KU1 Quartz Glass Research Articles

Radiation hardening and optical properties of materials based on SiO2

Preliminary studies have shown that the optical absorption spectra of radiation-colored glasses correspond to the spectral behavior of the scattering losses of an optically inhomogeneous medium. The reasons for the same optical changes in glasses of different compositions are the radiation-induced electric charge separation in the structurally nano-inhomogeneous glass volume, polarization and formation of nanometer optical inhomogeneities. The authors of this work prove that the radiation changes in the mechanical and optical properties of silicate glasses are of the same nature. The performed estimates indicate that the electric charge separation in the glasses occurs up to absorbed doses of about 1 MGy. The local electric charge separation due to the appearance of Coulomb forces leads to radiation hardening of the glasses. The estimated Coulomb hardening of the quartz glasses was ~ 107 Pa. The theoretical results were experimentally confirmed by measuring the mechanical properties of the glasses under high intensity proton irradiation as well as by testing the mechanical strength of a composite material based on quartz glass. Under proton irradiation with a dose rate of 5×103 Gy/s (energy of 8 MeV) up to threshold doses of ~ (1 – 5) ×106 Gy in the KU-1 quartz glasses, the decrement of acoustic vibrations decreased due to Coulomb hardening. After gamma irradiation with 1.34×105 Gy, the tensile strength of the composite material based on quartz glass increased by up to 20 MPa. This value is in the range of estimates of Coulomb hardening of quartz glasses. It is also shown that ionizing radiation does not affect the elastic modulus of materials based on SiO2.

Infrared Spectra of KU1 and KS-4V Quartz Glass Irradiated by Fast Neutrons

IR absorption spectra of quartz glass with varying contents of hydroxyl OH groups, namely, KU1 (1000 ppm OH) and KS-4V (≤0.1 ppm OH) are compared prior to and after exposure to fast neutron fluences of 1018–5 × 1019 cm–2. The appearance of the IR absorption band of 2260 cm–1 regardless of the large difference in the content of OH groups in nonirradiated KU1 and KS-4V glass is related to the bending vibrations of the bridging ≡Si−O−Si≡ bonds. A decrease in the amplitude of the band at 2260 cm–1 and shift of its maximum by 20 cm–1 to the IR range is caused by the decrease in the bridging ≡Si−O−Si≡ bond angle with the growth of the neutron fluence. The asymmetric band at 3674 cm–1, which is related to OH groups, is observed only in nonirradiated KU1 glass. An increase in the number of OH groups in KU1 glass and the formation of OH groups in KS-4V glass after the accumulation of the neutron fluence of ≥1019 cm–2 rationalizes the slow accumulation of the intrinsic defects such as nonbridging oxygen atoms and oxygen vacancies in both brands of the glass in the range of the neutron fluence.

Influence of the temperature of treatment of KU-1 quartz glass on the value of the elastic recovery of a microindentation imprint

The influence of the treatment temperature of KU-1 quartz glass on the value of the elastic recovery of the microindentation imprint of a Vickers diamond tetrahedral pyramid is studied. It is found that the value of the elastic recovery of the imprint’s diagonal and the fracture resistance of quartz glass upon microindentation varies depending on the preliminary thermal treatment. The obtained experimental results are compared with the data reported by other authors.

Efficiency of generation of optical centers in KS-4V and KU-1 quartz glasses at neutron and gamma irradiation

Pure quartz glasses of KS-4V and KU-1 types are candidates for optical plasma diagnostic system in ITER. The purpose of experiment was to study the efficiency of defect production in these glasses under irradiation with 60Со γ-quanta (5.7Gy/s) dose range of 102–107Gy and the fission reactor neutrons in the fluency range of 1020–1023n/m2 and gammas simulating the plasma influence. In KU-1 (1000ppm OH) the accumulation kinetics of E′-(5.75eV) and NBO-(1.9eV) centers at γ-doses⩾5×105Gy and neutron fluencies <1021n/m2 is faster, than that in KS-4V glasses (<0.1ppm OH) that is caused by rupture of hydrogen bonds. At fluencies >1021n/m2 the NBO accumulation kinetics is slower in KU-1 than in KS-4B, because highly mobile hydrogen atoms access to the generated NBO centers. In KS-4V irradiated to γ-doses102–5×103Gy a new unstable absorption band at 1.8eV was found, which is caused by the glass synthesis conditions and alkali metal impurities. The transparency at 3.5–6.2eV at fluencies 1020–5×1021n/m2 is higher in KS-4V than KU-1. However at fluencies >1021n/m2 in KS-4V the photoluminescence band at 2.7eV is more intensive and distorts a diagnosed signal. The transparency in 3.5–1.2eV at fluencies >1021n/m2 is higher in KU-1 than KS-4V.

Measurements of the refractometric characteristics of optical materials in the 248–5000-nm spectral region

Numerical values have been obtained for the refractive indices of calcium fluoride, KU-1 quartz glass, germanium, silicon, and PO-4 ceramic, used in creating high-resolution photolithographic and aerospace optical systems for the 248–5000-nm spectral region. The results of measurements of the refractive index of a new optical material (Elastosil RT-604A silicone compound) in the 296–1800-nm region are presented. The technique of measuring the characteristics of optical materials in the 248–12 000-nm region is analyzed.

