Development of low-Z surface coatings for JT-60 first wall

Impurity control is one of the essential elements in realizing the most favorable operating parameters of a beam-heated tokamak [I]. In JAERI, development of surface coatings of low-Z materials is intensively underway to take advantage of these materials in reducing the undesirable effect of wall-released impurities in JT-60. Work in this area includes development of coating techniques as well as evaluation of candidate coatings. The coating development plan consists of two stages [2,3]. The aim in the first stage is to develop low-Z coatings which are suitable for the attainment of operating parameters for the break-even condition. The goal of the second stage is to develop advanced materials which are applicable to fusion experimental reactors. The coating development includes precoating carried out before wall installation and in-situ coating carried out after the completion of the vacuum vessel.