Edge Thomson scattering diagnostic with compact polychromators on the HL-3 Tokamak

Abstract

The edge Thomson scattering (ETS) diagnostic with compact polychromators on the HL-3 Tokamak was developed recently. The energy and repetition frequency of the Nd: YAG laser are 2.0 J and 30 Hz, respectively. The laser beam propagates vertically through the plasma region and the scattered light is observed horizontally. The projected scattering region at the plasma midplane is from 0.6 < r/a < 1.0. The 5-channel compact polychromator (width 432 mm, depth 472 mm and height 88 mm) is developed to measure the Thomson scattering spectra. Modular design in the power supply and the amplifier circuits simplifies the assembly and maintenance of the polychromator. By using the new narrow band filters with cut-off depth larger than OD 4, the stray light resulted from Nd: YAG laser has been suppressed by the polychromator. The signal to noise ratio (SNR) range of each channel is from 10 to 200 depending on plasma parameters. The designed electron temperature measurement range is from 5 to 1000 eV and electron density measurement range is from 5 × 1018 to 1 × 1020 m-3. New measurement results of electron temperature by ETS are compared with that from the electron cyclotron emission (ECE) radiometer. The time evolution of ETS and ECE matches with each other in different plasma discharges. Combined with the data from the core Thomson scattering diagnostic system, the plasma electron temperature profile on the HL-3 tokamak is presented for the first time.