Modeling of Lyman-α line polarization in fusion plasma due to anisotropic electron collisions

We have derived a formula for calculating the polarization state of the Lyman-α line in plasma caused by anisotropy in the electron velocity distribution function. Calculation results under the condition of the magnetically confined fusion plasma show that the longitudinal alignment of 0.01 is caused by approximately 10%–20% difference in the electron temperature in the directions parallel and perpendicular to the magnetic field. It is also found that the polarization decreases with the increasing electron density, n_e, due to the collisional population averaging effect over the magnetic sublevels in the range of n_e > 10¹⁸ m⁻³ and is virtually extinguished at n_e = 10²¹ m⁻³.