Assessment of Laser Transmission Mirror Materials for ITER Edge Thomson Scattering Diagnostics

Kajita, Shin; Hatae, T.; Voitsenya, V.S.

doi:10.1585/pfr.3.032

Cited by 9 publications

(1 citation statement)

References 26 publications

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“…However, for a long-term service life of the laser mirror the absolute value of F N is of importance, and in this relation copper has a significant advantage, viz., after 10 8 pulses its F 8 will be equal to ~1.0 J/cm 2 , whereas for the Mo mirror F 8 ≈ 0.4 J/cm 2 . A detailed analysis of different metals (Au, Ag, Cu, Ta, Rh, and Mo) as candidate materials for laser mirrors has been carried out in ref [82]. The results of numerical calculations have shown that copper is only slightly inferior to silver and gold in its optical and thermomechanical properties.…”

Section: Influence Of Recurrent Laser Pulsesmentioning

confidence: 99%

Experimental Simulation of the Behaviour of Diagnostic First Mirrors Fabricated of Different Metals for ITER Conditions

Voitsenya¹,

Bardamid²,

Donné³

2016

PHY

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In the experimental fusion reactor ITER, the plasma-facing component of each optical and/or laser diagnostic needs to be based on reflective optics with at least one mirror (first mirror) facing the thermonuclear plasma. The different kinds of radiation emanating from the burning plasma (neutrons, neutral atoms, electromagnetic radiation) create hostile operating conditions for the first mirrors. Therefore, a special program has been set up under the ITER framework aimed at solving the first mirror problem. This paper will review the main results in this field that have been obtained in the Institute of Plasma Physics, National Science Center “Kharkov Institute of Physics and Technology” (in many cases in cooperation with groups of other countries, as indicated in corresponding parts of the manuscript) during long-term investigations directed to find a solution of this problem,i.e., to find a material and accompanying precautions in order to satisfy the requirements for first mirrors. The main efforts were devoted to finding solutions to overcome the impact of the most severe deteriorating factors resulting in degradation of the optical properties of mirrors: sputtering by charge exchange atoms and deposition of contaminants. The obtained results are focused on: the effects of long term sputtering on mirror specimens fabricated from different metals with different structures (polycrystals, single crystals, metal film on metal substrates, amorphous), the effects of contaminating film and the possible protection to avoid of its appearance, the role of chemical processes for some metal mirrors, and the choice of material of laser mirrors.

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Section: Influence Of Recurrent Laser Pulsesmentioning

confidence: 99%

Experimental Simulation of the Behaviour of Diagnostic First Mirrors Fabricated of Different Metals for ITER Conditions

Voitsenya¹,

Bardamid²,

Donné³

2016

PHY

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Optical design for divertor Thomson scattering system for JT-60SA

Kajita

Enokuchi

Hatae

et al. 2014

Fusion Engineering and Design

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Degradation of optical reflectivity of in-vessel mirror materials by helium bombardment

Kajita

Saeki

Ohno

et al. 2011

Journal of Nuclear Materials

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(Nagoya univ.) Masayuki Tokitani (NIFS) In future experimental fusion devices, many in-vessel mirrors will be used for optical diagnostics. It is generally recognized that metallic mirrors are used for them, and the candidate materials for the first mirror are molybdenum, tungsten, copper, stainless steel, and rhodium. Although it has been found that neutron irradiation does not have a significant influence on the optical reflectivity, there is concern that the reflectivity decreases by the exposure to charge-exchange neutrals, which cause erosion and deposition. In the present report, we will show the effect of low-energy helium bombardment to molybdenum and rhodium from the experiments conducted in a linear plasma device.The experiments were performed in the linear divertor simulator NAGDIS (NAGoya DIvertor Simulator)-I. The specimens were exposed to the helium plasma in the NAGDIS-I. The surface temperature and incident ion energy were controlled by changing the helium flux to the specimen. The incident ion energy was controlled by electrically biasing the specimen, and was ~ 50 eV. The wavelength dependence of optical reflectivity was measured with a spectrophotometer (Nihon Bunkosya: ARV-47S) for the wavelength from 200 to 900 nm.Figure 1(a) shows the wavelength dependences of the optical reflectivity of Mo-1 and Mo-2. The irradiation temperatures for Mo-1 and Mo-2 are 1200 and 1500 K, respectively, and the helium ion fluences for Mo-1 and Mo-2 were 1.8×10 26 m -2 and 1.1×10 27 m -2 , respectively. The reflectivity considerably decreased by the surface modifications due to the helium irradiation. The optical reflectivity was less than 10% for Mo-1, whereas, for Mo-2, it decreased to almost zero. Non-uniformity of Mo-1 surface is effectively averaged for the reflectivity measurement, because the spot size in the measurement is much larger than the crystal grain. Figure 1(b) shows the reduction factor of the reflectivity for Mo-1. Here, the reduction factor was defined as the original reflectivity divided by the decreased reflectivity. At 900 nm, the reduction factor was approximately 5; it increased as decreasing the wavelength, and was 30 at 200 nm. In general, optical reflectivity is strongly altered when the size of the structure on the surface is less than several times the wavelength [1]. From Fig. 1(b), the size of the structure is less than 1 �m; moreover, there may exist much finer structure on the surface.Figure 2(a) shows the wavelength dependences of nonirradiated rhodium, helium irradiated rhodium (Rh-1), and helium irradiated molybdenum (Mo-3). The incident ion energy, surface temperature, and helium ion fluence for Rh-1 and Mo-3 were, respectively, 45 eV, 600 K, and 8×10 24 m -2 and 45 eV, 850 K, and 3.7×10 25 m -2 . The exposure to the helium plasmas also decreased the optical reflectivity significantly for both rhodium and molybdenum even at those temperatures. Figure 2(b) shows the reduction factors for Rh-1 and Mo-3. In both cases, the factor increases as decreasing the wavelength. Th...

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Assessment of Laser Transmission Mirror Materials for ITER Edge Thomson Scattering Diagnostics

Cited by 9 publications

References 26 publications

Experimental Simulation of the Behaviour of Diagnostic First Mirrors Fabricated of Different Metals for ITER Conditions

Experimental Simulation of the Behaviour of Diagnostic First Mirrors Fabricated of Different Metals for ITER Conditions

Optical design for divertor Thomson scattering system for JT-60SA

Degradation of optical reflectivity of in-vessel mirror materials by helium bombardment

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