Ⅱ-8. Accelerator

RIKEN Accel. Prog. Rep. 50 (2017)

D evelopment of thin graphite carbon (GC) disks †H. Hasebe,1 H. Okuno,1 A. Tatami,2 M. Tachibana,2 M. Murakami,2 H. Kuboki,1 H. Imao,1N. Fukunishi,1 M. Kase,1 and O. Kamigaito1Graphite carbon sheet (GCS) disks have been used as thefinal charge stripper for U-beam acceleration since 2015and have successfully provided stable U beams. Whereas
the thickness of the GCS disk was 14 mg/cm2 (two layers of7.0-mg/cm2-thick sheets)1), disks with a thickness less than
4.45 mg/cm2 are also required for other ion beams. Agraphite carbon (GC) disk with a thickness of 2.2 mg/cm2
was fabricated for trial by Kaneka Corporation2). The
dimensions of the GC disk were identical to those of theGCS disk; the outer diameter was 110 mm with a hole at thecenter for mounting. The GC disk has sufficient flexibility
and high mechanical strength considering its thickness. ThisGC disk was used for a Ca beam time in November 2015.
The Ca16+ ions were stripped into Ca20+ with a fraction of87% at an incident energy of 45 MeV/nucleon. A total of
3.31 × 1018 Ca particles were irradiated on one disk at
10-electric-µA intensity, which corresponded to a thermalload of 6.4 W. Fig. 1 shows the GC disk before (left) andafter (right) Ca beam irradiation. There was no deteriorationin appearance except for a slight color change anddeformation. This deformation did not affect the beam
intensity at the downstream.Therefore, the GC disk wasstill usable.
A thinner GC disk with a thickness of 0.91 mg/cm2 has
also been fabricated for trial use. Although its thickness wasless than half that of the 2.2-mg/cm2-thick GC disk, themechanical strength was almost the same. This GC disk wastested for U-beam stripping at 50 MeV/nucleon inNovember 2015. In order to evaluate the thickness
uniformity of the GC disk, the disk was rotated at a highspeed, and the beam fluctuations were monitored at thedownstream. The rotation speed was 300 rpm for the first 2h, and it was increased up to 1000 rpm for five more
minutes. No intensity fluctuation was observed during themeasurement. In addition, charge distributions of U after
passing through the GC disk was measured with theincident U64+ beam. The beam intensity was 10 electric µA,
which corresponded to a thermal load of 8.5 W. Fig. 2shows the GC disk after the test. No damage was observed,
and it was in pristine condition. Fig. 3 shows the charge
distributions of U after passing through GC disks withthicknesses of 0.91 (blue) and 2.2 mg/cm2 (green), and aGCS disk with a thickness of 14 mg/cm2 (red). The mean
charge states of U behind the disks with thicknesses of 0.91,2.2, and 14 mg/cm2 were 78+, 82+, and 87+, respectively.
†Condensed from an article in the proceedings of the 28th worldconference of the International Nuclear Target Development Society.
1
RIKEN Nishina Center
2
Frontier Materials Development Laboratories, Kaneka Corporation

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Fig. 1. GC disk with a thickness of 2.2 mg/cm2 before (left)
and after (right) usage in Ca beam irradiation.







Fig. 2. GC disk with a thickness of 0.91 mg/cm2 after the Ubeam irradiation test.


Fig. 3. Charge distributions of U behind GC disks withthicknesses of 0.91 (blue) and 2.2 mg/cm2 (green), and a
GCS disk with a thickness of 14 mg/cm2 (red).
References
1) H. Hasebe et al., RIKEN Accel. Prog. Rep. 49, 14 (2016).
2) Kaneka Corporation,URL: http://www.elecdiv.kaneka.co.jp/english/index.html