We report the experimental demonstration of laser cooling of bunched Li-like 16O5+ O 5 + ion beams at similar to 64% of the speed of light in the storage ring CSRe. The longitudinal dynamics of laser-cooled bunched ion beams were investigated by observing the Schottky signals in real time with a high-sensitivity Schottky resonator. Furthermore, a multiparticle phase-space tracking code was developed to simulate the longitudinal Schottky spectrum of the ions inside the bucket and to interpret the experimental observations and derive the momentum distribution of the laser-cooled beams. We demonstrate that the relative longitudinal momentum spread of O5+ 5 + ion beams reached A p / p approximate to 2.0 . 0 x 10-6 - 6 with laser cooling, which is one order of magnitude smaller than what can be reached by electron cooling. The laser-cooling technique and the simulation method developed in this work can be applied to study phase-transition effects of bunched ion beams at storage rings and also pave the way for laser-cooling and precision laser spectroscopy experiments at the future large heavy-ion accelerator facilities HIAF (China) and FAIR (Germany), and the proposed Gamma Factory at CERN.

Laser spectroscopy stands out as a powerful tool to investigate atomic and nuclear properties and also test fundamental theories by precisely measuring the energy levels in highly charged ions. In this work, the finestructure splitting 1s 2 2s 2 S 1/2 - 1s 2 2p 2 P 1/2 transition in lithium -like 16 O 5+ has been investigated in a laser spectroscopy experiment at the heavy -ion storage ring CSRe. The excitation resonance of the tunable narrowband UV laser and the ions was observed using a Schottky resonator with very high sensitivity. The experimental uncertainties including the ion beam velocity determination, the space charge effects, laser wavelength calibration, and angular misalignment between the laser and ion beam were analyzed, and the 2 S 1/2 - 2 P 1/2 transition wavelength was determined to be lambda 0 = 103.45(38) nm. The primary source of experimental uncertainty arises from the inaccurate measurement of the high voltage applied on the electron cooler and therewith the ion beam velocity at the CSRe. In order to solve this problem, a high -precision divider to precisely measure the highvoltage of the electron cooler is under construction, which is expected to improve the present experimental accuracy by three orders of magnitude. In addition, an XUV optical detector equipped with an off -axis parabolic mirror has been developed and installed at the CSRe for the investigation of slow dipole -forbidden transitions in highly charged ions, such as hyperfine splitting and M1 transitions. The experimental studies presented here pave the way for future laser spectroscopy experiments at the CSRe as well as at the future larger -scale scientific facility HIAF in China.

A significant deceleration effect on a stored coasting ion beam by a continuous-wave laser light was observed in the Schottky-noise spectrum during the laser experiments with lithium-like oxygen ion beams stored at a relativistic energy of 275.7 MeV/u at the heavy-ion storage ring CSRe in Lanzhou, China. The observed deceleration range of the laser (Δp/p≈5.7×10−6) is much broader than the expected capture range (Δp/p≈3.6×10−8), as calculated from the natural linewidth of the O5+ ion’s electronic transition (2S1/2 −2 P1/2). In order to explain this huge deviation, a phase space tracking code has been developed to investigate the interaction between the stored coasting ion beam and the laser light. Simulations reveal that the deceleration range of the typically narrow CW laser force is highly enlarged by taking into account the transverse betatron oscillation of the ions with larger emittance and the angular misalignment of the laser light direction. The experimental observation is well described by the systematic simulations. The present work is crucial for forthcoming laser cooling and precision laser spectroscopy experiments and simulations on heavy highly charged ions at the CSRe and the future facility HIAF.

