Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 49 (2016)

Development of the He-filling system for the SAMURAI
spectrometer
V. Panin,∗1 S. Chebotaryov,∗1,∗2 S. Sakaguchi,∗3 Z. Elekes,∗4 N. Chiga,∗1 and H. Otsu∗1

C air (t) =C O2 (t)× 100%,
20.9%

Start
10 l/minConcentration [%]

100

(1)

where 20.9% is the C O2 in the air at normal conditions.
Hence, the He concentration is determined as:
C He (t) = 100% − C air (t).

(2)

The results of the gas-replacement test are summarized in Fig. 1. The total time of gas ventilation required to reach C He ≈95% (or C O2 ≈1%) was around3 h and 35 min with an average input He-flow Fin ≈20L/min.
The air replacement as a function of time t is described by the basic room-purge equation:
C air (t) = C air (t0 ) exp(−∗1∗2∗3∗4Fin(t − t0 )),V(3)RIKEN Nishina Center
Department of Physics, Kyungpook National Universityty
Department of Physics, Kyushu University
Institute for Nuclear Research, MTA Atomki- 168 -80

14 l/min20 l/minStop95%Helium6040200100

Concentration [%]In the upcoming Light-Ion experiments SAMURAI
12/13 and in the HI-Proton experiments SAMURAI
24/25/28/29, the SAMURAI gap will be filled by Heat 1 atm pressure, as required by the use of largesized windows at the entrance and exit ends of thespectrometer to maximize its angular acceptance.
A test window was constructed with the total areaof 1200 × 3340 mm2 , which can replace the existing
window for outgoing charged particles. The chosenmaterial for the He-window was the 100-µm PET film
KEL86W.
To validate the design of the He-window and the airreplacement method, a He filling test was performed
using a test chamber with volume V ≈1.4 m3 . The
PET film was superposed onto a 2-mm rubber frameand both were attached to the chamber’s flange by asegmented metal frame to provide sufficient gas tightness. He was injected into the chamber and the airHe mixture was ejected to the atmosphere through theoutlet port on the opposite side of the chamber. Timedependence of the absolute O2 concentration, C O2 (t),in the chamber was monitored by the O2 sensors witha precision of 0.1%. The sensors were placed at threedifferent heights: 2 cm (bottom), 27.5 cm (middle),
and 55 cm (top) in the center of the chamber to control the homogeneity of the He-air mixture. The O2sensors were controlled via an external PC and theirdata were read out every 5 seconds.
The air concentration, C air (t), at every moment oftime t was determined as follows:

80

Air
95%

Helium60
40
200Air
20 40 60 80 100 120 140 160 180 200 220 240 260
Time [min]Fig. 1. Top figure: time-dependence of the air (bold lines)
and He (faint lines) concentrations, derived from thedata of the bottom (red line), middle (blue line) andtop (black line) O2 sensors. Bottom figure: same as
the top figure, but the concentrations (He - red line,air - blue line) are averaged between the three sensors.
The dashed curves in the bottom figure are calculatedusing equation 3. The vertical dashed lines indicate
the start and the end of He injection as well as thetime points when the injected He-flow changed to theindicated values.

where V is the volume of the chamber and t0 is thestart time of the ventilation. This function is plottedin the bottom graph of Fig.1 (dashed curves) and isin good agreement with the data. Based on this, one
can estimate for the SAMURAI gap with V ≈10 m3and input He-flow Fin ≈20 L/min, the necessary time
to reach C He =95% is about 25 h with a consumptionof about 30 m3 of He-gas (at 1 atm).
No He leak was found after stopping the ventilationand sealing the chamber. C He and C O2 remained constant for at least 4 consecutive days. Moreover, nosignificant change in pressure (< 1mbar) was observed
during and after the ventilation.
In conclusion, good performance of the He-window
design and the feasibility of the applied gas-filling
method, which is in agreement with theoretical expectations, have been confirmed. In future, a large
exit window (5340×1000 mm2 ) will be constructed andtested with the SAMURAI gap under experimentalconditions.