Facilities

CSR

Date:21-07-2009   |   【Print】 【close

  

HIRFL-CSR, a new ion Cooler-Storage-Ring (CSR) project, is the post-acceleration system of the Heavy Ion Research Facility in Lanzhou (HIRFL). HIRFL-CSR is a multi-purpose CSR system that consists of a main ring (CSRm), an experimental ring (CSRe), and a radioactive beam line (RIBLL II) to connect the two rings. The two existing cyclotrons SFC (K = 69) and SSC (K = 450) of the HIRFL will be used as its injector system. The heavy ion beams with the energy range of 8–30 MeV/u from the HIRFL will be accumulated, cooled and accelerated to the high-energy range of 100–400 MeV/u in the main ring, and then extracted fast to produce RIB or highly charged heavy ions. The secondary beams (RIB or highly charged heavy ions) will be accepted and stored by the experimental ring for many internal-target experiments or high-precision spectroscopy with beam cooling. On the other hand, the beams with the energy range of 100–900 MeV/u will also be extracted from CSRm by using slow extraction or fast extraction for many external-target experiments.
Two electron coolers located in the long-straight sections of CSRm and CSRe, respectively, will be used for the beam accumulation and cooling. One internal target in the long-straight section of CSRe will be used for nuclear physics and highly charged state atomic physics, and many external targets of CSRm will be used for nuclear physics, cancer therapy study and other researches.

Major parameters of the CSR

 
CSRm
CSRe
Circumference (m)
161.00
128.80
Ion species
Stable nuclei: C–U, RIB(A<238)
Stable nuclei: C–U, RIB(A<238)
Max. energy (MeV/u)

900 (C6+), 400 (U72+)

600 (C6+), 400 (U90+)
Intensity (particles)
105–109 (stable nuclei)
103–109 (stable nuclei, RIB)
Time structure of beam
1 Pulse/cycle for fast extraction, 0.1–5 s for slow extraction
Quasi-continuous beam
Experiment mode
External target
Internal target
Bρmax (Tm)
10.64
8.40
Bmax (T)
1.4
1.4
Ramping rate (T/s)
0.1–0.4
0.1–0.4
Repeating circle (s)
~17 (~10 s for accumulation )
 
Acceptance
 
Normal mode
Ah (π mm mrad)
200 (ΔP/P= ±0.15%)
150 (ΔP/P= ±0.5%)
Av (π mm mrad)
30
75
ΔP=P (%)
1.25 (εh= 50 π mm mrad)
2.6 (εh= 10 π mm mrad)
e-Cooler
 
 
Ion energy (MeV/u)
8–50
25–400
Cooling length (m)
4.0
4.0
RF system
Acceleration
Accumulation
Capture
Harmonic number
1
16, 32, 64
1
fmin=fmax (MHz)
0.24/1.7
6.0/14.0
0.5/2.0
Voltages (n×kV)
1×7.0
1×20.0
2×10.0
Vacuum pressure (mbar)
6.0×10-11
 
6.0×10-11
 

Main Physics Goals at CSR:
1. Radioactive Ion Beam Physics
· Nuclear structure of unstable nuclei
· Isospin dependence nuclear matter
2. Meson-Nucleon Physics in Energy <1.1 GeV/u HI & <2.88GeV (3.7GeV/c) Proton
3. High Charge State of Atomic Physics
4. High Energy Density Matter
5. Applications
· Astrophysics (Key Point)
· *Irradiative Biology (Cancer Therapy)  

   

1. Normal operation mode
CSR is a double ring system. In every operation cycle, the stable-nucleus beams from the injectors are accumulated, cooled and accelerated in the main ring (CSRm), then extracted fast to produce RIB or highly charged ions. The experimental ring (CSRe) can obtain the secondary beams once for every operation cycle. The accumulation duration of CSRm is about 10 s. Considering the ramping rate of magnetic field in the dipole magnets to be 0.1–0.4 T/s, the acceleration time of CSRm will be nearly 3 s. Thus, the operation cycle is about 17 s.
In CSRe, two operation modes will be adopted. One is the storage mode used for internaltarget experiments or high-precision spectroscopy with electron cooling. Another one is the deceleration-storage mode used for atomic-physics experiments.

