Jiawen Xia

PRESENT STATUS OF HIRFL IN LANZHOU

HIRFL has been upgraded for basic research on nuclear physics, atomic physics, irradiative material and biology from beginning of this decade. So far, the main performances of HIRFL have improved in the beam species from light ion to uranium and the maximum beam intensities reaching ~10μA from SFC, 1.5 μA from SSC. Therefore, some experiments have been performed during this period, especially, on new isotope synthesis and unstable nuclear physics. The new upgrading project Cooling Storage Ring (CSR) is under commissioning by ~2p μA carbon beam stripping injection. About 109 C ion have stored inside CSRm, and part of them have been cooling down by the electron cooler. The acceleration of CSRm also has been test successful. Some future experiment are under development.

Design of a 7 T Superconducting Magnet for Lanzhou Penning Trap

A penning trap system called LPT (LANZHOU PENNING TRAP) is now being developed for precise mass measurements in IMP (Institute of Modern Physics). The most key component of LPT is a superconducting magnet. A 156 mm warm bore and two cylinder good field regions with a distance of 220 mm are required for trapping ions and measurements. As the required homogeneity is better than 0.5 ppm, several complicated coaxial coils are used to produce such a magnetic field. The size and position of these coils are optimized by using a method combining linear program with multiobjective optimization. Superconducting shim coils and passive shim pieces are used to eliminate inevitable winding tolerances and environmental influence. The fringe field is decreased to 5 Gs at 2 m line from the center of the magnet by active shielding coils. The designs of the mechanical structure, the quench protection system are also introduced in this paper.

Magnets for HIRFL-CSR Rings

The magnet design, fabrication, and measurement of HIRFL-CSR (Heavy Ion Research Facility in Lanzhou Cooling Storage Ring) are presented. All magnets will be laminated and welded with an armor-coated surface between two big endplates made of sticking glue 0.5 mm-thick sheets. The dipole of CSRm was chosen an H type with an air circle on the pole to improve the field uniformity. The dipole of CSRe was chosen the C type with an air circle and two air slots on the pole to improve the field homogeneity. Its reproducibility of magnet to magnet was adjusted with inserting small laminating pieces before demountable pole ends to reach less than plusmn2times10-4 at optimized field level. CSRm quadrupoles diameter is 170 mm and has two different lengths, and its endplates were made with punching pieces after coating with epoxy glue, there is chamfered directly on the pole ends to reduce 12th-order contribution of field and without the demountable pole ends. CSRe main quadrupoles diameter is 240 mm and has two different lengths, and its endplates were also made with punching pieces coated with epoxy glue, there is also chamfered directly on the pole ends to reduce 12th-order contribution of field like CSRm

Direct mass measurements of neutron-rich 86Kr projectile fragments and the persistence of neutron magic number N=32 in Sc isotopes

In this paper, we present direct mass measurements of neutron-rich 86Kr projectile fragments conducted at the HIRFL-CSR facility in Lanzhou by employing the Isochronous Mass Spectrometry (IMS) method. The new mass excesses of 52–54Sc nuclides are determined to be −40492(82), −38928(114), −34654(540) keV, which show a significant increase of binding energy compared to the reported ones in the Atomic Mass Evaluation 2012 (AME12). In particular, 53Sc and 54Sc are more bound by 0.8 MeV and 1.0 MeV, respectively. The behavior of the two neutron separation energy with neutron numbers indicates a strong sub-shell closure at neutron number N=32 in Sc isotopes.

Heavy-ion radiography facility at the Institute of Modern Physics

In order to identify the density and material type, high energy protons, electrons, and heavy ions are used to radiograph dense objects. The particles pass through the object, undergo multiple coulomb scattering, and are focused onto an image plane by a magnetic lens system. A modified beam line at the Institute of Modern Physics of the Chinese Academy of Sciences has been developed for heavy-ion radiography. It can radiograph a static object with a spatial resolution of about 65 mu m (1 sigma). This paper presents the heavy-ion radiography facility at the Institute of Modern Physics, including the beam optics, the simulation of radiography by Monte Carlo code and the experimental result with 600 MeV/u carbon ions. In addition, dedicated beam lines for proton radiography which are planned are also introduced.

