Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 47 (2014)

Vacuum system for the SAMURAI spectrometer†
Y. Shimizu,∗1 H. Otsu,∗1 T. Kobayashi,∗1,∗2 T. Kubo,∗1 T. Motobayashi,∗1 H. Sato,∗1 and K. Yoneda∗1
The first commissioning experiment of the SAMURAI spectrometer1) and its beam line was performed inMarch, 2012. The vacuum system for the SAMURAIspectrometer includes its beam line and the SAMURAI vacuum chamber with the windows for detecting
neutrons and charged particles.
The window for neutrons is made of 3 mm-thickstainless steel designed in the shape of a partial cylinder to support itself against atmospheric pressure. The
deflection of the window caused by the pressure difference and the induced stress are calculated using thegeneral purpose finite element analysis program code
ANSYS2) . Figure 1 shows the ANSYS calculation result. The calculated displacement by the atmosphericpressure at the central region and the maximum induced stress are 0.17 mm and 44 MPa, respectively. Itshould be noted that the latter is smaller than 1/10 of
the tensile strength. This window is achieved a safety
factor of 12.

the Kevlar textile are calculated by ANSYS. Since theelastic properties of the Kevlar textile are not known,
they are determined to reproduce the vacuum test3) .
In order to reduce the displacement and elongation of
the Kevlar textile, we performed a calculation considering a flexure of 193 mm in the initial condition. The
result is shown in Fig. 2. The displacement and elongation of the Kevlar textile are 73 mm and 6.3%, respectively.

Fig. 2. ANSYS calculation result for Kevlar textile with aflexure of 193 mm in the initial condition.

Fig. 1. ANSYS calculation result for the shape of a partial
cylinder with a thickness of 3 mm.

The window for charged particles was composed of
a combination of Kevlar and Mylar with thicknessesof 280 and 75 µm, respectively. The Kevlar and MyR
to the top of thelar were glued with an Araldite
window frame, which is made of SUS304. The open
geometry of the exit window of the vacuum chamberis 2800 × 800 mm2 , while a 2800 × 400 mm2 window was used in the commissioning experiment. This
was a result of tradeoff between the experimental requirement and the safety and risk management for thebreaking of the window. The deflection and stress for†∗1∗2

Condensed from the article in Nucl. Instr. Meth. B 317, 739(2013)RIKEN Nishina Center
Department of Physics, Tohoku University

In order to have a flexure of 40 mm around the centerregion in the initial condition, both sides of the Kevlarand Mylar were slacked by about 5 mm. The flexureof 40 mm was determined to be the maximum flexure
without inducing wrinkles in the Mylar at the corners.
The maximum deflection around the center region was
estimated to be approximately 60 mm. This indicatesthat the Mylar elongated about 3.2% due to air pressure, which was 1/3 smaller than that of the tensile
elongation at the break. Since this window is achieveda safety factor of only 2.8, the window materials haveto be replaced every year for reasons of safety.
The deflections of these windows by visual observation were consistent with the ANSYS calculation results. The pressure in the SAMURAI vacuum chamber was successfully maintained at a few Pa during
the commissioning experiment without any problems
caused by the windows.
References
1) Y. Shimizu et al., J. Phys.: Conf. Ser. 312, 052022(2011).
2) URL: http://www.ansys.com/
3) Y. Shimizu et al., RIKEN Accel. Prog. Rep. 44, 154(2011).

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