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Calculation of edge ion temperature and poloidal rotation velocity from carbon III triplet measurements on the COMPASS tokamak

100%

Tomeš M. , Weinzettl V. , Pereira T. , Imríšek M. , Seidl J.

Nukleonika

2016

tom Vol. 61, No. 4

443--451

A high-resolution spectroscopic system for the measurements of the CIII triplet at 465 nm was installed at the COMPASS tokamak. The Doppler broadening and shift of the measured spectral lines are used to calculate the edge ion temperature and poloidal plasma rotation. At first, the spectroscopic system based on two-grating spectrometer and the calibration procedure is described. The signal processing including detection and removal of spiky features in the signal caused by hard X-rays based on the difference in the behaviour of Savitzky-Golay and median filters is explained. The detection and position estimation of individual spectral lines based on the continuous wavelet transform is shown. The method of fitting of Gaussians using the orthogonal distance regression and estimation of the error of estimation of the rotation velocity and ion temperature is described. At the end, conclusions about the performance of the spectroscopic system and its shortcomings based on summary of results calculated from 2033 processed spectral lines measured in 61 shots are drawn and the possible enhancements are suggested.

Optimization of soft X-ray tomography on the COMPASS tokamak

86%

Imríšek M. , Mlynář J. , Löffelmann V. , Weinzettl V. , Odstrčil T. , Odstrčil M. , Tomeš M.

Nukleonika

2016

tom Vol. 61, No. 4

403--408

The COMPASS tokamak is equipped with the soft X-ray (SXR) diagnostic system based on silicon photodiode arrays shielded by a thin beryllium foil. The diagnostic is composed of two pinhole cameras having 35 channels each and one vertical pinhole camera with 20 channels, which was installed recently to improve tomographic inversions. Lines of sight of the SXR detectors cover almost complete poloidal cross section of the COMPASS vessel with a spatial resolution of 1–2 cm and temporal resolution of about 3 s. Local emissivity is reconstructed via Tikhonov regularization constrained by minimum Fisher information that provides reliable and robust solution despite limited number of projections and ill-conditionality of this task. Improved border conditions and numerical differentiation matrices suppressing artifacts in reconstructed radiation were implemented in the code. Furthermore, a fast algorithm eliminating iterative processes was developed, and it is foreseen to be tested in real-time plasma control.