Initial stage of turbulent heating of plasmas

Initial stage of linear turbulent heating of plasmas has been investigated by means of Thomson Scattering of ruby laser light with an eight-channel polychromator. In a low density discharge (n sub(e) asymptotically equals 5 x 1012 cm-3), an anomalously rapid electron heating was observed to start in association with the onset of the current driven ion acoustic instability. Flat-top velocity distributions of the electrons were observed after the onset of the instability, which was interpreted by the quasilinear diffusion process in the velocity space caused by the turbulent ion acoustic waves. In a high density discharge (n sub(e) asymptotically equals 2 x 1014 cm-3), the applied pulse voltage generated skin current distributions disappearing in less than 0.6 μsec, while skin profiles of the electron temperature remained longer, say for 2 μsec. It is concluded that the observed rapid current penetration is also due to the anomalous resistivity caused by the current driven ion acoustic instability. (author)