Plasma cleaning of ITER First Mirrors in magnetic field

Moser, L.; Steiner, Roland; Leipold, F.; Reichle, R.; Marot, L.; Meyer, Ernst

doi:10.1016/j.jnucmat.2014.11.087

Cited by 38 publications

(27 citation statements)

References 11 publications

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“…In the case of ITER, the working temperature range of the divertor starts around 345 K, making our study fully relevant. Additionally, a better knowledge of tungsten properties (optical and mechanical) is needed in order to prevent security issues or failing of aerospace missions [53][54][55][56].…”

Section: Discussionmentioning

confidence: 99%

The temperature dependence of optical properties of tungsten in the visible and near-infrared domains: an experimental and theoretical study

Minissale¹,

Pardanaud²,

Bisson³

et al. 2017

J. Phys. D: Appl. Phys.

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The knowledge of optical properties of tungsten at high temperatures is of crucial importance in fields such as nuclear fusion or aerospace applications. The optical properties of tungsten are well known at room temperature, but little has been done at temperatures comprised between 300 K and 1000 K in the visible and near-infrared domains. Here we investigate the temperature dependence of tungsten reflectivity from the ambient to high temperatures (<1000 K) in the 500-1050 nm spectral range, a region where interband transitions have a strong contribution. Experimental measurements, performed via a spectroscopic system coupled with a laser remote heating, show that the tungsten reflectivity increases with temperature and wavelength. We have described these dependences through a Fresnel and two Lorentz-Drude models. The Fresnel model reproduces accurately the experimental curve at a given temperature, but it is able to simulate the temperature dependency of reflectivity only thanks to an ad hoc choice of temperature formulae for the refractive indexes. Thus, a less empirical approach is preferred based on Lorentz-Drude models to describe the interaction of light and charge carriers in the solid. The first Lorentz-Drude model, which includes a temperature dependency on intraband transitions, fits experimental results only qualitatively. The second Lorentz-Drude model includes in addition a temperature dependency on interband transitions. It is able to reproduce quantitatively the experimental results, highlighting a non-trivial dependence of interband transitions as a function of temperature. Eventually, we use these temperature dependent Lorentz-Drude models to evaluate the total emissivity of tungsten from 300 K to 3500 K and we compare our experimental and theoretical findings with previous results.

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Section: Discussionmentioning

confidence: 99%

The temperature dependence of optical properties of tungsten in the visible and near-infrared domains: an experimental and theoretical study

Minissale¹,

Pardanaud²,

Bisson³

et al. 2017

J. Phys. D: Appl. Phys.

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“…The authors of [74,75] investigated the cleaning of a mirror surface from a deposit composed of Al, Al 2 O 3 , and W by the use of plasma with as working gas: Ar, Ne or a Ar+D 2 mixture. The most effective in this respect was the Ar plasma produced by a RF capacitively coupled discharge (at frequency 13.56 MHz) with the test mirror utilized as an electrode.…”

Section: Removal Of Deposited Filmmentioning

confidence: 99%

“…In some cases a full cleaning of deposits with initial reflectance restoration was achieved. For the first time a mirror with a size (98 mm in diameter) close to the size of a real first mirror in ITER was successfully cleaned from deposition by a 260 nm thick Al/Al 2 O 3 film on its surface [74]. This result is very important when considering the prospects for application of both these techniques (laser and plasma) to remove the contaminating layers from mirror surfaces in ITER environment.…”

Section: Removal Of Deposited Filmmentioning

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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“…It uses the mirror itself as the driven electrode, allowing good coupling of the cleaning plasma to the mirror surface, can build on the industrial experience with RF plasmas and has shown in lab experiments to be able to clean both small and large surfaces [7,8,10]. Also tests in magnetic field have been performed [11]. Figure 2 shows a sketch of the principle of RF discharge cleaning on the left and the total and diffuse reflectivity of both a pristine single crystalline molybdenum mirror (i.e.…”

Section: Jinst 11 P08010mentioning

confidence: 99%