Use of dual-pulse laser-induced breakdown spectroscopy for characterization of the laser cleaning of a first mirror exposed in HL-2A

Our recent investigations have indicated that dual-pulse laser-induced breakdown spectroscopy (DP-LIBS) has great potential in the online measurement of the laser ablation process of the ultrathin co-deposition layer on the first mirrors of HL-2A tokamak during the cleaning. The spectroscopic study of the plasma emission can be used to determine the elemental composition of the ablated materials. The co-deposition layer (approximately 0.8 μm) was completely removed after multiple pulses at 0.76 J/cm2, but the plasma initiated by the cleaning laser pulse was too weak to produce LIBS signals. Notable enhancement of the signal emission was observed using DP-LIBS. The real-time monitoring and accurate identification the interface boundary can provide important information regarding the cleaned mirror surface in order to avoid under-cleaning. This could help us to develop more effective automatic control of the laser cleaning processes for fusion devices.