Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 56 (2023)
RIKEN
Accel. Prog. Rep. 56 (2023)

Charge state distributions of 138 Ba ions trapped in the SCRITR. Ogawara,∗1,∗2 Y. Abe,∗1 T. Ohnishi,∗1 A. Enokizono,∗1 K. Kurita,∗3 Y. Maehara,∗1 K. Tsukada,∗1,∗2M. Wakasugi,∗1,∗2 M. Watanabe,∗1 and H. Wauke∗1,∗4

∗1
∗2
∗3
∗4

RIKEN Nishina Center
Institute for Chemical Research, Kyoto University
Department of Physics, Rikkyo University
Research Center for Electron Photon Science, Tohoku University- 90 -times. The incident energy of 138 Ba1+ ions to theSCRIT device was 6 keV. The energy and current of
the electron beam were 150 MeV and 210–270 mA, respectatively. The ﬁxed magnetic ﬁeld was 1850 G, andthe range of supply voltages for electric ﬁeld scanningwere 0–2400 V in 10 V steps.
Figures 1 (a), (b), and (c) show the charge state distributions of 138 Ba ions at trapping times of 30, 100,and 200 ms, respectatively. The 138 Ba1+ ∼ 138 Ba7+
ions were clearly identiﬁed, comﬁrming that the ionsin higher charge states can be identiﬁed compared tomeasurements for 133 Cs ions.2) The 138 Ba1+ ions weredominant at a short trapping time of 30 ms, but thecharge state distributions of the 138 Ba ions were bredand spread with increasing the trapping time. The average charge states at trapping times of 30, 100, and
200 ms were 1.3, 2.5, and 3.6, respectatively. These results show that the developed method is useful for evaluating the charge state distributions of trapped ions inthe SCRIT.
(a) trapping time: 30 ms500

138

Ba1+138

Ba2+

250
Ba4+

138
138

Event rate [/gate]

The self-conﬁning radioactive isotope ion target(SCRIT) method is an internal-target-forming technique for realizing electron scattering with unstable
nuclei.1) Target ions are injected into the SCRIT device and are trapped transversely by periodic focusing forces from electron beam bunches and longitudinally by the electrostatic well potential.2) While thetarget ions are trapped in the SCRIT device, SCRIT
performance (number of trapped ions, charge distributions, etc.) continues to change. Previous studies haveshown that the instability of the electron beam is oneof the major sources of trapped ions escaping from theSCRIT.3) The trapping lifetime of the ions with a small
mass-to-charge ratio (A/q) is shorter than that of theions with a large A/q. Therefore, to optimize SCRIT
performance, it is necessary to evaluate the charge state
distribution of the trapped ions.
After trapping ions in the SCRIT device, the target
ions are extracted and transported to an ion analyzer
consisting of a total charge monitor, an E × B velocity ﬁlter (Model 600-B, Colutron Research Corp.), anda 43-channeltron array (Photonis Scientiﬁc, Inc.).3) In
previous work,2) the charge state distributions of 133 Csions were measured by an ion analyzer with ﬁxed electric and magnetic ﬁelds in the E × B velocity ﬁlter.
The 133 Cs1+ ∼ 133 Cs3+ ions were identiﬁed clearly,
but it was diﬃcult to evaluate the abundance ratio of
the133 Cs1+ ∼ 133 Cs3+ ions because of the diﬃculty associated with correcting the detection eﬃciencies of thechanneltrons, which depended on the position and angle of incidence and the individual diﬀerences in thechanneltrons.
We developed a measurement method for the ion analyzer using a ﬁxed magnetic ﬁeld and an electric ﬁeld
scanning in the E × B velocity ﬁlter. In this method,
the same number of trapped ions are injected into allchanneltrons by electric ﬁeld scanning so the detection
eﬃciencies of all channeltrons can be measured simultaneously with measurements of the charge state distributions. The charge state distributions measured byeach channeltron are corrected for the detection eﬃciencies and added to improve the statistical accuracy. The
performance of the developed method was evaluatedby simulating 138 Ba ion trajectories using the RungeKutta method, and it was conﬁrmed that 138 Ba1+ ∼138
Ba10+ ions can be identiﬁed.
We measured charge state distributions of 138 Ba ionsusing the developed method while varing the trapping

138

Ba5+

Ba

3+0(b) trapping time: 100 ms
138

500
138

Ba4+

138

250

Ba

Ba2+

3+

138

Ba5+
138

Ba1+

138

Ba6+0(c) trapping time: 200 ms
500
Ba5+ 138 4+Ba

138

250

138

Ba

138

06+

138

Ba3+

138

Ba7+

101

Ba2+

102

Mass-to-charge ratio (A/q)

Fig. 1. Charge state distributions of 138 Ba ions with trapping times of (a) 30, (b) 100, and (c) 200 ms.

References
1) K. Tsukada et al., Phys. Rev. Lett. 118, 262501 (2017).
2) M. Wakasugi et al., Nucl. Instrum. Methods Phys. Res.
B 317, 368 (2013).
3) R. Ogawara et al., Nucl. Instrum. Methods Phys. Res. B
317, 674 (2013).