Pedestal Density Profiles from the Upgraded Lithium Beam Diagnostic at JET and Comparison to Expectations from Neutral Penetration

The lithium beam diagnostic at JET provides information about the electron density in the scrape-off-layer and pedestal region. The density is reconstructed from the spatial profile of the 2p line emission of a collisionally excited neutral lithium beam (energy typically 60keV), which is injected into the plasma edge from the top of the machine parallel to the direction of the Z coordinate. The spatial and temporal resolution achieved at JET is Dt10ms, DZ1cm. The beam emission is observed using a periscope. The reconstruction uses a probabilistic inversion procedure which is based on a collisional-radiative model for the beam-plasma interaction.
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