Parametric scaling studies of the energy confinement time for neutral beam heated Heliotron E plasmas

A kinetic analysis of the global energy confinement time for neutral beam heated Heliotron E plasmas has been performed with a 1-D, time independent transport analysis code, PROCTR-Mod. From a regression analysis of a representative sample selection of the presented data sets, the global energy confinement time, τEG(ms), is found to scale as τEG=13n-bareαPheatβBγ, where α=0.53±0.10, β=-0.71±0.09, and γ=0.35±0.14; the error bar indicates the 95% confidence region deduced from the limited data points; n-bare(1014cm-3) is the line average electron density; Pheat(MW) is the neutral beam heating power; and B(T) is the vacuum magnetic field at the magnetic axis. The data analysis shows that the favourable density dependence partially offsets the unfavourable power dependence and that anomalous electron transport loss becomes dominant in the overall energy balance as the beam power and the plasma density are increased. An alternative scaling law is also presented, which is to fit τEG(ms) by an 'offset linear' law, τEG=ζB2+η/Pheat, where ζ=1.1±0.33 and η=15.0±1.9; (1014cm-3) is the volume average electron density. The latter scaling is found to provide a better fit to the presented data sets, in spite of its simple form. The parametric scaling of the local electron thermal diffusivity, χe, is also discussed on the basis of the kinetic analysis. (author). 40 refs, 21 figs, 2 tabs