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Status of the JET LIDAR Thomson Scattering diagnostic

The LIDAR Thomson scattering concept was proposed in 1983 and then implemented for the first time on the JET tokamak in 1987. A number of modifications were performed and published in 1995, but since then no major changes were made for almost 15 years. In 2010 a refurbishment of the diagnostic was started, with as main goals to improve its performance and to test the potential of new detectors which are considered as candidates for ITER. During the subsequent years a wide range of activities was performed aimed at increasing the diagnostic's light throughput, improvement of signal to noise ratio and amendment of the calibration procedures. Previously used MA-2 detectors were replaced by fast GaAsP detectors with much higher average QE. After all the changes were implemented, a significant improvement of the measured data was achieved. Statistical errors of measured temperature and density were reduced by a factor of 2 or more, depending on plasma conditions, and comfortably surpassed the values requested for ITER Core Thomson Scattering (10% for Te and 5% for ne). Excellent agreement with other diagnostics (conventional High Resolution Thomson Scattering, ECE, Reflectometer) was achieved over a wide range of plasma conditions. It was demonstrated that together with long term reliability and modest access port requirements, LIDAR can provide measurements of a quality similar to a conventional imaging Thomson Scattering instrument.