II-9. Instrumentation

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Online extraction eﬃciency from RF ion guide gas cell at SLOWRI
S. Iimura,∗1,∗2,∗3 A. Takamine,∗1 D. Hou,∗4,∗3,∗5 M. Rosenbusch,∗3 M. Wada,∗3 S. Chen,∗3,∗6 J. Liu,∗4W. Xian,∗3,∗6 S. Yan,∗7,∗3 P. Schury,∗3 S. Kimura,∗1 T. Niwase,∗8,∗1,∗3 Y. Ito,∗9 T. Sonoda,∗1 T. M. Kojima,∗1Y. X. Watanabe,∗3 S. Naimi,∗1 S. Michimasa,∗10 S. Nishimura,∗1 A. Odahara,∗2 and H. Ishiyama∗1
We have been developing a radio-frequency carpet(RFC)–type ion guide1) gas catcher cell (RFGC) at theSLOWRI. In oﬄine tests, the maximam transport eﬃciency for the RFGC was more than 80%,2) where theeﬃciency was deﬁned as the ratio of ion current extracted from the cell to that corrected at the ﬁrst-stage
RFC. Here, the eﬃciency does not include factors suchas ion survival probability and ion losses due to molecular formation. In order to obtain the “real” eﬃciency,
an online test was performed using radioactive isotopes(RIs) provided by BigRIPS with an energy of several
100 MeV/nucleon as a symbiotic experiment behind theZeroDegree spectrometer (ZD), in conjunction with theHiCARI campaign.
A multi-reﬂection time-of-ﬂight (MRTOF) mass spectrometer3) installed at the downstream of the RFGC wasused for particle identiﬁcation (PID) and mass measurements, as shown in Fig. 1. The RIs partly stop in theRFGC, after passing through a rotational energy degrader. Subsequently, the stopped ions are extracted
from the RFGC and transported to the MRTOF systemthrough quadrupole ion guides and ﬂat-type ion trap.
Table 1 presents the preliminary result for the eﬃciencies for several RI species. After identiﬁcation at
ZD, the total eﬃciency (εtotal ) for each RI was deter!$  
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Fig. 1. Schematic view of the experimental setup. The RFGCis 50 cm long. It was operated at a nominal temperatureof 180 K and pressurized with helium to 200 mbar roomtemperature equivalent.
∗1RIKEN Nishina Center
Department of Physics, Osaka University∗3 Wako Nuclear Science Center (WNSC), IPNS, KEK∗4 Institute of Modern Physics, Chinese Academy of Sciences∗5 School of Nuclear Science and Technology, Lanzhou University∗6 Department of Physics, The University of Hong Kong
∗7 Institute of Mass Spectrometry and Atmospheric Environment, Jinan University∗8 Department of Physics, Kyushu University∗9 Advanced Science Research Center, JAEA Ibaraki∗10 Center for Nuclear Study, the University of Tokyo∗2Table 1. Total eﬃciencies (εtotal ) measured with the detectors on ZD and the MRTOF. Stopping eﬃciencies (εstop )were calculated from lise++ The transport eﬃciencies(εtrans ) correspond to ion transmission after stopping inthe gas cell.
Nuclide (ions)
134+

Sb
Te+
88
Se+
90
Se+
85
As+
55
ScOH+
48
CaOH+
137

εtotalεstop

εtrans

1.1%
1.3%
0.33%
0.36%
0.16%
0.0007%0.014%

9.1%
9.2%
3.4%
2.0%
3.6%
2.9%
3.2%

12%
14%
10%
18%
4%
0.02%
0.44%

mined as the ratio between the observed count rate after
the MRTOF and the count rate before the RFGC. Thestopping eﬃciency (εstop ) is the fraction of RIs stopped
in the RFCG, which was evaluated using lise++ basedon the measured energy distribution of each RI. By future application of mono-energetic beam optics,4) εstop
is expected to improve by a factor of more than 5.
The transport eﬃciency (εtrans ) was obtained to subtract εtotal from εstop . It should be noted that εtransincludes transmission not only for RFGC but also for
the ion guide, ion trap, and MRTOF. As indicated inTable 1, for many RIs, a reasonable εtrans higher than
10% could be obtained. In this situation, εtrans can depend on several factors such as the incoming beam intensity contributing to space-charge eﬀects,5) mass-tocharge ratio sensitive to RF trap stability,2) and half-life
providing decay loss. Another important dependency
originates from the chemical properties of the incoming species when impurities are present in the He gas;e.g., 55 ScOH+ was identiﬁed. Those molecular formations can be suppressed by further improvement of thecooling performance of the RFGC, based on our experience of the cryogenic gas cell at GARIS II.6) Further
improvement of the gas cell is ongoing.
We have successfully measured the masses of morethan 70 nuclides in this experiment and are in the processof further analysis and simulation.
References

1) M. Wada et al., Nucl. Instrum. Methods Phys. Res. B
204, 570 (2003).
2) A. Takamine et al., RIKEN Accel. Prog. Rep. 53, 108 (2020).
3) M. Rosenbusch et al., Nucl. Instrum. Methods Phys. Res.
B 463, 184 (2020).
4) S. Chen et al., RIKEN Accel. Prog. Rep. 53, 100 (2020).
5) A. Takamine et al., Rev. Sci. Instrum. 76, 103503 (2005).
6) P. Schury et al., Nucl. Instrum. Methods Phys. Res. B
407, 160 (2017).

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