2. Injector system
The existing HIRFL facility will be used as the injector system of CSR. It consists of two cyclotrons, the main accelerator Separated Sector Cyclotron (SSC, K = 450) and the preaccelerator Sector-Focusing Cyclotron (SFC, K = 69). The light heavy ions, example C, N, O etc., can be injected into CSRm directly from SFC without the acceleration of SSC, but those heavy ions (A > 40) should be accelerated by the combination of SFC and SSC before the injection. The mean extraction radii of SFC and SSC are 0.75m and 3.20 m, respectively.

3. Beam accumulation
Two methods will be used in CSRm to accumulate the heavy ions up to 106–109 in a short duration of 10 s. One is the Multiple Multiturn Injection (MMI) in the horizontal phase space with the acceptance of 150 π mm mrad. Another is the combination of the horizontal multi-turn injection and the RF Stacking (RFS) in the momentum phase space. In the second method, the horizontal acceptance is 50 π mm mrad used for the multi-turn injection and the momentum acceptance is 1.25% for the RFS. During the accumulation, electron cooling will be used for the cooling of beam in order to increase the accumulation ratio and efficiency.
 

4. Production of secondary beams
RIB will be produced by heavy ion projectile fragmentation (PF) method. The heavy ions from the present HIRFL system will be injected into CSRm for accumulating, cooling and accelerating to higher energies (100–400 MeV/u), and then extracted to bombard a primary target in order to produce radioactive beams. Finally, those RIB produced will be accepted by CSRe for physical experiments with beam cooling.
Highly charged ions, fully stripped heavy ions or H- and He-like heavy ions, are in demand in atomic physics researches. HIRFL-CSR will provide those heavy ion beams by multiple stripping shown in the figure below. In the energy range of CSRe, fully stripped ion as heavy as Gold could be obtained, while the highest charged state for uranium is 91+.

 

 

 

1. CSRm lattice
CSRm has a racetrack shape, and consists of four identical arc sections. Each arc section consists of four dipoles, two triplets and one doublet. Eight independent variables for a quadruple are used.
In the injection arc-section, three bump magnets (BP1, BP2, BP3) will be used to move the closed orbit from the center to the injection position in the horizontal plane, then injection beam will be deflected into the closed orbit by one static-electric septum (ES1) and one magnetic septum (MS1). During the multi-turn injection, the field of the three bumps will be reduced to zero isochronously, the closed orbit will move back to the center, and the horizontal acceptance (150 π or 50 π mm mrad) will be filled by injection beam simultaneously.

2. CSRe lattice
CSRe has a racetrack shape and consists of two quasi-symmetric parts. One is the internal-target part and another is the e-cooler part. Each part has a symmetric system and consists of two identical arc sections. Each arc section consists of four dipoles, two triplets or one triplet and one doublet. 11 independent variables for quadruple are used in CSRe.
In CSRe, three lattice modes will be adopted for different requirements. The first one is the internal-target mode with small β-amplitude in target point and the large transverse acceptance (Ah = 150 π mm mrad, Av = 75 π mm mrad) for internal- target experiments. The second one is the normal mode with a large momentum acceptance of ΔP/P = 2.6% for high-precision mass spectroscopy. The third one is the isochronous mode with a small transition γtr that equals the energy γ of beam in order to measure the mass of those short-lifetime RIB.
 

 

 

1. Magnets and correlative subsystems
All the magnetic cores of CSR will be laminated by 0.5 mm-thick sheets of electro-technical steel with high induction and cold-rolled isotropy. Coils will be made of T2 copper conductor with hollow and insulated polyimide stick tape, impregnated with vacuum epoxy resin. In order to reach the necessary field uniformity at the different levels of the range of 1000–14,000 Gs, a so-called modified H-type dipole was designed for CSRm. An air hole will be punched at the center of the pole to control the magnetic field flux flow at high magnetic fields. The magnetic field distribution on the median plane will be improved and a good field distribution in a wide field range can be obtained. In CSRe, the C-type dipole with a large useful aperture will be adopted for physics experiments.
All the power supplies for the ring magnets will need DC and pulse operation modes, while high current stability, low current ripple, good dynamic characteristic are necessary requirements. Two types of supply, a traditional multi-phase thyristor rectifier for dipoles and a switching mode convertor for quadruples, will be adopted.
 

