Characteristics of electron internal transport barrier in Heliotron J

The formation of an electron internal transport barrier (eITB) has been observed for the first time with centrally focused electron cyclotron heating (ECH) microwaves injected into plasma in Heliotron J. When the heating power per electron density (P-ECH/(n) over bar (e)) exceeds a threshold of 250 x 10(-19) kW m(3), transient increases of both the central T-e and the core T-e gradients are observed. A neoclassical (NC) calculation using the Sugama-Nishimura moment method predicts that the large positive radial electric field (E-r) is formed in the core region. Heat transport analysis shows a significant reduction of the effective electron thermal diffusivity in the plasma with the eITB related to that without the eITB. The large gap between the experimentally obtained effective thermal diffusivity and the NC thermal diffusivity suggests that the suppression of anomalous transport contributes to the core improved confinement of the eITB plasma. The electron cyclotron emission measurement shows both the transient increase and the hysteresis phenomena during the eITB formation.