title: Enhancements to the JET poloidally scanning vacuum ultraviolet∕visible             spectrometers.
abstract: Enhancements to the JET poloidally scanning spectrometers are presented, which             will aid the exploitation of the recently installed ITER-like wall in JET. They include             the installation of visible filter∕photomultiplier tube assemblies and             spectrometers and the replacement of large rotating mirrors in the JET vacuum with small             oscillating mirrors outside. The upgrade has resulted in a more robust and reliable             diagnostic than before, which is described. Drifts in the mirror angle reconstructed             from quadrature encoder signals are found, a reference signal being required. The use of             the small scanning mirrors necessitated the inclusion of focusing mirrors to maintain             throughput into the vacuum ultraviolet spectrometers. The mirror design has taken             account of the extreme sensitivity of the focusing to the grazing angle of incidence, an             aspect of importance in the design of grazing incidence focusing components on future             machines, such as ITER. The visible system has been absolutely calibrated using an             in-vessel light source.
authors.affiliation: Euratom∕CCFE Fusion Association, Culham Science Centre, Abingdon, Oxon OX14 3DB, United Kingdom. Kerry.Lawson@ccfe.ac.uk
authors.forename: K D
authors.initials: KD
authors.lastname: Lawson
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authors.lastname: Beldishevski
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authors.lastname: Brzozowski
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authors.lastname: Buckley
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authors.lastname: Cass
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authors.lastname: Elevant
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authors.lastname: Griph
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authors.lastname: Heesterman
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authors.lastname: Hogben
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authors.lastname: Jennison
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authors.lastname: Stamp
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authors.lastname: Williams
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authors.lastname: Zastrow