Polarization of incoherent Thomson scattering for electron temperature measurement

Abstract

This paper reviews the polarization properties of Thomson scattered (TS) light as applied to electron temperature measurement. The theoretical background is based on Stokes vector transformations and Mueller matrices. The review starts from scattering on a single electron and proceeds to the combined effect of many particles. Then, this general approach is subdivided into frequency-integrated and frequency-resolved applications. For each of them, the exact relativistic analytical solutions are presented in the form of Mueller matrix elements averaged over the relativistic Maxwellian distribution function. The dependencies of the elements on the scattering angle, electron temperature, and frequency of the scattered radiation (in the frequency-resolved case) are presented. These solutions form the basis for accurate analysis of the degree of depolarization of TS radiation. Results obtained for the frequency-integrated regime are reviewed and new solutions for the frequency-resolved case are reported, making a bridge between the two limiting cases. Experimental setups for polarization-based TS diagnostics are compared. A combination of polarization-based and spectral-based techniques are also described.

Relativistic electron kinetic effects on laser diagnostics in burning plasmas

“…Instead of using the time-dependent scattered field E s (r, t) involved in the definition of the Stokes vector (2.1), we operate with the Fourier transformed truncated electric field E (T ) s (r, ω). For a stationary incident laser beam characterized by an infinitely long wave packet of monochromatic radiation the truncation method is a substantial element of the Fourier transformation [18,19]. The integration over t associated with the time averaging in (2.1) is converted to integration over ω.…”

“…[15] and discussed in detail in ref. [19], this intuitive approach fails to accurately characterize the scattered radiation due to the interruptive nature of the signals emitted from the finite scattering volume. This effect is referred in the literature as to the finite transit time effect (FTT).…”

“…[18]. Analytical solutions for the frequency-resolved case were obtained recently and published in a topical review [19] of the Thomson scattering polarization concept. The newly derived analytical solutions for the frequency-resolved case have been lately verified by comparison with the pure numerical code developed by L. Giudicotti and co-authors.…”

Polarimetric Thomson scattering for high Tefusion plasmas

“…where S i is the Stokes vector of the incident laser radiation and M (ω, θ, T e ) is the TS spectral Mueller matrix which is a function of the frequency ω of the scattering radiation [3]. A convenient, almost completely analytical expression of M (ω, θ, T e ) has been calculated only recently [9]. We now discuss the spectrum and the polarization of the two components of the scattering radiation considering first the case in which the incident laser beam has LHP polarization.…”

“…This is a relativistic effect noticeable only in very hot (T e ≥ 10 keV) plasmas, whose existence has been recognized as early as in 1968 by Theimer and Hicks [1] who immediately suggested exploiting it for measuring the T e of very hot plasmas. Subsequently the method has been studied by Orsitto and Tartoni [2], Segre and Zanza [3] and, more recently by other authors [4][5][6][7][8][9]. So far polarimetric TS has never been used for diagnostic purposes because this depolarization effect is weak even in the hottest plasmas of fusion experiments operating today.…”