TY - JOUR
T1 - Optical transmittance investigation of 1-keV ion-irradiated sapphire crystals as potential VUV to NIR window materials of fusion reactors
AU - Iwano, Keisuke
AU - Yamanoi, Kohei
AU - Iwasa, Yuki
AU - Mori, Kazuyuki
AU - Minami, Yuki
AU - Arita, Ren
AU - Yamanaka, Takuma
AU - Fukuda, Kazuhito
AU - Empizo, Melvin John F.
AU - Takano, Keisuke
AU - Shimizu, Toshihiko
AU - Nakajima, Makoto
AU - Yoshimura, Masashi
AU - Sarukura, Nobuhiko
AU - Norimatsu, Takayoshi
AU - Hangyo, Masanori
AU - Azechi, Hiroshi
AU - Singidas, Bess G.
AU - Sarmago, Roland V.
AU - Oya, Makoto
AU - Ueda, Yoshio
N1 - Funding Information:
The authors are very grateful to Y. Fujimoto for the opportunity to use an electronic furnace. This work was likewise supported by the Japan Society for the Promotion of Science (JSPS) through the Grants-in-Aid for Scientific Research (KAKENHI) Grant Number 15K18304.
Publisher Copyright:
© 2016 Author(s).
PY - 2016/10/1
Y1 - 2016/10/1
N2 - We investigate the optical transmittances of ion-irradiated sapphire crystals as potential vacuum ultraviolet (VUV) to near-infrared (NIR) window materials of fusion reactors. Under potential conditions in fusion reactors, sapphire crystals are irradiated with hydrogen (H), deuterium (D), and helium (He) ions with 1-keV energy and ∼ 1020-m-2 s-1 flux. Ion irradiation decreases the transmittances from 140 to 260 nm but hardly affects the transmittances from 300 to 1500 nm. H-ion and D-ion irradiation causes optical absorptions near 210 and 260 nm associated with an F-center and an F+-center, respectively. These F-type centers are classified as Schottky defects that can be removed through annealing above 1000 K. In contrast, He-ion irradiation does not cause optical absorptions above 200 nm because He-ions cannot be incorporated in the crystal lattice due to the large ionic radius of He-ions. Moreover, the significant decrease in transmittance of the ion-irradiated sapphire crystals from 140 to 180 nm is related to the light scattering on the crystal surface. Similar to diamond polishing, ion irradiation modifies the crystal surface thereby affecting the optical properties especially at shorter wavelengths. Although the transmittances in the VUV wavelengths decrease after ion irradiation, the transmittances can be improved through annealing above 1000 K. With an optical transmittance in the VUV region that can recover through simple annealing and with a high transparency from the ultraviolet (UV) to the NIR region, sapphire crystals can therefore be used as good optical windows inside modern fusion power reactors in terms of light particle loadings of hydrogen isotopes and helium.
AB - We investigate the optical transmittances of ion-irradiated sapphire crystals as potential vacuum ultraviolet (VUV) to near-infrared (NIR) window materials of fusion reactors. Under potential conditions in fusion reactors, sapphire crystals are irradiated with hydrogen (H), deuterium (D), and helium (He) ions with 1-keV energy and ∼ 1020-m-2 s-1 flux. Ion irradiation decreases the transmittances from 140 to 260 nm but hardly affects the transmittances from 300 to 1500 nm. H-ion and D-ion irradiation causes optical absorptions near 210 and 260 nm associated with an F-center and an F+-center, respectively. These F-type centers are classified as Schottky defects that can be removed through annealing above 1000 K. In contrast, He-ion irradiation does not cause optical absorptions above 200 nm because He-ions cannot be incorporated in the crystal lattice due to the large ionic radius of He-ions. Moreover, the significant decrease in transmittance of the ion-irradiated sapphire crystals from 140 to 180 nm is related to the light scattering on the crystal surface. Similar to diamond polishing, ion irradiation modifies the crystal surface thereby affecting the optical properties especially at shorter wavelengths. Although the transmittances in the VUV wavelengths decrease after ion irradiation, the transmittances can be improved through annealing above 1000 K. With an optical transmittance in the VUV region that can recover through simple annealing and with a high transparency from the ultraviolet (UV) to the NIR region, sapphire crystals can therefore be used as good optical windows inside modern fusion power reactors in terms of light particle loadings of hydrogen isotopes and helium.
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U2 - 10.1063/1.4965927
DO - 10.1063/1.4965927
M3 - Article
AN - SCOPUS:84991768879
VL - 6
JO - AIP Advances
JF - AIP Advances
SN - 2158-3226
IS - 10
M1 - 105108
ER -