KU1 Quartz Research Articles

Studies on proton irradiation-induced modifications of KU1 and KS-4V quartz glasses ultraviolet transmission properties

KU1 and KS-4V quartz glasses, known to be radiation-resistant insulator materials, are potential candidates for manufacturing diagnostics windows and optical fibres for ITER. KU1 and KS-4V quartz glass samples were irradiated with 12.6 and 14 MeV protons, respectively, at the Bucharest Tandem accelerator to simulate ionization and displacement damage and study the ultraviolet (UV) transmission properties modification. The proton irradiations produce absorption bands in KU1 at 215 and 265 nm, and in KS-4V at 215 and 245 nm, which saturate by about 10 MGy. This behaviour is very similar to results obtained for gamma, electron, and neutron irradiations, highlighting the importance of ionization, and indicating that proton irradiations may be used to simulate low dose neutron (⩽10 20 n/m 2) irradiations.

Radiation-optical characteristics of quartz glass and sapphire

The systems registering plasma radiation comprise optical elements, which may distort a diagnostic signal if they are not radiation resistant. The work was aimed at experimental study of optical absorption and γ-induced luminescence of KU-1 quartz glass and sapphire crystals in the range of 200–900nm, which were irradiated in the 60Co γ-ray source of 6.7Gys−1 up to the dose of 108Gy and in the water cooled nuclear reactor of WWR-SM type with neutron fluences of 1017–1020cm−2, in order to imitate plasma effect. The transparency window (minimal optical losses) and the intrinsic luminescence bands were determined in the studied materials. The advantages of KU-1 type glass over sapphire as optical elements at 300–350K have been demonstrated.

Studies on proton irradiation-induced modifications of KU1 quartz glass ultraviolet transmission properties

The optical transmission components of the future thermonuclear reactor will be expected to maintain their transmission properties under high levels of ionizing radiation for hundreds of hours. The degradation of the optical transmission properties of the candidate materials has to be studied to assess the lifetimes of such systems. KU1 quartz glass, known to be a radiation-resistant insulator material, is a potential candidate for manufacturing diagnostics windows and optical fibers for the ITER project. Some KU1 samples were irradiated with 12.6 MeV protons in the Bucharest Tandem accelerator to study their ultraviolet (UV) transmission properties modification. In the absorption spectra, the presence of a 215 nm peak and a big reduction of the 260 nm peak were observed. The effects of the 12.6 MeV proton irradiation on KU1 quartz glass optical properties were compared with the effects on similar KU1 samples irradiated with gammas and high-energy electrons at CIEMAT, Madrid. The comparison led to the conclusion that the saturation effect in absorption for proton is obtained at a 10 MGy irradiation dose, while the same effect is obtained at 4–5 MGy for gamma rays and 11–12 MGy for electrons, suggesting that the ionization process is essential for the formation of defect absorption centers.

Laser damage of KU-1 quartz glass coated with hydrocarbon films

Abstract The effect of high power pulsed YAG:Nd laser radiation on KU-1 quartz glass coated with CH- and CD-films of different thickness and properties has been investigated experimentally. The laser energy densities for film ablation and optical breakdown of glasses coated with the films have been determined. The film cleaning thresholds have been found to be in the range of 0.1–0.3 J/cm2, whereas the optical breakdown thresholds were as high as 50–70 J/cm2. All measurements have been performed in atmosphere.

Temperature dependence of the transmission loss in KU-1 and KS-4V quartz glasses for the ITER diagnostic window

Quartz glasses of KU-1 and KS-4V are candidate window materials for the ITER optical diagnostics in UV and visible range. The temperature dependence of the radiation-induced transmission losses in UV range has been investigated under γ-ray irradiation for the KU-1 and KS-4V quartz glasses up to 10 MGy. The KU-1 and KS-4V quartz glass samples were irradiated at room temperature, 100, 200 and 300 °C. Dose rate was 0.46–1.1 MGy, and 2.6 Gy/s from 1.1 to 10.4 MGy. It was confirmed that there is no significant loss in wavelength range longer than 350 nm for both window materials. Transmission loss in KU-1 is larger than that in KS-4V under temperature below 200 °C. KU-1 has large temperature dependence. On the other hand, temperature dependence is not clear in KS-4V above 100 °C. Prominent recover of the transmission loss was not observed after irradiation for each sample. From the transmission loss point of view, KS-4V is better window material than KU-1 at temperature below 200 °C. KU-1 is available at 300 °C.

