Aachen PK 2003 – wissenschaftliches Programm

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P: Plasmaphysik

P 4: Poster I

P 4.22: Poster

Montag, 17. März 2003, 17:45–19:15, Foyer

Fast data acquisition for fluctuation measurements in the plasma of TEXTOR — •O. Schmitz, U. Kruezi, B. Unterberg, B. Schweer, and Ph. Mertens — Institut für Plasmaphysik, FZ Jülich, EURATOM-Association, TEC, 52425 Jülich, Germany

To acquire spectroscopic data of a new Supersonic Helium beam a fast VXI data acquisition system has been developed. To characterize fast transport processes, the fluctuations of the electron temperature T_e and electron density n_e with frequencies of up to about 250 kHz will be explored. Both parameters T_e and n_e will be determined from the ratio of the intensities of three helium lines at eight spatial points in the plasma. Therefore, the new 24 channel system consists of six separate digitizers, accessible in the register based modus. Every channel gets at a sample rate of up to 800 kHz with 14 bit resolution, so it is possible to resolve the 250 kHz signal frequency as well as the low SNR of fluctuation signals. With a 64 MB FIFO memory in each digitizer, all data produced during one TEXTOR-shot of 10 seconds can be acquired.

To avoid the loss of data and damages to the hardware while it is used in the TEXTOR environment, the system works as a workstation without internal harddisc inside the bunker. It boots its operation system via NFS-mount from an external harddisc and all data produced and C programs developed are stored there, too.

The given specifications of the digitizers have been verified and the I/O-performance of the modules has been optimized. To compress the data a Huffman code and a common Unix GZip code has been tested. The entropie based Huffman code has been more effective.