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Abstract |
A probe array consisting of three emissive and one cylindrical probe was developed for edge plasma measurements in ISTTOK. The emissive probes measure the plasma potential, Phi(pl), independently of electron drifts or electron temperature fluctuations. The probe array has the advantage of to record the density, the poloidal and radial electric field, and their fluctuations simultaneously. Radial plasma profiles were recorded with and without negative edge biasing with an emissive electrode. The statistical properties of the poloidal electric field and of the turbulent particle flux, measured with cold and emissive probes, were compared. Both the root mean square of the poloidal electric field and the fluctuations-induced particle flux were found to be significantly larger when measured with the emissive probes, indicating that temperature fluctuations are important for the particle flux determination. The flux distribution was also found to be more peaked and asymmetric when measured with the emissive probes. A clear reduction of the turbulent particle flux and an improvement of the plasma confinement are observed during the negative emissive electrode biasing. |
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