Implementation of Low Temperature spectrometers for the JET High Resolution Thomson Scattering diagnostic for disruption plasma measurements
This work presents a system upgrade of the High Resolution Thomson Scattering (HRTS) diagnostic on JET that allows it to measure low temperature (1 to 500 eV) plasma pre- and post-Thermal quench (TQ), which would help to further the understanding of the physics in SPI experiments. The upgrade was done by connecting optic fibres from the original HRTS system to four spectrometers specialized in measuring low temperature plasmas. The upgraded system allows measurement of low temperature plasma in up to 12 spatial points which can be flexibly distributed throughout JET outer midplane during the dedicated SPI experiments. In other JET experiments, four previously unused groups of fibres were used to measure central plasma to provide disruption data without changing the standard HRTS system. In dedicated SPI experiments, the timing of the Thomson scattering measurement with respect to the TQ was adjusted by changing the SPI timing and speed. The low temperature Thomson scattering (LTTS) system was installed, tested and cross calibrated against the standard HRTS diagnostic in a calibration pulse. The system worked reliably during the JET experiments and provided electron density and temperature profiles for pre- and post-TQ low temperature plasma in the SPI experiments.