Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 52 (2019)

Status and future plans of the MRTOF MS constructed at the SLOWRI
facility
M. Rosenbusch,∗1 M. Wada,∗1,∗2 H. Ishiyama,∗1 P. Schury,∗2 Y. Ito,∗3 H. Haba,∗1 S. Ishizawa,∗1 D. Kaji,∗1S. Kimura,∗1 H. Miyatake,∗2 J. Y. Moon,∗4 K. Morimoto,∗1 K. Morita,∗1,∗5 T. Niwase,∗1,∗5 A. Takamine,∗1T. Tanaka,∗1,∗5 and H. Wollnik∗6A new multi-reﬂection time-of-ﬂight mass spectrograph (MRTOF MS) for the precise measurement of nuclear masses has been assembled at the SLOWRI facility
at RIKEN. The device is designed and sized following
the successful apparatus1–4) presently installed at thegas-ﬁlled ion-recoil separator GARIS-II. Two concentric
ion mirrors separated by a central drift tube of 26 cm
length are facing each other, where each mirror consistsof eight electrodes enabling deceleration and reﬂectionof ions and two electrostatic lenses enabling radial conﬁnement (length of each mirror: 35 cm, total length ofMRTOF MS: 96 cm). For mass resolving powers in theorder of m/δm > 105 (m as the mass and δm as measured FWHM of the mass according to the TOF signal),
ion-optical aberrations must be reduced accordingly toallow for a narrow time-of-ﬂight focus. Several measures
have been undertaken: As radial aberration coeﬃcientsfrom initial angles and diameters of the beam decrease
rapidly with the diameter of the ion optics, the electrode diameter has been chosen as large as 10 cm, while
the beam diameter is expected to be at the order of amillimeter for the major part of the trajectory. All electrodes consist of precision-machined stainless steel (providing high stability), and have been coated with gold toensure an excellent electric-ﬁeld distribution in the absence of chemical compounds bound to the surfaces. The
electrodes are further mounted on a precision-machined
single solid piece of alumina, where the position of theelectrodes (concentric on the outer side as well) is deﬁned
by a V-shape of the ceramic support (see photo). Oneof the technical goals of this setup is the acceptance andstorage of ions with kinetic energies of 5 keV or above
present at the position of the drift tube. In presently
well-known and successful conﬁgurations of the electricﬁelds (for positive ions), this requires negative voltagesof up to −15 kV at the electrostatic lenses (the broadelectrodes at each mirror). Thus, special attention has
been given to the choice of the electric feedthroughs,distances of cables, and vacuum compatible insulationof the wires. The wires inside the vacuum allow for biases of more than 10 kV at zero distance between each
two cables. The vacuum system of the MRTOF MS device is presently operational, and ion traps for guidanceand preparation of radioactive ions are existing and to∗1∗2∗3∗4∗5∗6

RIKEN Nishina Center
Wako Nuclear Science Center (WNSC), IPNS, KEK
Advanced Science Research Center, JAEA
Institute for Basic Science
Department of Physics, Kyushu University
Department of Chemistry and Biochemistry, New Mexico
State University

Fig. 1. Top: Photo from the top showing the assembly withgold-coated electrodes. Bottom left: Precision machined
ceramic support with V-shape to define the electrode position. Bottom right: Cabling of the electrodes for thesuppression of electric discharges.

be installed in near future.
The new MRTOF device has been constructed fortwo major purposes, which is a coupling to the gas
cell presently developed for SLOWRI5) to operate insymbiosis with other BigRIPS experiments, and the development and test of novel technologies for MRTOF
mass spectrometry. In collaboration with experimental groups operating at BigRIPS, a new project of theSLOWRI facility aims at the installation of a cryogenic
helium gas cell at the end of the BigRIPS beam line
to accept unused reaction products measured at various
in-beam experiments, which are guided to beam dumps
otherwise. Application of state-of-the-art technologies
as using the in-trap lift technology6) and an in-trap deﬂector7) are further planned for the MRTOF MS operation at SLOWRI in future.
References

1) P. Schury et al., Nucl. Instrum. Methods Phys. Res. B
376, 425 (2015).
2) P. Schury et al., Int. J. Mass Spectrom. 359, 19 (2014).
3) Y. Ito et al., Phys. Rev. Lett. 120, 152501 (2018).
4) M. Rosenbusch et al., Phys. Rev. C 97, 064306 (2018).
5) A. Takamine et al., in this report.
6) R. N. Wolf et al., Int. J. Mass Spectrom. 313, 8 (2012).
7) P. Fischer et al., Int. J. Mass Spectrom. 435, 305 (2012).

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