Scientific session of the Division of General Physics and Astronomy of the Russian Academy of Sciences (April 23, 1997)

Abstract

Eigenmodes play an important role in the dynamics of spatially extended systems. Using arrays of probes, it is possible to measure the spatial structure of experimentally observed fluctuations. But the interpretation of the measured data becomes very difficult if the number of probes is low, the probes are not evenly spaced or different sample rates are used. This is a common situation in magnetically confined fusion plasmas. A method is proposed that allows the time-resolved reconstruction of the mode numbers and frequencies of eigenmodes in such a situation. It is based on the well known Lomb periodogram and has the following properties: statistical interpretation of the results, combined analysis of spatial and temporal data and effective noise reduction. Though this method can be generalized to arbitrary geometries, this work is dedicated to the analysis of Alfvén eigenmodes in stellarators. The method is applied to Mirnov probes which are found in many stellarators to diagnose Alfvén eigenmodes.