Aaron LaForge

Projectile coherence effects in single ionization of helium

We have measured fully differential cross sections for ionization of He by 3 MeV proton impact. A projectile beam with a coherence length larger than typical atomic scales was prepared at the Test Storage Ring taking advantage of electron cooling. Pronounced effects due to the projectile coherence are observed which are absent for an incoherent 100 MeV u−1 C6 + projectile beam and the present data are in much better agreement with theory. Thus, these results represent a major advancement in resolving the so far unexplained discrepancies between experiment and theory for the 100 MeV u−1 C6 + case.

Initial-state selective study of ionization dynamics in ion-Li collisions

Kinematically complete experiments were performed on the ionization of a laser-cooled lithium target from different initial states, Li(2s), Li(2p) and Li(1s), by 6 MeV H+ and 1.5?MeV?amu?1 O8 + impact. In the measured doubly differential cross sections as a function of electron energy and transverse momentum transfer, a significant initial state dependence is found. Furthermore, comparison to quantum mechanical theory shows surprising discrepancies for Li(2s) and Li(1s) while there is good agreement for the Li(2p) initial state.

Scattering-angle dependence of doubly differential cross sections for fragmentation of H{sub 2} by proton impact

We have measured double differential cross sections (DDCS) for proton fragment formation for fixed projectile energy losses as a function of projectile scattering angle in 75 keV p + H{sub 2} collisions. An oscillating pattern was observed in the angular dependence of the DDCS with a frequency about twice as large as what we found earlier for nondissociative ionization. Possible origins for this frequency doubling are discussed.

Ion-Li collision dynamics studied with a MOTReMi

In a novel experimental approach a magneto-optical trap (MOT) is combined with a Reaction Microscope (ReMi) and implemented in an ion storage ring. Single ionization measurements were performed with 24 MeV O8+ and 6 MeV H+ projectiles and a state prepared lithium target. We obtained single-, double- and fully differential cross sections and observed features that we attribute to the structure and polarization of target initial states.

Effect of Projectile Coherence on Atomic Fragmentation Processes

We demonstrate that the projectile coherence can have a major impact on atomic fragmentation processes. This has been overlooked for decades in formal scattering theory and may explain puzzling discrepancies between theoretical and experimental fully differential cross sections for single ionization.

The PRIOC experiment - precision studies on ion collisions using a magneto-optically trapped lithium target

With the PRIOC setup, for the first time three experimental techniques are combined in order to study ion-atom collisions in unprecedented detail: It consists of a reaction microscope to monitor the momenta of charged collision fragments, a magneto-optical trap (MOT) to provide an ultra-cold lithium target, and both implemented in an ion storage ring which delivers brilliant and intense projectile beams of highly charged ions. This combination will allow studying the few-particle dynamics in ionising and charge changing ion-atom collisions with utmost resolution and will help to solve present discrepancies between experiments and theory.

Double differential projectile angular distributions for single ionization of atomic hydrogen by 75 keV proton impact

Doubly differential cross sections (DDCSp) for single ionization of atomic hydrogen by 75-keV proton impact as a function of the projectile scattering angle and energy loss have been measured.