F. W. Meyer

ON THE NEUTRALIZATION OF SINGLY AND MULTICHARGED PROJECTILES DURING GRAZING INTERACTIONS WITH LIF(100)

Abstract Measurements are reported of scattered neutral fractions for Na, K, Cs and Ne singly and multicharged ions, and of scattered negative ion fractions for incident O, F and B projectiles grazingly incident on LiF(100) as function of projectile velocity. In the case of the Na and Ne incident ions, significant dependence of the scattered neutral fractions on incident charge state is found, which is most pronounced at the lowest investigated velocities. Possible reasons for the observed initial charge state dependence are considered. In addition, results are reported for the target azimuthal dependence of the final neutral fraction observed for grazingly incident 35 keV Cs7+ ions.

Angular and charge state distributions of highly charged ions scattered during low energy surface-channeling interactions with Au(110)

The authors have measured scattered projectile angular and charge state distributions for 3.75 keV/amu O{sup q+} (3 {le} q {le} 8) and 1.2 keV/amu Ar{sup 1+} (3 {le} q {le} 14) ions grazingly incident along the [110] and [100] directions of a Au(110) single crystal target. Scattered projectile angular distribution characteristic of surface channeling are observed. For both incident species, the dominant scattered charge fraction is neutral, which varies only by a few percent as a function of incident charge state. Significant O{sup {minus}} formation is observed, which manifests a distinct velocity threshold. For incident Ar projectiles with open L-shells, the positive scattered charge fractions, while always less than about 10%, increase linearly with increasing number of initial L-shell vacancies.

Charge exchange processes between highly charged ions and metal surfaces

Abstract The interaction of highly charged ions with metal surfaces causes the emission of secondary electrons. Energy spectra of the emitted electrons reveal, for sufficiently high charge states of the projectile, the occurence of Auger deexcitation projectile inner shell vacancies brought into the interaction as well inter-atomic charge exchange processes leading to the emission of target Auger electrons.

Enhancing the performances of traditional electron cyclotron resonance ion sources with multiple-discrete-frequency microwave radiation

The performances of electron cyclotron resonance (ECR) ion sources, in terms of high-charge-state yields and intensities within a particular charge state, can be enhanced by increasing the physical sizes of the ECR zones in relation to the sizes of their plasma volumes. The creation of a large ECR plasma “volume” permits coupling of more power into the plasma, resulting in the heating of a much larger electron population to higher energies, the effect of which is to produce higher charge-state distributions and higher intensities within a particular charge state than possible in present forms of the ECR source. The ECR plasma “volumes” of traditional B-minimum ECR sources can be increased by injecting broadband microwave radiation (multiple-discrete-frequency, variable frequency, or broad-band-width frequency microwave radiation) derived from standard klystron, gyrotron, or traveling-wave-tube (TWT) technologies (frequency domain). To demonstrate that the frequency domain technique can be used to enhance ...

Fast neutralization of highly charged ions in grazing incidence collisions with surfaces

We present first results of simulations for the neutralization and relaxation of multiply charged Oq+ ions in grazing incidence collisions with a gold surface. The simulation treats the direct quasi-resonant charge transfer into the L shell of the projectile within the over-the-barrier model. The speed of neutralization is significantly enhanced by the upward shift of energy levels at the surface due to dynamical screening. We find complete relaxation, neutralization, and negative ion formations within the available interaction time of a few times 10−14 s in agreement with experiment.

Simultaneous energy distribution and ion fraction measurements using a linear time-of-flight analyzer with a floatable drift tube

A technique for simultaneous energy distribution and ion fraction measurements using a linear time-of-flight analyzer with a floatable drift tube is described. Analytical expressions for the relative collection efficiency and viewing region of the apparatus are developed as functions of the analyzed particle reduced energy and dimensionless apparatus parameters. The method was applied to studies of large-angle scattering of singly charged oxygen ions incident on Au(110), and carried out at the Oak Ridge National Laboratory’s Multicharged Ion Research Facility. Energy distributions of the scattered projectiles and the negative ion fraction are presented as a function of scattered projectile energy. As a by-product of the measurements, the relative ion detection efficiency of the particle detector was reconstructed as a function of ion impact energy on the detector.

Projectile image acceleration, neutralization and electron emission during grazing interactions of multicharged ions with Au(110)

Recent Oak Ridge work is summarized on projectile energy gain by image charge acceleration, scattered ion charge distributions, and K-Auger electron emission during low energy grazing interactions of highly charged Pb, I, O and Ar ions with a Au(110) surface.

The ORNL ECR multicharged ion source

A multicharged ion source based on Electron Cyclotron Resonance (ECR) heating has been designed and built at ORNL. The ECR ion source, which is completely dedicated for atomic physics collision studies, produces higher charge states and higher beam intensities than the present ORNL PIG multicharged ion source, and will thus permit study of collision processes involving ions of higher charge states in experiments requiring higher beam intensities than could be previously obtained in our laboratory. The source has already produced up to fully stripped C and O beams, as well as up to He-like Ar beams. Measurements of the energy spread of ions extracted from the ion source operating in both single-stage and two-stage mode are described. In addition, initial results of total cross section measurements for fully stripped light ions incident on atomic hydrogen in the energy range 0.2 to 10 keV are presented. 13 references, 7 figures, 1 table.

Low energy chemical sputtering of ATJ graphite by atomic and molecular deuterium ions

We present experimental chemical sputtering results for D+, D2+ and D3+ ions incident on ATJ graphite in the energy range 5–60 eV D−1, and compare them with simulations for deuterated amorphous carbon impacted by neutral D, D2 and D3. The measured methane yields/D for the different species compared at the same energy/D diverge below about 60 eV D−1, the incident triatomic molecular ions leading to the largest yields/D, and the atomic ions to the smallest, reaching a factor of two difference at 10 eV/D. The measured yields/D are in reasonable agreement with molecular dynamics simulations over the entire calculated energy range. The model surfaces were prepared by D, D2 and D3 impacts in a way that mimics the experiment. For D2 incident at energies below 15 eV/D, the simulations show a strong dependence of the sputtering yields on the vibrational state of the incident projectile.

The histrap proposal: Heavy-ion storage ring for atomic physics

Abstract HISTRAP, Heavy-Ion Storage Ring for Atomic Physics, is a proposed 46.8-m-circumference synchrotron-cooling-storage ring optimized to accelerate, decelerate, and store beams of highly charged very-heavy ions at energies appropriate for advanced atomic physics research. The ring is designed to allow studies of electron-ion, photon-ion, ion-atom, and ion-ion interactions. An electron cooling system will provide ion beams with small angular divergence and energy spread for precision spectroscopic studies and also is necessary to allow the deceleration of heavy ions to low energies. HISTRAP will have a maximum bending power of 2.0 T m and will be injected with ions from either the existing Holifield Heavy Ion Research Facility 25-MV tandem accelerator or from a dedicated ECR source and 250 keV/nucleon RFQ linac.