Laser ablation of thin tungsten layers deposited on carbon substrate

The aim of the present study was to develop in situ control methods for erosion of layers and deposition on the main wall of a fusion reactor. For this purposes laser induced breakdown spectroscopy (LIBS) was applied to specially manufactured samples with coatings of known thickness and composition in vacuum. The whole laser induced spectrum in range 200–850 nm was recorded for every laser shot. Our results demonstrated that the equipment used has sufficient sensitivity for recording of the spectrum during a single laser shot. The diagnostic lines most suitable for characterization of layers were determined. Tungsten layer on carbon substrate is detectable and its ablation rate is 0.5–1 µm per laser pulse. From the recorded spectra it is possible to estimate tungsten coating thickness, but for a complex coating where tungsten layer was covered with diamond-like carbon (DLC), tungsten was spectroscopically not detectable. Additional information about charge concentration and movement is possible to obtain by measuring the current pulses in the sample circuit.