# Polarization of Lyman-α Line Due to the Anisotropy of Electron Collisions in a Plasma

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## Abstract

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## 1. Introduction

## 2. Theoretical Model for the Line Emission Polarization

#### 2.1. Polarization Formation of the Lyman-$\alpha $ Line

#### 2.2. Polarization Due to Anisotropic Electron Collisions

## 3. Results and Discussion

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**Line components included in the Lyman-$\alpha $ line. The solid and dashed lines represent the $\pi $- and $\sigma $-light, respectively. The numbers next to the lines indicate relative values of the Einstein A coefficient.

**Figure 2.**Examples of the electron velocity distribution function $f(v,\theta )$ for (

**a**) ${T}_{\perp}=30$ eV and ${T}_{\Vert}=10$ eV, and (

**b**) ${T}_{\perp}=30$ eV and ${T}_{\Vert}=100$ eV cases.

**Figure 3.**${A}_{\mathrm{L}}$ values under an assumption of a mono-energetic beam collision experiment (

**a**) and ${Q}_{0}^{0,0}$ and ${Q}_{0}^{0,2}$ (

**b**) for the $1{\phantom{\rule{0.222222em}{0ex}}}^{2}{\mathrm{S}}_{1/2}$ – $2{\phantom{\rule{0.222222em}{0ex}}}^{2}{\mathrm{P}}_{3/2}$ transition. The actual ${Q}_{0}^{0,2}$ labeled with $(-)$ takes negative values.

**Figure 4.**Alignment destruction rate ${C}^{2,2}(p,p){n}_{\mathrm{e}}$ evaluated from the Stark broadening width [15].

**Figure 5.**Example of the calculation results for P with several ${n}_{\mathrm{e}}$ values. ${T}_{\perp}$ is fixed at 32 eV and ${T}_{\Vert}$ is scanned. The open circle represents the combination of ${n}_{\mathrm{e}}=9.6\times {10}^{19}\phantom{\rule{0.166667em}{0ex}}{\mathrm{m}}^{-3}$ and $P=-0.033$ corresponding to the experimental value in Ref. [9], from which ${T}_{\Vert}=4.2$ eV is derived.

**Figure 6.**Fractions of breakdowns for the (

**a**) population inflow to the level $p=2$ and (

**b**) population outflow from the level $p=2$ as a function of ${n}_{\mathrm{e}}$ at ${T}_{\mathrm{e}}=10$ eV. The numbers represent the principal quantum number of the levels and the arrows indicate the transition direction. The hatched and open areas indicate the radiative and collisional transitions, respectively. The label “ioniz”. means the ionization.

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**MDPI and ACS Style**

Goto, M.; Ramaiya, N.
Polarization of Lyman-*α* Line Due to the Anisotropy of Electron Collisions in a Plasma. *Symmetry* **2021**, *13*, 297.
https://doi.org/10.3390/sym13020297

**AMA Style**

Goto M, Ramaiya N.
Polarization of Lyman-*α* Line Due to the Anisotropy of Electron Collisions in a Plasma. *Symmetry*. 2021; 13(2):297.
https://doi.org/10.3390/sym13020297

**Chicago/Turabian Style**

Goto, Motoshi, and Nilam Ramaiya.
2021. "Polarization of Lyman-*α* Line Due to the Anisotropy of Electron Collisions in a Plasma" *Symmetry* 13, no. 2: 297.
https://doi.org/10.3390/sym13020297