The fibered LIBS (Laser-Induced Breakdown Spectroscopy) technique was tested for the first time in the vacuum chamber of a fusion machine by the CEA and CORIA (. Installed on an inspection robot equipped with an articulated arm, the LIBS tool consists of a fiber carrying the incident laser light and the light emitted during the interaction of the laser beam with the material under study. This device allows to characterize all the internal surfaces of the machine and to follow their evolution during its operation.
During the operation of a fusion machine, it is important to know the composition of the surface of the Plasma Facing Components (PFCs) in interaction with the plasma. Indeed, it is likely to evolve (erosion, oxidation...) modifying the interaction conditions. On ITER, we will also try to determine:
The first in-situ tests took place in December 2021 in WEST and were performed at atmospheric pressure. The nanosecond laser source and the spectrometer for the optical analysis of the LIBS plasma were placed in the machine hall, outside the WEST vacuum chamber. The AIA equipped with the fiber LIBS tool has been deployed in the tokamak vacuum vessel to perform LIBS analysis on a tungsten PFCs of the divertor. These first measurements are currently being analyzed.
The CEA has an inspection robot with articulated arms, called the AIA (Articulated Inspection Arm), which allows inspecting during in between plasma the status of the CFPs thanks to an embedded camera. A fibered LIBS tool has been installed on the AIA in order to be able to characterize the CFPs surface during operation. It was designed and tested by the CEA in close collaboration with the CORIA.
In the following figure, the evolution of the intensity of copper, nickel and boron lines are presented as a function of thickness, each point corresponding to a laser pulse. These elements are impurities present in a deposited layer on the surface of the analyzed PFCs. This layer results from the erosion of the material due to the plasma-wall interaction and from its deposition after transport by the plasma.
From this figure, we can deduce that the layer deposited during the plasmas has a thickness of about 600 nm.
After this first experiment of fibered LIBS in a tokamak, the CEA and CORIA are now aiming at the following steps:
Maj : 04/03/2022 (852)