X-ray spectroscopy at TEXTOR

At TEXTOR, an X-ray spectrometer in a Johann mount is utilized to measure the X-ray spectra of He-like elements with intermediate Z. Up to now, the spectra of He-like argon have been investigated. The spectra have been modeled with the most recent atomic data using physically relevant parameters only. Good agreement has been found both in modeling the experimental spectra and in the determination of the plasma parameters, such as ion temperature and plasma motion and electron temperature. The deviations between the theoretical and experimental spectra are below 7% for all lines; the precision of the plasma parameters obtained by X-ray spectroscopy agrees with the accuracy of the standard diagnostics at TEXTOR.In addition, the abundance of Li-/He-like ions, as well as the H-/He-like ions, has been measured. For the higher densities, the abundance approaches the coronal expectation. Larger deviations to the coronal limit have been found with neutral beam injection. The system is now being upgraded for spatial resolution

The construction of knowledge-based economies versus knowledge societies: The cases of Germany and Singapore

In the past decades, terms such as knowledge-based economy (KBE)\u27, and \u27information/knowledge society\u27 have been adopted by governments worldwide in order to underline their interest in developing their economies and societies further and assure future growth. Many governments used these catchwords as labels for government programs and action plans aiming at economic and social prosperity. This aim of national governments to construct knowledge-based economies, information/knowledge societies, the actions taken and especially the ability or disability to do so, is the topic of this paper. As two cases of comparison act Singapore and Germany. (DIPF/Orig.

Strong Scattering of High Power Millimeter Waves in Tokamak Plasmas with Tearing Modes

In tokamak plasmas with a tearing mode, strong scattering of high power millimeter waves, as used for heating and noninductive current drive, is shown to occur. This new wave scattering phenomenon is shown to be related to the passage of the O point of a magnetic island through the high power heating beam. The density determines the detailed phasing of the scattered radiation relative to the O-point passage. The scattering power depends strongly nonlinearly on the heating beam power

Development and testing of a fast fourier transform high dynamic-range spectral diagnostics for millimeter wave characterization

A fast Fourier transform (FFT) based wide range millimeter wave diagnostics for spectral characterization of scattered millimeter waves in plasmas has been successfully brought into operation. The scattered millimeter waves are heterodyne downconverted and directly digitized using a fast analog-digital converter and a compact peripheral component interconnect computer. Frequency spectra are obtained by FFT in the time domain of the intermediate frequency signal. The scattered millimeter waves are generated during high power electron cyclotron resonance heating experiments on the TEXTOR tokamak and demonstrate the performance of the diagnostics and, in particular, the usability of direct digitizing and Fourier transformation of millimeter wave signals. The diagnostics is able to acquire 4 GHz wide spectra of signals in the range of 136-140 GHz. The rate of spectra is tunable and has been tested between 200 000 spectra/s with a frequency resolution of 100 MHz and 120 spectra/s with a frequency resolution of 25 kHz. The respective dynamic ranges are 52 and 88 dB. Major benefits of the new diagnostics are a tunable time and frequency resolution due to postdetection, near-real time processing of the acquired data. This diagnostics has a wider application in astrophysics, earth observation, plasma physics, and molecular spectroscopy for the detection and analysis of millimeter wave radiation, providing high-resolution spectra at high temporal resolution and large dynamic range

Self-organized Te redistribution during driven reconnection processes in high-temperature plasmas

Two-dimensional (2D) images of electron temperature fluctuations with high temporal and spatial resolution were employed to study the sawtooth oscillation in Toroidal EXperiment for Technology Oriented Research [S. S. Abdallaev et al., Nucl. Fusion 43, 299 (2003)] tokamak plasmas. The new findings are: (1) 2D images revealed that the reconnection is localized and permitted the determination of the physical dimensions of the reconnection zone in the poloidal and toroidal planes. (2) The combination of a pressure bulge due to finite pressure effects or a kink instability accompanied with a sharp pressure point leads to an "X-point" reconnection process. (3) Reconnection can take place anywhere along the q similar to 1 rational magnetic surface (both high- and low-field sides). (4) Heat flow from the core to the outside of the inversion radius during the reconnection time is through the finite opening on the poloidal and toroidal planes and the flow is highly collective. These new findings are compared with the characteristics of various theoretical models and experimental results for the study of the sawtooth oscillation in tokamak plasmas. (c) 2006 American Institute of Physics

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