title: A new visible spectroscopy diagnostic for the JET ITER-like wall main             chamber.
abstract: In preparation for ITER, JET has been upgraded with a new ITER-like wall (ILW),             whereby the main plasma facing components, previously of carbon, have been replaced by             mainly Be in the main chamber and W in the divertor. As part of the many diagnostic             enhancements, a new, survey, visible spectroscopy diagnostic has been installed for the             characterization of the ILW. An array of eight lines-of-sight (LOS) view radially one of             the two JET neutral beam shine through areas (W coated carbon fibre composite tiles) at             the inner wall. In addition, one vertical LOS views the solid W tile at the outer             divertor. The light emitted from the plasma is coupled to a series of compact overview             spectrometers, with overall wavelength range of 380-960 nm and to one high             resolution Echelle overview spectrometer covering the wavelength range 365-720             nm. The new survey diagnostic has been absolutely calibrated in situ by means of a             radiometric light source placed inside the JET vessel in front of the whole optical path             and operated by remote handling. The diagnostic is operated in every JET discharge,             routinely monitoring photon fluxes from intrinsic and extrinsic impurities (e.g., Be, C,             W, N, and Ne), molecules (e.g., BeD, D(2), ND) and main chamber and divertor             recycling (typically Dα, Dβ, and Dγ). The paper presents a             technical description of the diagnostic and first measurements during JET             discharges.
authors.affiliation: Max-Planck-Institut für Plasmaphysik, EURATOM Association, D-85748 Garching, Germany. Costanza.Maggi@ccfe.ac.uk
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authors.lastname: Maggi
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authors.lastname: Brezinsek
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authors.lastname: Horton
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authors.lastname: Meigs
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authors.lastname: Zastrow