Ⅰ. HIGHLIGHTS OF THE YEAR
RIKEN
Accel. Prog. Rep. 56 (2023)

RIKEN Accel. Prog. Rep. 56 (2023)

Improved transmission of OEDO
T. Chillery,∗1 S. Michimasa,∗1 N. Imai,∗1 D. Suzuki,∗2 M. Dozono,∗2,∗3 N. Fukuda,∗2 T. Haginouchi,∗2,∗4S. Hanai,∗1 S. Hayakawa,∗1 Y. Hijikata,∗2,∗3 J. W. Hwang,∗5 S. Ishio,∗2,∗4 N. Iwasa,∗2,∗4 K. Kawata,∗1R. Kojima,∗1 K. Kusaka,∗2 J. Li,∗1 M. Ohtake,∗2 K. Okawa,∗1 T. Saito,∗5 Y. Shimizu,∗2 T. Sumikama,∗2H. Suzuki,∗2 H. Takeda,∗2 H. Tanaka,∗2,∗6 T. Teranishi,∗2,∗6 Y. Togano,∗2 Y. Yanagisawa,∗2 R. Yokoyama,∗1K. Yoshida,∗2 and M. Yoshitomo∗2∗1∗2∗3∗4∗5∗6a)Center for Nuclear Study, University of Tokyo
RIKEN Nishina Center
Department of Physics, Kyoto University
Department of Physics, Tohoku University
CENS, Institute for Basic Science
Department of Physics, Kyushu University
S0 focal plane = target position in the TINA silicon-detector
array, as used in the 130 Sn experiment.

Fig. 1. COSY-calculated beam trajectories in the X andY planes between F3 and S1 for low energy tuning inOEDO.

F3 – S0: ~ 85%

S0 Y [mm]The optimized energy degrading optics (OEDO) system1) was installed at RIBF in 2017. The principle
aim of OEDO is to decelerate and focus medium-heavy
radioactive ion beams provided by BigRIPS from approximately 200 to 15–50 MeV/nucleon. The system
was commissioned in the day 0 campaign by studying
transfer reactions on 77 Se, 93 Zr, and 107 Pd. During
this, the transmission from F3 decreased from 61% at
FE9 to 18% at S0, despite the eﬀective focusing effort of the RF-Deﬂector (RFD) at FE10. This poortransmission was attributed to the small bore radiusof the quadrupole magnet, i.e. QE19, located at FE11,and thus, during 2021, the OEDO beamline was reconﬁgured. The QE20 (STQ18) magnet was installed
upstream of FE11 (FE12), and the QE19 magnet wasentirely removed from the beamline. The impact toOEDO’s low-energy focusing capabilities was tested
in April 2022 during the machine study “MS22-1”
followed by the SHARAQ18 experiment2) measuring130
Sn(d, p)131 Sn. This report summarises the new lowenergy optics of the OEDO beamline, including the improved transmission.
The ion-optical transport code COSY-Inﬁnity (v 9.0)
was used to simulate the beam transport through theupdated F3–S1 beamline. The beam trajectories in X
and Y planes are shown in Fig. 1. Compared with theprevious beam trajectories,1) the new magnet setup between the RFD and S0a) should enable higher transmission to the secondary target. In addition, the QE20
magnet placed downstream of the RFD enables the ﬁnetuning of the parallel beam condition, which was notpossible in the previous conﬁguration.
COSY matrix elements for the new OEDO transport
were incorporated into the CNS-developed Monte Carlosimulation code. The simulation used the measured
condition at F3 from MS22-1 and included beamline
materials, the opening of the beam pipes, and the RFD.
The simulated spot size at S0 was X(Y ) = ±5 (10) mm,within the target radius of 25 mm. The estimated F3–S0 transmission was 97% till third-order aberrations.
Following optics tuning in April 2022, the measured
130
Sn beam spot at S0 is shown in Fig. 2. The beam wasS0 X [mm]130Fig. 2.
Sn Beam focus at S0. Red circle represents theCD2 target’s radius of 25 mm.

centred at X(Y ) = −2(−1) mm with a spot size of ±8(12) mm, within the CD2 target’s radius of 25 mm. The
beam energy was degraded to 23.3 ± 1.1 MeV/nucleon
at S0. The measured F3–S0 transmission of 85% islower than the calculated value of 97%; however, it still
improves OEDO’s transmission by a factor of 4.7 overthe previous condition.1) Following this improved transmission of low-energy beam, we performed the OEDO
experiment2) to measure 130 Sn(d, p)131 Sn.
References
1) S. Michimasa et al., Prog. Theor. Exp. Phys. 2019
043D01 (2019).
2) N. Imai et al., in this report.

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