Spatial inhomogeneity effects on burst temperature estimation using a triple probe configuration in Tokamak Chauffage Alfvén Brésilien tokamak

Abstract

The effects of coherent structures in plasma edge turbulence are an important topic in the study of plasma cross-field transport in magnetically confined plasmas. To properly characterize these structures, their temperature must be measured, which is often done by using Langmuir probes. In this work, the techniques of Langmuir sweep and triple probe are used, considering the effect of plasma sheath expansion in both methods. It is shown that if the sheath expansion is ignored, the triple probe technique gives overestimated temperature values. In addition, the conditional analysis is applied to both techniques in order to evaluate the mean temperature time trace of the coherent structures. It is shown that these time traces can be distorted in the case of the triple probe technique, due to fact that coherent structures destroy the homogeneity condition on the pins array. Therefore, the sweep technique with a conditional selection of points is more suitable than the triple probe to study coherent structures related to bursts, as it performs a local measurement.