2.Electron-cooler system
Two electron coolers will be equipped in CSRm and CSRe, respectively, for heavy ion beam cooling. In CSRm, e-cooling will be used for the beam accumulation at the injection energy range of 8–30 MeV/u to increase the beam intensity. In CSRe, e-cooling will be used to compensate the growth of beam emittance during internal-target experiments or to provide high-quality beams for the high-resolution mass measurements of nuclei. The two coolers are similar with the only difference in the high voltage unit in order to reduce the time of the development and the production cost of the devices.
 

3. RF system
Two RF cavities will be used for the accelerating beam and RFS in CSRm, respectively. The stacking cavity with the frequency range of 6.0–14.0MHz will be used to secure the SSC or SFC beam bunches with harmonic number h = 16; 32 or 64 during the beam accumulation in the momentum acceptance. After beam accumulation, the heavy ion beams will be accelerated by the accelerating cavity from the low energy range of 8–30 MeV/u to the high-energy range of 100–900MeV/u with harmonic number h = 1. In CSRe, two identical RF cavities will be installed in two drift sections, which will be used for beam capture, bunching, de-bunching and deceleration with harmonic number h = 1 or 2. The four RF cavities are ferrite-loaded coaxial resonators, and the resonance frequency is controlled by tuning the magnetic biasing current of ferrite.
 

4. Ultra-high vacuum system
The vacuum system is divided into four parts, the two storage rings of CSRm and CSRe, and the two beam lines of the injection line from HIRFL, and RIBLL II. The pressure of <6 × 10-11 mbar (N2 equivalent) will be required in CSRm and CSRe, and 1 × 10-9 mbar will be necessary for the two beam lines.
For CSR UHV system, titanium sublimation pump and sputter ion pump are chosen as the main pumps, and about 160 titanium pumps and 85 ion pumps will be equipped in CSR. For each part, two or three movable oil-free turbo-molecular pumping station will be equipped for prepumping, leak detecting and back out. Many allmetal gate valves will be used to divide each part into several sections, and fast-closed valves will also be installed in injection and extraction positions for protecting the two rings from possible accidents. A lot of bellows with the length of 0.2–0.28m will be installed at those possible positions, specially the two sides of the dipole chambers, in order to correct installation error and absorb the heat expansion during the bake-out process.
The vacuum bake-out temperature will be 300°C. And all the components of the two rings will be equipped with permanent back-out jackets. The dipole and quadruple chambers will be heated by coaxial heaters with an out-diameter of 2 mm. A special insulation material (Microtherm) will be used for these chambers to avoid thermal loss and protect the magnet coils from damage. This insulation will keep the outside temperature lower than 80°C with the thickness of 3–5 mm. Other chambers are baked by heating tapes which are made of glass fiber with the thickness of 10–25 mm.

5. Beam diagnosis system
For the CSR beam diagnosis, the standard synchrotron and cooling ring instrumentation is to be used and has to be developed to cover the wide range of beam characteristics. In each ring, two or three viewing screens and one Faraday-cup will be used for the first-turn tuning, one combined vertical and horizontal Schottky detector, one phase pick-up and two beam transformers will be used for the machine operation, one magnesium jet monitor will be used to detect the beam profile, and 14 or 10 position pick-ups will be equipped for the global closed-orbit correction in the two transverse planes. In beam lines, only viewing screen and Faraday-cup will be used.

6. Internal-target system
The CSRe internal target is designed to provide both polarized and unpolarized atomic jets for physics experiments. In the target source of the polarized mode, sextuple magnets will be used to get the high-polarized H or D atomic jets with the expected spin state, and after the state selection in multiple magnets a desired jet density of 5 × 1011 atoms/cm2 will be obtained. In the normal unpolarized mode, the jet is a cluster jet and the density of 1 × 1012 atoms/cm2 can be achieved by cooling the nozzle to the given temperature.

7. Survey and alignment
One permanent standard point near the ring center and many normal control-network points in each ring will be used for the survey and alignment. According to the control-networks design, the maximum point-position error of the horizontal control-network should be < 0.06 mm, and the vertical one should be < 0.05 mm.
For the CSR alignment, the installation errors of magnets should be less than the desired values. According to the error simulation results, the desired misalignments of dipole and quadruple are shown as follows, where six misalignments are three position errors, Δx (horizontal), Δy (vertical), Δz (beam direction) and three angle errors, ΔΦ, Δθ, Δψ, around x-, y-, z-axis, respectively.
In order to meet the requirements of survey and alignment, the traditional optical instruments will be used for the pre-installations, and one laser tracker, a digital-levelling device will be used for the final survey and alignment adjustment.