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

Symmetry ◽  
2021 ◽  
Vol 13 (2) ◽  
pp. 297
Author(s):  
Motoshi Goto ◽  
Nilam Ramaiya
Keyword(s):  
Polarization State ◽  
Diagnostic System ◽  
Nonequilibrium State ◽  
Thomson Scattering ◽  
Electron Collision ◽  
Polarization Degree ◽  
Fusion Plasma ◽  
Density Region ◽  
Electron Collisions ◽  
Model Calculations

We have developed an atomic model for calculating the polarization state of the Lyman-α line in plasma caused by anisotropic electron collision excitations. The model assumes a nonequilibrium state of the electron temperature between the directions parallel (T‖) and perpendicular (T⊥) to the magnetic field. A simplified assumption on the formation of an excited state population in the model is justified by detailed analysis of population flows regarding the upper state of the Lyman-α transition with the help of collisional-radiative model calculations. Calculation results give the polarization degree of several percent under typical conditions in the edge region of a magnetically confined fusion plasma. It is also found that the relaxation of polarization due to collisional averaging among the magnetic sublevels is effective in the electron density region considered. An analysis of the experimental data measured in the Large Helical Device gives T⊥/T‖=7.6 at the expected Lyman-α emission location outside the confined region. The result is derived with the absolute polarization degree of 0.033, and T⊥=32 eV and ne=9.6×1018m−3 measured by the Thomson scattering diagnostic system.

Design of a Thomson scattering diagnostic system for VEST

2015 ◽  
Vol 96-97 ◽  
pp. 882-886 ◽  
Author(s):  
Young-Gi Kim ◽  
Jong Ha Lee ◽  
Jeongwon Lee ◽  
YoungHwa An ◽  
Jeong Jeung Dang ◽  
...  
Keyword(s):  
Diagnostic System ◽  
Thomson Scattering ◽  
Thomson Scattering Diagnostic

scholarly journals Spectral and polarization properties of black hole accretion disc emission: including absorption effects

2020 ◽  
Author(s):  
R Taverna ◽  
L Marra ◽  
S Bianchi ◽  
M Dovčiak ◽  
R Goosmann ◽  
...  
Keyword(s):  
Black Hole ◽  
Polarization State ◽  
General Rule ◽  
Accretion Disc ◽  
Accretion Discs ◽  
Polarization Degree ◽  
Monte Carlo Code ◽  
Black Hole Spin ◽  
Black Hole Accretion ◽  
Hole Accretion

Abstract The study of radiation emitted from black hole accretion discs represents a crucial way to understand the main physical properties of these sources, and in particular the black hole spin. Beside spectral analysis, polarimetry is becoming more and more important, motivated by the development of new techniques which will soon allow to perform measurements also in the X- and γ-rays. Photons emitted from black hole accretion discs in the soft state are indeed expected to be polarized, with an energy dependence which can provide an estimate of the black hole spin. Calculations performed so far, however, considered scattering as the only process to determine the polarization state of the emitted radiation, implicitly assuming that the temperatures involved are such that material in the disc is entirely ionized. In this work we generalize the problem by calculating the ionization structure of a surface layer of the disc with the public code cloudy, and then by determining the polarization properties of the emerging radiation using the Monte Carlo code stokes. This allows us to account for absorption effects alongside scattering ones. We show that including absorption can deeply modify the polarization properties of the emerging radiation with respect to what is obtained in the pure-scattering limit. As a general rule, we find that the polarization degree is larger when absorption is more important, which occurs e.g. for low accretion rates and/or spins when the ionization of the matter in the innermost accretion disc regions is far from complete.

Data processing and analysis of the imaging Thomson scattering diagnostic system on HT-7 tokamak

2013 ◽  
Vol 84 (5) ◽  
pp. 053502 ◽  
Author(s):  
Xiaofeng Han ◽  
Chunqiang Shao ◽  
Xiaoqi Xi ◽  
Junyu Zhao ◽  
Zang Qing ◽  
...  
Keyword(s):  
Data Processing ◽  
Diagnostic System ◽  
Thomson Scattering ◽  
Thomson Scattering Diagnostic

Screened Collision-Induced Quantum Interference in Collisional Plasmas

2009 ◽  
Vol 64 (3-4) ◽  
pp. 233-236 ◽  
Author(s):  
Sang-Chul Na ◽  
Young-Dae Jung
Keyword(s):  
Cross Section ◽  
Quantum Interference ◽  
Potential Model ◽  
Collision Cross Section ◽  
Electron Collision ◽  
Particle Collision ◽  
Interference Effects ◽  
Particle Collisions ◽  
Collision System ◽  
Electron Collisions

Abstract The effects of neutral particle collisions on the quantum interference in electron-electron collisions are investigated in collisional plasmas. The effective potential model taking into account the electronneutral particle collision effects is employed in order to obtain the electron-electron collision cross section including the total spin states of the collision system. It is found that the collision effects significantly enhance the cross section. In addition, the collision-induced quantum interference effects are found to be significant in the singlet spin state. It is shown that the quantum interference effects decrease with increasing the thermal energy of the plasma. It is also shown that the quantum interference effects increase with an increase of the collision energy

scholarly journals First observation of the depolarization of Thomson scattering radiation by a fusion plasma

2018 ◽  
Vol 58 (4) ◽  
pp. 044003
Author(s):  
L. Giudicotti ◽  
M. Kempenaars ◽  
O. McCormack ◽  
J. Flanagan ◽  
R. Pasqualotto ◽  
...  
Keyword(s):  
Thomson Scattering ◽  
Fusion Plasma

Progress of development of Thomson scattering diagnostic system on COMPASS

2010 ◽  
Vol 81 (10) ◽  
pp. 10D531 ◽  
Author(s):  
P. Bilkova ◽  
R. Melich ◽  
M. Aftanas ◽  
P. Böhm ◽  
D. Sestak ◽  
...  
Keyword(s):  
Diagnostic System ◽  
Thomson Scattering ◽  
Thomson Scattering Diagnostic

scholarly journals NIFS Atomic and Molecular Numerical Database for Collision Processes

Atoms ◽  
2020 ◽  
Vol 8 (4) ◽  
pp. 71 ◽  
Author(s):  
Izumi Murakami ◽  
Masatoshi Kato ◽  
Masahiko Emoto ◽  
Daiji Kato ◽  
Hiroyuki A. Sakaue ◽  
...  
Keyword(s):  
Cross Sections ◽  
Numerical Data ◽  
Data Sources ◽  
Rate Coefficients ◽  
Electron Collision ◽  
Fusion Plasma ◽  
Scattering Coefficients ◽  
Bibliographic Information ◽  
Ion Collisions ◽  
Collision Processes

The National Institute for Fusion Science (NIFS) has compiled and developed atomic and molecular numerical databases for various collision processes and makes it accessible from the internet to the public. The database contains numerical data of cross sections and rate coefficients for electron collision or ion collisions with atoms and molecules, attached with bibliographic information on their data sources. The database system provides query forms to search data, and numerical data are retrievable. The graphical output is helpful to understand energy dependence of cross sections and temperature dependence of rate coefficients obtained by various studies. All data are compiled mainly from published literature, and data sources can be tracked by the bibliographic information. We also have data of sputtering yields and back-scattering coefficients for solid surfaces collided by ions in the database. All data in the database are applicable to understand atomic and molecular processes in various plasmas, such as fusion plasma, astrophysical plasma and applied plasma, as well as for understanding plasma–surface interaction in plasmas.

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