The electron cooler at the experimental Cooler Storage Ring (CSRe) has been upgraded with an embedded electron energy fast detuning system for the merged-beams electron–ion collision experiments. A plastic scintillation detector (PSD) and a multi-wire proportional chamber (MWPC) detector have been developed and installed downstream of the electron cooler to detect the recombined and ionized ions in the electron–ion collision experiments at the CSRe. Both detectors have been tested successfully in a recent dielectronic recombination (DR) experiment of Na-like Kr25+ ions at the CSRe. In addition, the measured DR rate coefficients for Kr25+ ions from both detectors were compared with the flexible atomic code (FAC) calculations, and a very good agreement is achieved. The present experimental results demonstrate that the new experimental setups at the CSRe including the electron energy fast detuning system and the particle detectors have high stability and efficiency and meet the needs of the forthcoming electron–ion collision precision spectroscopy at the CSRe.

High precision spectroscopy of the low-lying dielectronic resonances in fluorine-like nickel ions were determined by employing the merged electron-ion beam at the heavy-ion storage ring CSRm. The measured dielectronic resonances are identified by comparing with the most recent relativistic calculation utilizing the FAC code. The first resonance at about 86 meV due to the dielectronic recombination via (2s2p6[2S1/2]6s)J=1 intermediate state was recognized. The experimental determination of the resonance position at 86 meV reaches an uncertainty of 4 meV, which allows precise determination of the 2s22p5[2P3/2] - 2s2p6[2S1/2] transition energy. The Rydberg binding energy of the 6s electron in the (2s2p6[2S1/2]6s)J=1 state is calculated by the multi-configurational Dirac-HartreeFock and stabilization methods. The determined transition energies are 149.056(4)exp(10)theo and 149.032(4)exp(6)theo, respectively. Moreover, the transition energy has also been calculated by fully relativistic and ab initio approaches. Individual theoretical contributions are evaluated by employing the core-Hartree and Kohn-Sham screening potentials, respectively. High-order QED and correlation effects contribute prominently to the total transition energy. The present DR precision spectroscopy study at the CSRm paves the way for future precision measurements of atomic energy levels with heavier highly charged ions.

The High Intensity heavy-ion Accelerator Facility (HIAF) is under constructed at IMP in China, which is used to provide high intensity heavy ion beam pulse. A 450 keV electron cooler was proposed to boost the luminosity of high-density internal targets experiment in the spectrometer ring (SRing) at HIAF. The cooler is designed based on changes of the 300 keV cooler at IMP, which was made by BINP in 2004. In this paper, experimental testing results of the prototypes of the coils, the electron gun and the collector are reported. The technical challenges and solutions on the 450 keV high voltage system are discussed.

Cooling of hadron beams is critically important in the next generation of hadron storage rings for delivery of unprecedented performance. One such application is the electron-ion collider presently under development in the US. The desire to develop electron coolers for operation at much higher energies than previously achieved necessitates the use of radio-frequency (rf) fields for acceleration as opposed to the conventional, electrostatic approach. While electron cooling is a mature technology at low energy utilizing a dc beam, rf acceleration requires the cooling beam to be bunched, thus extending the parameter space to an unexplored territory. It is important to experimentally demonstrate the feasibility of cooling with electron bunches and further investigate how the relative time structure of the two beams affects the cooling properties; thus, a set of four pulsed-beam cooling experiments was carried out by a collaboration of Jefferson Lab and Institute of Modern Physics (IMP). The experiments have successfully demonstrated cooling with a beam of electron bunches in both the longitudinal and transverse directions for the first time. We have measured the effect of the electron bunch length and longitudinal ion focusing strength on the temporal evolution of the longitudinal and transverse ion beam profile and demonstrate that if the synchronization can be accurately maintained, the dynamics are not adversely affected by the change in time structure.

Synopsis 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 (2S1/2)61 resonances. In addition, we have also derived plasma rate-coefficients from our data for applications in astrophysics.

