Principles for local measurement of anisotropic electron temperature of plasma using incoherent Thomson scattering

Abstract

Anisotropic electron temperature can be measured by utilizing two Thomson scattering spectra from different scattering angles. The ideal conditions for measurement are as follows: the sum of the two scattering angles is 180°, and the magnetic field is parallel to the bisector of the angle formed by the direction of laser propagation and the line of sight or is perpendicular to this bisector. When these conditions are satisfied, one of the spectra predominantly reflects the parallel electron temperature, and the other spectrum predominantly reflects the perpendicular electron temperature. A deviation in the direction of magnetic field of the order of approximately a few tens of degrees from the ideal direction is acceptable in terms of the deviation obtained by both rotating parallel to and tilting from the scattering plane.

Anisotropic electron temperature measurements without knowing the spectral transmissivity for a JT-60SA Thomson scattering diagnostic

“…The detailed calculation process to obtain the scattered spectrum is basically the same as in Ref. 4. The following expression of the spectral density 5 of the scattered light was employed:…”

“…Their temperature can be measured by a double-pass scattering system as the electron temperatures for parallel (T e|| ) and perpendicular (T e⊥ ) to the magnetic field. 3,4 This paper shows how the new method can be applied to the anisotropic measurements. Evaluation of the accuracy of T e in the (T e|| , T e⊥ ) space is then introduced by simulating measured signals based on a diagnostic design of the JT-60SA (under construction for the first plasma in 2019).…”

Off-Axis Temperature Anisotropy Measurement by Double-Pass Thomson Scattering Diagnostic System on TST-2

“…At the Thomson scattering system in the Tokyo Spherical Tokamak 2 (TST-2) device, backward and forward Thomson-scattered light are measured via a double-pass configuration. In this case, the temperature anisotropy can be measured directly depending on the angle between k i − k s ≡ Δ k and the magnetic field, where k i denotes the incident wave vector of the laser irradiation and k s denotes the scattered wave vector [2]. Temperature anisotropy may appear in low-density collisionless ST plasmas because of the large mirror effect.…”

An in-situ Relative Calibration Method for Thomson Scattering Diagnostics Using a Double-Pass Scattering System

“…1). This is a simpler laser system in contrast with another calibration method using two different wavelength lasers [4,5]. The authors show that the calibrated T e is corrected and independent of unknown transmissivity degradation.…”

“…The calibration factors (C j n e ) do not have clear systematic errors and their statistical errors are less than 8%, with the exception of one spectral channel for Rayleigh calibration. In future, error dependencies on θ and T e and comparison with another method in [4,5] will be discussed.…”