Speaker
Ilya Orlovskiy
(NRC "Kurchatov Institute")
Description
First mirrors (FMs) for ITER optical diagnostics induce a number of specific requirements including low sputtering rate, high neutron/gamma radiation and thermal stability to keep the optical performance in the DT plasma shots. Additionally, the FM surface must withstand the discharges by a cleaning system aimed to eliminate Be deposits. A number of experiments have shown that the mirrors made of single crystal molybdenum (SC-Mo) retain their reflectivity under surface sputtering by high energy particles in plasma devices.
Unfortunately, large SC-Mo ingots for manufacturing of the full size mirrors for ITER from a single piece are not commercially available. A sandwich-like design has been proposed in which the mirror is made of a few SC-Mo segments bonded to the polycrystalline molybdenum (PC-Mo) substrate. Since the FMs for H-alpha and Visible Spectroscopy (HA&VS) is planned to be uncooled, their temperature can reach 350-400°C, and a difference in CTE of SC-Mo and PC-Mo may affect the thermal stability of the sandwich structure.
In order to test the thermal stability of the sandwich SC/PC-Mo mirrors, two full-scale prototypes of the flat and the focusing FMs were manufactured according to the current HA&VS design. The 200×60×40 mm samples were made of two 200×30×4 mm SC-Mo segments bonded to the PC-Mo plate by the hot isostatic pressing technology.
Few cycles of thermal heating in vacuum have been performed up to 350°C. The curvature of their surface during testing was monitored optically by illuminating the mirrors with a set of parallel beams and analyzing the variation of the directions of reflected beams.
As a result, minor changes in the mirrors' curvature ~10-3 -3 m were observed in a heated state. After cooling down the mirrors' shape return back with high accuracy. The results prove the applicability of current approach to the uncooled FM design for HA&VS.
Co-authors
Aleksey Gorshkov
(NRC "Kurchatov Institute", Moscow, Russian Federation;International Fusion Projects Coordinating Centre, Moscow, Russian Federation)
Andrey Alekseev
(NRC "Kurchatov Institute", Moscow, Russian Federation;International Fusion Projects Coordinating Centre, Moscow, Russian Federation)
Evgeny Andreenko
(NRC "Kurchatov Institute", Moscow, Russian Federation;International Fusion Projects Coordinating Centre, Moscow, Russian Federation)
Gleb Asadulin
(NRC "Kurchatov Institute", Moscow, Russian Federation;NRNU “MEPhI”, Moscow, Russian Federation)
Ilya Orlovskiy
(NRC "Kurchatov Institute", Moscow, Russian Federation;International Fusion Projects Coordinating Centre, Moscow, Russian Federation)
