Atomic Spectroscopy on Fusion Relevant Ions and Studies of Light Impurities in the JET Tokamak
Abstract: The spectrum and energy levels C IV and the 3l4l' system of the Mg-like ions in the iron group elements has been investigated. This has led to several hundred identified transitions, many of them previously unknown. Using the Charge Exchange diagnostic system at JET, ion temperatures, rotation velocities and densities have been derived from visible spectroscopic measurements on fully ionised light impurities such as He, C, N and Ne. The existence of plume contribution from beam produced hydrogen-like ions has been proven beyond any doubt to affect the deduction of the active charge exchange signal of He II. In the case of C VI, the plume signal was estimated to be at least a factor of five lower than the active charge exchange signal. Line integrated passive charge exchange emission between neutral background atoms and fully ionised impurities has been investigated and modelled. When the synthetic spectrum is fitted to the experimentally detected spectra the neutral background density can be deduced. The importance of including background atoms (H,D and T) as charge exchange donors, not only in state 2s, but also in state 1s, has been shown to be crucial in high temperature shots. Transport of light impurities has been studied with gas puff injections into steady state H-mode plasmas. The results suggest that light impurities are transported as desribed by the neo-classical Pfirsch-Schlueter regime at the edge, whilst in the centre, sawtoothing, preferably to Banana transport, is is mixing the plasma and increases the measured values on the diffusion. For the peaking of impurities in a steady state plasma an anomalous treatment was more in agreement with the experimental data. Certain confinement informations, previously predicted theoretically as a part of the peaking equation, has been experimentally verified.
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