Statistische Beschreibung von intermittenten Ereignissen in der Plasmarandschicht des Tokamaks TEXTOR

Schmitz, Daniela

Diploma Thesis

Statistische Beschreibung von intermittenten Ereignissen in der Plasmarandschicht des Tokamaks TEXTOR

Schmitz, D. (Corresponding author)FZJ*

2006
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Jülich : Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag, Berichte des Forschungszentrums Jülich 4221, II, 91 S. (2006) = Ulm, Univ., Dipl., 2006

Please use a persistent id in citations: http://hdl.handle.net/2128/2504

Report No.: Juel-4221

Abstract: Within the scope of this work itermittent events in the plasma edge of the tokamak TEXTOR were characterized. For that data of measurements of the density and the poloidal electrical field were analysed. The data was collected by a reciprocating and a fixed probe as well as by a Lithium beam. The intermittent behaviour was quantified by the statistical moments of the data. If intermittency is high, coherent structures (also called blobs) can be detected. The detected blobs were described using the statistical method of conditional averaging. The main results can be summarised as follows: Intermittent behaviour has been detected in the scrap off layer of the tokamak TEXTOR and it is increasing with the radius from the last closed flux surface (LCFS) on. On the midplane the blobs in the limiter geometry have a radial size of up to 8 cm and move onto the wall with velocities as high as (1-7)% of the ion sound speed. It was found that intermittent transport causes 40% of the total perpendicular transport in the investigated discharges. In the upper part of the tokamak there is less intermittency. This is reasonable if intermittency is caused by interchange instabilities which mainly occur on the low field side of the tokamak. With the Dynamic Ergodic Divertor (DED) and the associated formation of tearing modes intermittency is increasing. This can also be due to the steeper gradient of density in the scrap off layer close to the LCFS which is caused by gas puffing used for the regulation of the density. Outside the LCFS the ergodic field does not have any influence on the characteristics of blobs. Within the LCFS density holes have been found which propagate towards the centre of the plasma. The radial transport due to blobs is still the same. In general the velocity of the detected blobs is proportional to the square root of their poloidal size. That confirms the prediction of the blob model in which the nonlinear development of interchange instabilities causes the propagation of blobs.

Note: Record converted from VDB: 12.11.2012
Note: Ulm, Univ., Dipl., 2006

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