A database of the confinement properties of the toroidal pinch experiment (TPE) series reversed-field pinch (RFP) devices was established, and an empirical scaling law for the energy confinement time, tau(E), was deduced for a consistently selected set of the database (Yagi Y. et al 2003 Nucl. Fusion 43 1787). The scaling for tau(E) [TPE-scaling; tau(E) similar to a(1.7)I(p)(0.8) (I-p/N)(0.3)Theta(3)], in particular, is a power law similar to that predicted on the basis of the tearing modes, P as a function of the plasma minor radius (a), plasma current (I-p), and I-p/N, where N is the column density. On the other hand, the TPE-scaling has a strong dependence on the pinch parameter, Theta, namely tau(E) similar to Theta(3). Recently, we have investigated the database of the improved confinement in the pulsed poloidal current drive (PPCD). We show that the TPE-scaling agrees well with the improved tau(E) in the PPCD database, because of its strong Theta dependence. Namely, Theta(3) is a factor of merit for RFP plasmas. We discuss why this agreement is obtained in spite of the general difference between the underlying transport mechanisms of the standard and PPCD discharges. We also show that this improvement, represented by Theta(3), is related to the increase in magnetic shear with Theta.
2005. Vol. 45, no 2, 138-142 p.