RIKEN Accel. Prog. Rep. 48 (2015)

Ⅱ-9. Instrumentation

Status of the resonant Schottky pick-up for the Rare RI Ring project
F. Suzaki,∗1,∗2 Y. Abe,∗1,∗3 S. Naimi,∗1 A. Ozawa,∗3 T. Suzuki,∗2 T. Uesaka,∗1 M. Wakasugi,∗1 K. Yamada,∗1T. Yamaguchi,∗2 Y. Yamaguchi,∗1 J. Zenihiro,∗1 and Rare-RI Ring collaboration
Precise mass measurements of rare RI make a substantial contribution to the study of nucleosynthesis
and nuclear structure. Rare RI Ring is an isochronousstorage ring for precision mass measurements of rare RI1,2). The Rare RI Ring allows us to determine masses
with a precision of 10−6 . For such high precision measurement, it is essential to maintain the isochronous
condition at 10−6 . We are interested in neutron-richnuclei that have short lifetimes and low production
rates. To measure such nuclei, we adopted the individual injection technique, in which a single particle isinjected to the ring and stored.
Resonant Schottky pick-up is a beam diagnostic device which can detect non-destructively the signal froma particle passing through the resonant cavity at theresonance frequency, fres . With the resonant Schottky
pick-up we acquire revolution frequencies of nuclei circulating in the ring. The distribution of the revolution
frequency corresponds to the distribution of the momentum of nuclei. We adopted the resonant Schottky
pick-up as a monitor for tuning the isochronous ﬁeld
in the ring. Similar resonant Schottky pick-ups havebeen used for the same purpose at GSI3) in Germanyand IMP4) in China.
We performed the oﬄine performance test of theresonant cavity with a network analyzer5) . From themeasurements, fres = 171.43 MHz, shunt impedance
Rsh = 161 kΩ, unloaded quality factor Q0 = 1880,
and Rsh /Q0 = 86 Ω were obtained. With results of
the oﬄine test, the output signal power corresponding
to a single ion with charge q at resonance3) is estimated to be P = q 2 × 2.7 × 10−21 W and the power ofthermal noise Pnoise is estimated to be 7.1 × 10−19 W.
For q ≥ 17, the signal from a single particle could be
detected by the present Schottky pick-up.
We have started new oﬄine test to investigate thesensitivity of the resonant Schottky pick-up. We developed a test system using the electron beam generated
by an electron gun. Figure 1 shows the schematic viewof the setup. We used a Ta ﬁlament cathode. A gridis connected to a function generator. With the output
coupler, we detect the induced electromagnetic wave
inside the resonant cavity at the resonance frequency.
Usually, we obtain a DC electron beam when thermal
electrons are accelerated. However, the DC electron
beam does not induce the alternative electromagnetic
ﬁeld in the resonant cavity. Therefore, we add a frequency modulation at the desired frequency and am∗1
∗2
∗3

plitude into the grid. The modulated frequency is set
to the resonance frequency. This simulates the ion circulation in the storage ring at the frequency. Changing
the amplitude of the modulation controls the ion beam
current. Therefore, we quantitatively evaluate the sensitivity of the resonant Schottky pick-up. The resultsof the test will be reported in coming publications.

CavityCathodeRF
Function
generator

Grid

Faradaycup

Outputcoupler
RSAFig. 1. Schematic view of the oﬄine test using an electron
beam. To induce an alternative electromagnetic ﬁeld
inside the resonant cavity, we use the grid to modulate the DC electron beam at the resonance frequency.
Therefore alternative electromagnetic ﬁelds are induced
by electrons passing through the resonant cavity. We
detect the induced signals with a real time spectrum
analyzer (RSA).

References
1) Y. Yamaguchi et al.: Nucl. Instrum. Methods. Phys.
Res. B 317 (2013) 629.
2) A. Ozawa et al.: Prog. Theor. Exp. Phys. 2012 Issue 1(2012) 03C009.
3) F. Nolden et al.: Nucl. Instrum. Methods. Phys. Res. A
659 (2011) 69.
4) J. X. Wu et al.: Nucl. Instrum. Methods. Phys. Res. B
317 (2013) 623.
5) F. Suzaki et al.: JPS. Conf. Proc. (ARIS2014) in press.

RIKEN Nishina Center
Department of Physics, Saitama University
Institute of Physics, University of Tsukuba- 232 -

完全版2014_本文.indd 232

15/10/16 17:56