Surface ripple of resolidified stainless steel after disruption load

The lifetime the first wall in fusion reactor depends on its durability against plasma disruption loads that may cause the melting and evaporation of the surface layer. Irradiation tests for stainless steels were made using a neutral beam injector. It was found that high sulfur and oxygen contents in the steels made the resolidification surfaces rough and wavy, while high calcium, aluminum and titanium contents were revealed to effectively offset the sulfur and oxygen. These impurity contents affect the temperature coefficient of surface tension in liquid iron. The surface temperature in the wider sections declines more slowly than in the thinner parts, therefore, the surface temperature is nonuniform. When the liquid iron has a positive temperature coefficient of surface tension, the surface tension in the denser parts becomes relatively greater than in the thinner parts. Consequently, the former expands and the thinner section contracts. (orig.)