Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 53

Second report on oﬄine tests for RF carpet transportation in RF ion
guide gas cell at the SLOWRI facility
S. Iimura,∗1,∗2,∗3 A. Takamine,∗1 M. Rosenbusch,∗3 M. Wada,∗3 S. Chen,∗4 J. Liu,∗4 P. Schury,∗3 T. Sonoda,∗1T. M. Kojima,∗1 Y. X. Watanabe,∗3 A. Odahara,∗2 and H. Ishiyama∗1Transport Efficiency to 2nd RFCP100%

He: 133 mbar
He: 200 mbar
He: 267 mbar

80%
60%
40%
20%
0%

050100150
RF Voltage on the 1st RFCP [Vpp]200Fig. 1. 1st RFCP transportation test results in three diﬀerent helium gas pressures: 133 mbar, 200 mbar, and 267mbar. In this test, the drag dc ﬁeld on the 1st RFCP, theextraction DC ﬁeld between the 1st and 2nd RFCPs, andeach RF frequency were 4 V/cm, 20 V/cm, and ∼5 MHz,
respectively.
∗1
∗2
∗3
∗4

RIKEN Nishina Center
Department of Physics, Osaka University
Wako Nuclear Science Center (WNSC), IPNS, KEK
Department of Physics, The University of Hong Kong

100%
Transport Efficiency to 2nd RFCPWe are developing a radio frequency carpet (RFCP)-type ion guide1) gas catcher cell (RFGC) at theSLOWRI facility. In the previous version,2) we could
achieve a transport eﬃciency of ∼60% only in 133 mbar
helium gas on the ﬁrst carpet from oﬄine measurements.
In these developments, to improve the transport eﬃciency, we changed the carpet pitch (the distance between the center of neighboring RF electrodes) from
0.32 mm to 0.25 mm.
In our oﬄine measurements, we evaluated the transport eﬃciency of the RFGC using a surface ionization Cs
ion source placed at the inner wall of the gas cell. Firstly,
we measured the ion reaching onto the 1st RFCP by using it as a Faraday cup. Subsequently, we used the 2ndRFCP as a Faraday cup to measure ions transported by
the 1st RFCP after applying appropriate RF and DCﬁelds. The eﬃciency was deﬁned by the current measured at the 2nd RFCP divided by that measured at the1st RFCP.
Figure 1 shows the result of the obtained transport
eﬃciency as a function of the RF voltages applied to
the 1st RFCP in three diﬀerent helium gas pressures.
The transport eﬃciency reached ∼80% at each pressure,which is ∼1.3 times greater than in the previous measurements.2)
In an online experiment, the total extraction eﬃciency
is determined by the product of stopping, ion survival,

He: 133 mbar
Ne: 133 mbar
Ne: 55 mbar
Ar: 31 mbar

80%
60%
40%
20%
0%

050
100
150
RF Voltage on the 1st RFCP [Vpp]200Fig. 2. 1st RFCP transportation test results for three kindsof gases: helium, neon, and argon. The DC ﬁelds condition and RF frequency were the same as in the previoustests.

and transport eﬃciencies. In order to enable more efﬁcient stopping, heavier species of buﬀer gas have been
investigated. Figure 2 shows the result of the measured
transport eﬃciency for three kinds of buﬀer gases. Thegas pressures of neon (55 mbar) and argon (31 mbar)
were adjusted so that the beam would be stopped withthe same eﬃciency as that achieved for 133 mbar of helium. It was found that helium (133 mbar) and neon
(55 mbar) gases gave comparable transport eﬃciencies.
On the other hand, with a higher pressure for neon, i.e.,equal to the helium pressure, the transport in neon gas
was observed to be four times less eﬃcient. In addition
to these results, considering that the ion survival probability in helium is 1.3 times higher than that in neon,as shown previously,3) the total eﬃciency in helium gas
may be the best performance.
We will keep testing the RFCP to search for the optimum conditions, especially for the parameters of the 2ndRFCP. Furthermore, the ion-guide system to be placed
behind the 2nd RFCP is under assembly; it consistsof a quadrupole ion beam guide and an ion trapping
system. After that, we can provide a low-energy RI
beam to a multi-reﬂection time-of-ﬂight mass spectrograph (MRTOF-MS), which is under preparation. We
plan to start online commissioning of the RFGC and theMRTOF-MS in spring FY2020 at the downstream of theZeroDegree Spectrometer.
References

1) M. Wada et al., Nucl. Instrum. Methods Phys. Res. B
204, 570 (2003).
2) A. Takamine et al., RIKEN Accel. Prog. Rep. 52, 139 (2019).
3) P. Dendooven et al., Nucl. Instrum. Methods Phys. Res.
A 558, 580 (2006).

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