The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

Development of Long-Lived Carbon Stripper Foils
H. HASEBE* 1 , I. SUGAI* 2 , H. AKIYOSHI, M. KASE andY. YANORII<EN (The Institute of Physical and chemical Research)
2-1 Hirosawa, Wako, Saitama 351-0198, Japan*1 SHI Accelerator Service, Ltd.
2
* High Energy Accelerator Research Organization (KEK)
AbstractLong-lived carbon foils have been developed for theRIKEN RI beam factory project. The lives of C-foils
produced by a new method were 40 times longer than thefoils produced by a conventional method

1INTRODUCTION

Carbon foils (C-foils) are extensively used as charge
strippers for heavy-ion beams. However, the C-foils haveserious disadvantage of short life with a high-intensity
heavy-ion beam. The C-foil lifetime is very short in theRII<EN RI beam factory (RffiF). Therefore, theproduction of long-lived C-foils is urgently required for
the RffiF project. Large progress has been made in
developing long-lived C-foil prowction techniques [e.g.1].
We are planning to produce a self-sufficient number oflong-lived C-foils according to the technicpes presented inRef. [1].

Fig. 2: The inside view of vacuum chamber.

·2Fig. 1: High vacuum evaporation system (EBX-2000C byULVAC).

PRODUCTION OF CARBON FOIL

C-foils with a thickness of 10 f.lg/cm 2 were produced by
the arc discharge evaporation method The arc discharges
were generated by AC voltage as well as DC voltage.
Figure 1 shows a external view of the high vacuum
evaporation system. A rectangular vacuum chamber witha dimension of 750 mm X 750 mm X 900 mm isevacuated by two oil-sealed pumps and a 5000 1/s
cryogenic pump. The ultimate vacuum pressure of thevacuum chamber is 1.0 X 10·5 Pa, and it takes less than
15 minutes to evacuate the chamber from atmosphericpressure to 1.3 X 104 Pa It was typically 1 X 10·3 Pa
while the evaporation was performed Figure 2 shows ainside view of the vacuum chamber. The AC and DC arc
discharge evaporation sources are placed in the mid:Be of
the vacuum chamber. The angle between the direction ofarc discharge and the horizontal plane was varied from 0 to45 degrees. The discharge currents were varied to be 300A,350A, 400A, 450A, and 500A. The thickness of the Cfoil was continuously measured by a quartz crystal
thickness gauge. The gauge was calibrated by measuring
the mass and the area of a C-foil. Two resistance-heatedsources for releasing agent are placed in both sides of the-369-

The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

vacuum chamber. A substrafce rotation mechanism wasused in order to make the film thickness uniform. Theangle between the substrates and the horizontal plane wasvaried according to the position of the evaporation source.

3 BEAM TESTThe durability of C-foils under beam irradiation wasmeasured A 32 keV/u 136Xe9+ beam with an intensity ofl.lpJ.!A from a 500kV terminal was focused on a C-foil.
The beam spot has rectangular shape with a size of 5 mm
X 5 mm. The beam spot was carefully made to form auniform beam. The break of the C-foil was detected by thebeam current measured at downstream of the foil also andobserving the foil by TV camera Figure 3 shows a C-foil
mounted on an aluminum folder in vacuum chamber. Thischamber was set on beam line. The C-Foil folders of 40sheets were moved in the chamber automatically. Thelifetime of commercially available C-foils (ArizonaCarbon Foil Co.) with the same thickness were measured
to be 60 s on average. Its lifetime is taken as the standard
in this workof the AC discharge, and 300A in the case of the DC
discharge. The lifetime of C-foils also depends upon thereleasing agent. Three releasing agents, LaC1 3, NaCI, andNiC1 2 , were tested, and NiC1 2 was found to be preferable.
The lifetime was improved by 20% when a DC arc
discharge was applied with N2 gas flow. We successfully
produced C-foil whose lifetime is 40 times longer thanthe commercial foil when the discharge was made by AC450 A, 0 degree between the direction of the arc discharge
and the horizontal plane, OT-5200N(S) graphite rods, andusing a releasing agent of NiC1 2 •03045Discharge angle (degrees)Fig. 4: C-foil lifetime dependence on the angle betweenthe direction of arc discharge and the horizontal plane.

Table I: The dependence of C-foil lifetime on the type ofDC 300A (s)1539
EG-30XSH

1572

1590

ER-38NSH

1509

1436

ER-38SH453

966

Fig. 3: This photograph is C-foil folder in vacuum
chamber. 10 Jlg/cm2 C-foil was mounted on the folder.

41597
1489

RESULTS

Figure 4 shows the result of the lifetime of the C-foil
depending on the angle between the direction of the arc
discharge and the horizontal plane. The C-foils had
longest lifetimes when the angle was set to 0 degree inthe case of the AC discharge and 30 degrees in the case ofthe DC discharge, respectively.
Table 1 shows thedependence of C-foil lifetime on the types of graphite rods.
The best results were obtained by OT-5200N (S) in thecase of AC discharge and EG-20SH in the case of DCdischarge. Figure 4 shows the dependence of the C-foil
lifetime upon the discharge current. The C-foils had
longest lifetimes when the current was 450A in the case5CONCLUSION

The conditions for production of a long-lived C-foil
have been searched We successfully produced C-foils witha lifetime 40 times longer than the commercial one. The
preparation of thicker C-foils with 80 Jlg/cm 2 is inprogress. We will soon test this C-foil with a few Mev/u
intense heavy-ion beam in the realistic case for the RIBF.

-370-

The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

c ACIIIII DC
(Qc:

2~

B·csu...

Iu
0~.~
....
(Q(jjIX

300A

350A

400A

450A

Discharge current(A)Fig. 5: The dependence of C-foillifetime on the discharge current.

REFERENCES[1]1. Sugai, M. Oyaizu, H. Kawakami, C.Ohmori, T.Hattori, K
Kawasaki, M. J. Borden, and R. J. Macek, Nucl. Instr .and Meth. A362, (1995) 70-371-

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