Transport and turbulence in Tore Supra

Abstract

Several discharges have been analysed in Tore Supra in order to improve the understanding of anomalous transport. In ohmic discharges, it has been shown that both particle and heat diffusion coefficients improve with increasing density, then saturate. The level of edge density fluctuations behave in the same way. In the presence of additional heating, the bulk and the edge turbulences behave differently. The level of edge density fluctuations remains constant in most discharges with additional heating (up to 8 MW). In practice, it only depends on edge conditions. On the contrary, the level of core magnetic fluctuations increases systematically with any additional power. Finally, a lowering of the level of the edge density fluctuations has been observed when using the Tore Supra ergodic divertor. This improvement is accompanied by the onset of a temperature pedestal between the plasma bulk and the ergodic layer. This explains why the global confinement remains unchanged in presence of the ergodic divertor in spite of the reduced radius of the last closed magnetic surface.

A comparative study of transport in stellarators and tokamaks

“…This might indicate that the dependence of confinement on the heating power has a origin different from that of the dependences on other plasma parameters. For a power scan in Tore Supra similar results are reported for the edge density fluctuations (Garbet et al 1995). More recently, however, in Tore Supra a strong increase of the magnetic fluctuation level with increasing heating power or temperature gradient was measured (Laviron et al 1996) suggesting that magnetic fluctuations might be important to explain the increasing transport with power.…”