Melnick, Ian Mark; (1995) A diagnostic study of chlorine X-ray line emission from the COMPASS-D tokamak. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

A high resolution Johann spectrometer has been used to observe the spectrum of He-like Cl and its satellites (4.4 - 4.5Å) on the COMPASS-D tokamak at Culham Laboratory. This narrow spectral region is a rich source of plasma diagnostic information. The spectra obtained have been fitted with Voigt profiles and interpreted in terms of plasma parameters. The core temperatures of the electron and ion fluids have been derived from the intensity ratio of the dielectronic satellite line, k, to the He-like resonance line, u; and from Doppler broadening of spectral lines respectively. Heat transport coefficients have been estimated from the measured temperatures and are used to explain temperature differences between the two fluids. The impurity ion diffusion coefficient, D), has been derived from the intensity ratio of the Li-like inner shell excitation satellite line, q, to the w line. The values obtained are in good agreement with those derived from laser ablation experiments. At high temperatures (Te > 800eV) this ratio and the G (ratio of the intercombination lines (x + y + z) to the w line) and R (z /x+y) ratios are close to coronal predictions, but at lower temperatures there are large departures from coronal values. This indicates an increase in the Li-like population compared with the He-like population and an enhancement of the triplet levels over the singlet levels due to inner shell ionisation from the Li-like ground state. Absolute calibration of the spectrometer sensitivity has been used to measure the continuum and line intensities and these have been modelled in terms of impurity concentrations. The intensity of the w line increases during ELM free H-modes consistent with weak impurity accumulation. Core toroidal rotation has been measured during ELM free H-modes and mode-locking experiments from Doppler shifts of spectral lines. In both cases a change of rotation of ~ 20km/s is seen in the ion drift direction at the onset of the H-mode or mode-lock. Li the absence of an external momentum source these changes are accounted for by pressure gradient and viscous forces.

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