projectile energy loss

The stability of nonlinear laser light filaments in a homogeneous isothermal plasma with respect to coupled electromagnetic and density perturbations is examined. In addition to the previously known modulational instability of a trapped electromagnetic mode, a new fast growing resonant instability is found. It corresponds to the growth of an excited eigenmode in the waveguide formed by the filament density depletion, the associated density response being supersonic and transversally localized. The evolution of the instability is illustrated by numerical simulations in two and three spatial dimensions.     

On the semiclassical impulse approximation for electron capture in asymmetric ion-atom collisions

A derivation of the impulse approximation for the capture of a targetK-shell electron by a light projectile in ion-atom collisions is given in the framework of the semiclassical approximation. The impact-parameter dependence of the capture probability is calculated numerically without further approximations, and shows good agreement with recent experimental results for protons colliding with Ne and Ar. The validity of several peaking approximations and the relation to ionisation theories is briefly discussed.     

Electron capture processes in ion-atom collisions

The development of the theory of electron capture processes in ion-atom collisions is reviewed in the present work. The formal theory of scattering is used to obtain the Born and the distorted wave Born series for the rearrangement scattering matrix. On the basis of these series, the applications of the first and second Born approximation, the OBK approximation, the DWBA and the Padé approximants to electron capture processes are discussed. The impulse approximation, the Faddeev method and the second order potential method are also explained. The results of the investigations of the high energy behaviour of the charge transfer cross section based on the Faddeev-Watson multiple scattering expansion are analysed.The methods of molecular and atomic eigenfunction expansions are presented and their relative merits discussed. The semi-classical treatment for determining the differential electron capture probability is reviewed. Results obtained in works utilising expansions in Sturmian, Gaussian and pseudo-state wave functions are also presented. An integral equation approach to the close coupling approximation is described. The field theoretic approach to investigate the electron capture process is discussed in the last section.The results obtained by different theoretical methods are compared with available experimental results.     

Electron capture in high-energy ion-atom collisions

We discuss the non-relativistic theory of electron capture from atoms (or ions) by ions when the relative velocity of the collision is greater than the orbital velocity of the captured electron. We emphasize the specific difficulties due to the two-body Coulomb potentials occurring in this process We show how the simplifications introduced by the small value of the electron to proton mass ratio can be used to provide a valuable tool to evaluate the adequacy of the existing theories. Extensive comparisons between theory and experiment are carried out and a number of new theoretical results are presented.     

Radiative ionization in slow ion-atom collisions

Bremsstrahlung from the ionization of inner shell electrons in slow ion atom collisions is considered. The yield predicted by the binary encounter approximation is small compared with experiment in 12–33 MeV O + Zr and O + Au collisions.     

Statistical treatment of the inner M-shell excitation in heavy ion-atom collisions

A statistical treatment has been applied to interpret the experimental data on the Xe M-shell vacancy production in slow 1.05 MeV XeXe collisions and is shown to give better agreement with experiment than that of the molecular-orbital models.     

X-ray productions in symmetric heavy ion-atom collisions

X-ray measurements for 50–200 keV impact Ne⁺ → Ne, Ar⁺ → Ar and Kr⁺ → Kr show an increase of a factor of 10 in the flourescence yield for Ar-L₂₃, a similar increase may occur for Kr-M₂₃, but for Ne-K the yield does not vary much.     

Impact-parameter dependence of 3dσ excitation in very asymmetric W,Pb, U 1.4 MeV/N ion-atom collisions

The impact-parameter dependence of 3dσ excitation has been derived from measurements of K- and L-shell excitation probabilities in very heavy, asymmetric collision systems (96?Z₁+Z₂?124). The first systematic evidence for the mechanism of the 3dσ-3dπ-3dδ rotational coupling has been found and is briefly discussed.     

Variational method for electron excitation in ion-atom collisions

The variational principle is formulated for wave functions with complex time-dependent parameters. Their properties are illustrated by exactly solvable models. The problem of finding the relevant parameters is investigated. As an example we study the energy transfer to an electron during a symmetric ion-atom collision.     

Dynamical recoil effects in a distorted-wave treatment of heavy-ion transfer reactions

The classical conditions of optimum particle transfer in heavy-ion reactions are shown to follow from a quantal distorted wave theory. To that purpose the method of three dimensional time dependent JWKB approximation is used.     

Excitation in ion-atom collisions inside subfemtosecond laser pulses

We discuss new excitation mechanisms in energetic ion-atom collisions embedded in short laser pulses. For comparable duration and strength of the pulse and collisional interaction, the laser field will probe and modify the interaction between projectile and target. Coherence effects emerge, insight into reaction dynamics is gained, and new dynamical features are discovered. As an example, we show (i) how a propensity rule for s-p excitation can be dramatically changed, and (ii) how the presence of the laser pulse modifies the ionization process in ion-atom collisions.     

Spectator recoil in intermediate-energy heavy-ion collisions

Recoil momenta of heavy spectators in intermediate-energy heavy-ion collisions of the order of 50–500 MeV per nucleon have been investigated within a statistical transfer model. Special emphasis was put on the role of fluctuations in defining the reaction geometry from correlation experiments involving recoil momenta and masses.     

Information-theoretical description of charge-state distributions in heavy ion-atom collisions

Universal equations for asymmetric equilibrium charge-state distributions are derived using the maximum-entropy principle. They are tested on chlorine, bromine, and iodine projectiles in several gases at various incident energies. A single energy-independent parameter relates the rate of charge formation to the observed asymmetries.     

Peculiarities in charge symmetry of energy loss in ion-atom collisions

Systematic experimental studies on energy loss (?dE/dx) were performed for ions with nuclear charge Z = 2–18 in various gases. The energy range ～0.001 to ～1 MeV/amu was considered. Detailed analysis confirmed the oscillating character of the energy loss dependence on the ionic nuclear charge associated with the ions’ electron shell structure. The symmetry of the energy loss dependence on the nuclear charges of projectile Z and target Z _t is examined.     

Radiation field and resonant two-center dielectronic transitions in relativistic ion-atom collisions

We consider projectile-electron excitation and loss in relativistic collisions of ionic projectiles with excited atoms. We show that under certain conditions electron transitions in the ion and atom can be resonantly coupled in the collision via the radiation field. The resonance becomes possible due to the Doppler effect, has a well-defined impact energy threshold, and clearly manifests itself in the cross sections. Since the range of the ion-atom interaction in the resonance case is very long, the presence of other atoms in the target medium as well as the size of the space occupied by the medium have to be taken into account. As a result, the cross section may become dependent on the density of the target atoms and/or the target size.     

Polarization and angular correlation studies of X-rays emitted in relativistic ion-atom collisions

Particle and photon polarization phenomena occurring in collisions of relativistic ions with matter have recently attracted particular interest. Investigations of the emitted characteristic x-ray and radiative electron capture radiation has been found to be a versatile tool for probing our present understanding of the dynamics of particles in extreme electromagnetic fields. Owing to the progress in x-ray detector technology, in addition, accurate measurements of the linear polarization for hard x-ray photons as well as the determination of the polarization plane became possible. This new diagnostic tool enables one today to derive information about the polarization of the ion beams from the photon polarization features of the radiative electron capture process.