Fusion Science and Technology / Volume 41 / Number 1 / January 2002 / Pages 32-43
A technique based on laser-induced breakdown spectroscopy is proposed for detecting in situ dust on the plasma-exposed surfaces and in the grooves of plasma-facing components in the next generation of fusion devices (e.g., ITER). It is based on laser-induced ablation of wall material and spectral analysis of the laser spark flash-light collected by imaging optics and transmitted to the detection system. This could give space- and time-resolved information on the presence of dust or loosely bound films, their characteristic deposition patterns, elemental composition, and possibly their hydrogen content, without the necessity of breaking the machine vacuum. We have performed some simple proof-of-principle experiments to demonstrate the suitability of this technique, which might provide an effective nonintrusive in situ surface analysis method for surveying in-vessel dust accumulation in future fusion devices. The preliminary results are discussed, and some of the inherent advantages and difficulties of this method are highlighted. The usefulness of this technique to provide reliable information on the quantity of dust at the probed location still depends on the resolution of several aspects, which are the subject of ongoing experimental investigation. Areas of further research and development are identified, and some of the design issues to integrate this system in a next-step fusion device such as ITER are briefly discussed.