Studies of protection and recovery techniques of diagnostic mirrors for ITER

Litnovsky, A.; Matveeva, Maria; Buzi, L.; Vera, Liliana; Krasikov, Yu.; Kotov, V.; Panin, A.; Wienhold, P.; Philipps, V.; Bardawil, D.A. Castaño; Akiyama, Tsuyoshi; Biel, W.; Neubauer, O.; Mertens, Philippe; Linsmeier, Ch.; Reiter, D.; Börner, P.; Freisinger, M.; Richter, Silvia

doi:10.1088/0029-5515/55/9/093015

Cited by 12 publications

(9 citation statements)

References 19 publications

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“…Various methods including thermooxidative wall conditioning [303] or seeding of gas as a protective method have been evaluated [304]. It was shown by experiment and modeling that passive methods like shaped ducts and introduction of fins can mitigate the particle flux and hence the damage behavior [305][306][307]. Dedicated mirror test stations have been installed in several tokamaks while a coordinated effort was undertaken to select materials [292,301,308,309].…”

Section: Erosion-migration-depositionmentioning

confidence: 99%

Material testing facilities and programs for plasma-facing component testing

et al. 2017

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Component development for operation in a large-scale fusion device requires thorough testing and qualification for the intended operational conditions. In particular environments are necessary which are comparable to the real operation conditions, allowing at the same time for in situ/in vacuo diagnostics and flexible operation, even beyond design limits during the testing. Various electron and neutral particle devices provide the capabilities for high heat load tests, suited for material samples and components from lab-scale dimensions up to full-size parts, containing toxic materials like beryllium, and being activated by neutron irradiation. To simulate the conditions specific to a fusion plasma both at the first wall and in the divertor of fusion devices, linear plasma devices allow for a test of erosion and hydrogen isotope recycling behavior under well-defined and controlled conditions. Finally, the complex conditions in a fusion device (including the effects caused by magnetic fields) are exploited for component and material tests by exposing test mock-ups or material samples to a fusion plasma by manipulator systems. They allow for easy exchange of test pieces in a tokamak or stellarator device, without opening the vessel. Such a chain of test devices and qualification procedures is required for the development of plasma-facing components which then can be successfully operated in future fusion power devices. The various available as well as newly planned devices and test stands, together with their specific capabilities, are presented in this manuscript. Results from experimental programs on test facilities illustrate their significance for the qualification of plasma-facing materials and components. An extended set of references provides access to the current status of material and component testing capabilities in the international fusion programs.

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Section: Erosion-migration-depositionmentioning

confidence: 99%

Material testing facilities and programs for plasma-facing component testing

et al. 2017

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“…In [76] cleaning of an Al (80 nm)+Al 2 O 3 (20 nm) film deposited on a single crystal Mo mirror was realized by exposing it in the TOMAS toroidal facility operating with a steady-state ECR-generated He plasma (n e~3 ·10 10 cm -3 and T e~5 eV) at 2.45 GHz. The plasma ions were accelerated to the mirror by applying a negative voltage -100 V).…”

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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“…More than 20 optical diagnostics, operating in the UV/Vis range, are directly affected by this phenomena and will require mirror surface recovery techniques, currently foreseen in in situ plasma sputtering [4,5]. The removal of these deposits in order to increase the lifetime of the FMs has seen significant progress over the past years [6][7][8][9][10][11]. Nevertheless, it is to be noted that all of those experiments have been conducted either on carbon, outdated material for ITER's first wall, or on a Be proxy with similar chemical properties, namely aluminium [12].…”

Section: Introductionmentioning

confidence: 99%

Investigation and plasma cleaning of first mirrors coated with relevant ITER contaminants: beryllium and tungsten

et al. 2017

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In order to extend the investigation of the plasma cleaning of ITER first mirrors, a set of molybdenum mirrors was coated in a laboratory with ITER-relevant contaminants, namely beryllium and tungsten. Different coating techniques as well as several contaminant compositions were used to ensure a large variety of films to clean, completing a previous study conducted on mirrors exposed in the JET ITER-like wall (tokamak deposits) [1]. Due to the toxicity of beryllium, the samples were treated in a vacuum chamber specially built for this purpose. The cleaning was performed using capacitively coupled RF plasma and evaluated by performing reflectivity measurements, scanning electron microscopy, x-ray photoelectron spectroscopy and ion beam analysis. The removal of all types of contaminants was achieved by using different plasma compositions (argon, helium and mixtures of the two) with various ion energies (from 200-600 eV) and in some cases the mirror's reflectivity was restored towards initial values. Pure helium discharges were capable of removing mixed beryllium/ tungsten layers and oxidized molybdenum. In addition, no significant increase in the diffuse reflectivity of the mirrors was observed for the helium cleaning, though this was the case for some samples cleaned with argon. Helium is therefore appropriate for cleaning all mirrors in ITER leading to a possible cleaning regime where the entire vessel is filled with He and all mirrors are cleaned simultaneously without damaging their surfaces.

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Studies of protection and recovery techniques of diagnostic mirrors for ITER

Cited by 12 publications

References 19 publications

Material testing facilities and programs for plasma-facing component testing

Material testing facilities and programs for plasma-facing component testing

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

Investigation and plasma cleaning of first mirrors coated with relevant ITER contaminants: beryllium and tungsten

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