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Featured researches published by W. Wu.


The 19th international conference on the physics of electronic and atomic collisions | 2008

Cold Target Recoil Ion Momentum Spectroscopy

R. Dörner; V. Mergel; L. Spielberger; O. Jagutzki; M. Unverzagt; W. Schmitt; J. Ullrich; R. Moshammer; H. Khemliche; M. H. Prior; R. E. Olson; L. Zhaoyuan; W. Wu; C. L. Cocke; H. Schmidt-Böcking

The experimental technique of Cold Target Recoil Ion Momentum Spectroscopy (COLTRIMS) is described. It allows a three dimensional imaging of momentum space of the recoiling ion for all ionizing atomic reaction with 4π solid angle for momentum measurement. The resolution presently achieved is ±0.035 a.u.. Depending on the collision system this corresponds to a resolution in projectile energy loss of down to ΔE/E=10−9 and a scattering angle resolution of down to 10−9 rad for fast heavy ion collisions. We discuss the experimental technique and some recent results on dynamics of recoil ion production for electron capture, target ionization and projectile electron loss.


Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms | 1995

Capture, ionisation and loss in swift He1,2+He collisions investigated by cold target recoil ion momentum spectroscopy

R. Dörner; V. Mergel; L. Spielberger; O. Jagutzki; S. Nüttgens; M. Unverzagt; H. Schmidt-Böcking; J. Ullrich; R. E. Olson; K. Tökesi; W. E. Meyerhof; W. Wu; C. L. Cocke

Abstract For 0.25 – 2MeV He 2+ He and He + He collisions we have measured the recoil ion momentum distribution in three dimensions for single capture, target ionisation and projectile electron loss. From these double differential cross sections we obtain state selective and scattering angle dependent cross sections for the single capture process and are able to distinguish between electron-electron and nucleus-electron interactions for the projectile electron loss.


Physica Scripta | 1997

Production, operation and status of the KSU CRYEBIS facility

Martin P. Stockli; R. Ali; C. L. Cocke; S Cowherd; D Fry; P E Gibson; S Lampenscherf; R A Mack; D C Parks; M. L. A. Raphaelian; L Rebohle; N. Renard; P. Richard; T. N. Tipping; T Werner; J Werrick; Slawomir Winecki; W. Wu

The KSU CRYEBIS is a CRY ogenic Electron Beam Ion Source located on a high voltage platform, dedicated to the exploration of the physics of the highly-charged, low-energy ions. This paper summarizes the research accomplished by our users over the last three years. It discusses the experiences encountered in the operation and production over the last three years. The major improvements accomplished over the last three years and the present capabilities are also described. The paper ends with a discussion of the user facility, the available techniques and equipment.


Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms | 1995

Electron-electron interaction in projectile ionization

R. Dörner; V. Mergel; R. Ali; U. Buck; C. L. Cocke; K. Froschauer; O. Jagutzki; S. Lencinas; W. E. Meyerhof; S. Nüttgens; R. E. Olson; H. Schmidt-Böcking; L. Spielberger; K. Tökesi; J. Ullrich; M. Unverzagt; W. Wu

For simultaneous projectile and target ionisation in He+- He collisions the momentum distribution of the singly and doubly charged recoil ions has been measured. A new cold target recoil ion momentum spectrometer with a momentum resolution of +0.13 au., based on a precooled supersonic He gas jet, has been used. The experimental doubly differential cross section shows two prominent structures which can be attributed to the two center electron-electron interaction and the nucleus-electron interaction. The contribution due to the electron-electron interaction is found to be negligible at 0.5 MeV impact energy and to be dominant at 2 MeV. The two center electron-electron interaction contributes much less to target double than to single ionisation.


AIP Conference Proceedings (American Institute of Physics); (United States) | 2008

One and two electron processes in 0.9 keV/u to 60 keV/u Ar16++He collisions

W. Wu; J. P. Giese; P. Richard; Martin P. Stockli; R. Ali; C. L. Cocke; H. Schöne

We have studied one‐ and two‐electron processes in the collision of 0.9 to 60 keV/u Ar16+ on He target using the KSU CRYEBIS facility. The cross sections for single and double captures, single ionization, and transfer ionization were measured by observing the final Ar charge states in coincidence with the recoiling He ions. Single capture (SC) is dominant and relatively independent of projectile energy. Single ionization (SI) is very small but spans the measured energies. Transfer ionization (TI) dominates the two‐electron processes and slowly increases with energy. Double capture (DC) is much smaller and independent of the projectile energy. The average Q‐values were also determined by measuring the momentum of the recoil ions. The average Q‐values for both SC and TI were found to decrease with increasing projectile energy.