Electron-ion recombination of carbon-like Ar12+ forming Ar11+ has been investigated for the first time by using the cooler storage ring CSRm at the Institute of Modern Physics in Lanzhou, China. The absolute recombination rate coefficients are derived from the measurement in the electron-ion collision energy range of 0–50 eV, covering dielectronic recombination (DR) resonances associated with 2s22p2 and 2s2p3 (Δn = 0) core excitations. Theoretical results are obtained by employing FAC code and compared with the experimental recombination spectrum. An overall agreement is found in resonance energy positions between merged-beam and calculated spectra. Temperature dependent rate coefficients are derived from the measured DR spectrum by convoluting it with a Maxwell–Boltzmann energy distribution and compared with the calculations from the literature. In the presented temperature range 103–107 K, the experimentally derived rate coefficients agree with the theoretical results of Gu (2003 Astrophys. J. 590 1131) within the experimental uncertainties. The calculation by Zatsarinny et al (2004 Astron. Astrophys. 417 1173) underestimates the rate coefficients in the temperature range 103–5 × 104 K. The combination of the experimental results and theoretical calculation provides a benckmark for Ar12+ recombination data used in astrophysical modeling.

Dielectronic recombination (DR) rate coefficients for carbon-like 40 Ca 14+ forming nitrogen-like 40 Ca 13+ have been measured using the electron–ion merged-beam technique at the heavy-ion storage ring CSRm at the Institute of Modern Physics in Lanzhou, China. The measured DR rate coefficients in the energy range from 0 to 92 eV cover most of the DR resonances associated with 2 s 2 2 p 2 → 2 s 2 2 p 2 and 2 s 2 2 p 2 → 2 s 2 p 3 core transitions (Δ N = 0). Theoretical calculations of the DR cross sections were carried out by using two different state-of-the-art atomic theoretical techniques, multiconfiguration Breit–Pauli (MCBP) code AUTOSTRUCTURE and relativistic configuration interaction code FAC, to compare with the experimental rate coefficients. The theoretical calculations agree with the experimental results at collision energy higher than 10 eV. However, significant discrepancies of resonance energies and strengths can be found at collision energy below 8 eV. Temperature-dependent plasma recombination rate coefficients were derived from the measured DR rate coefficients in the energy range from 0.1 to 1000 eV and compared with the recommended atomic data from the literature. The theoretical data of Gu et al. and Zatsarinny et al. are 30% lower than the experimental results at the temperatures of photoionized plasmas, but have a very good agreement at the temperatures of collisionally ionized plasmas. Other previously published theoretical data of Jacobs et al. and Mazzotta et al. by using Burgess formula and LS-coupling calculations significantly underestimate the plasma rate coefficients in the low temperature range. The present results comprise a set of benchmark data suitable for astrophysical modeling.

The absolute rate coefficients for dielectronic recombination (DR) of sodiumlike krypton ions were measured by employing the electron-ion merged-beam technique at the heavy-ion storage ring CSRm at the Institute of Modern Physics in Lanzhou, China. The measured DR spectrum covers the electron-ion collision energy range of 0--70 eV, encompassing all of the DR resonances due to $3s\ensuremath{\rightarrow}3p$ and part of the DR resonances from $3s\ensuremath{\rightarrow}3d(\mathrm{\ensuremath{\Delta}}n=0)$ and $3s\ensuremath{\rightarrow}4l(\mathrm{\ensuremath{\Delta}}n=1)$ core excitations. A series of peaks associated with DR processes have been identified by the Rydberg formula. The experimental DR results are compared with the theoretical calculations using a relativistic configuration interaction flexible atomic code and the distorted-wave collision package autostructure. A very good agreement has been achieved between the experimental results and the theoretical calculations by considering the strong mixing among the low-energy resonances in both calculations. The experimentally derived DR spectrum is then convolved with a Maxwellian-Boltzmann distribution to obtain the temperature dependent plasma recombination rate coefficients and compared with previously available results from the literature. The present experimental result yields a precise plasma rate coefficients at the low temperature range up to $\ensuremath{\sim}1\ifmmode\times\else\texttimes\fi{}{10}^{6}\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and the calculated data by Altun et al. [Z. Altun, A. Yumak, N. R. Badnell, S. D. Loch, and M. S. Pindzola, Astron. Astrophys. 447, 1165 (2006)] provide reliable plasma rate coefficients at high temperature range above $2\ifmmode\times\else\texttimes\fi{}{10}^{6}\phantom{\rule{0.16em}{0ex}}\mathrm{K}$.

