Scaling of Incremental Energy Confinement Time in the JFT-2M Tokamak

The decay time of stored energy was measured when additional heating power decreased abruptly. The energy decay time is almost constant at 15 ms, irrespective of the gross energy confinement time τEG, which is changed by ion-cyclotron range of frequency heating up to 1.5 MW. The decay time coincides with a confinement time of the additionally heated power defined by τad=ΔWTΔPₜₒₜ, which indicates that the incremental energy from the additional heating behaves independently of the gross plasma energy. It is also shown that τad is almost independent of density and plasma current as well as heating power.