Status of the JET LIDAR Thomson scattering diagnostic

Abstract

The LIDAR Thomson scattering concept was proposed in 1983and then implemented for the first time on the JET tokamak in 1987. A numberof modifications were performed and published in 1995, but since then nomajor changes were made for almost 15 years. In 2010 a refurbishment of thediagnostic was started, with as main goals to improve its performance and totest the potential of new detectors which are considered as candidates forITER. During the subsequent years a wide range of activities was performedaimed at increasing the diagnostic's light throughput, improvement of signalto noise ratio and amendment of the calibration procedures. Previously usedMA-2 detectors were replaced by fast GaAsP detectors with much higheraverage QE. After all the changes were implemented, a significantimprovement of the measured data was achieved. Statistical errors ofmeasured temperature and density were reduced by a factor of 2 or more,depending on plasma conditions, and comfortably surpassed the valuesrequested for ITER Core Thomson Scattering (10% for Te and 5% forne). Excellent agreement with other diagnostics (conventional HighResolution Thomson Scattering, ECE, Reflectometer) was achieved over a widerange of plasma conditions. It was demonstrated that together with long termreliability and modest access port requirements, LIDAR can providemeasurements of a quality similar to a conventional imaging ThomsonScattering instrument.