Development of 2-D Thomson Scattering Measurement Using Multiple Reflection and the Time-of-Flight of Laser Light

Abstract

A new two-dimensional Thomson scattering measurement (2-D TS) system has been developed using multiple reflections and time-of-flight (TOF) of laser light. Its new ideas of our 2-D TS system are (1) to reflect YAG laser light for multiple times to cover the whole r − z plane of the ST (Spherical Tokamak) plasma, and (2) to reduce the number of polychromators and detectors using the time delay of the scattered light along the laser beam. We measured for the first time, Rayleigh scattering light signals with 50 ns time difference from two measurement points using a single detector, demonstrating the basic principle of the 2-D Thomson scattering system.

Development of a Thomson Scattering System in the TST-2 Spherical Tokamak

“…The system has a large solid angle (88 msr). This is larger than those achieved on other plasma devices, which are typically less than 20 msr [3][4][5][6]. The length of the scattering volume along the laser is 5.3 mm and the scattering angle is 120 • .…”

Basic Study of Two‐Dimensional Thomson Scattering Measurement by Multiple Reflections and Time‐of‐Flight of Laser Beam

“…Finally, it should be noted that calibration using measured Raman scattering data [4] would make possible 2-D measurement of not only the electron temperature but also the electron density. We plan to use more measurement points, with regard to the abovementioned problem of increased background light, so as to realize a precision TS measurement system.…”

“…In order to solve this problem, we earlier proposed a new method [4] in which (1) multiple YAG laser channels are arranged in a plasma chamber using a folded optical system, and (2) the time-of-flight (TOF) difference is measured by a single spectrometer using the temporal separation of scatter points on different paths; the proposed method was then applied to multipoint measurement [5].…”

Analysis method for Thomson scattering diagnostics in GAMMA 10/PDX

“…Thomson scattering (TS) diagnostics is one of the most useful methods for measuring electron temperature, T e , and density, n e , in fusion plasmas. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] For the tandem mirror GAMMA 10/PDX, we developed TS diagnostics for T e and n e measurements for single laser and plasma shots. 6 The value of n e (∼2 × 10 18 m −3 ) in the GAMMA 10/PDX plasma is typically lower than that in other fusion plasmas.…”

“…1,2,4 Some TS systems use high-speed analog-todigital converters or oscilloscopes to obtain the raw signal waveforms. [6][7][8][9][10][11] The output signals of the polychromators in a TS system are normally fitted to a Gaussian function in order to obtain the single-pass TS signal intensities. [7][8][9][10][11] TS data processing methods for raw TS signals with high-timeresolution data acquisition systems have been developed for electron temperature and density measurements, e.g., Monte-Carlo simulation for analyzing TS signals, 12 maximumlikelihood fitting method for TS fitting data, 13 and non-Gaussian pulse shape fitting method.…”