RIKEN Accel. Prog. Rep. 50 (2017)

Ⅱ-9. Instrumentation

Momentum acceptance of the Rare RI Ring studied from revolution
frequency measurements
F. Suzaki,∗1 Y. Abe,∗1 D. Nagae,∗1 S. Omika,∗1,∗2 A. Ozawa,∗1,∗3 T. Uesaka,∗1 M. Wakasugi,∗1 K. Yamada,∗1
∗2 ∗2
∗1 ∗1
∗1 ∗1
T.T.Yamaguchi,Y.Y.
Yamaguchi,
J. J.
Zenihiro,
and
Rare
Ring
collaboration
Yamaguchi,
Yamaguchi,Zenihiro,
forforthethe
Rare
RIRI
Ring
collaboration

∗1∗2
∗3

RIKEN Nishina Center
Department of Physics, Saitama University
Institute of Physics, University of Tsukuba- 184 -could be identiﬁed as the momentum acceptance of thering. The estimated momentum acceptance is approximately 0.6%.
0dp/p [%]

-0.1
-0.2
-0.3
-0.4
-0.5
-0.6
012354

Time [s]Fig. 1. Simulation result of momentum change as afunction of time under the vacuum condition of
3.9×10−5 Pa.

2.6399

Revolution frequency [MHz]The Rare RI Ring was constructed1,2) to investigate the nuclear structure and nucleosynthesis of unstable nuclei. The ring is a storage ring that measures the masses of unstable nuclei. Aiming at a relative mass precision of 10−6 , we employ the isochronous
mass spectrometry method in the ring having precisely
tuned isochronism. We developed a resonant Schottky
pick-up for measuring revolution frequency.3) Electromagnetic ﬁeld is induced in the cavity by a circulating
ion which periodically passes through it. The revolution frequency is obtained from frequency measurement of the ﬁeld stored in the cavity. Basic parameters
representing the performance of the resonant cavity,
such as resonance frequency fres = 172.9 ± 1.6 MHz,
shunt impedance Rsh = 161 kΩ, and unloaded quality
factor Q0 = 1880, were acquired.
The ﬁrst commissioning of the Rare RI Ring using a168-MeV/u Kr beam was conducted in June 2015. In
the experiment, the signal of a single Kr nucleus wasdetected with the resonant Schottky pick-up. A frequency resolution of 1.3×10−6 was obtained from 32
ms-long measurements4) . We observed that the revolution frequency gradually varies with time during theion accumulation for 5 s. This is caused by the imperfection of isochronism and momentum change due
to a ﬁnite vacuum condition. Under the current vacuum condition of 3.9×10−5 Pa, the momentum decrease shown in Fig. 1 is expected. This enables us
to convert the time to the momentum change.
We acquired 14 events, each exhibiting their revolution frequencies as functions of time. Figure 2 shows
the individual trajectories for the 14 events in a momentum change-frequency two-dimensional plane, forwhich the momentum change is obtained by the conversion from time according to Fig. 1. We note herethat the initial momenta for the individual events are
unknown and may not be identical, and some of the
trajectories seem to be discontinued owing to possible hard collisions. Since the revolution frequency
trajectories should be identical as far as the machinecondition remains constant, each event in Fig. 2 hasbeen appropriately shifted along the horizontal axis toconform to a single trajectory. The conformability isimperfect as evident in Fig. 2, because the momentum change shown in Fig. 1 is a stochastic process.
Each event may not cover full momentum acceptance.
The full momentum width in the total data, however,2.63982.63972.6396
2.63952.6394
0-0.1

-0.2

-0.3

-0.4

-0.5

-0.6

-0.7

dp/p [%]

Fig. 2. 14 events of revolution frequency as a function ofthe momentum change obtained through the conversion
from time according to Fig. 1.

References
1) A. Ozawa et al., Prog. Theor. Exp. Phys. 03C009(2012).
2) Y. Yamaguchi et al., Nucl. Instrum. Methods Phys. Res.
B 317, 629 (2013).
3) F. Suzaki et al., JPS Conf. Proc. 6, 030119 (2015).
4) F. Suzaki et al., Proceedings of 13th International Conference on Heavy Ion Accelerator Technology (HIAT).