Abstract. Wavelet analysis results are presented for evolution of the spectral fluctuation characteristics of the edge plasma density and potential in the L-2M stellarator for fast and slow transport transitions. The fast transition comes out as a sharp increase of the energy and electron density within ~0.1ms and the slow one as a weak parameter change during a 0.5 to 1 ms time interval. It is shown that the use of the "Mexican hat" and Morlet wavelets allows one to detect the moment of the fast transition, whereas applying the Haar wavelet adds to this also an estimate of its duration, conforming to the analytical calculations, and reveals the temporal structure of the slow transition.
IntroductionTransport transitions (TT) in the L-2M at the stationary discharge stage were first discovered in experiments with the maximum heating power of 250 kW [1]. They appeared as short-time processes being accompanied with a sudden increase of the energy and electron density by 15% (or by 50% with the 500 kW heating power) and a reduction of the plasma potential and density fluctuations at the plasma edge. This paper presents the wavelet analysis of the plasma edge fluctuations for the fast and slow TTs. The fast TTs are the ones with the duration significantly shorter than the energy confinement time of the plasma. If the transition duration and the energy confinement time are comparable, then such TTs are called slow. Wavelet analysis allows detecting the temporal changes in the process parameters [3] and that is why it is suitable for the time sample research in different plasma diagnostics: dispersion, interferometry, Doppler reflectometry etc. It is shown that the Morlet wavelet and the "Mexican hat" [4] allow to detect the moment of the fast TT, whereas applying the Haar wavelet [4] adds to this also evaluation of its duration in a good accordance with the theory [2] and reflects the slow TT characteristics in more detail than with the two other functions.