CNS Radio Isotope Beam separator (CRIB)

CRIB can produce low energy (<10 MeV/u) radio isotope (RI) beam from the stable nuclei beam accelerated at an AVF cyclotron (K=70) by in-flight method. Using two dipole magnets, produced particles are separated, and we can obtain various radioisotopes as secondary beams. A Wien filter, installed downstream of the two dipole magnets, gives further separation according to the velocity of the beam. With the latest technology of the heavy-ion source and accelerator, this facility can provide intense and good-quality RI beams, which are applicable for various fields of physics research, especially for the nuclear astrophysics.




RI Beam Production

The RI beam is produced at the primary target, usually by a reaction of a stable nuclei beam and gas of light elements (solid targets such as beryllium are also used). The primary beam current is typically a few 100 pnA. The RI beam energy is relatively low (<10 MeV/u), and typical intensity is 104 to 106 particles per second.

RI beams produced at CRIB until 2007
primary beam secondary beam
10B 11C, 12N, 10C
20Ne 21Na, 22Mg
18O 17N, 18F, 18N
14N 14O, 13N
24Mg 25Al,26Si
7Li 7Be, 8Li
40Ar 39Ar
6Li 8B
28Si 30S



Separation by Dipoles

CRIB has two dipole magnets, called D1 and D2. The momentum of the secondary beam is analyzed in D1, and reaches at the momentum dispersive focal plane, called F1. At F1, the momentum of the particle is selected (usually &Delta p/p ~ 1%) by a movable slit. Then, the beam is focused achromatically at the second focal plane, F2.

Specifications for the dipole section
Orbit radius 84-98 cm
Maximum energy 110Z2/A MeV
Maximum magnetic rigidity 1.1 T m
Analyzable energy range 30%
Solid angle acceptance 5.6 msr
Resolution 1/850
Momentum dispersion ~0



Separation by Wien Filter

The Wien filter can separate the beam by the horizontal electric field and vertical magnetic field. The forces from the electric and magnetic field balance at a fixed velocity, for given B and E fields (since qE=qvB ). Therefore, we are able to set the B and E fields so that only the beam with a desired velocity can pass through the Wien filter. The electric field is produced by 1.5 m-long high voltage electrodes, 8 cm distant from each other. The maximum applicable voltage is ± 200 kV, and so far we confirmed a stable operation is possible up to ± 150 kV. The dipole magnet can produce maximum magnetic field of 0.3 T. Four quadrupole magnets are also installed for the beam transport. The beam is transported with unity magnification from F2 to F3. We can change the focal point to the downstream by weakening the Q6 and Q7 magnets, in case we focus the beam at a distant target. The Wien filter can produce a velocity dispersion of 0.43 cm/% at F3, with high voltages of ± 100 kV. When we have a separation of few cm between the necessary beam and unnecessary beam (and the unnecessary beam is not too strong), we can completely eliminate the unnecessary beam by the movable slit located after Q7.


Side view of the Wien filter



Experimental chamber

There is a large vacuum chamber for the detectors and targets, in the downstream of the Wien filter. This chamber is called "experimental chamber" or "F3 chamber". A typical setup is shown in the picture below. Two PPACs (Parallel-Plate Avalanche Counter) are thin and position sensitive (~1 mm resolution) detectors for measuring the position and timing of the RI beam. An extrapolated image of the beam at the target can be constructed from the data measured by these PPACs. The target is put on a remote-controlled movable table. Stacked silicon detectors (often called "telescopes") were also put inside to measure the energies of charged particles. In this case, energies of recoiled protons up to 25 MeV were measured. Each "telescope" consists of a position sensitive (16 x 16 stripped) detector with a thickness of 70&mu m, and 2 or 3 layers of position-insensitive and 1.5 mm-thick detectors. The area is 50 mm x 50 mm for all of them.

Drawing of the experimental ("F3") chamber



Typical detector setup in the experimental chamber (7Be+p exp., Sep. 2005)



Links

Primary beam stopping position
F0 Heat deposition calculator (now testing)