Experimental study of a high intensity radio-frequency cooler

Abstract

International audienceWithin the framework of the DESIR/SPIRAL-2 project, a radio-frequency quadrupole cooler named SHIRaC has been studied. SHIRaC is a key device of SPIRAL-2, designed to enhance the beam quality required by DESIR. The preliminary study and development of this device has been carried out at Laboratoire de Physique Corpusculaire de CAEN (LPC Caen), France. The goal of this paper is to present the experimental studies conducted on a SHIRaC prototype. The main peculiarity of this cooler is its efficient handling and cooling of ion beams with currents going up as high as 1 μA which has never before been achieved in any of the previous coolers. Much effort has been made lately into these studies for development of appropriate optics, vacuum and rf systems which allow cooling of beams of large emittance (∼80π mm mrad) and high current. The dependencies of SHIRaC’s transmission and the cooled beam parameters in terms of geometrical transverse emittance and the longitudinal energy spread have also been discussed. Investigation of beam purity at optimum cooling condition has also been done. Results from the experiments indicate that an emittance reduction of less than 2.5π mm mrad and a longitudinal energy spread reduction of less than 4 eV are obtained with more than 70% of ion transmission. The emittance is at expected values whereas the energy spread is not

Development of a radio-frequency quadrupole cooler for high beam currents

“…Existing RFQCs can only handle beams with low intensities (∼100 nA) and small emittances (∼10π mm mrad). As SPIRAL-2 typical beams are of higher currents and larger emittances, a new RFQC called SPIRAL-2 high intensity radiofrequency cooler (SHIRaC) has been developed and tested at LPC-Caen laboratory in France [16,17].…”

“…Like existing RFQCs, SHIRaC optics system is divided into three sections: injection section, cooling section and extraction section, Fig. 1 [16]. These sections are connected by exchangeable apertures, Fig.…”

“…electrodes forming the extraction section. In addition to the improved optics system which captures large beam emittances of some tens of π mmmrad, its vacuum system and rf system were also developed [16] in such a way more than 60% of incoming ions can be transmitted. The vacuum system, based on a differential pumping, allows the reduction of the buffer gas pressures to less than 0.01 Pa outside the RFQ chamber.…”

“…Simulation [17] and experimental studies [16] of a SHIRaC prototype have shown unexpected results. Using rf voltage parameters of 4.5 MHz frequency and 4 kV amplitude (Mathieu parameter q ¼ 0.4) and 2.5 Pa buffer gas pressure, this prototype allows handling and cooling beams with current going up to 1 μA.…”

Optimizing charge breeding techniques for ISOL facilities in Europe: Conclusions from the EMILIE project

“…The trap is installed on the SHIRaC 16 test bench, which is equipped by standard turbo-molecular pumps: at the present stage, a pressure down to 10 −7 mbar is achieved, not suited for tests with highly charged ions. Such tests will have to be done at a later stage, using getter pumps and highly charged ions at GANIL and/or ISOLDE.…”