Rollover: confinement degradation during TFTR discharges

The time evolution is described of TFTR neutral beam heated plasmas that of ten featured a decreasing energy content called 'rollover'. Rollover affect s the gross plasma parameters such as energy contest and fusion power produ ced, as well as the central plasma parameters and the plasma transport coef ficients. Rollover was studied using a database of all the TFTR plasmas pro duced over a two year period. The plasma behaviour at the time of peak ener gy content was related to the behaviour at a later quasi-equilibrium time. The main conclusion is that limiter power handling issues were the underlyi ng cause of TFTR rollover. This study re-emphasizes the fact that power han dling is an important issue for plasma facing components in tokamaks.