MEASUREMENTS AND MODELING OF ELECTROSTATIC FLUCTUATIONS IN THE SCRAPE-OFF LAYER OF ASDEX

In the edge plasma of the ASDEX tokamak, electrostatic fluctuations we re observed with Lang muir probes and in H-alpha light with high poloi dal and temporal resolution. These fluctuations contribute a significa nt fraction to the 'anomalous' radial particle transport in the scrape -off layer (SOL). The basic properties and the dependence of the fluct uation parameters on the discharge conditions are documented. A model for an instability mechanism specific to the SOL is introduced and the experimentally observed fluctuation parameters are compared with the predictions of the Linearized version of this model. For plasma temper atures above similar to 10eV in the SOL the observed parameter depende nces of the fluctuations are well reproduced by the model. By mixing l ength arguments the radial transport and the resulting density and pre ssure gradients in the SOL are estimated from the model. Their depende nce on plasma temperature and density qualitatively agrees with the be haviour observed in ohmic discharges on ASDEX.