AIP Conference Proceedings (American Institute of Physics); (United States) | 2008

One and two electron processes in collisions of highly charged ions with He at velocities around 1 a.u.

J. P. Giese; W. Wu; Itzik Ben-Itzhak; C. L. Cocke; R. Ali; P. Richard; Martin P. Stockli; H. Schöne

We have studied one and two electron processes in collisions of Ar16+ and O8+ ions with He atoms at velocities between 0.23 and 1.67 a.u. These processes were identified by measuring the final charges of the projectile and recoil ions in coincidence. Single electron capture (SC) is the dominant process at all our velocities. Transfer ionization (TI), where the He loses both electrons but the projectile captures only one, is next largest. Double capture (DC) and single ionization (SI) are about 10 times smaller, with DC larger for Ar and SI negligible for O. None of these processes show any dramatic velocity dependence. The energy independence of SI is somewhat surprising as our measurements span the velocity region where ionization would be expected to increase. Our analysis suggests that the ionization process is being suppressed by SC and TI processes. The average Q‐values for capture channels were determined by measuring the longitudinal momenta of the recoiling target ions. The Q‐values for both SC an...


Journal of Physics B | 1996

Inclusive multi-channel measurement of the impact-parameter distribution in collisions of swift heavy ions with He

K.L. Wong; W. Wu; E.C. Montenegro; Itzik Ben-Itzhak; C. L. Cocke; J. P. Giese; P. Richard

Recoil ion momentum spectroscopy is used to study the impact-parameter dependence of the single-ionization, double-ionization, single-capture and transfer-ionization channels in fast collisions of highly charged ions with He. The possibility of obtaining a relationship between the impact parameter and the transverse momentum of the recoil in inelastic collisions is investigated. It is found that a deflection function based on a static screening potential gives consistent agreement between model calculations based on the independent electron approximation and the experimental data for all channels investigated and over the whole range of impact parameters deduced from the measurement.


Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms | 1995

Single capture and transfer ionization in collisions of Clq+ projectile ions incident on helium

K.L. Wong; W. Wu; E.C. Montenegro; Itzik Ben-Itzhak; C. L. Cocke; J. P. Giese; P. Richard

Abstract The Kansas State University linac has been used to measure the ratio of the cross sections for the processes of transfer ionization (TI) and single capture (SC) for 2 MeV/amu Clq+ where q = 7, 9, 13, 14, and 15 projectile ions incident on a helium target. The ratio was determined using a helium gas jet target by measuring coincidences between projectile-ion and recoil-ion final charge states. The σ TI σ SC for Clq+ were compared to measurements of bare F9+ and hydrogenlike F8+ and O7+ taken at the same velocity. The ratios deviate from a q2 scaling which is predicted in the perturbative regime. This deviation is attributed to screening by the projectile electrons for low q = 7 and 9, and to the collision being non-perturbative for high q. A possible saturation effect in the ratio was observed for q ∼ 14.


Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms | 1995

Recoil momentum dynamics for the antiscreening process

E.C. Montenegro; W. Wu; K.L. Wong; C. L. Cocke

Abstract The Iongitudinal momentum transferred to the target nucleus in the electron-loss process is investigated. In particular, we analyze the resulting target recoil momentum when the antiscreening contribution takes place. This contribution is due to the electron-electron interaction and gives a smaller momentum transfer to the target when compared with the screening mode, where the target nucleus is the effective agent in the loss process.


Physical Review Letters | 1997

INTRA-ATOMIC ELECTRON-ELECTRON SCATTERING IN P-HE COLLISIONS (THOMAS PROCESS) INVESTIGATED BY COLD TARGET RECOIL ION MOMENTUM SPECTROSCOPY

V. Mergel; R. Doerner; M. Achler; Kh. Khayyat; S. Lencinas; J. Euler; O. Jagutzki; S. Nuettgens; M. Unverzagt; L. Spielberger; H. Schmidt-Boecking; W. Wu; R. Ali; C. L. Cocke; J. Ullrich; H. Cederquist; D. Belkic; A. Salin; C. J. Wood; R.E. Olson

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C. L. Cocke

Kansas State University

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J. P. Giese

Kansas State University

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R. Ali

University of Nevada

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P. Richard

Kansas State University

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V. Mergel

Goethe University Frankfurt

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R. E. Olson

Missouri University of Science and Technology

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M. Unverzagt

Lawrence Berkeley National Laboratory

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