RIKEN Accel. Prog. Rep. 50 (2017)

Ⅱ-9. Instrumentation

Helium ﬁlling method for SAMURAI spectrometer†∗1∗2∗3∗4∗5∗6RIKEN Nishina Center
Department of Physics, Kyungpook National University
Department of Physics, Kyushu University
Institute for Nuclear Research, MTA Atomki
Oak Ridge National Laboratory
Department of Physics, University of Hong Kong

BottlestandGas-control panel
He
BottleHe
BottleHe

He-injection
tube

BottlePressure
monitorPC

O2 monitors

Gas-ejection port(to atmosphere)

FDC1A helium ﬁlling method was developed for theSAMURAI spectrometer and successfully tested in theSAMURAI13 experiment. The method allowed the useof an extra-large exit window to maximize the geometrical acceptance of the spectrometer and preserved theacceptable momentum resolution for charged particles
by minimizing multiple scattering in the gas with asmall Z number.
A schematic layout of the He-ﬁlling system is shownin Fig. 1.
??.TheThevacuum
vacuumextension
extension duct,duct, neutron
neutron window, and large ”megane” ﬂange of the spectrometer
were replaced by a large window with a total area of
5.2 × 1 m2 . The design of the exit window was based1)
on a previously
previously tested prototype.
prototype.?)Two O22 sensors
sensors
were placed inside the SAMURAI gap to monitor theconcentration of air in a volume of ∼10 m3 . Helium
was supplied into the gap at a rate of 20 L/min via
an injection ﬂange, which also contained feedthroughs
for signal cables from the O2 sensors. In addition, aninternal pressure monitor was attached to the injection
ﬂange to control gas pressure inside the gap. Anotherexternal monitor measured ambient pressure in the experimental area. The data from the O2 and pressure
sensors were monitored and recorded on the external
PC. During He injection, the air-He mixture was freely
exhausted to the atmosphere via NW25 port. Slow gas
ventilation allowed maintaining a pressure nearly equal
to atmospheric pressure inside the gap without significant stress on the exit window.
The results
The operaresults areare summarizedsummarizedininFig.
Fig.??.
2. Thetion was performed in three stages. During the ﬁrst period (∼11 h), a He concentration of 76% was reached.
Subsequently, He injection was interrupted, and theexhaust port was sealed for 11 h to check the leak rate.
No leak was observed during this period, and the ﬁnalventilation was performed to reach the desired He content of ∼95%. The concentration was maintained at
this level throughout 13 consecutive days without continuous gas supply and keeping a sealed ejection port.
In the following, an insigniﬁcant air leak of ∼2 L/day
into the gap was observed, which was partially compensated by adding small amounts of helium once per
two days. No signiﬁcant changes (<1 mbar) in the internal pressure relative to the exterior were observed
during and after the ventilation procedure. Small ﬂuctuations of the absolute pressure coincided with theReadoutstation

∗1∗1
∗1,∗2
∗3∗3
∗1,∗2
∗1,∗2
∗1,∗2
V.V.Panin,
S.S.Chebotaryov,
S.S.Sakaguchi,
E.E.Milman,N.
Panin,
Chebotaryov,
Sakaguchi,
Milman,N.Chiga,
Chiga,∗1∗1Z.Z.Elekes,
Elekes,∗4∗4B.
B.Heﬀron,
Heffron,∗5∗5S.
∗6
∗6∗6
∗1∗1
∗6T.Lokotko
Lokotko, andandH.H.Otsu
Otsu
S.Leblond,
Leblond, T.

O2 sensors

95% 4He + 5% air~10m3 @ 1 atm

PET Exit window(5.2 m x 1 m)

N usedNotFig. 1. Schematic layout of the He-ﬁlling system. The red
shaded area indicates the volume ﬁlled by helium.

Fast replacement
11 hours @ 20 l/min
0% 76% (He)Night break
sealed gap, 76% (He)Helium (76%)

Steady11 hours @ 20 l/min
76% 95.2% (He)Stop gas95.2%

Air (24%)
4.8%

Inside SAMURAI

AtmosphericFig. 2. He-ﬁlling performance with SAMURAI. Top ﬁgure:gas concentration in the gap as a function of time, estimated from the measurements in O2 sensors. Bottom ﬁgure: data form the internal and external pressuremonitors.

ambient pressure due to changing weather conditions
as can be seen in Fig.
2.
Fig.??.
The presented results clearly demonstrate the feasibility of the He-ﬁlling of the SAMURAI spectrometer.
The method can be potentially applied in the upcoming experiments at SAMURAI, for example, in heavyion-proton measurements, which require the maximum
geometrical acceptance for protons in the focal planeowing to 90◦ rotation of the spectrometer.
Reference1) V. Panin et al., RIKEN Accel. Prog. Rep. 49, 168(2016).

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