A new spectrometer, provided by the Plasma Physics Laboratory of Princeton University (New Jersey, USA), has been installed during the last shutdown at JET.

This new instrument provides a detailed spectrum of the pellet ablation light and allows improved studies of the processes involved in the ablation of injected pellets.

It has recently been commissioned successfully and the result of first measurements during pellet injection experiments in Campaign 5 (18 March – 31 May 2002) are promising. For example the line width of the spectrum, which is broadened by the Stark effect, delivers information on the density of the pellet ablation cloud. The spectrometer can also measure the ratio of the intensities of the Dα and Dβ lines, which reflects the electron temperature of the pellet ablation cloud. Thus simultaneous time resolved measurements of the electron density and temperature of the pellet cloud are now possible for the first time at JET. This will provide significant additional data for use in the modeling of the ablation of a pellet and of the drift of the ablated pellet mass in the plasma.

Pellet Injection:
Firing little cubes (‘pellets’) of frozen deuterium or deuterium- tritium mixtures into the plasma to increase its core density.

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