Spektroskopische Untersuchung der poloidalen Plasmarotation unter dem Einfluß statischer und dynamischer Ergodisierung am Tokamak TEXTOR

Busch, Christian

Dissertation / PhD Thesis/Book

Spektroskopische Untersuchung der poloidalen Plasmarotation unter dem Einfluß statischer und dynamischer Ergodisierung am Tokamak TEXTOR

Busch, C. (Corresponding author)FZJ*

2006
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 3-89336-433-1

Jülich : Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag, Schriften des Forschungszentrums Jülich. Reihe Energietechnik / Energy Technology 50, IV, 78 S. (2006) = Universität Düsseldorf, Diss., 2006

Please use a persistent id in citations: http://hdl.handle.net/2128/2502

Abstract: The subject of this thesis was the implementation of an observation system to measure the poloidal plasma rotation spectroscopically and to study the impact of static and dynamic ergodization on rotation. Radial profiles of poloidal rotation have been determined by charge exchange spectroscopy on completely ionized carbon, C$^{6+}$, by means of a highenergy hydrogen beam. Furthermore, this method provides the ion temperature and the C$^{6+}$ density. Together with the toroidal rotation measured at another system, it is possible to analyze the radial electric field. In addition, the poloidal rotation of C$^{2+}$ ions has been measured via passive spectroscopy at a fixed radial position. A high resolution Echelle-spectrometer has been installed for the Doppler-spectroscopic measurement of the rotation velocities. Lines of sight looking both into and against the direction of rotation provide an automatic calibration of the wavelength. The precision of the active measurement accounts for ±(1-2)km/s at a time resolution of 1s, which could be decreased to 50ms for the passive measurement. A new method also realized here uses the emission of the diagnostic beam for an improved radial calibration of the channels. In an ohmic discharge without ergodization, the carbon rotates with velocities of typically −5km/s against the direction of the poloidal magnetic field ($\textit{counter}$). The related radial electric field of −5kV/m points towards the plasma center and is dominated by the poloidal rotation. For the actual experimental conditions, the measured rotation is only reproduced in parts by the calculated neoclassical rotation. This can be attributed to effects not included in the model like anomalous viscosity or damping of the rotation by neutrals. Under the influence of a static magnetic perturbation field the rotation in the ergodized region at the plasma edge reverses into the co-direction. This is connected to a reversal of the electric field pointing outward. These observations on $\textit{carbon}$ agree with calculations of both the radial electric field and the rotation for the background plasma composed of $\textit{deuterium}$. The impact of the ergodization on the rotation and the electric field can be explained qualitatively by a torque, which is generated by the interaction between the toroidal field and an outward compensation current. The latter compensates the electron losses along the magnetic field in the ergodic zone. The measurements on C$^{2+}$ ions show a linear increase of the rotation with the strength of the perturbation field. In dynamic operation, this field predominantly rotates in the poloidal direction with frequencies up to ±1kHz. Here the measured rotation is independent from frequency and from the direction of rotation of the perturbation. Like in the static case, the rotation increases linearly into co-direction with increasing strength of the perturbation. Small differences might be due to the impact of magnetic modes on the ergodization. Therefore, the mechanism found here, which leads to the plasma acceleration by a compensation current, dominates any possible additional interaction between the perturbation field and induced shielding currents.

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