Turbulent fluctuations and confinement in JET

Publisher Website
Google Scholar
Abstract
High frequency fluctuations are observed in JET by edge magnetic probes and arrays of visible radiation detectors even in the absence of Mirnov activity (typical frequency: ~1 kHz); cross-correlation techniques are applied in order to study the broadband activity. Magnetic fluctuations (θ) in the range of 1 to 20 kHz are strongly correlated along a direction parallel to the edge magnetic field lines; above ~10 kHz, a substantial fraction of these fluctuations (30-60%) have low wavenumbers (m ≤ 5, n ~ 1). Fluctuations in visible radiation coming from the edge are detected by soft X-ray diodes (without absorptive foil) up to ~ 100 kHz: correlation analysis indicates the presence of rather high m numbers (m ~ 10-100) with a correlation time of τc ~ 100 μs. This type of activity is also seen by the magnetic probes and a good correlation between the two diagnostics is observed. The edge magnetic root mean square level is continuously monitored with eight hardware filters over the 5 to 60 kHz frequency range. Database analysis of additionally heated discharges shows a proportionality between θN = |θ|BT/Bθ and the inverse energy confinement time, .