Ⅱ-1. Nuclear Physics
RIKEN
Accel. Prog. Rep. 56 (2023)

Retracted on February 1, 2024

RIKEN Accel. Prog. Rep. 56 (2023)

Development of dispersion matching optics in OEDO beamline
S. Hanai,∗1 S. Michimasa,∗1 T. Chillery,∗1 S. Ota,∗1 N. Imai,∗1 S. Shimoura,∗1 N. Fukuda,∗2 Y. Hijikata,∗3,∗2K. Kameya,∗4,∗2 S. Kitayama,∗4,∗2 K. Kishimoto,∗5,∗2 K. Kusaka,∗2 J. Li,∗1 Y. Maeda,∗6,∗2 Y. Maruta,∗4,∗2T. Matsui,∗4,∗2 K. Miki,∗4,∗2 D. Nagae,∗2 H. Nishibata,∗5,∗2 D. Nishimura,∗7,∗1,∗2 M. Sasano,∗2 Y. Shimizu,∗2S. Sugawara,∗2 T. Sumikama,∗2 H. Suzuki,∗2 H. Takahashi,∗7 H. Takeda,∗2 T. Uesaka,∗2 R. Urayama,∗4,∗2T. Wakasa,∗5 K. Yako,∗1 Y. Yamaguchi,∗2 Y. Yanagisawa,∗2 N. Yokota,∗5,∗2
C. Yonemura,∗5,∗2 and K. Yoshida∗2tectors, a parallel-plate avalanche counter and a lowpressure multiwire drift chamber, were placed at thefoci from F3 to S2, to measure the transfer matrix elements at each focal plane. We veriﬁed the consistencyof the measured matrix elements by comparison withion optics calculation results.
By evaluating the matrix elements, the momentum
dispersion at S0 was deduced as 16.3 m, which corresponds to a dispersion of 0.025 mm/% and satisﬁes the lateral dispersion matching condition with theSHARAQ spectrometer. Figure 2(a) shows that there
is no correlation between the horizontal position (momentum dispersion) at S0 and that at S2 and therefore,
the condition of momentum dispersion matching is fulﬁlled. Figure 2(b) shows the correlation between thehorizontal position (momentum dispersion) at S0 andthe horizontal angle at S2, which suggests that angular dispersion matching is eﬃciently satisﬁed. We conclude that angular momentum dispersion matching isalso achieved at S2.

S0 horizontal Position [mm]

The Optimized Energy Degrading Optics (OEDO)
beamline provides potential opportunities to perform
nuclear physics experiments with spatially and achromatically well-forcused low-energy RI beams1) or highmomentum resolution by selecting a suitable ion transportation method. High-quality low-energy RI beam
production has been achieved.2) Recently, several
beamline magnets in the OEDO beamline were rearranged aiming at the realizing a high momentum resolution. To conduct nuclear spectroscopy with a resolution
greater than the energy width of the incident beam, lateral and angular momentum dispersion matching techniques are essential. Figure 1 shows a designed dispersion matching ion optics from BigRIPS F3 to SHARAQ
S2 foci through the OEDO beamline. The S0 intermediate focus, where a target will be inserted in a future
experiment, has the largest momentum dispersion in
the beamline of 14.7 m, and this momentum dispersion vanishes at the ﬁnal focus, S2. We report here astudy showing dispersion matching optics of the OEDObeamline.

±±±

32
1-±±BigRIPSOEDO

Consequently, we achieved dispersion matching ion
transportation through the OEDO beamline. Using
this ion-optical mode, we plan to conduct an approved
experimental program of direct mass measurements ofvery rare RI nuclei.

We performed the study using an 82 MeV/nucleon
triton beam produced by the BigRIPS separator fromthe 200 MeV/nucleon 4 He primary beam. Position de∗2
∗3
∗4
∗5
∗6
∗7S2 horizontal Angle [mrad]Fig. 2. (a) Correlation between S0 and S2 horizontal positions. (b) Correlation between S0 horizontal position
and S2 horizontal angle. (a|δ) term is approximately
0.4 mrad/%.

SHARAQ

Fig. 1. Trajectories of ion beam with dispersion matching
setting in BigRIPS-OEDO-SHARAQ beamline. Trajectories are calculated from ﬁrst-order matrix elements.

∗10S2 horizontal Position [mm]Center for Nuclear Study, University of Tokyo
RIKEN Nishina Center
Department of Physics, Kyoto University
Department of Physics, Tohoku University
Department of Physics, Kyushu University
Faculty of Engineering, University of Miyazaki
Department of Natural Sciences, Tokyo City University

References
1) S. Michimasa et al., Prog. Theor. Exp. Phys. 2019,043D01 (2019).
2) S. Michimasa et al., CNS Annu. Rep. 2018, CNS, REP98-35 (2020).

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