KU1 and KS-4V quartz glass lenses for remote handling and diagnostic optical transmission systems

Radiation resistant KU1 and KS-4V quartz glasses are candidate ITER materials for remote handling and diagnostic optical transmission components such as windows, lenses, and optical fibres. 60Co gamma irradiations at different temperatures have been carried out to study ionizing radiation effects on refractive index, optical absorption, and the quality of lenses made from KU1 and KS-4V. No effect has been observed on the refractive index of KU1 for irradiations up to 100 MGy and temperatures up to 170 °C. Lenses made from both materials show acceptable quality before and after irradiation. Irradiation induced absorption is confined to the blue and UV region, however, KS-4V shows anomalous behaviour with irradiation temperature. In situ 1.8 MeV electron irradiations have been used to clarify this anomalous absorption.

Laser induced damage enhancement due to stainless steel deposition on KS-4V and KU1 quartz glasses

LIDAR (light detection and ranging) diagnostic systems for fusion devices will require windows with extremely high transmission in the visible range as a consequence of the use of high power lasers. Within the ITER diagnostics programme, KU1 and KS-4V quartz glasses (OH contents: 800–900 ppm for KU1 and <0.2 ppm for KS-4V) are being examined for such applications. A comparison between the two materials has been carried out in terms of laser induced damage and it was observed that both materials exhibited almost identical behaviour. Laser induced damage enhancement due to stainless steel deposition on both materials has been studied, as well as the possibility of `in situ' cleaning. Important differences between sputtered and evaporated layers, as well as type of material deposited, were observed.

Highly radiation resistant KU1 quartz glass

Radiation induced optical absorption and radioluminescence impose important limitations on the use of any optical materials under ionizing radiation. Optical transmission of a type of high purity silica glass, KU1 quartz glass, has been studied under radiation (gamma 60 Co and 1.8 Mev electrons). The results show that this material maintain their transmission properties, from 400 to 2600 nm under high levels of ionizing radiation and with atomic displacements, during long time. Also radioluminescence produced by electrons and radiation effect on laser damage in this material have been studied.

Surface degradation effects on laser damage in KU1 quartz glass windows for LIDAR applications

For LIDAR applications in fusion devices, surface degradation effects (erosion and deposition of a thin contaminating layer) on laser damage in KU1 quartz glass material has been assessed. To study surface quality effects, roughly polished samples have been examined. For surface deposition effects, thin gold layers were deposited by sputtering on to KU1 quartz samples in order to study the influence of the layer thickness on the laser damage probability. For the thinnest layer of 5 nm a decrease in threshold to produce laser damage by several orders of magnitude is observed, implying a serious risk of breakdown for the laser window from the onset of reactor operation.

In situ transmissivity measurements of KU1 quartz in the UV range under 14 MeV neutron irradiation

The transmissivity of KU-1 quartz which is a candidate of the window material for UV and visible spectroscopy in ITER was measured under the irradiation of 14 MeV neutrons up to the fluence of 7.4×10 19 n/m 2 in the UV range (200–400 nm). Significant transmission loss was observed in the wavelength range of 200–300 nm. Two absorption peaks were identified: an E ′-center at 215 nm and Si(III) defects at 245 nm. The E ′-center absorption is much larger than the Si(III) defect absorption. The transmission loss increased with the neutron fluence, decreased during the irradiation breaks and returned almost to the same level as before when the irradiation resumed. This phenomenon indicates that an absorption induced by the neutron irradiation is caused by stable scattering and short lifetime centers.

