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22-27 October 2018
Mahatma Mandir Conference Centre
Asia/Kolkata timezone

Dielectric windows as front-end diagnostic elements in ITER

23 Oct 2018, 08:30
Mahatma Mandir Conference Centre

Mahatma Mandir Conference Centre

Gandhinagar (nearest Airport: Ahmedabad), India
Poster FIP - Fusion Engineering, Integration and Power Plant Design P1 Posters


Mr Alexey Razdobarin (Ioffe Institute)


The performance of front-end elements of optical diagnostics in ITER under long-term operation and with limited access for their maintenance is in the focus of extensive R&D program involving laboratory study and testing in working tokamaks. The requirements to the front-end element design are driven by high-energy neutron and gamma radiation, intense particle fluxes and thermal loads at the element location on the one hand and necessity to provide periodic or continuous surface recovery on another. The insulating diagnostic window as an alternative to commonly accepted first mirror option is discussed in the presentation. The approach implementation is illustrated for the divertor Thomson scattering (DTS) optical scheme using front-end windows for injection of laser beam and collecting of scattered light. Surface recovery techniques based on plasma cleaning and laser ablation are described with the focus on the performance of the windows under laser and plasma treatment. The windows made from fused silica glass KU-1 and Al2O3 were tested. Plasma cleaning experiments have been performed for clean windows and windows coated with Al films. As was shown by the means of optical microscopy, XPS and AFM the dominant mechanism of window optical degradation is surface roughening. The development of surface relief becomes more intensive after deposition and removal of Al. The clear indication of the dependence of surface degradation rate on the initial polishing quality was also obtained for the windows with and without Al deposition. Laser experiments reveal the decrease in laser-induced damage threshold by the factor of~ 3 for both window materials under continuous tungsten deposition. In the case of Al droplets spraying, damage threshold is about 6 times as low as that of pure KU-1 window. The experiments on the long-term laser cleaning under continuous contamination showed that the evolution of tungsten film stops over the first hundreds of pulses and further exposition has no effect on the film thickness. The steady-state thickness of tungsten deposit in the beam spot was found to be ~ 5 nm for the deposition rate of ~10nm/min and laser (3 ns) energy density of ~ 2 J/cm2, forming almost transparent coating in visible and near-IR regions. Radiation-induced effects in silica glass and sapphire and corresponding limitations are also discussed.
Paper Number FIP/P1-5
Country or International Organization Russian Federation

Primary author

Mr Alexey Razdobarin (Ioffe Institute)


Dr Aleksander Bazhenov (Ioffe Institute) Mr Aleksander Chernakov (Spectral-Tech, ZAO) Dr Aleksander Gorodetsky (IPCE RAS) Mr Aleksander Koval (Ioffe institute) Ms Alla Sitnikova (Ioffe Institute) Mr Andrey Litvinov (Ioffe Istitute) Dr Andrey Markin (IPCE RAS) Dr Andrey Zakharov (IPCE RAS) Mr Artem Dmitriev (Ioffe Institute) Dr Demid Kirilenko (Ioffe Institute) Mr Denis Elets (Spectral-Tech, ZAO) Dr Dmitry Samsonov (Ioffe Institute) Dr Eugene Mukhin (Ioffe Institute) Dr Gleb Kurskiev (Ioffe Institute) Mr Ivan Bukreev (Ioffe Institute) Mr Ivan Tereschenko (Ioffe Institute) Ms Lidia Varshavchik (Ioffe Institute) Dr Mark Kempenaars (ITER Organization) Mr Nikita Babinov (Ioffe Institute) Dr Philip Andrew (ITER Organization) Dr Rinad Zalavutdinov (IPCE RAS) Mr Sergey Masyukevich (Ioffe Institute) Dr Sergey Tolstyakov (Ioffe Institute) Dr Valentin Bukhovets (IPCE RAS) Mr Vladimir Solokha (Ioffe Institute)

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