Damage to JET beryllium tiles

JET has operated with beryllium limiters such that up to 180 MJ could be coupled to the plasma. Approximately 2-4% of the surface of the limiter has been melted near the plasma contact point. Another 10-15% of the surface shows evidence of edge heating. Some 5% of tiles have been subjected to abnormal loads at points distant from the contact area. Damage shows strong correlation of localised heating of the limiter with toroidal field ripple. Edge heating rates of 260 MW/m2 have not caused gross mechanical failure of the limiter. The mechanical damage comprises fatigue cracks analogous to those due to sustained loading at low power levels. (orig.)