Electrical and dielectric properties of irradiated KU1 quartz glass from DC to 145 GHz

To characterize and examine the possible use of the KU1 quartz glass for both diagnostic and remote handling applications, the radiation induced conductivity and electrical degradation (RIC & RIED), together with dielectric loss and permittivity (10 mHz–145 GHz) have been determined for as-received, electron and neutron irradiated material. Results show that the RIC is extremely low (<10 −8 S/m compared with about 10 −7 S/m) for candidate oxide materials at the same dose rate, but markedly increases for doses up to about 3×10 −5 dpa while the conductivity without radiation is reduced with dose. Dielectric measurements from 1 kHz to 20 GHz during electron irradiation show that prompt effects are only observed at very low frequencies, consistent with the low RIC results. For neutron irradiation to 10 −4 dpa, post-irradiation measurements indicate a permanent increase in loss by up to a factor of 2 below 60 MHz. No effect is observed in the GHz range.

Irradiation Effects on Diagnostic Components for ITER.

Irradiation tests on many diagnostic components have been carried out as a part of the R&D program of the ITER Engineering Design Activities (EDA). Five kinds of ITER round robin fibers were irradiated in JMTR and60Co γ-rays. Induced transmission loss of those fibers are much smaller than that of pure SiO2 core fiber. Especially, KU-H2G from Russian Federation and F-doped fibers from Japan have rather good radiation hardness even in the visible range. Those fibers might be available in the diagnostic port of ITER. The transmissivity of KU-1 quartz, which is a candidate of the window material for UV and visible spectroscopy in ITER, was measured under the irradiation of 14 MeV neutrons and γ-rays in the UV range (200 - 400 nm). Significant transmission loss was observed in the wavelength range of 200-300 nm. The Mica substrate bolometer was irradiated in JMTR during three irradiation cycles. Total neutron fluence was about 1×1024 n/m2 which was equivalent to 0.1 dpa. Significant increase in the meander resistance was observed, which was causedby the nuclear transmutation of gold into mercury. The use of gold meanders might be problematic in ITER.

Neutron irradiation tests on diagnostic components at JAERI

As a part of the R&D program of the ITER Engineering Design Activities (EDA), we have carried out irradiation tests on a number of diagnostic components. In this paper the recent results of neutron irradiation tests on diagnostic windows, bolometer substrates and magnetic coils at JAERI are described. UV range transmission losses of a KU-1 quartz glass were measured during 14 MeV neutron irradiation at the Fusion Neutronics Source (FNS) with neutron fluences of up to 7.4×10 19 n/m 2. Significant transmission losses were observed in the wavelength of 200–300 nm. Mica substrates of bolometers were irradiated at the Japan Material Testing Reactor (JMTR) with neutron fluence between 1×10 22 and 2.2×10 23 n/m 2. The size expansion was found to be only 0.13% at 2.2×10 23 n/m 2 and 150 °C, which gives us the good prospect of the bolometer in the ITER-FEAT application. Magnetic coils made with four kinds of Mineral Insulated (MI) cables have been irradiated in JMTR up to a fast neutron fluence of 1.1×10 24 n/m 2. Radiation Induced Electrical Motive Force (RIEMF) of several volts was observed between core inductor and sheath of the MI cable.

Investigation of the Effect of Radiation and High-Temperature Treatment on the x-Ray Luminescence of Quartz Glasses

The x-ray luminescence of KI, KV, and KU-1 quartz glasses, irradiated with γ and n–γ radiation in the dose range 102–107 Gy and neutron fluence range 1015–1017 cm–2 and subjected to high-temperature annealing in air at 450 and 900°C is investigated. It is shown that the spectra of the nonirradiated and the γ and n–γ irradiated glasses of the first two types are a superposition of bands with λmax = 410 and 460 nm, which are due to an impurity center initially present in the glasses (λmax = 410 nm) and the initial and radiation-generated with dose ≥106 Gy and fluence ≥1016 cm–2E' centers (λmax = 460 nm). X-Ray luminescence is not observed in nonirradiated KU-1 glasses; a band with λmax = 460–470 nm, due to radiation-generated E' centers, appears in the spectra of γ and n–γ irradiated glasses. As the γ radiation dose and the neutron fluence increase, the number of impurity centers decreases and the number of E' centers increases. It is established that the 410 nm band is due to the γ component of the n–γ radiation. High-temperature annealing in air at 900°C induces in the spectra new bands with λmax = 470 and 520–540 nm, which are believed to be due to interstitial defects of the type O– and O2–, formed when oxygen from air diffuses into the glass and localizes in interstices. 6 figures, 7 references.

