| Laser Thomson scattering (TS) is a very reliable tool to diagnose plasma electron temperature, and the electron density in the measurement region can be measured after absolute calibration with Raman or Rayleigh scattering of neutral gas. TS is incoherent TS. All the electrons are the same, and the scattering light intensity equals to the summation of all the electron scattering lights intensity. The different scattering systems of high special and interval resolution have been developed to measure electron temperature and density of different plasma region. The system is designed and will be made to diagnose electron temperature and density in major plasma region, divertor region and x point on the international thermonuclear experimental reactor (ITER).The multi-channel laser TS system has been introduced on HL-2A, which includes a Nd:YAG laser, 5-channel polychromators, a calibration system, a scattering light collective system, data collection & analysis system and so on. The system provides electron temperature and relative density data of 6 spatial points below the mid-plane (the measurement of the scattering light is along the vertical laser beam, which is displaced by 1.75cm from the vessel centre towards the high field side). A central point z1 is fixed at -3.3cm, the distance of two nearby points from z2 to z6 is 2.2cm, and the 5 points can be moved. Thus the measured plasma region is z = -3 ~ -35cm, and the profile of electron temperature is measured. The spatial resolution is about 2.2cm along the z axis, the interval is 100ms, and the measurement range of electron temperature is 0.5keV≦ Te≦ 8keV.The scattering coefficient respect to geometric parameters such as solid angle and scattering length with Raman scattering of nitrogen gas, and electron temperature is primary calculated. The cross section and scattering signal of Raman scattering are smaller and stronger than those of TS, so the stray light level of the system should be very low. The wavelength/band of the interference filter of the polychromator for Raman calibration channel is 1040/20nm. By measuring Raman scattering signal of several different pressures, and averaging 30 scattering signals, the curve of scattering intensity and gas pressure is fitted, and then the electron density is calculated using Raman scattering cross section.Geometric parameters of plasma can be calculated timely by CF code. In the case that plasma pressure, electron temperature and density are the same in the same flux surface, using the calculated results of CF code, the electron temperature is translated to the flux surface coordinates, and the profiles are fitted as a kind of para-curve. The volume-averaged electron temperature is calculated.
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