AMPLITUDE - MODULATED LASER VIEWING SYSTEM IN APPARATUS FOR CONTROLLED THERMONUCLEAR STUDIES

摘要

Any large fusion machine, as ITER (International Thermonuclear Experimental Reactor), will need periodic in-vessel inspections to check for damages due to plasma disruptions. In addition, due to its size and to the large in vessel activation, this machine will strongly require extensive use of both remote maintenance and in vessel high resolution hard-rad imaging systems. For this purpose different systems have been proposed, based on optical devices or laser applications. In this paper a laser in vessel viewing system (LIVVS), based on an amplitude modulated (AM) laser, is described: the diode laser source and all electronics are located outside the bioshield, far away the machine, and the laser beam is transmitted & received through fused silica optical fibers. A transceiving module, containing only fused silica optics, is located near the viewing probe where the beam is collimated and launched, unguided, to the scanning head (fused silica prism). This one is tilted and panned in such a way to make the beam able to scan the in vessel surface with an accuracy of ～1mm @ 10m. The backscattered beam is received through the same path tracked by the scanning beam, with a suitable telescope optics and then detected by an avalanche photodiode, located near the laser source. In this way a target high resolution image is then performed by means of the analysis of the intensity and the phase shifting of the reflected, RF modulated, beam. Millimetric ranging, is also possible using, as transmitting line, coherent fibre optic. A LIVVS probe mock-up has been built and the experimental activity has been successfully completed. This paper reports: the LIVVS main features and operating principle (AM mode); the optical & mechanical design and the experimental results of the imaging viewing & ranging activity performed with the mock-up.