KU1 quartz glass for remote handling and LIDAR diagnostic optical transmission systems

KU1 quartz glass, a radiation-resistant material, is being considered for use in different fusion applications such as remote handling optical transmission components and diagnostic windows. Gamma ( 60Co) and 1.8 MeV electron irradiations have been carried out to study the ionizing radiation-induced optical absorption in this material. The results show that while the optical absorption induced by irradiation in the KU1 silica is acceptable for the remote handling optical transmission components, this is not the case with diagnostic window applications, where background absorption may pose a problem for LIDAR. However, this disadvantage may be minimised by pre-irradiation at about 200°C.

Radiation effects on laser damage in KU1 quartz glass

Both in-beam and post-irradiation effects on laser damage have been studied for three different materials: high purity UV grade sapphire, common glass and KU1 quartz glass. No in-beam effects have been observed. Notable changes in the laser damage sensitivity due to the accumulated dose occur in common glass and KU1 quartz glass, but not in sapphire. KU1 quartz glass becomes less sensitive with increasing dose, and one concludes that this material may be used as a window for LIDAR systems at dose rates of at least 70 Gy/s, to total doses of up to 100 MGy.

Luminescence kinetics in proton-irradiated quartz glasses

It is experimentally demonstrated that the intensity of the radiation-induced luminescence (RIL) of KU-1 and KI quartz glasses at 450 nm increases more than ten times upon the proton irradiation (proton energy, 8 MeV; dose rate, 5×103 Gy/s; dose, up to 1.2×107 Gy) to a dose of 106 Gy. At a dose exceeding 106 Gy, the spectral efficiency of the ionizing radiation energy conversion reached ∼10−6 nm−1 in the maximum of the RIL band at 450 nm for all types of glasses. After preliminary low-rate γ-irradiation (below 0.5 Gy/s), the RIL intensity in the beginning of the proton irradiation and its variation with the proton dose depend on the concentration of impurities in the quartz glass. The RIL intensity buildup depends on the formation of positively and negatively charged microscopic regions in glasses.

Transient optical phenomena in quartz fibers under high-power pulsed reactor irradiation

Measurements of the intensity of emission and induced optical absorption at 400–750 nm in KU-1 quartz fibers were performed under pulsed irradiation in a BARS-6 reactor (pulse duration, 80 μs; dose per pulse, up to 5×1012 neutrons/cm2 (E>0.2 MeV); dose rate, up to 105 Gy/s). The nondelayed emission component is due to the Cerenkov radiation, the weak relaxation component has a relaxation time of ∼150±50 μs, and the radiation-induced optical absorption reaches a value of 2.5×10−4 cm−1 (relaxation time, 600–1200 μs). A nonlinear dependence of the Cerenkov radiation on the dose rate and the presence of the relaxation emission component and the transient optical absorption may be associated with an optical inhomogeneity of glass induced by the high-power reactor irradiation.

Radiation induced optical absorption and radioluminescence in electron irradiated SiO 2

Optical absorption and radioluminescence spectra from 2000 to 8000 Å have been measured for two different types of SiO 2 (Anhydroguide silica and KU1 quartz glass) irradiated at ionizing and displacement dose rates, and temperatures of relevance for ITER optical diagnostic components. Radioluminescence intensity has been quantified in terms of photon emission and shown to be up to two orders of magnitude less than that found earlier for high purity sapphire. Cherenkov radiation sets a lower limit on the radioluminescence intensity for these SiO 2 materials. On the other hand optical absorption is considerably higher for the SiO 2 materials than for sapphire. Considerable advantage may be obtained by operating these materials at about 300°C.

Time variation of the optical absorption of quartz KU-1 induced by gamma irradiation

The induced optical absorption in KU-1 quartz glass under gamma irradiation at the electron accelerator LU-10-20 was measured. It was shown that the absorption in the UV spectral region varies very quickly during the first few minutes after the start and after the interruption of the irradiation. In the middle and red parts of the visible spectrum the sample transparency changes very slowly or does not change at all.