Laser Cleaning of ITER's Diagnostic Mirrors
Authors: C. Skinner, C.A. Gentile and R. Doemer
Abstract:
Practical methods to clean ITER's diagnostic mirrors will be essential to ITER's plasma
operations. We report on laser cleaning of ITER-candidate single crystal molybdenum mirrors
that were plasma coated with either carbon or beryllium films 150 - 420 nm thick. A pulsed Nd
laser beam was focused to 1-2 J/cm2 and scanned at various speeds across the surface of a mirror.
The cleaning effect was measured with a novel method that combined microscopic imaging and
reflectivity measurements in the red, green and blue spectral regions and at the H-alpha and H-beta
wavelengths. No damage of the molybdenum mirror substrates were observed at the range
of laser intensities used. For carbon coated mirrors, complete removal of the film and restoration
of the reflectivity was measured in some conditions. For the beryllium coated mirrors restoration
of reflectivity has so far been incomplete. Heat transfer calculations suggest a shorter ~ 5 ns laser
pulse would be optimal.
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Submitted to: Fusion Science and Technology, October 2012)
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Download PPPL-4829 (pdf KB 18 pp)
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