All operational electron cooling systems employ a DC electron beam that generated by an electrostatic electron gun. This paper is devoted to the simulation of the electron cooling process with a pulsed electron beam, in which the electron cooling, Intra Beam Scattering and the space-charge field of the pulsed electron beam are included. A simulation of coasting ion beam cooling with a pulsed electron beam showed that the ion beam is cooled down to a small momentum spread, and all ions are captured by the bucket created by the pulsed electron beam space-charge field simultaneously. Finally, a cold pulsed ion beam with length the same as the electron pulse is obtained. In this article, the structure of the particle tracking simulation code is described and the simulation results of coasting and bunched ion beam cooling with a pulsed electron beam are presented and analyzed. Moreover, the preliminary experiment on CSRm is introduced and the result shows an agreement with the simulation.

The Spectrometer Ring (SRing) is an essential part of the High Intensity heavy-ion Accelerator Facility project (HIAF) in China. It is designed as a multi-functional experimental storage ring, which will be able to operate in three ion optical operation modes. The SRing will be used as a time-of-flight mass spectrometer for short-lived, especially neutron-rich nuclei. It will also be used to collect and cool Rare Isotope Beams (RIBs) or highly-charged stable ion beams for nuclear and atomic physics experiments. The design magnetic rigidity is in the range 1.5 to 15 Tm. The beam cooling system consists of stochastic cooling and electron cooling devices. With a help of an electron cooler, stored ions will be decelerated to a minimum energy of 30 MeV/u by RF cavities. The extraction system of the SRing will allow cooled ion beams to be extracted to an external target for further ion manipulations or reaction experiments. The general ion optics design and technical requirements of SRing subsystems are presented and discussed in this paper.

The use of an electronic cooling system at the High Intensity heavy ion Accelerator Facility (HIAF) accelerator complex, which is being developed at the Institute of Modern Physics (China), to improve the efficiency of ion injection into the accelerator and reduce the spread of ion pulses in the beam has been proposed. Electron cooling of the ion beam was carried out due to the interaction of ions with a continuous electron beam with a current of up to 3 A, energy of up to 450 keV, and energy stability at the level of 10–4 or better. The electron beam energy recuperation was carried out at the expense of a power source with a power of 5–15 kW, which was located at the top of a high-voltage column—a high-voltage terminal. The operation of a prototype of power transmission system, which was based on a cascade transformer with a volumetric coil, has been considered. Such a transformer has a relatively low scattering inductance, which can significantly reduce the number of capacitors to compensate for it. It has been shown that this design made it possible to transfer power of up to 40 kW at small dimensions of the transformer and heat dissipation in it was not more than 10 kW.

Electron-ion recombination rate coefficients for beryllium-like calcium ions in the center of mass energy from 0 to 51.88 eV have been measured by means of the electron-ion merged-beam technique at the main cooler storage ring at the Institute of Modern Physics in Lanzhou, China. The measurement energy range covers the dielectronic recombination (DR) resonances associated with the 2s(2) S-1(0) -> 2s2p P-3(0,1,2), P-1(1) core excitations and the trielectronic recombination (TR) resonances associated with the 2s(2) S-1(0) -> 2p(2) P-3(0,1,2), D-1(2), S-1(0) core excitations. In addition, the AUTOSTRUCTURE code was used to calculate the recombination rate coefficients for comparison with the experimental results. Resonant recombination originating from parent ions in the long-lived metastable state 2s2p P-3(0) ions has been identified in the recombination spectrum below 1.25 eV. A good agreement is achieved between the experimental recombination spectrum and the result of the AUTOSTRUCTURE calculations when fractions of 95% ground-state ions and 5% metastable ions are assumed in the calculation. It is found that the calculated TR resonance positions agree with the experimental peaks, while the resonance strengths are underestimated by the theoretical calculation. Temperature dependent plasma rate coefficients for DR and TR in the temperature range of 10(3) -10(8) K were derived from the measured electron-ion recombination rate coefficients and compared with the available theoretical results from the literature. In the temperature range of photoionized plasmas, the presently calculated rate coefficients and the recent results of Gu & Colgan et al. are up to 30% lower than the experimentally derived ones, and the older atomic data are even up to 50% lower than the present experimental result. This is because strong resonances situated below electron-ion collision energies of 50 meV were underestimated by the theoretical calculation, which also has a severe influence on the rate coefficients in low-temperature plasmas. In the temperature range of collisionally ionized plasmas, agreement within 25% was found between the experimental result and the present calculation as well as the calculation by Colgan et al. The present result constitutes a set of benchmark data for use in astrophysical modeling.

