II-9. Instrumentation

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Improvement of kicker system for rare-RI ring
Y. Yamaguchi,∗1 D. Nagae,∗1,∗2 S. Naimi,∗1 A. Ozawa,∗1,∗3 and M. Wakasugi∗1,∗4
The kicker system at the rare-RI ring (R3) facility has
contributed to successful event-by-event measurements.
Thus far, three kicker units have been utilized for injecting and ejecting particles using the same ﬁeld waveform.
However, this is not ideal because the top of waveform isnot ﬂat (see Fig. 1(a)). It causes an approximately 10%
ﬂuctuation in the kick angle within an eﬀective injection duration of 100 ns. In addition, because the ejection duration is the same as the injection duration, it
is impossible to eject all nuclides having diﬀerent revolution times.1) In the following, we report a successful
improvement in these issues by the addition of a kicker
magnet.
Recent R3 experiments are conducted with an injection energy of around 165 MeV/nucleon. Revolution
time at R3, which has a circumference of 60.35 m, isapproximately 380 ns. It is necessary to make the magnetic ﬁeld strength negligibly small when particles pass
the kicker in the next revolution after injection. Hence,
a ﬂat-top with a duration of 100 ns is appropriate considering the fall time of the magnetic ﬁeld. Furthermore,
it is possible to eject all circulated particles in a single
ejection duration by lengthening the ﬂat-top to 380 nsor more.
The magnetic ﬁeld shown in Fig. 1(a) is achieved by

Fig. 1. Black line shows measured magnetic field, whereas
blue line shows field experienced by particle (see text).
Black and Blue dots indicate kicked events of 78 Kr and75Ga, respectively.
∗1
∗2
∗3
∗4

RIKEN Nishina Center
Research Center for SuperHeavy Elements, Kyushu University
Institute of Physics, University of Tsukuba
ICR, Kyoto UniversityFig. 2. Time-of-flights of ejected nuclides in single ejection
as function of their momentum.

trial and error by adding a capacitor to suppress thereﬂections.2) In this study, two diﬀerent types of magnetic ﬁeld waveforms with and without this additional
capacitor are produced. When passing through thesetwo diﬀerent ﬁelds, which are generated by two kickerunits, a particle experiences a total magnetic ﬁeld thathas a ﬂat-top (see Fig. 1(b)). Each kicker unit can generate a magnetic ﬁeld twice within 0.7 ms. For injection,
two kicker units are used, whereas for ejection, two additional kicker units are needed. To ensure a long ﬂattop ejection waveform, the delay between the ﬁring of
the ﬁrst two kicker units and the additional two units is
ﬁxed to approximately 350 ns.
Blue dots in Fig. 1(b) indicate the kicked 75 Ga particles counted by a plastic scintillator with a width of
5 mm installed in the center orbit of the R3. This measurement was performed while changing the kicker trigger timing in 10 ns steps. It can be clearly seen that thecount rate is constant compared with the 78 Kr case in
the range of 100 ns, for which a ﬂat-top has been realized. Kick angle ﬂuctuation on the ﬂat-top is expected
to be 1%.
Figure 2 shows the measured ﬂight times of the ejectednuclides as a function of momentum obtained from theposition information of the PPAC at BigRIPS-F5. We
succeeded in ejecting all injected nuclides in a single ejection. The events of 76 Ge that were not ejected in the ﬁrst
kick were ejected in the next kick. Thus, a long ﬂat-topof approximately 400 ns was realized. Consequently, experimental eﬃciency became at least twice better thanthat achieved using the previous method, where diﬀerent
ejection timings were needed to eject all particles.
References

1) S. Naimi et al., J. Phys. Conf. Ser. 1643, 012058 (2020).
2) H. Miura et al., RIKEN Accel. Prog. Rep. 49, 154 (2016).

- 100 -1