W T Feng

A Progress Report of 320 kV Multi-discipline Research Platform for Highly Charged Ions

A dedicated platform for multi-disciplinary research with highly charged ions has been constructed, and an all-permanent magnet ECR ion source was built and installed in the beamline. Five experimental terminals are established for interdisciplinary Research. The high voltage supplied to the platform has reached 320 kV. The commissioning of the platform is successful, different ion beams have been provided for experimental studies, and the current status will be reported.

Signatures of the projectile electron–target core elastic scattering in Ar (e, 2e) reactions at low and intermediate impact energies

The momentum distributions of the recoil ions Ar+ in Ar (e, 2e) reactions are obtained at incident electron energies from 80 to 220 eV by using the reaction microscope. The contributions of large longitudinal momentum corresponding to the large scattering angle are significant. By comparing the single differential cross sections of the Ar (e, 2e) with those of the electron–argon elastic scattering process, it is concluded that the elastic scattering between the incident electron and the target core plays an important role in the large angle ionization scattering process, and the additional phase shift introduced by the ionized electron results in the disappearance of the sharp minimum that was observed in the elastic scattering. A qualitative explanation of the bigger relative contributions of recoil ions with large longitudinal momenta in Ne (e, 2e) compared to the case in Ar (e, 2e) is given.

High negative ion production yield in 30 keV F2+ + adenine (C5H5N5) collisions

In collisions between slow F2+ ions (30 keV) and molecular targets, adenine, scattered particle production yields have been measured directly by simultaneous detection of neutrals, positive and negative ions. The relative cross-section for a negative ion formation channel was measured to be 1%. Despite a slight decrease compared to a larger target, the fullerene C60, the measured negative ion formation cross section is still at least one order of magnitude larger than the yield in ion–atom interactions.

A newly built setup for small bio-molecule fragmentation study in Lanzhou

A new setup for studying ion induced small bio-molecule fragmentation processes has been built in Lanzhou, China. A preliminary collision experiment between a 30 keV He2+ ion beam and gas phase adenine molecules was performed. Partial TOF spectra associated to well-defined scattered projectile final charge states, He+ or He0 were recorded. Coincidence spectra between fragments were also obtained.

Progress of highly charged atomic physics at IMP

The progress of atomic physics researches at the Institute of Modern Physics (IMP) is reviewed, covering the studies on ion-atom/molecule collisions, ion-cluster interaction, negative ion formation, state-selective electron capture studied by COLTRIMS, as well as the progress of a new experimental area dedicated for atomic researches at moderate energies, and the advances of the cooler storage rings at the Heavy Ion Research Facility in Lanzhou (HIRFL). New opportunities to study collision dynamics from femto-second to atto-second regime are opened based on the present facilities and the on-going projects.

Investigation of fragmentation dynamics of nitrogen dimers by collisions with highly charged ions

Synopsis The fragmentation dynamics of nitrogen molecule dimers have been studied by using highly charged Ne8+ ions at impact energy of 1.0 MeV. For its three-body fragmentation, three fragmentation mechanisms have been identified by analyzing Dalitz plot and Newton diagram of the momenta of three fragment ions. The sequential dissociation of covalent first breakdown is quite surprising in contrast to the fragmentation of triatomic molecule.

Signature of Single Binary Encounter in Intermediate Energy He2＋-Ar Collisions

We experimentally observe the signature of electron emission resulting from a single binary encounter mechanism in the intermediate collision energy regime of 30 keV/u He2+ on argon. Electron emission spectra in the transfer ionization are obtained and compared with classical calculations from a two-step model considering the initial electron velocity and re-scattering of the binary encounter electron in the recoil potential. Although the present reaction is actually a four-body problem, the model starting from a binary encounter gives out surprisingly good agreement with the experimental data. Our studies show that orbital velocities of the electron affect the emission patterns of ionized electrons significantly.

Kinematically complete experiment for ionization-excitation of helium

We present a newly built reaction microscope for electron induced ionization-excitation of helium. Kinematically complete measurement with 2p state excitation is achieved by detecting the radiated photon, one electron and the He+ ion in the final state in triple coincidence. Near threshold behavior of the ionization- excitation to 2p state is investigated.

The nucleus-nucleus scattering in transfer ionization of helium by He2+ impact

We have performed kinematically complete measurement on transfer ionization of He by 50 keV/u He2+ impact. The data were analyzed in terms of Dalitz spectrum. We evaluated the role of three particles interactions and found that the main momentum exchange occurs between the projectile and the recoil ion. This result indicate that the nucleus-nucleus high order interaction could not be overlooked in transfer ionization collision dynamics of atom by intermediate energy ion impact.

The fragmentation of neon dimer induced by low energy O6+ ions

We have investigated the fragmentation channels Ne+-Ne+ and Ne2+-Ne+ from Ne2 dimer induced by O6+ ions at impact energy of 15 keV/u. The Ne+-Ne+ fragmentation channel mainly results from three pathways: the interatomic coulombic decay of Ne2+(2p4)-Ne initial state, the direct columbic explosion and the radiation charge transfer. Nevertheless, the fragmentation channel Ne2+-Ne+ is predominant by the direct coulombic explosion.