Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 53

First test of graphenic carbon vacuum windows with heavy ionsS. Purushothaman,∗1 H. Haba,∗2 E. Haettner,∗1 S. Ishikawa,∗3 K. Itahashi,∗2 S. Y. Matsumoto,∗2,∗4
Y. Miyake,∗2 A. Sakaue,∗4 R. Sekiya,∗4 Y. K. Tanaka,∗1,∗5 and M. Tomut∗6
Currently, one of the main concerns in experiments
involving high-luminosity hadron beams is the limitations imposed by the materials directly interactingwith the beam. Beam windows are essential components in every accelerator and many experimental systems, and they experience enhanced radiation damage,high operation temperatures, and high thermal andtransient stresses, adding to pressure diﬀerences between the beam vacuum and atmosphere. Graphenic
carbon membranes are an excellent replacement for
conventionally used window materials such as steel,beryllium, aluminum, or Inconel alloys because of their
low atomic number and excellent thermomechanicalproperties. The excellent mechanical properties andmolecular impermeability of suspended graphenic carbon membranes1,2) make them an ideal vacuum window material with an extremely low window thickness
that meets the mechanical stability requirements.
Due to the ultrahigh electron transmissivity in awide electron energy range, high electrical conductivity, and high chemical stability of suspended graphenic
carbon membranes, their use as a vacuum window material is currently being explored, and they are being
implemented in ﬁelds such as electron microscopy and
X-ray photoelectron spectroscopy. In a recent development, a novel x-ray transmission window based onpolycrystalline graphene or graphenic carbon (GC) has
been developed1,2) as a replacement for the beryllium
transmission windows in X-ray detectors. A maximum
burst pressure of about 0.5–0.6 MPa at a window thickness of 1 µm and a diameter of 7.5 mm has been reported in Ref. 2).
The work outlined here aims intended to explore
the outstanding mechanical properties demonstrated
by the above-mentioned GC X-ray window within thecontext of hadron beams. As the ﬁrst step, diﬀerent aspects of irradiation-induced damage in the material were investigated in detail using 200 particle nA,
5 MeV/nucleon 20 Ne ion beam from the AVF accelerator at RIKEN. GC samples were placed at the E7Btarget position and irradiated. The total dose of eachirradiation procedure was quantiﬁed by measuring thebeam current with an accuracy of 5%. A collimator slitof a 3 mm width was used to limit the beam size on thesamples. A Faraday cup downstream of the collimator
was used to quantify the ﬂuence.
∗1
∗2
∗3
∗4
∗5
∗6

GSI Helmholtzzentrum für Schwerionenforschung
RIKEN Nishina CenterTohoku UniversityKyoto University
RIKEN CPR
University of MünsterFig. 1. (a) Non-irradiated sample. Foil irradiated at
200 particle nA for (b) 1 h 51 min at a total fluenceof 9.7 × 1016 particles/cm2 , (c) 3 h 30 min at a total
fluence of 2.1 × 1017 particles/cm2 , and (d) 10 h at a
total fluence of 2.1 × 1017 particles/cm2 . Although thebeam was collimated using a 3 mm collimator slit, theobtained beam spot was “comma” shaped with a nonuniform intensity distribution. This is reflected in theshape of the beam-induced compaction (marked withred dotted curves).

Five graphenic carbon samples of thickness 1 µm anddiameter 7.5 mm were irradiated for diﬀerent time intervals (ﬂuences ranging from 9.7 × 1016 particles/cm2
to 9.7 × 1017 particles/cm2 ) to study the evolution ofirradiation-induced structural change.
The foil could mechanically withstand a 200 particle nA DC beam up to 10 h. A detailed investigation of
the eﬀects of irradiation-induced damage in the material is ongoing at the University of Münster and at GSI
using Raman spectroscopy, scanning and transmission
electron microscopy, and nanoindentation.
The next step will be to evaluate the performance
under pressure during the irradiation under a diﬀerential helium pressure of 0.2 MPa across the membranes
while monitoring the evolution of helium leakage. Thiswill check the feasibility of the GC vacuum window as
a candidate for hadronic ion beams.
References
1) S. Huebner et al., MRS Adv. 1.20, 1441 (2016).
2) S. Huebner et al., IEEE Trans. Nucl. Sci. 62.2, 588(2015).

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