Ablative removal of codeposits on JT-60 carbon tiles by an excimer laser

The codeposits on JT-60 tiles experienced hydrogen plasma burning were irradiated by focused beams of an excimer laser. The removal rate of the JT-60 codeposits was low when the laser energy density was smaller than the ablation threshold (1.0 J/cm(2)), but reached to 1.1 mum/pulse at the laser energy density of 7.6 J/cm(2). The effective absorption coefficient k in the JT-60 codeposits at ArF excimer laser wavelength was determined to be 1.9 mum(-1), which is almost one order smaller than the optical absorption coefficient at the same wavelength in graphite (16.4 mum(-1)). In the process of ablative removal of the codeposits, hydrogen was released predominantly in the form of hydrogen molecule and water formation could be ruled out. The temperature rise on the surface was measured on the basis of Planck's law of radiation, and the temperature during the irradiation at the laser energy density of 0.5 J/cm(2) decreased from 3570 K at the beginning of the irradiation to 2550 K at 1000th pulse of the irradiation. (C) 2003 Elsevier Science B.V. All rights reserved.