  The traditional Thomson scattering diagnostic is based on measurement of the
wavelength spectrum of scattered light, where electron temperature measurements
are inferred from thermal broadening of the scattered laser light. At
sufficiently high temperatures, especially those predicted for ITER and other
burning plasmas, relativistic effects cause a change in the polarization state
of the scattered photons. The resulting depolarization of the scattered light
is temperature dependent and has been proposed elsewhere as a potential
alternative to the traditional spectral decomposition technique. Following
similar work, we analytically calculate the degree of polarization for
incoherent Thomson scattering. For the first time, we obtain exact results
valid for the full range of incident laser polarization states and electron
temperatures. While previous work focused only on linear polarization, we show
that circularly polarized incident light optimizes the degree of depolarization
for a wide range of temperatures relevant to burning plasmas. We discuss the
feasibility of a polarization based Thomson scattering diagnostic for ITER-like
plasmas with both linearly and circularly polarized light and compare to the
traditional technique.
