Multipoint vertical-Thomson scattering diagnostic on HL-2A tokamak

Electron temperature and density measurement by Thomson scattering with a high repetition rate laser of 20 kHz on LHD

Thomson scattering measurements with a high-repetition-rate laser have commenced in the Large Helical Device. As an example of the fast phenomena captured by this diagnostic system, measurements at a 20 kHz repetition-rate in hydrogen pellet-injected plasmas are presented. Signal processing methods for this measurement have been developed and electron temperature profiles with almost 70 spatial points were evaluated at time intervals of 50 [Formula: see text]s. After Raman scattering calibration, electron density profiles were derived. Fast changes in the electron temperature and density profiles within 1 ms were observed.

Simulation of stray laser light of Thomson scattering systems in the HL-2M tokamak

Stray laser light is a serious problem that interrupts the measurement of electron temperature and density in Thomson scattering (TS) systems. This paper presents a ray-tracing simulation of stray laser light in HL-2M TS systems. A model including (i) a simplified laser-beam injection system, (ii) the scattered-light collection systems for central-point TS (CPTS) and edge TS (ETS), and (iii) the HL-2M vessel is built using the TracePro and CATIA software packages based on measurements of the bidirectional scattering distribution function at a wavelength of 532 nm. The simulation results show that no stray laser light reaches the injection surface of the collection lens of the CPTS system, and only a few stray laser rays of all the rays reaching the injection surface of the collection lens of the ETS system can be collected when the energy threshold per ray is 1 × 10^-16. The stray laser rays that reach the scattered-light collection systems are mainly from the first and second parts of the slides of the beam dump, so decreasing the roughness of those parts could be effective in reducing the level of stray laser light.