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SHIRAC

SPIRAL-2 High-Intensity Radiofrequency Cooler (SHIRAC)

The next-generation facilities for radioactive beams will have stringent requirements for mass separation which will, in turn, require beams of small emittance. In order to cool the intense beams of the new facilities, new developments are required to increase the capacity and confining power of beam coolers to accept microampere-intensity beams.

Figure 1: Schematic diagram of the SHIRAC (Spiral2 High Intensity Radio-frequency Cooler) set-up. The entire system is mounted in a high-voltage cage to decelerate beams of 30 keV energy.

The SHIRAC (SPIRAL-2 High Intensity Radiofrequency Cooler) project aims at the development of a high-voltage (20 kV), high-frequency (20 MHz) quadrupole for strong confinement of microampere beams. Using smaller geometries for higher confinement requires extra care in the design of the electrode surfaces to avoid electrical discharges. Also, a new injection geometry using a mass-dependent quadrupole field has been developed. The details of these new approaches can be found in [1,2,3].

Figure 2: Details of the hyperbolic injection electrodes (operated with DC voltages) and the first trapping segments (operated at radiofrequency voltage). The final system will comprise about 30 segments and similar extraction geometry.

A test bench (see Figures 1-5) has been set up at the SIDONIE isotope separator and first tests on injection dynamics and RF generation (at 10 MHz) have been carried out. Meanwhile the whole setup was moved to the LPC Caen where further tests and development work is pursued.

Figure 3: Drawing of the cooler assembly, insulators, and injection beam line. Length of the cooler electrodes is 652 mm. Distance between the entrance and exit insulators is 1075 mm. Diameter of the insulators is 400 mm.

The aim is to achieve beam emittances between 1 $\pi$ mm mrad and 10 $\pi$ mm mrad. This development work for SPIRAL2 is carried out within the framework of the EURISOL Design Study.

Figure 4: Photograph of the cage assembly (with O. Gianfrancesco, left and S. Cabaret, right). Inner, high-voltage cage dimensions are: 800 mm wide by 1400 mm long by 1500 mm high. The insulators are 300 mm high and the support stand 400 mm high. Outer, ground cage (with sliding doors on each side) is 1.7 m by 2.2 m by 2.3 m.

Other specifications

He gas flow: 1 mbar-l/s

Power in cage: 5 kVA (isolation transformer)

Figure 5: Photograph of the cooler electrodes, including (hyperbolic) injection and extraction electrodes.

Construction of SHIRaC2

After the studies performed with the first prototype of SHIRaC, notably in the PhD thesis of F. Duval from LPC Caen, a new design, based the experience gained during these studies has been worked out and the construction of SHIRaC2 has been initiated. As of January 2010, the installation of SHIRaC2 is basically finished and new tests will start in spring 2010.