Table of contents

At the main cooler storage ring (CSRm) of IMP, Lanzhou, we have measured merged-beams rate coefficients for dielectronic recombination (DR) of F-like Ni in the energy range 0-160 eV which comprises all DR resonances associated with ΔN = 0 core excitations. We compare our results with calculations by the flexible atomic code (FAC). Good agreement is found between calculated and measured resonance parameters except for the low-energy 2s 2p⁶ (²S_1/2)61 resonances. In addition, we have also derived plasma rate-coefficients from our data for applications in astrophysics.

We studied radiative cooling dynamics of the triatomic molecular ion N₂O⁺ stored in RICE. We observed the evolution of the populations at vibrational and rotational levels up to several 100 s by measuring neutral fragments from the laser-induced predissociation process. We found clear evidence of radiative cooling of the vibrational level populations with a time constant of several seconds. In contrast, absence of significant changes in the rotational levels revealed that the time scale of the rotational cooling is far longer, which is consistent to our simulation.

A new cryogenic linear ion trap beamline has been commissioned for use with the RIKEN Cryogenic Electrostatic (RICE) storage ring. Testing of the beamline at room-temperature and cryogenic conditions was conducted using methylene blue cations MB⁺ and carbon cluster anions C_n⁻. Action spectroscopy measurements of pre-cooled C_n⁻ anions injected into RICE will help determine the effectiveness of the so-called Pre-Trap Beamline, as well as provide structural and dynamical information on these cluster anions at cryogenic temperatures.

We discuss the electron-optical properties of a toroidal magnetic sector spectrometer and its suitablilty for electron-positron pair spectroscopy in relativistic ion-atom collisions in the future HESR storage ring at FAIR. With the simultaneous mapping of electrons and positrons and geometric invariants in the lepton trajectorties this instrument offers a very high efficiency for studies of vector momentum correlation in free-free pair production.

A brief introduction to the undergoing HIAF projects in China is given, and the scientific goals as well as the atomic physics programs are discussed. A new science center in the Gulf area near Hongkong will pro-vide unprecedented opportunities for novel scientific researches based on large scale facilities.

A detector based on the scintillator material YAP:Ce and capable of counting single ions is present-ed. The detector consists of a YAP:Ce crystal and a light guide operating in ultra high vacuum and a convention-al photomultiplier outside the vauum. The crystal demonstrated the necessary radiation hardness against heavy ion irradiation. The detector has been commissioned at CRYRING@ESR and its detection capabilities have been confirmed with beam from the local source.

CRYRING was moved from Stockholm to Darmstadt, modernized and integrated into the GSI/FAIR beamline topology behind ESR. As CRYRING@ESR, it will receive and store heavy, highly charged ions from all species the present accelerator chain is capable of producing. An extensive research program on low-energy atomic collisions, spectroscopy and nuclear reactions was proposed. The facility is gradually completing commissioning, ion beams from the local injector branch have already been stored and prototype experiments performed. We present the machine status and highlight some planned experiments.

We have performed a merged beam experiment on mutual neutralization of Li⁺ and D⁻, at center of mass energies close to 0 eV using the DESIREE storage rings. The final state channels Li(3s) and Li(3p+3d) are resolved and the branching ratio is found to be more equal than predicted from theoretical models.

O₂⁺ molecular ion is produced by photoionization close to threshold at SOLEIL, DESIRS beam line. By means of coincidence methods, ions are prepared in selected vibrational and electronic states (X, v=0,3,15 and a, v=3). Their reactivity with the propene in single collision regime is studied in the guided ion beam in-strument CERISES, adding ability to vary the collision energy. Absolute reaction cross section and branching ratio are recorded for the 5 most intense reactive channels, described as dissociative charge transfer. Contrasted effects of internal and collision energy are observed.

The capability of helium droplets to isolate cryogenic molecular ions at a temperature of 0.4 K is exploited to observe ultracold molecular processes in the RIKEN Cryogenic Electrostatic (RICE) storage ring. The development of a pulsed droplet beam consisting of extremely large helium droplets up to 10¹¹ atoms is a promising step to apply this unique and robust cooling method to a wide variety of molecular ions. Production of ions by photoionization of neutral species inside helium droplets will provide internally cold ions below the ring temperature of 4 K.

Stored and cooled highly-charged ions offer unprecedented capabilities for precision studies in realm of atomic-, nuclear-structure and astrophysics. In context of the latter, after the successful investigation of the cross section of ⁹⁶Ru(p,γ) in 2009, in 2016 the first measurement of the ¹²⁴Xe(p,γ)¹²⁵Cs reaction was performed at the Experimental Storage Ring (ESR) at GSI.

The decay of hot copper dimer anions is studied in a cryogenic storage ring. We detect atomic anion and neutral products and determine the fragmentation and vibrational autodetachment (VAD) rates separately. For short storage times the dimer anions predominantly decay by fragmentation of highly rotationally excited ions by tunneling through the rotational barrier. For storage times exceeding 100 ms, however, VAD is dominating. This process is driven by the very weak direct coupling between nuclear and electronic degrees of freedom.

Anthracene cations (C₁₄H₁₀⁺) have been stored in the cryogenic (13 K) electrostatic storage ring DESIREE in Stockholm to study their radiative cooling dynamics on a long time scale up to 2 s. By monitoring the laser-induced delayed dissociation curves during the storage, the evolution of the dissociation rate was obtained. Its decrease as a function of time is closely related to the time evolution of the internal energy distribution of the stored anthracene cations and consequently to the energy loss due to radiative cooling, including both Poincaré and infrared fluorescences.

We have studied the stabilities of small carbon dianion clusters, ${{\rm{C}}}_{{}^{{\rm{n}}}}^{2-}$(n = 7 – 11) in the cryogenic electrostatic ion storage ring, DESIREE. We observe spontaneous electron emission for tens of milliseconds, where dianions containing an even number of carbons decay slower in comparison to their neighbouring cluster sizes. For all the systems considered here, we find that there is a component which is stable at least on the time scales of hundreds of milliseconds.