Commissioning of HIRFL‐CSR and its Electron Coolers

The brief achievements of HIRFL‐CSR commissioning and the achieved parameters of its coolers were presented. With the help of electron cooling code, the cooling time of ion beam were extensive simulated in various parameters of the ion beam in the HIRFL‐CSR electron cooling storage rings respectively, such as ion beam energy, initial transverse emittance, and momentum spread. The influence of the machine lattice parameters‐betatron function, and dispersion function on the cooling time was investigated. The parameters of electron beam and cooling devices were taken into account, such as effective cooling length, magnetic field strength and its parallelism in cooling section, electron beam size and density. As a result, the lattice parameters of HIRFL‐CSR were optimal for electron cooling, and the parameters of electron beam can be optimized according to the parameters of heavy ion beam.

Particle-in-cell mode beam dynamics simulation of the low energy beam transport for the SSC-linac injector

A new SSC-linac system (injector into separated sector cyclotron) is being designed in the HIRFL (heavy ion research facility of Lanzhou). As part of SSC-Linac, the LEBT (low energy beam transport) consists of seven solenoids, four quadrupoles, a bending magnet and an extra multi-harmonic buncher. The total length of this segment is about 7 meters. The beam dynamics in this LEBT has been studied using three-dimensional PIC (particle-in-cell) code BEAMPATH. The simulation results show that the continuous beam from the ion source is first well analyzed by a charge-to-mass selection system, and the beam of the selected charge-to-mass ratio is then efficiently pre-bunched by a multi-harmonic buncher and optimally matched into the RFQ (radio frequency quadrupole) for further acceleration. The principles and effects of the solenoid collimation channel are discussed, and it could limit the beam emittance by changing the aperture size.

Magnet system for HIRFL-CSR project

The magnet design choices and calculations for HIRFL-CSR (Heavy Ion Research Facility in Lanzhou Cooling Storage Ring) are presented. CSR desires the dipole magnet field uniformity B/B/sub 0/ /spl les/ /spl plusmn/10/sup -4/ and good field width reaching to /spl plusmn/ 70 mm and /spl plusmn/110 mm for the main ring and experimental ring respectively. For the dipole of CSRm, an H type was chosen with an air circle on the pole to improve the field homogeneity that was obtained with 2-D and 3-D code calculations. For CSRe, because the demand by the physics experiments, the dipole was chosen as C type. Many ideas were adopted to reduce its size, for it is very difficult to fabricate such a large laminated dipole in our country. All quadrupole lenses need field nonlinear gradient better than /spl plusmn/ 2 /spl times/ 10/sup -3/ in the good field region which width is 80 mm and /spl plusmn/ 140 mm for the main ring and experimental ring respectively. All magnets will be laminated of 0.5 mm-thick sheets of cold rolled electrical steel with an armor-coated surface.

Injection method of barrier bucket supported by off-aligned electron cooling for CRing of HIAF

A new accelerator complex, HIAF (the High Intensity Heavy Ion Accelerator Facility), has been approved in China. It is designed to provide intense primary and radioactive ion beams for research in high energy density physics, nuclear physics, atomic physics as well as other applications. In order to achieve a high intensity of up to 5e11 ppp 238U34+, the Compression Ring (CRing) needs to stack more than 5 bunches transferred from the Booster Ring (BRing). However, the normal bucket to bucket injection scheme can only achieve an intensity gain of 2, so an injection method, fixed barrier bucket (BB) supported by electron cooling, is proposed. To suppress the severe space charge effect during the stacking process, off-alignment is adopted in the cooler to control the transverse emittance. In this paper, simulation and optimization with the BETACOOL program are presented.

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.