Fractal growth of deposited films in tokamaks

Surface topography of some amorphous films from the T-10 tokamak has been analyzed by using the scanning tunnel microscope. Film surfaces on the scale from 10 nm to 100 μm have stochastic topography and a hierarchy of granularity. Fractal geometry and statistical physics techniques have been used to study a variety of irregular films within a common framework of the invariance under scaling. Quantitative analysis of a local fracture surface has been made. Experimental probability density functions of surface height increments resemble the Cauchy distribution rather than the Gaussian function. Stochastic topography of the film surface is characterized by the Hurst exponent in the range of 0.68–0.85, indicating non-trivial self-similarity of the structure. A fractality (porosity) of deposited films has to be considered as a critical issue of the tritium inventory in fusion devices. The process of film growth on plasma-facing materials (PFMs) in tokamaks is considered in a frame of the surface growth problem.