D C Zhang

Laser cooling of relativistic heavy-ion beams for FAIR

Laser cooling is a powerful technique to reduce the longitudinal momentum spread of stored relativistic ion beams. Based on successful experiments at the experimental storage ring at GSI in Darmstadt, of which we show some important results in this paper, we present our plans for laser cooling of relativistic ion beams in the future heavy-ion synchrotron SIS100 at the Facility for Antiproton and Ion Research in Darmstadt.

The first test experiment performed at the electron cooler of storage rings in Lanzhou

The cooler storage ring (CSR) project was launched in 2000 at the Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou. In 2007, the installation was completed and the commissioning of CSRs gained great success, a new highly precise generation of collision experiments will become accessible even for the heaviest ion species. A commissioning RR experiment was performed at the electron cooler with Ar18+ ions, the results are reported. And the further development of the experiments at cooler will be discussed.

Preparations for laser cooling of relativistic heavy-ion beams at the CSRe

Laser cooling is one of the most promising techniques to reach high phase-space densities for relativistic heavy-ion beams. Preparations for laser cooling of relativistic lithium-like ions, such as C3+ and N4+, are being made at the experimental cooler storage ring (CSRe) in Lanzhou, China. In December 2011, a new buncher was installed and tested with a 70 MeV u−1 22Ne10+ ion beam by electron cooling at the CSRe. The longitudinal momentum spread of the bunched ion beam was measured by the new resonant Schottky pick-up. As a result, Δp/p ≈ 2 × 10−5 has been reached at ion numbers less than 107. According to this test result, the RF-buncher is suitable for the upcoming experiment of laser cooling at the CSRe. Laser cooling of heavy-ion beams will also be applied at future storage ring facilities, e.g. FAIR in Darmstadt, and HIAF in Lanzhou.

RF-bunching of relativistic 12C3+ ion beam for laser cooling experiment at the CSRe

To prepare the upcoming experiment of laser cooling of relativistic 12C3+ ion beams at the experimental cooler storage ring (CSRe), a test experiment was performed with 12C3+ ion beams at an energy of 122 MeV/u on the CSRe, at the Institute of Modern Physics, Lanzhou, China. In this experiment, the main storage ring of CSRm was employed to accumulate and accelerate the ion beam which was injected into the CSRe for the experiments. The number of 12C3+ ions at the CSRe reached 5×108 for every injection, which satisfied the experimental requirement. To fulfil the laser cooling experiment, the 12C3+ ion beams were bunched by sinusoidal waveforms with fixed and sweeping frequencies, respectively. A resonant Schottky pick-up was employed to record the Schottky spectra of these ion beams. The test experimental results demonstrated that the RF-buncher and diagnostic systems at the CSRe worked well and the CSRe was very stable with 12C3+ ion beams, hereby the CSRe is suitable for laser cooling experiment.

Progress of laser cooling of 12C3+ ions at the CSRe

We have performed a test run for laser cooling experiments with 12C3+ ion beams at an energy of 122 MeV/u at the CSRe with a pulsed laser. During this beamtime a lot of progress have been made. This was the first time we could successfully separate the 12C3+ ions and 16O4+ ions in the Schottky spectrum with the help of electron cooling. And our newly installed CPM detector worked well during the experiment. We tried to see effects from the interaction of the pulsed laser light with the stored 12C3+ ion beams, but no cooling effects could yet be observed.

Laser cooling of stored relativistic ion beams with large momentum spreads using a laser system with a wide scanning range

New results on laser cooling of stored, bunched, relativistic ion beams are presented. For the first time it has been possible to cool an ion beam with large momentum spread without initial electron cooling or scanning of the bunching frequency by using a single cw laser system.

State-selective single electron capture studied for C4+ ions on H2 at 40 keV

The experiment on state-selective single electron capture process of C4+ ions with molecular hydrogen at 40keV was performed by reaction microscope. The differential cross sections have been obtained by measuring the longitudinal and transverse momentum of recoil ions. The results show that single electron capture into M shell is by far the dominant reaction channel. The results can be qualitatively understood by reaction window of molecular coulomb barrier model.

News from the CSR storage ring

Testing runs of experiments were performed at the Cooler Storage Ring in Lanzhou. The recombination of bare argon ions and electron was observed at the electron. The masses of radioactive nuclei produced by projectile fragmentation were measured in isochronous mode. An overview of the most recent experiments will be presented.

Recent progresses on atomic physics with highly charged ions in Lanzhou

Storage rings, dedicated small accelerators and experimental setups have been established during past few years in Lanzhou China. The commissioning of the heavy ion Cooler Storage Rings gained great success. These advances give good opportunities for atomic physics researches using highly charged ions. The current status of the accelerators, some experimental setups will be introduced. Examples of some research results will be selected and reported. The future aspects of atomic physics related to ion-matter interactions will be outlined.

Progress of laser cooling of relativistic Li-like C 3+ ion beams at the CSRe*

Laser cooling is one of the most promising techniques to reach high phase-space densities for relativistic heavy ion beams. Realizing a crystalline ion beam is one of the ultimate goals of laser cooling of heavy ion beams at storage rings [1]. Preparations for laser cooling of relativistic lithium-like C are being made at the experimental cooler storage ring (CSRe) in Lanzhou, China [2]. In September 2014 a test experiment was performed with C ion beams at an energy of 122 MeV/u on the CSRe with a pulsed laser system. A schematic view of the experimental setup is shown in figure 1. In the experiment C ions were produced by an Electron Cyclotron Resonance ion source (ECR). In the ECR, a significant fraction of O was produced alongside. Then the ions were accelerated by a Sector Focused Cyclotron (SFC), and injected into the main Cooler Storage Ring (CSRm). After accumulation and acceleration in the CSRm, the ion beams were extracted and injected into the CSRe at the energy of 122 MeV/u (at a velocity of 47% of the speed of light). Since the circumference of the CSRe is 128.8 m, this beam energy lead to the revolution frequency of 1.087 MHz. A pulsed UV laser system from HZDR was employed for this test laser cooling experiment. The closed 2s1/2―2p1/2 optical transition at a wavelength of 0 155.07   nm of the Li-like carbon ions was Doppler-