An H-mode-Like Bifurcation in Core Plasma of Stellarators

The radial electric field, reduction of anomalous transport, and ion temperature profile are simultaneously analysed in the Wendelstein-VIIA (W VII-A) stellarators. Neoclassical formula is used to determine the radial electric field. Bifurcation of the anomalous transport is found at a critical injection power, above which improved confinement is possible. Experimental results of W VII-A. which have shown the sharp reduction of the H_ alpha signal after the injection of the neutral beam, are revisited