Ⅰ. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 49 (2016)

Measurement of isochronism using 78 Kr beam for the Rare RI Ring
Y. Abe,∗1 Y. Yamaguchi,∗1 M. Wakasugi,∗1 T. Uesaka,∗1 S. Ohmika,∗3 A. Ozawa,∗2 Z. Ge,∗1,∗3F. Suzaki,∗1,∗3 S. Naimi,∗1 D. Nagae,∗1 H. Miura,∗3 T. Yamaguchi∗3 and for the Rare RI Ring collaboration

∗1∗2
∗3

RIKEN Nishina Center
Institute of Physics, University of Tsukuba
Department of Physics, Saitama University- 19 -Since we succeeded in the ﬁrst beam commissioning
using a primary beam, we performed an experimentusing a secondary beam in December 2015. In thisexperiment, we succeeded in extracting two kinds ofRI produced from 48 Ca.6) In the near future, the Rare
RI Ring will be able to measure the masses of exotic
nuclei, which will have a signiﬁcant impact on the understanding of the r-process.
70100010(∂B/∂r)/B0 = 0.279 m-1

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10(∂B/∂r)/B0 = 0.277 m-1

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Fig. 1. TOF spectra as a function of the momentum spreadwith diﬀerent values of the radial gradient of the magnetic ﬁeld (∂B/∂r)/B0 . The solid lines show the resultsof ﬁtting with a quadratic function.
120(∂B/∂r)/B0 = 0.279 m-1

100Counts [ /bin]We constructed a new storage ring based on theisochronous mass spectroscopy technique, named the“Rare RI Ring,” to measure the masses of rare nuclei
with high precision.1) An oﬄine machine study using
an α-source (241 Am) was performed last year. In theoﬄine machine study, we succeeded in tuning the ﬁrstorder isochronous ﬁeld using trim coils.2)
In June 2015, the ﬁrst beam commissioning of theRare RI Ring was performed, where a 78 Kr beam at
345 MeV/nucleon was used. To perform an individualinjection using a self-trigger signal from F3, the energyof 78 Kr beam was degraded to 168 MeV/nucleon byusing a degrader.
First, we transported the beam to the ring with adispersion matching at the center of kicker magnets inaccordance with the optical calculations.3) After that,
we injected 78 Kr particles individually using the fastkicker system.4) After the individual injection was successful, we conﬁrmed whether the particle was stored.
We conﬁrmed the periodic signals of the circulated particle through a foil detector, which was located on theclosed orbit of the ring.5) Once the storage was conﬁrmed, the extraction was performed. After removing
the foil detector from the closed orbit, we succeededin extracting the particles from the ring after about
700 µs.
Figure 1 shows the TOF of 78 Kr particles asa function of the momentum spread with diﬀerent
values of the radial gradient of the magnetic ﬁeld(∂B/∂r)/B0 and results of ﬁtting with a quadratic
function. From the ﬁtting results, we found thatthe isochronous condition was changed according to
the value of (∂B/∂r)/B0 . Furthermore, to evaluate
the isochronism of the ring, the width of the TOFspectrum was extracted. Since the spectrum has along tail due to higher-order isochronous ﬁeld contributions in the ring, we ﬁtted the spectrum using aGaussian function with an exponential tail to evaluate the width that included the tail. Figure 2 shows
the TOF spectrum and the result of ﬁtting in thecase of (∂B/∂r)/B0 = 0.279 m−1 . The TOF widthof (∂B/∂r)/B0 = 0.279 m−1 was obtained about 12
ns in FWHM. Therefore, we found that the degree ofisochronism achieved is about 1.9 × 10−5 . Thus, wewere able to achieve a 10-ppm isochronism by adjusting the ﬁrst-order isochronous ﬁeld. Furthermore, we
found that the optimum value would be slightly larger
than 0.279 m−1 from these results.

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TOF + 700,000 [ns]880890900Fig. 2. TOF spectrum and the result of ﬁtting using aGaussian function with an exponential tail.

References
1) Y. Yamaguchi et al.: RIKEN Accel. Prog. Rep. 46 xiv(2013).
2) Y. Abe et al.: RIKEN Accel. Prog. Rep. 48 24 (2015).
3) Z. Ge et al.: In this report.
4) H. Miura et al.: In this report.
5) D. Nagae et al.: In this report.
6) Y. Yamaguchi et al.: In this report.