EPR study of gamma and neutron irradiation effects on KU1, KS-4V and Infrasil 301 silica glasses

Electron paramagnetic resonance (EPR) studies have been carried out on KU1 and KS-4V high purity quartz glasses and commercial silica Infrasil 301, irradiated with gamma rays up to a dose of 11.6MGy and neutron fluences of 1021 and 1022n/m2. Gamma irradiations produce a much higher concentration of defect centres (mainly E′, POR and NBOHC) for KU1 and I301 than for KS-4V silica. In contrast, neutron irradiation at the highest fluence produces similar concentrations in all silica types. These results agree to a good extent with those obtained in previous optical absorption measurements. Moreover, oxygen-related centres (POR and NBOHC) have been well characterized by means of electron paramagnetic resonance.

Vacuum ultraviolet excitation spectra of the 1.9 eV luminescence in neutron irradiated KU1 and KS-4V quartz glasses and Infrasil 301

The photoluminescence emission around 1.9 eV, excited from the ultraviolet to vacuum ultraviolet was investigated in neutron irradiated silica (at 1021 and 1022 n/m2 fluences) with different OH and impurity content: KU1 and KS-4V high purity silica and Infrasil 301. The measurements were made at different temperatures from 300K to 10K. The three irradiated silica grades show similar excitation spectra shape, although the band intensities are different depending on silica grade and temperature. Neutron irradiated KU1, with the highest OH content, shows the highest red emission attributed to nonbridging oxygen hole centers (NBOHCs). The excitation profile, from 4.0 to 8.8 eV, has two bands, which are centered around 4.85 eV and 6.5 eV. The band intensities increase with decreasing temperature from 300 to 10K for the three types of silica.

Neutron irradiation effects on optical absorption of KU1 and KS-4V quartz glasses and Infrasil 301

In this work we have compared the effects of neutron (10 21–10 22 n/m 2 fluences) and gamma irradiation (23.8 MGy dose) on the IR–vis–UV optical absorption spectra of high purity silica with different OH content: KU1 (∼800 ppm), KS-4V (<0.2 ppm), and commercial silica Infrasil 301 (<8 ppm). The results show that the UV–vis optical degradation of the silica, after neutron irradiation at the highest fluence is similar for the three grades studied, while gamma-induced optical absorption depends on the material grade (KS-4V shows the lowest optical absorption). The effects of both types of radiation on the IR band related with the hydroxyl group (3650 cm −1) depend on the silica grade. For KU1, the shape of this band changes with neutron fluence. For Infrasil 301 gamma and neutron irradiated, this band height increases, possibly due to free molecular or hydrogen atoms. The shift to lower energies observed for the 2260 cm −1 band in the three neutron irradiated silica grades, reflects the changes induced by neutrons in the lattice bonding angle distribution.

Radiation induced absorption and luminescence of selected alternative radiation resistant glasses

Two types of multicomponent glasses, 75% SiO 2: Na, Ca, one 0.05% Ce doped, have been studied in terms of radioluminescence, radiation induced optical absorption, and photoluminescence. The samples were irradiated with 1.8 MeV electrons at different temperatures and dose rates. During irradiation radioluminescence and optical absorption measurements were performed at different doses. The results show that both types of glasses are highly sensitive to radiation damage. For irradiation at 200 °C, some improvement is observed, but the behaviour of these glasses is worse than for KU1 quartz glass.

Thermal stability of neutron irradiation effects on KU1 fused silica

Optical absorption spectra of neutron irradiated (1021n/m2 and 1022n/m2) KU1 quartz glass samples have been measured. The effects of post-irradiation isochronal thermal annealing, up to 850°C, have been investigated. The general effect of the isochronal annealing is a decrease in the optical absorption bands as the temperature increases. Optical absorption bands have been identified with known defects from the literature, and their concentration temperature dependence has been analyzed. While the annealing curves of the E′ and non-bridging oxygen hole centres (NBOHC) are similar, that corresponding to oxygen deficiency centres (ODC(II)) is quite different suggesting that the recombination of E′ and NBOHC is part of the same process whereas the recombination of ODC is controlled by the presence of another undetected defect.

Radiation resistance of optical materials for windows of UV and VUV excimer lasers

The behaviour of modern quartz glasses and fluo-rite is studied experimentally under a prolonged action of the 280-keV electron beam pulses and an overall fluence of up to ∼30 kJ cm-2. The induced absorption in all investigated mate-rials saturates with increasing the fluence. The maximum variation of transmission in high-purity CaF2 samples does not exceed 5%–10% in the wavelength range 120–1000 nm. Quasi-stationary absorption in the region of ∼180–300 nm in the KS-4V quartz glass sample is approximately four times smaller than that in the KU-1 quartz glass and half the value for Corning 7980 glasses.

Radioluminescence behaviour for electron irradiated KS-4V

KS-4V, a low OH silica, is being considered for use in different fusion applications such as diagnostic windows and remote handling optical transmission components. For these applications radioluminescence (RL) is an important issue. A systematic study of RL as a function of temperature, dose rate and dose has been made using 1.8 MeV electron irradiations. The behaviour has been compared with KU1 quartz glass (high OH content) and the results indicate that KU1 is much better than KS-4V in terms of RL. Intense RL bands associated with self trapped excitons are observed for KS-4V but not for KU1. Furthermore the KS-4V RL exhibits a complex dependence on irradiation temperature, however the RL intensity decreases with irradiation dose.

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.