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Optical and surface characterization of the copper mirrors: ~a! dependence of specular reflectivity on wavelength and ~b! elemental distribution along the depth for the copper mirror exposed at 1608C in the remote area of DIII-D; ~c! a view of the part of copper mirror after exposure at 3508C, the lighter color represents a virgin surface of copper; ~d! dependence of specular reflectivity on wavelength and ~e! elemental distribution along the depth for the copper mirror exposed at 3508C in the main chamber of DIII-D.
Source publication
Thermo-oxidation is controlled exposure in an oxygen-containing atmosphere at elevated temperature and is being considered as a technique for the de-tritiation of carbon-based codeposits in ITER. In addition, unplanned oxidation may also occur during accidental air ingress. The impact of thermo-oxidation on ITER diagnostic mirrors causes concerns....
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The First Mirror Test for ITER has been carried out in JET with mirrors exposed during: (i) the third ILW campaign (ILW-3, 2015–2016, 23.33 h plasma) and (ii) all three campaigns, i.e. ILW-1 to ILW-3: 2011–2016, 63,52 h in total. All mirrors from main chamber wall show no significant changes of the total reflectivity from the initial value and the...
Citations
... Other studies suggest that oxidation of molybdenum in water vapor environments begins below 450 • C [17]. Thermo-oxidation of Mo mirrors, at different levels of oxygen exposure, was also checked in [18]. In contrast, Rh exhibits resistance to oxidation at very high temperatures. ...
Abstract—The need for a steam ingress environmental experiment
is very significant to understand the impact of accidental
in-vessel coolant leaks at ITER and to study the exposure of
optical diagnostics to steam and humid conditions. This could
happen as a result of the damage to the cooling pipes due
to runaway electrons generated during plasma disruptions in
ITER. In order to know the scope of this potential impact,
an assessment was carried out to simulate and to study the
exposure of optical elements to strong and hostile moisture
conditions. After test, different measurements on optical mirrors
were performed to characterize the reflectance properties,
observed both in the visible and infrared spectral ranges, as well
as the analysis of wavefront error, coating adherence test, and
X-ray spectroscopy. Modification of properties and fluctuations
in the physical behavior of optical materials and components
were observed. Substrates and coatings were affected at different
levels due to corrosion and oxidative depositions that modify their
optical performances. In general, there are large differences in the
results obtained for the same material manufactured by different
manufacturing processes. Steam and humidity affected, especially
substrates and metal coatings. Substrates made of silicon carbide
and stainless steel were the least affected by corrosion. Rhodium
coating suffered less damage than the molybdenum coating.
... By means of the manipulator systems or dedicated mirror stations expositions studies on the selection of candidate material have been performed The tokamaks EAST [292], DIII-D [293,294] and TEXTOR [295][296][297] among others [298][299][300][301][302] have participated in these studies. 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]. ...
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.
... The reflectivity of metal mirrors without a transparent coating is negligibly affected by the deposition of few nanometers of Be or W. The absorption bands, however, may also appear in their optical spectra if the oxide top layer is eventually formed. As shown in [21] the oxide film formed on the surface of molybdenum and copper mirrors subjected to thermooxidising in O-baking experiments in DIII-D may reach dozens of nanometers in thickness. Metal mirrors can also be easily oxidised during accidental events like air ingress or water leaks. ...
Almost all optical diagnostic systems in ITER will require the implementation of mirror
recovery and protection systems. Plasma cleaning is considered to be the most promising
technique for the removal of metal deposits from optical surfaces. The engineering and
physical aspects of RF discharge application for continuous or periodic plasma treatment are
discussed with a focus on implementation under ITER conditions. The ion flux parameters
obtained in capacitively coupled (CC) RF discharge were measured in the mock-up of a
plasma cleaning system. The uniformity of sputtering in CC RF discharge with and without a
magnetic field was studied experimentally for the cylindrical discharge reactor geometry and
compared with numerical simulations. The sharp increase in the sputtering rate resulting from
the non-uniform radial distribution of the ion flux was observed near the electrode edges. The
longitudinal magnetic field improves sputtering uniformity. It was demonstrated that
Al/Al2O3 deposits can be removed in the Ne and D2 plasma of CC RF discharge but longterm
exposition results in the degradation of the polycrystalline molybdenum mirror surface.
The efficiency of Al sputtering in the atmosphere containing O2 and N2 fractions was studied
in the D2/O2 and D2/N2 plasma of glow discharge. The addition of 2% of oxygen or nitrogen
increases the sputtering yield by 3–4 times as compared with that in a nominally pure D2
discharge. The impact of metal deposits on the performance of diagnostic mirrors is discussed.
It was shown that an ultrathin metallic film with a thickness as low as a few nm may cause a
significant degradation of diagnostic mirrors with a transparent coating.
The need for a steam ingress environmental experiment is very significant to understand the impact of accidental in-vessel coolant leaks at ITER and to study the exposure of optical diagnostics to steam and humid conditions. This could happen as a result of the damage to the cooling pipes due to runaway electrons generated during plasma disruptions in ITER. In order to know the scope of this potential impact, an assessment was carried out to simulate and to study the exposure of optical elements to strong and hostile moisture conditions. After test, different measurements on optical mirrors were performed to characterize the reflectance properties, observed both in the visible and infrared spectral ranges, as well as the analysis of wavefront error, coating adherence test, and X-ray spectroscopy. Modification of properties and fluctuations in the physical behavior of optical materials and components were observed. Substrates and coatings were affected at different levels due to corrosion and oxidative depositions that modify their optical performances. In general, there are large differences in the results obtained for the same material manufactured by different manufacturing processes. Steam and humidity affected, especially substrates and metal coatings. Substrates made of silicon carbide and stainless steel were the least affected by corrosion. Rhodium coating suffered less damage than the molybdenum coating.
In April 2010, two thermo-oxidation experiments ('O-bakes') were performed in the DIII-D tokamak. Internal surfaces of the tokamak, as well as a number of specimens inserted into the torus, were exposed to a mixture of 20% O2/80% He at a nominal pressure of 9.5 Torr (1.27 kPa) at a temperature of 350–360 °C for a duration of 2 h. Three primary conclusions have been drawn from these experiments: (1) laboratory measurements on the release of deuterium from tokamak codeposits by oxidation have been duplicated in a tokamak environment, (2) no internal tokamak components or systems were adversely affected by the oxidation and (3) the recovery of plasma performance following oxidation was similar to that following regular torus openings.
