JET-R(85)03
LowZ Material for Limiters and Wall Surfaces in JET: Beryllium and Carbon
It is proposed to use in JET a single low-Z material for the belt limiters and the walls to reduce impurity radiation losses to the lowest level. The only practical materials are graphite and beryllium. Their relative merits are compared in this paper. Graphite has better thermomechanical properties than beryllium, but simulation experiments on beryllium carried out at Sandia National Laboratory and in ISX-B have proved these properties sufficient for the belt limiters. Recent measurements indicate that beryllium retains 2­3 times less hydrogen than graphite. The ISX-B experiments have shown that beryllium has an excellent gettering action also. The main drawback of beryllium is the toxicity of its dust, but the control of beryllium dust is well within standard industrial techniques. It is concluded that beryllium offers the best prospects as a material for the JET belt limiters and walls.