Scaling of incremental energy confinement time of L-mode plasma and comments on improved confinement in tokamaks

Incremental energy confinement time defined by τEad = ΔWp/ΔPt is reviewed for L-mode plasmas in various tokamaks with various heating methods where ΔWp is incremental plasma energy with increase of heating power ΔPt. It is shown that τEad ∼ 0.12ap2 s and τEad is almost independent of other plasma parameters, heating power and heating methods where ap is a plasma minor radius in m and ap = 0.1 - 1.15 m. In an optimum H-mode plasma, the incremental energy confinement time is improved by a factor of 4 but the scaling is not clear because of lack of data. (author)