J.W. Xia

The heavy ion cooler-storage-ring project (HIRFL-CSR) at Lanzhou

HIRFL-CSR, a new ion Cooler-Storage-Ring (CSR) project, is the post-acceleration system of the Heavy Ion Research Facility in Lanzhou (HIRFL). It consists of a main ring (CSRm) and an experimental ring (CSRe). From the HIRFL cyclotron system the heavy ions will be accumulated, cooled and accelerated in the CSRm, then extracted fast to produce radioactive ion beams (RIB) or highly charged heavy ions. Those secondary beams will be accepted and stored by the CSRe for many internal-target experiments with electron cooling.

Mass Measurement of 45Cr and Its Impact on the Ca-Sc Cycle in X-Ray Bursts

Masses of neutron-deficient 58Ni projectile fragments have been measured at the HIRFL-CSR facility in Lanzhou, China employing the isochronous mass spectrometry technique. Masses of a series of short-lived Tz = –3/2 nuclides including the 45Cr nucleus have been measured with a relative uncertainty of about 10–6-10–7. The new 45Cr mass turned out to be essential for modeling the astrophysical rp-process. In particular, we find that the formation of the predicted Ca-Sc cycle in X-ray bursts can be excluded.

OVERVIEW ON THE HIRFL-CSR FACILITY

The status of the HIRFL (Heavy Ion Facility in Lanzhou) – Cooler Storage Ring (CSR) at the IMP is reported. The main physics goals at the HIRFL-CSR are the researches on nuclear structure and decay property, EOS of nuclear matter, hadron physics, highly charged atomic physics, high energy density physics, nuclear astrophysics, and applications for cancer therapy, space industries, materials and biology sciences. The HIRFL-CSR is the first ion cooler-storage-ring system in China, which consists of a main ring (CSRm), an experimental ring (CSRe) and a radioactive beam line (RIBLL2). The two existing cyclotrons SFC (K = 70) and SSC (K = 450) are used as its injectors. The 7 MeV/u 12C6+ ions were stored successfully in CSRm with the stripping injection in January 2006. After that, realized were the accelerations of 12C6+, 36Ar18+, 78Kr28+ and 129Xe27+ ions with energies of 1 GeV/u, 1 GeV/u, 450 MeV/u and 235 MeV/u, respectively, including accumulation, electron cooling and acceleration. In 2008, the first two isochronous mass measurement experiments with the primary beams of 36Ar18+ and 78Kr28+ were performed at CSRe with the Δp/p ~ 10-5.

A performance evaluation system for photomultiplier tubes

A comprehensive performance evaluation system for Photomultiplier tubes has been built up. The system is able to review diverse cathode and anode properties for PMTs with different sizes and dimensions. Relative and direct methods were developed for the quantum efficiency measurement and the results are consistent with each other. Two-dimensional and three-dimensional scanning platforms were built to test both the cathode and anode uniformity for either the plane type or spherical type photocathode. A Flash Analog-to-Digital Convertor module is utilized to achieve high speed waveforms sampling. The entire system is highly automatic and flexible. Details of the system and some typical experimental results are presented in this paper.

FIRST ISOCHRONOUS MASS MEASUREMENTS AT CSRe

With the commissioning of the Cooler Storage Ring at the Heavy Ion Research Facility in Lanzhou (HIRFL-CSR), a pilot experiment operating the CSRe in isochronous mode to test the power of HIRFL-CSR for measuring the mass of the short-lived nucleus was performed in December of 2007. The transition point γt of CSRe in isochronous mode is 1.395 which corresponds to the energy about 368 MeV/u for the ions with atomic number-to-charge ratio A/q = 2. The fragments with A/q = 2 of 36Ar were injected into CSRe and their revolution frequencies were measured with a fast time pick-up detector with a thin foil in the circulating path of the ions. A mass resolution of better than 105 for m/Δm was achieved.

Study of dielectronic recombination at the CSRm using lithium-like Ar15+ ions

The main cooler storage ring (CSRm) of the HIRFL facility in Lanzhou, China is equipped with an electron-cooler and denotes an ideal platform for dielectronic recombination (DR) experiments. In order to fully understand our DR experimental setup and especially the electron energy detuning system, we have performed a DR calibration experiment using the Li-like argon ions at the CSRm because Ar15+ has a simple electronic structure and the DR spectrum can be calculated with an ultra-high precision and be compared with the existing experimental data. The experiment was carried out over the center-of-mass energy range 0–32 eV that includes all DR resonance associated with 2S1/2 → 2p1/2 and most of the 2S1/2 → 2p3/2 excitations. We present the details of the experimental technique and the DR experimental resonance spectrum of the Ar15+.

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.

Test of IMME in fp shell via direct mass measurements of TZ = -3/2 nuclides

Isochronous mass spectrometry has been applied to neutron-deficient Ni-58 projectile fragments at the HIRFL-CSR facility in Lanzhou, China. Masses of four short-lived T-z = -3/2 nuclides Ti-41, Cr-45, Fe-49, and Ni-53 have been measured with a precision of 20 - 40 keV. The new mass data enabled for the first time to test the isobaric multiplet mass equation (IMME) in fp-shell nuclei. We observed that the IMME is inconsistent with the generally accepted quadratic form for the A = 53, T = 3/2 quartet. We performed full space shell model calculations and compared them with the new experimental results. The main results were published in Y.H. Zhang et al., Physical Review Letters 109 (2012). Here we give details on the experiment and data analysis as well as summarize the main findings.

ATOMIC PHYSICS RESEARCHES AT COOLER STORAGE RING IN LANZHOU

The commissioning of the cooler storage rings (CSR) was successful, and the facility provides new possibilities for atomic physics with highly charged ions. Bare carbon, argon ions, were successfully stored in the main ring CSRm, cooled by cold electron beam, and accelerated up to 1 GeV/u. Heavier ions as Xe44+ and Kr28+ were also successfully stored in the CSRs. Both of the rings are equipped with new generation of electron coolers which can provide different electron beam density distributions. Electron-ion interactions, high precision X-ray spectroscopy, complete kinematical measurements for relativistic ion-atom collisions will be performed at CSRs. Laser cooling of heavy ions are planned as well. The physics programs and the present status will be summarized.

Mass Measurements of Proton‐rich Nuclides at the Cooler Storage Ring at IMP

Recent results and progress of mass measurements of proton‐rich nuclei using isochronous mass spectrometry (IMS) are reported. The nuclei under investigation were produced via fragmentation of relativistic energy heavy ions of 78Kr and 58Ni. After in‐flight separation by the fragment separator RIBLL‐2, the nuclei were injected and stored in the experimental storage ring CSRe, and their masses were determined from measurements of the revolution times. The impact of these measurements on the stellar nucleosynthesis in the rp‐process is discussed.