Ⅱ-8. Accelerator

RIKEN Accel. Prog. Rep. 47 (2014)

Charge state distribution measurement of 86 Kr in H2 and He gases at
2.7 MeV/nucleon
H. Kuboki,∗1 H. Okuno,∗1 H. Hasebe,∗1 N. Fukunishi,∗1 E. Ikezawa,∗1 H. Imao,∗1 O. Kamigaito,∗1and M. Kase∗1∗1

RIKEN Nishina Center

the maximum magnetic rigidity of the dipole magnet
for selecting charge states was 0.97 T·m, the data are
insufficient to reproduce charge distributions in N2 gas.
It is found that the H2 gas stripper can be used for86
Kr acceleration. In addition, the charge states inHe are sufficiently high for 78 Kr acceleration, since thelowest charge state of 78 Kr acceptable for RRC is 23+.
Further development of a differential pumping systemusing orifices with a bore diameter larger than 10 mm
is necessary for practical use.
cold cathode gauge (PU3)sapphire capacitancepirani gauge (PU3)diaphragm gauge (PD1)baratron gauge (PU1)e42: 8.0 m

aperture 4 mmφstage U2
MBP
365 m3/hcold cathode gauge (PD3)pirani gauge (PD3)stage D2
MBP
365 m3/h

XReb: 3.1 m
J28: 7.5 mchamber X51b

stage 1: 100 cm

chamber X51a

length 10 cm
TMP
792 m3/hstage U3
TMP
1980 m3/hpirani gauge (PX51)
pirani gauge (PU2)
cold cathode gauge (PX51)

gas inlet

stage D3
TMP
1980 m3/h

TMP
792 m3/hpirani gauge (PD2)050

100 cmFig. 1. Schematic of the gas charge stripper. Please see thetext for details.
0.4
0.3(a) H2

0.2
Fraction (normalized)

We can obtain heavy ions with higher charge statesin gases with small atomic numbers (low-Z gas) suchas hydrogen (H2 ) or helium (He) as compared to otherstandard gases (nitrogen (N2 ) or argon).1) Recently,
a windowless He gas stripper utilizing a strong differential pumping system has been constructed for
uranium (U) beams at the RIKEN RI Beam Factory (RIBF).2) It has successfully functioned and has
provided high intensity U beams stably.
The possibility of application of low-Z gas charge
strippers to krypton (Kr) beam acceleration at theRIBF has been studied. The first stripper for 86 Kr acceleration is located downstream of the RILAC, wherethe exit energy becomes 2.7 MeV/nucleon. Carbonfoils with thicknesses of 40–80 µg/cm2 have been usedas the first stripper to obtain 86 Kr26+ for accelerationby the subsequent cyclotron RRC.3) A low-Z gas stripper can be one of the candidates for a long-lived stripper if a sufficient fraction of 26+ is obtained.
We have developed a prototype of a gas stripper
and measured the charge state distributions of 86 Krin H2 and He with different thicknesses. The 86 Kr20+
beams at 2.7 MeV/nucleon were transported to thegas stripper. A schematic of the gas stripper with its
differential pumping system is shown in Fig. 1. Gases
were injected in the target region (stage 1) located atthe center. The length of the target region was 100 cm.
The other stages, U2, D2, U3, and D3, are also shown
along with the pumping speeds of their respective attached pumps. A 10-cm-long tube with 4-mm inner diameter was installed between each stage. The charge
state distributions of 86 Kr in H2 and He are shownin Fig. 2. The fractions calculated for H2 , He, andN2 are plotted in the figure. In Fig. 2 (a), the data
for the H2 gas with thicknesses of 10, 23, 46, 68, and107 µg/cm2 are denoted by asterisks, x-marks, opentriangles, open squares, and open diamonds, respectively. In Fig. 2 (b), the data for the He gas withthicknesses of 16, 29, 59, 124, and 247 µg/cm2 are denoted by asterisks, open triangles, open circles, opensquares, and open diamonds, respectively. Finally, inFig. 2 (c), The data for N2 gas with thicknesses of13, 36, 817, and 1221 µg/cm2 are denoted by asterisks, open triangles, open circles, open squares, andopen diamonds, respectively. The mean charge statesof 86 Kr in H2 and He gases attained equilibrium at 25.1
and 23.2, respectively. The fraction of 86 Kr26+ in H2
is 32% at equilibrium. The mean charge state in N2 atequilibrium was estimated to be lower than 20+. Since

10 µg/cm2 ( 107 Pa)
23( 227)
46( 467)
68( 693)
107(1093)

0.1
00.3(b) He

0.2

16 µg/cm2 ( 80 Pa)
29( 160)
59( 320)124( 667)
247(1333)

0.1
00.3(c) N20.213 µg/cm2 ( 9 Pa)
36( 27)817(547)
1221(813)

0.1
016 17 18 19 20 21 22 23 24 25 26 27 28 29
Charge stateFig. 2. Charge distributions of 86 Kr in (a) H2 , (b) He, and(c) N2 gases. Please see the text for details.

References
1) H. Okuno et al.: Phys. Rev. ST Accel. Beams 14 033503(2011).
2) H. Imao et al.: Proc. of IPAC’13, Shanghai, China(2013), p. 3851.
3) H. Hasebe et al.: Proc. of 17th Int. Conf. on Cyclotrons
and Their Applications, Tokyo, Japan (2004), p. 313.

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