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Abstract

The strong striation observed in large tokamaks when a pellet crosses the q=1 surface has been shown to be due to an almost shearless annular region and to be extremely sensitive to the details of the magnetic structure. Therefore, if this q-profile exists before pellet injection, analysis of the shape of the striation can be a powerful diagnostic of the local current density distribution. The paper presents a method of precisely calculating the width, depth and shape of the striation of an arbitrary pellet trajectory throughout a discharge. Different mechanisms that are possibly responsible for the flattening of q in the vicinity of q=1 (e.g. turbulence or magnetic reconnection) are discussed and it is shown that pellet induced perturbation is not likely to produce such a feature (which confirms its interest as a diagnostic). A simple parameterisation of plasma rotation and of a magnetic island is introduced and the model is applied in a simulation of striations displaying important profile distortions even for shallow current perturbations, which could therefore be detected, demonstrating the strong sensitivity of the method.

Additional information

Authors: PÉGOURIÉ B, CEA, Département de Recherches sur la Fusion Contrôlée, Saint-Paul-lez-Durance (FR);DUBOIS M A, CEA, Département de Recherches sur la Fusion Contrôlée, Saint-Paul-lez-Durance (FR);PEGOURIE B, CEA, Departement de Recherches sur la Fusion Controlee, Saint-Paul-lez-Durance (FR)
Bibliographic Reference: Article: Nuclear Fusion, Vol. 30 (1990) No. 8, pp. 1575-1584
Record Number: 199011438 / Last updated on: 1994-12-02
Category: PUBLICATION
Original language: en
Available languages: en