Ⅱ-8. Accelerator

RIKEN Accel. Prog. Rep. 47 (2014)

Test of diﬀerential pumping system with plasma window using gascell
H. Kuboki,∗1 H. Okuno,∗1 A. Hershcovitch,∗2 T. Dantsuka,∗1 H. Hasebe,∗1 K. Ikegami,∗1 H. Imao,∗1O. Kamigaito,∗1 M. Kase,∗1 T. Maie,∗1 T. Nakagawa,∗1 and Y. Yano∗1∗1∗2

RIKEN Nishina CenterBrookhaven National Laboratory (BNL)

the conventional differential pumping system withouta PW, as estimated in advance.3) Also, P0 reached
130 kPa, which is the maximum value of the gauge.
The P1 and P2 values were 30 and 4.5×10−2 Pa for
Ar and 36 and 1.4×10−1 Pa for He, respectively. Further tests using a PW with an enlarged orifice of 4 mmdiameter are planned in the near future.
1st chamber

Gas feed (Ar/He)
Baratron gauge(measure P0)

Mechanical Booster Pump
+ Rotary Pump
+ Scroll Pump
365 m3/h × 2 (Total 730 m3/h)

2nd chamber

Pirani gauge(measure P2) Cold cathode gauge
Flow constrictor(measure P2)
φ6, L=150 mm

Plasma Window

P1P0P2

Gas cellWater Jacket0

Pirani gauge
and Cold cathode gauge(measure P1)
50

Turbomolecular Pump
792 m3/h
100 cm

P2 Pressure (Pa) P1 Pressure (Pa)Fig. 1. Differential pumping system with PW.

Flow rate (SLM)

A differential pumping system with a plasma window (PW)1) has been developed for application tocharge strippers using high-density hydrogen or helium (He) gases, which have a small atomic number.
We tested the system with a PW operation using a gas
cell where argon (Ar) or He gases were confined up to100 kPa (1 atm). Figure 1 shows a schematic of thesystem. The system consists of a gas cell, a PW, andtwo chambers. The PW has a central bore of 2 mm diameter, which isolates the gas cell from the first chamber. Gas was injected to the gas cell and flowed into
the first chamber through the PW. As stated in theprevious report,2) the two chambers were differentiallypumped. The first chamber was mainly evacuated by
two mechanical booster pumps with a total pumping
rate of approximately 730 m3 ·h−1 . The second chamber was evacuated by a turbomolecular pump (TMP)
with a pumping rate of 792 m3 ·h−1 . The first andsecond chambers were connected via a flow constrictor
with an inner diameter of 6 mm and length of 15 cm.
At first, the plasma was ignited by Ar gas injection.
Next, gas flow rates were increased so that a pressureof 100 kPa was attained at the gas cell (P0 ). The typical flow rate for Ar was maintained at 2.3 SLM to keep
P0 at 100 kPa at an arc current of 15 A per cathode.
Subsequently, we replaced the injected Ar gas with Hegas. We successfully operated the PW with He gas
maintaining P0 at 100 kPa. The flow rate of He forkeeping P0 = 100 kPa was 4.5 SLM at an arc current of 26 A. The differential pumping efficiency wasevaluated by the pressures at the first (P1 ) and secondchambers (P2 ). The pressures P1 and P2 in the casesof Ar and He are plotted as functions of arc currents
in Figs. 2 (a) and (b), respectively. The solid circles
and triangles denote Ar and He data, respectively. The
plotted data were adequately corrected depending on
the gas species. The maximum pressures of P0 in theabsence of the PW operation were 15 and 9 kPa, maintaining P1 at 20 and 40 Pa in the cases of Ar and He,respectively. The maximum P0 values were increased
by 6.7 times for Ar and 11.5 times for He when thePW operation occurred. We found that the lowest arc
currents per cathode for keeping P0 at 100 kPa were
11 and 26 A for Ar and He, respectively.
The gas flow rates for keeping P0 at 100 kPa are also
dependent on the arc currents, as shown in Fig. 2 (c).
It is noteworthy that the flow rate of He can be reducedby more than one order of magnitude as compared to4030(a) P1ArHe20100.15(b) P20.100.05054(c) Flow rate

32110 12 14 16 18 20 22 24 26 28 30 32 34 36 38
Arc current (A)Fig. 2. Pressures (a) P1 and (b) P2 , and (c) flow rates
in cases of Ar and He are plotted as functions of arc
current. Please see the text for details.

References
1) A. Hershcovitch: J. Appl. Phys. 78 5283 (1995).
2) H. Kuboki et al.: J. Rad. Ana. Nucl. Chem. 297 (2013).
3) H. Okuno et al.: Phys. Rev. ST Accel. Beams 14 033503(2011).

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