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During high heating power operation with neutral beam injection (NBI) and/or cyclotron resonance heating (ICRH) in JET, a large increase in the flux of low Z impurities (carbon and beryllium) entering the discharge is often observed shortly after the start of additional heating. High impurity concentrations lead to an increase of radiation losses and a degradation of the plasma performance. These influxes result from a fraction of the total area of the carbon (beryllium) surface in contact with the plasma reaching a high temperature range. Great efforts are made to minimise the impurity influx from the wall by using beneficial configurations. To assess the level of plasma purity and the location of the impurity sources from internal structures, spectroscopy is widely used. Traditionally, spectroscopic impurity measurements have focussed on the central plasma. At JET, two poloidally scanning vacuum ultraviolet (VUV) spectrometers are used for the study of the distribution of impurity line radiation coming from the upper X-point region and the upper half of the bulk plasma cross section.

Additional information

Authors: COULON J-P, CEA, Département de Recherches sur la Fusion Contrôlée, CEN Cadarache, Saint-Paul-lez-Durance (FR);JÄCKEL H, JET Joint Undertaking, Abingdon, Oxon. (GB);JANESCHITZ G, JET Joint Undertaking, Abingdon, Oxon. (GB);GIANNELLA R, JET Joint Undertaking, Abingdon, Oxon. (GB)
Bibliographic Reference: Paper presented: Diagnostics for Contemporary Fusion Experiments, Varenna (IT), Aug. 27 - Sept. 6, 1991
Availability: Available from (1) as Paper EN 36321 ORA
Record Number: 199210476 / Last updated on: 1994-12-02
Original language: en
Available languages: en
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