H. Merabet

Spatial and temporal correlation in dynamic, multi-electron quantum systems

Cross sections for ionization with excitation and for double excitation in helium are evaluated in a full second Born calculation. These full second Born calculations are compared to calculations in the independent electron approximation, where spatial correlation between the electrons is removed. Comparison is also made to calculations in the independent time approximation, where time correlation between the electrons is removed. The two-electron transitions considered here are caused by interactions with incident protons and electrons with velocities ranging between 2 and 10 au. Good agreement is found between our full calculations and experiment, except for the lowest velocities, where higher Born terms are expected to be significant. Spatial electron correlation, arising from internal electron-electron interactions, and time correlation, arising from time ordering of the external interactions, can both give rise to observable effects. Our method may be used for photon impact.

Double-electron capture and radiative stabilization processes in slow ion-atom collisions

Abstract Mechanisms for double-electron capture producing projectile doubly excited states in O6++He and Ne10++He collisions are studied. Emphasis is given to slow collisions with projectile energies of a few keV. At these impact energies the production of configurations nln′l′ of nonequivalent electrons (n′≫n) is dominant. It is shown that the creation of nonequivalent electron states O4+(1s22pn′l′) and Ne8+(3ln′l′) with n′⩾6 originates from dielectronic processes involving electron–electron interaction. After the collision the populated excited states decay either by Auger electron emission or by radiative (photon) emission. Individual contributions to radiative stabilization of the Ne8+(nln′l′) states (n=3–4) are studied in the impact-energy range from 1–150 keV. The relative importance of the different contributions to stabilization changes significantly with varying collision energy. At 1 keV the major contribution is due to the decay of the configurations 3lnl′ (n⩾6) created by collisional dielectronic processes.

Time ordering in multi-electron dynamics

Time ordering of interactions in dynamic quantum multi-electron systems provides a constraint that interconnects the time evolution of different electrons. In energy space, time ordering appears as the principal value contribution from the Green function, which corresponds to the asymptotic condition that specifies whether the system has outgoing (or possibly incoming) scattered waves. We report evidence of effects of time correlation found by comparing calculations to recent spectropolarimetric data.

Zero-degree target electron spectroscopy: autoionizing resonances of helium excited by fast H+, He+ and He2+ impact

Two-electron excitation and decay of the autoionizing (2p2)1D and (2s2p)1P states of helium in collisions with fast protons and helium ions have been studied using zero-degree target electron spectroscopy. The energy resolution of electron emission spectra is 80 meV. Experimental spectra were processed using a parametrization with allowance for the Coulomb interaction in the final state (CIFS) between the ejected electron, the scattered ion and the recoil helium ion. The Shore formula was applied as well. Calculations have been carried out with inclusion of CIFS in both direct and resonant ionization amplitudes and within an expansion of a two-electron excitation amplitude in powers of projectile-target interaction up to the second order. Influence of the three-body Coulomb interaction and effects of the charge and mass of the projectiles are studied.

Dielectronic processes producing radiative stabilization in 150 keV Ne10+ + He collisions

Abstract Different contributions to radiative stabilization in the collision 150 keV Ne10+ + He are discussed. Stabilization is shown to represent 30% of the total double capture. The main contribution (0.51) to stabilization follows from the population of near-equivalent electron configurations 3 l n l ′ (n = 4, 5) and 4 l n l ′. Further stabilization is due to the decay of configurations 3 l n l ′ of nonequivalent electrons which are populated by means of dielectronic processes during the collision (0.26). The contributions due to configuration interaction in the postcollisional and asymptotic regions are relatively small.

Model for oscillations in the guidance of ions through insulating nanocapillaries

The pre-equilibrium period of the ion guiding through insulating nanocapillaries is characterized by the production of temporary charge patches inside the capillaries. The dynamics of the charge patch creation is revealed by oscillations of the mean emission angle of the emerging ions. To understand the oscillations, we propose a phenomenological model based on the retardation between charging and discharging of the patches.

Permanent Magnet Microwave Source For Generation Of EUV Light

A permanent magnet 6.4 GHz microwave plasma generator has been designed and constructed at Plasma and Ion Source Technology group at Lawrence Berkeley National Laboratory for applications in Extreme Ultraviolet Lithography (EUVL). In order to produce 13.5 nm EUV light, Xenon plasma was formed with the goal of producing Xe10+ ions, which are associated with the formation of 13.5 nm radiation. The goal was to diagnose the source plasma by extracting Xe‐ ions from the source plasma and by measuring the EUV light spectrum with a grazing incidence monochromator. 13.5 nm light was observed in the measurements indicating that Xe10+ existed in the plasma.

Magnetic sublevel population in 1s-2p excitation of helium by fast electrons and protons

We report experimental and theoretical results for the magnetic sublevel population of the helium atom in collisions with fast (vi = 3-9 au) electrons and protons. Cross sections for excitation of magnetic sublevels with M = 0 and ±1 have been obtained using polarization measurements of emitted radiation in combination with differential cross sections. Calculations have been carried out using the expansion of the transition amplitude in the Born series over the projectile-target interaction through the second order. Results of calculations are in agreement with experimental data. We find that the particle-antiparticle Z± difference exceeds the statistical error of measurement up to collision velocities vi≈6 au for excitation of sublevels with M = 0.

Uger-electron spectroscopy in slow highly charged ion-atom collisions: Double capture and stabilization

The method of Auger electron spectroscopy was used to measure the cross sections for Auger decay of the configurations 3lnl′ and 4lnl′ (n⩾4) created in the collision system Ne10++He at impact energies ranging from 10 keV to 250 keV. Auger yields were calculated to convert the experimental cross sections for Auger-electron emission into the corresponding cross sections for double electron capture. The different contributions to stabilization were extracted from the experimental double-capture cross sections and calculated fluorescence yields. For all energies, radiative stabilization is found to be about 0.3 when referred to the total double capture. At energies lower than 100 keV, the major contribution to the stabilization originates from the states 3lnl′ (n⩾6) which are populated by the collisional dielectronic process of autoexcitation. A small contribution is found to be due to the configurations 3lnl′ (n>9) created by dielectronic process phenomena in the postcollisional and asymptotic regions (≈0.04).