Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 56 (2023)
RIKEN
Accel. Prog. Rep. 56 (2023)

Energy-degraded beam on BigRIPS F0H. Otsu,∗1 N. Fukuda,∗1 T. Nishi,∗1 and T. Sumikama∗1
Uranium (and Xe, Kr) beams, which are accelerated up to the SRC, have a ﬁxed beam energy of345 MeV/nucleon because ﬁxed-frequency accelerators
are operated upstream. If a lower energy beam is required, the beam energy would be lowered with material as an energy degrader at the ﬁrst stage of BigRIPS. Subsequently, the lower energy beam would bedelivered into the downstream beamline. The energydegraded beam would be transported to F2 or F3,
where reaction targets would be placed. The disadvantages of the method are: 1) Transport of a relatively
intense primary beam to F2 or F3 is required for themeasurement of the reaction cross section, which might
be subject to radiation shielding limitations. 2) Reaction products should be separated using downstreamof F3 in BigRIPS, which requires a completely diﬀerent
approach compared to the measurement of production
cross sections at 345 MeV/nucleon. This in turn mightlead to large systematic errors.
Based on these reasons, the possibility of providing
energy degraded beam to BigRIPS F0 was investigatedand tested. A primary beam transport beamline is located from the G01 port to BigRIPS F0 downstream ofthe SRC exit. At an intermediate beam proﬁle monitor
port T11 beam can focus in both X and Y directions.
Therefore, if this type of transport optics are used andan energy degrader material are located at T11, it isexpected that the primary beam can be transported
to the F0 focal plane without increasing phase spaceof the primary beam largely. Figure 1 shows the calculated transport from T11 to the F0 focal plane. Infact, this transport method has been previously usedin dispersion matching experiments1) for veriﬁcationof dispersion matching. Conversely, an energy degrade
material has never been placed here before. This test
was the ﬁrst attempt to investigate the transport ofenergy-degraded primary beam to BigRIPS F0.
SRC-BIGRIPS

BEAM PLOTThe energy degrader plate was inserted from oneof the ports at T11. It made of aluminum with 8steps, each with a thickness ranging from 1.7 mm
to 9.3 mm. After passing through each steps, uranium primary beam with 345 MeV/nucleon was degraded into 300, 250, 200, 150, 100, 75, 50 and
25 MeV/nucleon. When the energy degrader plateis withdrawn, the 345 MeV/nucleon U beam passes
unchanged with the 86+ charge 345 MeV/nucleon U
beam passes unchanged with the 86+ charge state. The
beam is then transported to F0 by adjusting the magnetic ﬁeld of the dipole magnets DMT2,3 to match themagnetic rigidity required for the 86+ beam.
The U beam that has passed through the energy
degrade plate has a dispersed charge state, and it isdeﬂected by the DMT2 and DMT3 magnets from T11
and transported to F0 as shown in Fig. 1. It can beobserved that a beam with a charge state whose rigidity is tuned to the central trajectory can pass throughthe triplet quadrupole magnets between DMT 2 and3, while beams with neighboring charge states are considered to be partially blocked by walls in the middleof the Q magnet.
Tests of the transport were performed as a program DA03 on 2021/11 and 2022/03. Figure 2(a)shows one of the results on a proﬁle monitor at T21
with the 250 MeV/nucleon transport. The neighboring charge state was actually observed as a separate
peak on the momentum dispersion axis (X) in theproﬁle monitor located at T21. The magnetic rigidity was set at 92+ in the central trajectory. The results veriﬁed that the beam passing through the central orbit is 92+ of the charge state, because 91+ beam
was observed at neighboring higher momentum while
93+ was not observed. In this condition, the beam
spread was conﬁrmed by an alumina ﬂuorescent plateat F0 shown in Fig. 2(b1), which is comparable withthose observed at 345 MeV/nucleon (Fig. 2(b2)). At
150 MeV/nucleon, the condition was not as good asthat at 250 MeV/nucleon and the T21 separation wasXX.XX.XXX YY:YY:YY

U 92+
U 91+

T21

MQ

MQ

MAGNETICQUADRUPOLMAGNETIC
SECTOR

MQ

MAGNETIC
SECTOR

MQ

MQ

T11

U 90+

BigRIPS F0

X-MAX 0.100 ma)

x

U 93+

U 92+

U 91+

252 MeV/u

Beam on F0 Target

Y-MAX 0.100 m

Fig. 1. Beam envelop from the T11 focus to BigRIPS F0. U
beams with three diﬀerent charge states are transported
in the calculation.
∗1b1)b2)c.f. 345 MeV/uFig. 2. a) Beam proﬁle at T21 with U 250 MeV/nucleon.
b1) Beam spot at F0 and b2) that of 345 MeV/nucleon
for comparison.

RIKEN Nishina Center

2.000 m- 80 -Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 56 (2023)

not suﬃcient. The beam spread, as monitored by thealumina ﬂuorescent plate, was signiﬁcantly larger thanthose at 345 or 250 MeV/nucleon.
In conclusion, the energy degraded beam from345 MeV/nucleon at BigRIPS F0 was successfully delivered. This method proved that the energy-degradedbeam can be delivered without using the ﬁrst stageof BigRIPS, by utilizing the primary beam transportbeamline from T11. On the other hand, it should be
noted that the use of beams with diﬀerent charge states
are blocked by the beam duct along the beam line, especially at DMT2 or Q magnets between DMT2 and 3.
Therefore, the eﬀects of heat and radiation should beconsidered, not only for normal high-intensity beams
but also for suﬃciently reduced intensity beams.
Reference1) T. Nishi et al., Nucl. Instrum. Methods Phys. Res. B
317, 290 (2013).

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