A windowless gas-cell cooler-buncher at RIKEN/SLOWRI

For future experiments at RIKEN/SLOWRI, ion preparation, e.g., cooling and bunching, are indispensable for various precision experiments. The ion beams from SLOWRI gas cells will be continuous with a beam energy of $\le$30~keV/$q$, and must be decelerated and cooled in an ion trap to bunch ions. In order to achieve higher efficiency with much simpler structures than conventional RFQ cooler-buncher [1,2], we are developing an windowless gas-cell cooler-buncher (GCCB). The GCCB consists of a gas cell with a small hole at the entrance and an RF-carpet followed by a flat trap [3]. The GCCB will be cryogenically cooled to $\sim$77~K and filled with He gas at up to 2 mbar. According to calculations with TRIM, a stopping efficiency of 100\% can be obtained for any $\le$30~keV/q beams with $Z > 3$ if the GCCB is at least 420 mm long. A large radial geometry will provide a larger effective acceptance than any conventional RFQ cooler-buncher, allowing for higher efficiency. This will allow further reach into exotic nuclei. We will present current status and future outlook.\\[4pt] [1] F.\ Herfurth et al., Nucl.\ Instrum.\ Meth.\ A 469, 254 (2001)\\[0pt] [2] T.\ Brunner et al., Nucl.\ Instrum.\ Meth.\ A 676, 32 (2012)\\[0pt] [3] Y.\ Ito et al., Nucl.\ Instrum.\ Meth.\ B 317, 544 (2013)