Speaker
Andrey Ushakov
(TNO)
Description
The PBS55 Upper-port Wide Area Viewing System (UWAVS) provides real-time, simultaneous visible and IR images of the ITER diverter region via optical systems located in the upper port plugs of the ITER vacuum vessel. Wall temperature and radiance measurements are performed based on the IR-images. Due to mirror contamination with reactor material deposits the optical performance will deteriorate during operation. As a result the imaging and temperature measurements will be compromised. To recover performance, a mirror cleaning system will be implemented. Cleaning optical surfaces with ion fluxes produced in a gas discharge plasma is considered as a preferred method for the ITER UWAVS first and second mirrors cleaning. Selective ion energy sputtering process with the appropriate ion flux and energy can remove contaminants while preserving the mirror optical surface. For specific conditions, threshold energies and sputtering rates are yet to be determined. To demonstrate a cleaning effect, a representative experimental prototype is developed. It reproduces the part of the Front End Optical Tube of the UWAVS diagnostic system in a 1:1 scale. The experimental prototype surfaces simulate the first and second mirrors with correct angle and separation. The surfaces hold coupons of desired material. The prototype is installed inside a larger vacuum chamber kept at low pressure mimicking the tokamak chamber. Both vacuum volumes are connected through adjustable leak valves to set the pressure for RF plasma ignition in the selected gas. Ion energies, fluxes and sputtering rates are investigated in the capacitively coupled 13.56 MHz CW and PP RF discharges and at higher RF frequencies up to 80 MHz. Experiments run in Helium, Argon and other gases at pressures between 1-50 Pa. Ion fluxes and energies are measured with the compact ion energy spectrometer placed at the high voltage RF electrode.
Co-authors
Ad Verlaan
(TNO, P.O. Box 155 NL-2600 AD, Delft, Netherlands)
Andre Rijfers
(TNO, P.O. Box 155 NL-2600 AD, Delft, Netherlands)
Andrey Ushakov
(TNO, P.O. Box 155 NL-2600 AD, Delft, Netherlands)
Anthony Gattuso
(General Atomics, P.O. Box 85608, San Diego, CA 92186-5608, United States)
Brentley Stratton
(Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, United States)
Jos van der List
(TNO, P.O. Box 155 NL-2600 AD, Delft, Netherlands)
Mark Smith
(Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, United States)
Matthew Smiley
(General Atomics, P.O. Box 85608, San Diego, CA 92186-5608, United States)
Norbert Koster
(TNO, P.O. Box 155 NL-2600 AD, Delft, Netherlands)
Oana van der Togt
(TNO, P.O. Box 155 NL-2600 AD, Delft, Netherlands)
Peter Verhoeff
(TNO, P.O. Box 155 NL-2600 AD, Delft, Netherlands)
Ray O’Neil
(General Atomics, P.O. Box 85608, San Diego, CA 92186-5608, United States)
Rob Ebeling
(TNO, P.O. Box 155 NL-2600 AD, Delft, Netherlands)
Russell Feder
(Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, United States)
