High power COIL fiber transmission for D and D application

Kurzfassung

Unprecedented 11 kW of COIL power are successfully transmitted through a 20 meter long modified commercial fiber system with optical losses below 10%. The fiber delivery system is used to demonstrate cutting of various materials pertinent to dismantling & decommissioning of nuclear installations. The 10 kW-class Chemical Oxygen-Iodine Laser (COIL) of the German Aerospace Center (DLR) is used for the demonstration of efficient coupling of high laser power into a modified commercial optical fiber system. Power values up to 11 kW at a wavelength of 1.315 µm are provided to the front end of the fiber. The laser beam is matched to a 1000 µm core diameter fiber by introducing intra-cavity apertures into the stable resonator of COIL. The fiber has a numerical aperture of 0.125 and a length of 20 m. In the experimental set-up, the fiber is bended 4 times with radii close to the bending limit of 30 cm. The laser power is measured simultaneously behind the total reflector and the end effector. Transmission ratios exceeding 90 % are demonstrated for the complete beam delivering system, consisting of coupling unit, optical fiber, and end effector. Cutting experiments are performed with the fiber delivered laser beam aimed at D and D (Dismantling and Decommissioning) tasks. Cutting samples of structural steel, aluminum, concrete and graphite are selected as required from radioactive containment areas of nuclear power plants. Nitrogen and oxygen are used as processing gases. Cutting depths are evaluated as a function of incident laser power and cutting velocities. The experimental results are validated with available theoretical models. The present cutting performance is compared with published cutting data related to CO_2-lasers, Nd:YAG-lasers and COIL. Based on the experimental results scaling studies for higher power level COIL systems, and hence greater cutting depths, are presented.