Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 49 (2016)

Construction of OEDO beamline
S. Michimasa,∗1 S. Shimoura,∗1 M. Matsushita,∗1 N. Imai,∗1 K. Yako,∗1 H. Yamaguchi,∗1 S. Ota,∗1E. Ideguchi,∗2 H. Sakurai,∗3 K. Yoshida,∗3 and K. Yamada∗3The OEDO system is a new beamline proposed forhigh-quality slow-down RI beams1) . The OEDO is anabbreviation of Optimized Energy Degrading Optics
for RI beam. The idea behind it is to manipulate
the timing degree-of-freedom in the phase space of RIbeam. To obtain a high-quality beam with a small
spot size and a small energy spread, the OEDO systemshifts the spreads of positions and angles to the timing
spread of the beam, which corresponds to the rotation of the phase space ellipse on the position- (angle)timing plane to obtain a small position (angle) spread.
Radiofrequency (RF) electric ion-optical elements canrotate a phase space ellipse of spatial and timing components, as beams from a cyclotron have an RF bunch
structure.
The main components of the OEDO system are:
An RF deﬂector2) synchronized with the cyclotron’s
RF and 2 sets of triplet quadrupole (TQ) magnets toachieve point-to-parallel/parallel-to-point ion optics.
The OEDO system is to be installed downstream ofa momentum-dispersive focus with a reasonable dispersion. The ﬁrst TQ associates the beam energy
with beam angle at the RF deﬂector, and the second TQ makes a small achromatic focus. This dispersion condition is fulﬁlled in the ﬁrst half of the HighResolution (HR) beamline3) . Therefore, the OEDO
system will be implemented in the HR beamline by installing new electric/magnetic elements and rearranging the existing magnets. In FY2014, the main partof the construction budget was funded and the OEDO
project was launched. We are continuously improving
the design of the beamline with respects to the magnet
conﬁguration and an ion-optics.
Figure 1 shows the magnet arrangement for theOEDO beamline downstream of the F6 focal plane of
the BigRIPS. The speciﬁcations of the RF deﬂector
for the OEDO system are shown in the inset table ofFig. 1. The magnet conﬁguration was conﬁrmed tofunction as a phase-space rotator for slow-down beams
by ion optics calculation. The slow-down scheme ofthe OEDO beamline is shown in Fig. 2. In Fig.2(a),anRI beam at 250 MeV/u is transported to FE8, where
the momentum dispersion is tuned to be 1 m. A monoenergetic degrader is installed at FE8 to slow RIs down
to 50 MeV/u, which corresponds to a rotation of thephase space ellipse on the plane of the beam energy(δ) and ﬂight time (t). In Fig.2(b), the ﬁrst half of
the OEDO system, set to be point-to-parallel optics,∗1∗2∗3Center for Nuclear Study, University of Tokyo
RCNP, Osaka University
RIKEN Nishina Center- 177 -Frequency
Maximum Voltage
Gap between electrodes
Length of electrodes
Width of electrodes
Vacuum

18.25 0.25 MHz> 300 kV
200 mm1200 mm
400 mm
5 10-6 Pa

Specifications of RF deflector for OEDO

Fig. 1. Magnet configuration of the OEDO beamline(b) RF(Deflector)(a) FE8(Degrader)

FE8-RF

F3-FE8δ(c) FE9(S0: Target)

RF-FE9δδFig. 2. Phase space rotation in OEDO beamline

rotates the phase space ellipse on the x-a plane. Then,the RF deﬂector reduces the timing (t) dependence ofangle (a). In Fig.2(c), the second half of the OEDO
system, also set to be parallel-to-point optics, rotates
the phase space ellipse on the x-a plane in the reverse
direction. Finally, a small beam spot and a small energy spread are achieved at the FE9 and S0 foci.
Based on the result, we estimated the higher orderaberrations of the OEDO beamline using a MonteCarlo simulation5) .
This work was funded by ImPACT Program ofCouncil for Science, Technology and Innovation (Cabinet Oﬃce, Government of Japan).
References
1) S. Shimoura et al., CNS Annual Report 2013, CNSREP-93, 56 (2015) 56.
2) K. Yamada et al., Nucl. Phys. A 746, 156c (2004).
3) S. Michimasa et al., Nucl. Instrum. Meth. in Phys. Res.
B317, 305 (2013).
4) T. Kubo et al., Nucl. Instrum. Meth. in Phys. Res.
B204, 97 (2003).
5) M. Matsushita et al., In this report.