4-16 Triple Coincidence (e, γ2e) Experiment for Ionization-excitation of Helium*

Electron induced ionization-excitation (IE) of helium is a basic four-body Coulomb problem in which all thefour charged particles are actively involved. It is much more challenging to both experiment and theory in contrastto direct ionization with the residual He+ ion in the ground state. The 2s or 2p separated TDCS data, especially atlow incident energy range where the high order effects are expected to play a significant role, would offer the moststringent test to theoretical models. However, only one experiment at high incident energy achieved the TDCSs for2p state till now due to the small cross section and the low detection efficiency for multi-coincidence events[1].

4-15 Electron Emission in the Transfer Ionization Process of Intermediate Multi-charged Ion - He Collisions

The momentum projecting techniques have been well applied so as to explore the mechanisms of electronemissions as well as the dynamical effects which influenced the momentum distribution of the electrons ionized inion-atom collisions[1??3]. Usually, the emitted electrons will be projected onto the scattering plane, which was definedas the plane containing the initial and the final momentum vectors of the projectile, considering the conservationlaws and rotational symmetry around the beam axis. It is well known that the ejected electrons will be influencedsimultaneously by a combined coulomb potential from the recoil ions and the projectile ions. Qualitatively, this

4-6 Measurement of the Ratio of C3+ and O4+ Ions Produced by ECR Source to Prepare a Laser Cooling Experiment at Storage Rings

The cooling of heavy ions can provide high-quality beams that are especially important for high-precisionexperimental nuclear and atomic physics. The laser cooling of relativistic C3+ ion beams at the experimental coolerstorage ring (CSRe) is being currently prepared at Institute of Modern Physics (IMP) in Lanzhou. An electroncyclotron resonance ion source (ECRIS) will be used to produce C3+ ion beams. Meanwhile, O4+ ions could alsobe produced due to residual gas because of the same mass-to-charge ratio. Therefore, both C3+ and O4+ ion beamswill be injected and circulate in a storage ring during the laser cooling experiment at the same time. A higher ratioof C3+ ions will lead to a better result for the laser cooling experiment.

Fragmentation Dynamics of a Carbon Dioxide Dication Produced by Ion Impact

The three-body fragmentation of CO_(2)^(2+)to C++O++O induced by 1 keV/u Ar^(2+)impact is investigated employing the Reaction microscope.Three different dissociation mechanisms are clearly identified,and their branching ratios are determined.The concerted fragmentation with two CO bonds breaking simultaneously is dominant(61.7%),while the sequential pathway with CO+as the intermediate also makes a significant contribution(36.6%).

Orientation Effect in Ar Dimer Fragmentation by Ne^(8+) Ion Impact

The experiment was carried out using the Reaction Microscope mounted at the 320 kV platform for multidisciplinary research with highly charged ions at the Institute of Modern Physics,CAS[1,2].For reaction channel of(Ar2)^(2+)→Ar^(+)+Ar^(+),the kinetic energy release(KER)distribution clearly shows two peaks.The left peak locates at 3.7 eV approximately,and the right one lies at about 5.3 eV.From the classical reflection approximation KER/(Z1-Z2)=R,the internuclear distance R can be deduced.We find that the corresponding internuclear distance of the left peak is 3.8˚A,which is the equilibrium internuclear distance of the Ar2 dimer.This indicates that coulomb explosion takes place immediately after the double ionization process,without the involvement of the geometry change of the cluster ion.Therefore,the left peak dominantly arises from two-site double ionization.

Investigation of ion-atom collision dynamics through imaging techniques

The principle and technique details of recoil ion momentum imaging are discussed and summarized. The recoil ion momentum spectroscopy built at the Institute of Modern Physics (Lanzhou) is presented. The first results obtained at the setup are analyzed. For 30 keV He2+ on He collision, it is found that the capture of single electron occurs dominantly into the first excited states, and the related scattering angle results show that the ground state capture occurs at large impact parameters, while the capture into excited states occurs at small impact parameters. The results manifest the collision dynamics for the sub-femto-second process can be studied through the techniques uniquely. Finally, the future possibilities of applications of the recoil ion momentum spectroscopy in other fields are outlined.