Effects of repetitive ELM-like heat pulses on tungsten surface morphology

The effects of ELM-like heat pulses on tungsten surface morphology were studied by using a fundamental wave (wavelength of 1.06 μm) of a YAG laser, which was operated in a multi-pulsed mode with an effective pulse length of about 100 μm, typical pulse length of ELMs. Tungsten base temperature was 640 °C, heated by a sheath heater and laser pulse heating. The energy absorption rate of the laser light was about 30% for mirror finished surface. Under non-melting conditions (laser pulse energy fluence: ≤0.1 kJ/cm2), roughening and cracking formation within the laser spot appeared. As the energy fluence decreased, the larger shot number was necessary for the surface morphology change to appear. Even at the highest temperature of around 1240 °C, surface roughening and fine cracking appeared at the large shot number (200,000 shots).