Recent development of the helium-gas-filled ion catcher at BigRIPS at RIKEN RIBF*

The BigRIPS separator at the RIKEN RIBF facility provides a variety of high energy (~300 A MeV) radioactive isotope (RI) beams produced by the in-flight method. A new cryogenic ion catcher filled with helium gas has been developed to convert the beams into thermalized RI beams, as a part of the SLOWRI facility. The ion catcher is combined with a multi-reflection time-of-flight mass spectrograph downstream of the ZeroDegree spectrometer (ZD MRTOF-MS). The setup had its first on-line commissioning run in December 2020 and measured more than 70 nuclear masses, including 3 new masses [1, 2]. 

The ion catcher consists of an inner cryogenic catcher gas cell and an outer vacuum chamber. The inner catcher gas cell has a two-stage RF carpet configuration [3]. In off-line tests, the ion transport was first investigated using surface ionization ion sources. Later, we performed offline tests for Ar and Kr ions produced by alpha particle emission in the helium gas cell. Recently, we have started ion transport tests for the fission products from a ²⁴⁸Cm fission source. We are investigating the ion transport efficiency and charge state distributions for the fission products of different elements. In addition, the performance of the two transport methods, RF+AF [4] and 4-phase RF [5] transport, is being compared.

In this contribution, the overview of the development of the ion catcher and the recent performance test results will be given.

[1] S. Iimura et al., Phys. Rev. Lett. 130, 012501 (2023). 

[2] M. Rosenbusch et al., Nucl. Instrum. Meth. A 1047, 167824 (2023).

[3] A. Takamine et al., RIKEN Accel. Prog. Rep. 52, 139 (2019).

[4] G. Bollen, Int. J. Mass Spectrom. 299, 131 (2011).

[5] B.J.P. Jones et al., Nucl. Instrum. Meth. A 1039, 167000 (2022).