Countermeasures for the mirror carbonization in ELI-NP

We report the current observations of the carbonization problem in ELI-NP laser beamlines. All the beamlines of 0.1 to 10 PW had the carbonization of the beam transport mirrors at fs pulse in vacuum. We tested 3 different cleaning methods to remove this carbonization, namely the dip cleaning in the water-alcohol mixture, oxygen plasma cleaner, and pump down with silica gel. The dip cleaning was applied to 1 PW mirror to remove the contamination before the carbonization was observed. For the first time for large mirrors. The oxygen plasma can remove surface carbon, but it is not enough to remove the carbon inside the coating. Silica gel provides some slow pumping of the vacuum and some increase of low-mass gasses due to the increased surfaces. The method to identify the pass-way of the contamination into the vacuum chamber was proposed.