Edge fluctuation studies in ATF

Transport studies in tokamaks have shown that processes involving electrons are anomalous (i.e., transport is faster than predicted by the neoclassical theory). One of the key issues in fusion research is to understand the basic mechanisms causing the experimentally observed anomalous transport. Much effort is being done to elucidate if it can be explained by the presence of either electrostatic or magnetic fluctuations. Electrostatic fluctuations have been studied in the edge region of many tokamaks. Detailed experiments carried out in TEXT tokamak have shown that electrostatic fluctuations are large enough to explain anomalous transport in the plasma edge. It is now generally accepted that energy and particle losses in the edge plasma region of tokamaks are predominantly due to plasma turbulence. Transport studies carried out in stellarators have shown that transport coefficients evaluated in the core region are consistent with neoclassical predictions under some conditions, whereas in the boundary the transport is anomalous. Tokamak and stellarators share similar properties (nested magnetic field lines with rotational transform) but they also have important differences. In stellarators the magnetic configuration is produced by external currents; this allows to access to a wide range of magnetic configurations without requiring any driven plasma current. By comparing the structure of edge turbulence in both tokamaks and stellarators one can expect to get information about the dominant drive of the turbulence as well as about the role of the magnetic configuration on edge turbulence. The purpose of the present investigation is to characterize edge fluctuations in ECH plasmas in the Advanced Toroidal Facility (ATF). (author) 11 refs., 4 figs