Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 52 (2019)

Development of multiple reflection time of flight mass spectrograph atKISS
J. Y. Moon,∗1 S. C. Jeong,∗1 M. Wada,∗2 P. Schury,∗2 Y. X. Watanabe,∗2 Y. Hirayama,∗2 Y. Ito,∗6
M. Rosenbusch,∗3 S. Kimura,∗3 S. Ishizawa,∗5 T. Niwase,∗4 H. Wollnik,∗7 and H. Miyatake∗2
KEK Isotope Separation System (KISS) dedicated tothe study of the third peak around A ∼ 195 in thesolar abundance can produce pure low-energy beamsof neutron-rich isotopes around N = 126 using multinucleon transfer reaction and in-gas cell laser ionizationand spectroscopy technique.1)
The KISS facility mainly performing beta-decay lifetime study and beta-delayed γ-ray spectroscopy so far,by a multi-reﬂection time-of-ﬂight (MRTOF-MS), will
be able to measure masses of RIs by steering the beam
direction toward the MRTOF-MS system while the betadecay curve is being measured at the decay station. TheMRTOF-MS, competitive to the state-of-art Penning
trap, features a high mass resolving power of >100000
even in the short measurement time (∼30 ms). Together
with its lower yield requirement, remarkable strengths
the device has are suitable for the short-lived RIs of low
production yield.2)
Recently, construction of a new MRTOF-MS has been
completed (Fig. 1), and presently in the performance
test. It consists of a gas cell to cool down the injected
ions, a trap system, and a MRTOF chamber. The trapsystem thermalizes the ions, and converts a continuousFig. 1. MRTOF-MS system, constructed and coupled to theKISS beam line.
∗1
∗2

∗3
∗4
∗5
∗6
∗7

Institute for Basic Science, Rare Isotope Science Project
Wako Nuclear Science Center (WNSC), Institute of Particle
and Nuclear Studies (IPNS), High Energy Accelerator Research Organization (KEK)
RIKEN Nishina Center
Department of physics, University of Kyushu
Department of physics, University of Yamagata
JAEA
Department of Chem. & Bio.chem. New Mexico state university

Fig. 2. Ion currents measured at the outer-ring and the faraday cup, respectively for the diﬀerent pressures – (A) PHe= 100 Pa, (B) PHe = 174 Pa.

beam into a pulsed beam for further MRTOF operation.
In this report, for the gas cell ﬁlled with the helium
buﬀer gas, its ion extraction eﬃciency experimentallymeasured has been briefed. The investigation has been
performed at two diﬀerent pressures of PHe = 100 and174 Pa. Using a radio frequency (RF) carpet (ϕ190 mm)
with a pitch of 0.64 mm, an exit hole with ϕ1.28 mm anda thermal K+ ion source. The “ion surﬁng” mode developed by the combination of a repelling RF potential,
a DC potential gradient, and a 4-phase audio frequency(AF) potential has been implemented, by which the ionsstopped in the gas cell are quickly transported.3) Whenthe ion surﬁng mode with ion drift direction opposite
to the exit hole applied, the current measured at theoutermost ring of RF carpet (Iouter ) showed only small
diﬀerence of around 1%, compared to that at the carpet
surface of no RF applied. A faraday cup was installednear the exit, whose current is IFC . Figure 2 shows theevidence of the ion surﬁng mode created, in which therelative phase of AF voltages was changed by time from+90◦ (to exit hole) to −90◦ (to outer-ring). It has beenachieved that most of ions arrived on the carpet wereextracted by the “ion surﬁng” mode, i.e. the ratio of theextracted ions to the collected (“extraction eﬃciency”)
close to 100%.
References

1) Y. Hirayama et al., Nucl. Instrum. Methods Phys. Res. B
353, 4 (2015).
2) P. Schury et al., Nucl. Instrum. Methods Phys. Res. B
335, 39 (2014).
3) G. Bollen, Int. J. Mass Spectrom. 335, 131 (2011).

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