Rollover: confinement degradation during TFTR discharges

The time evolution is described of TFTR neutral beam heated plasmas that often featured a decreasing energy content called 'rollover'. Rollover affects the gross plasma parameters such as energy contest and fusion power produced, as well as the central plasma parameters and the plasma transport coefficients. Rollover was studied using a database of all the TFTR plasmas produced over a two year period. The plasma behaviour at the time of peak energy content was related to the behaviour at a later quasi-equilibrium time. The main conclusion is that limiter power handling issues were the underlying cause of TFTR rollover. This study re-emphasizes the fact that power handling is an important issue for plasma facing components in tokamaks.