16 Electron-ion recombination rate coefficients for beryllium-like calcium ions in the cen17 ter of mass energy from 0 to 51.88 eV have been measured by employing the electron18 ion merged-beam technique at the cooler storage ring CSRm at the Institute of Mod19 ern Physics, Lanzhou, China. The measurement energy range covers the dielectronic 20 recombination (DR) resonances associated with the 2s S0 → 2s2p P0,1,2, P1 core 21 Corresponding author: W. Q. Wen wenweiqiang@impcas.ac.cn Corresponding author: X. Ma x.ma@impcas.ac.cn Corresponding author: L. F. Zhu lfzhu@ustc.edu.cn 2 Shu-Xing Wang et al. excitations and the trielectronic recombination (TR) resonances associated with the 22 2s S0 → 2p P0,1,2,D2, S0 core excitations. In addition, theoretical calculations 23 of the recombination rate coefficients have been performed for comparison with the 24 experimental results using the state-of-the-art multi-configuration Breit-Pauli atomic 25 structure code. Resonant recombination originating from parent ions in the long-lived 26 metastable state 2s2p P0 ions has been identified in the recombination spectrum below 27 1.25 eV. A good agreement is achieved between the experimental recombination spec28 trum and the result of the AUTOSTRUCTURE calculations when fractions of 95% 29 ground-state ions and 5% metastable ions are assumed in the calculation. It is found 30 that the calculated TR resonance positions agree with the experimental peaks while 31 the resonance strengths are much underestimated by the theoretical calculation. Tem32 perature dependent plasma rate coefficients for DR and TR in the temperature range 33 10−10 K were derived from the measured electron-ion recombination rate coefficients 34 and compared with the available theoretical results from the literature. In the temper35 ature range of photoionized plasmas, the presently calculated rate coefficients and the 36 recent results of Gu (2003) and Colgan et al. (2003) are up to 30% lower than the 37 experimentally derived plasma rate coefficients, and the older atomic data are even up 38 to 50% lower than the present experimental result. This is because strong resonances 39 situated below electron-ion collision energies of 50 meV were underestimated by the 40 theoretical calculation, which also has a severe influence on the rate coefficients in low 41 temperature plasmas. In the temperature range of collisionally ionized plasmas, agree42 ment within 25% was found between the experimental result and the present calculation 43 as well as the calculation by Colgan et al. (2003). The present result constitutes a set 44 of benchmark data for use in astrophysical modeling. 45

At the heavy ion storage ring HIRFL-CSRe an electron cooler is operated to improve the beam conditions for experiments. The properties of cooled beams have been studied. The longitudinal beam dynamics during the cooling process was measured by a resonant Schottky detector. The dependencies of the parameters electron beam density and profile on cooling times were investigated. The friction force was measured directly with the aid of the high voltage system of the cooler and with the application of the beam bunching system as well. An experiment with bunched cold beam showed a dependence of the bunch length on the beam density.

China Spallation Neutron Source (CSNS) is the first high-performance pulsed neutron source in China, which will meet the increasing fundamental research and technique applications demands domestically and overseas. A new distributed data processing and analysis environment has been developed, which has generic functionalities for neutron scattering experiments. The environment consists of three parts, an object-oriented data processing framework adopting a data centered architecture, a communication and data caching system based on the C/S paradigm, and data analysis and visualization software providing the 2D/3D experimental data display. This environment will be widely applied in CSNS for live data processing.