Study on Electron Density Diagnostics of Si VIII Ion for Non-Maxwellian Distribution in Solar Transition Region
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Study on Electron Density Diagnostics of Si VIII Ion for Non-Maxwellian Distribution in Solar Transition Region Jian He* and Qingguo Zhang School of Physics and Engineering, Henan University of Science and Technology, Luoyang, 471023 China Received March 27, 2019; revised November 19, 2019; accepted December 5, 2019
Abstract—For accurate electron density diagnostics in the solar transition region, the principle of electron density diagnostics are discussed by lines from Si VIII ion for kappa and Maxwellian distributions By observed line ratio of the Si VIII 1440.50 to 1445.75 A˚ lines in quiet sun and active region, the electron density is discussed for any observed line ratio, and results are consistent with reported values in literature. The relationships between line ratio and electron density for the kappa and Maxwellian distributions are also discussed, in the case of lower and higher electron density limits, and results indicate that different distributions have no effect on relationships between the line ratio and the electron density at lower or higher electron density limit. This discussion is significant for accurate electron density diagnostics in the solar transition region, which will be important for study on coronal heating and acceleration of solar wind. DOI: 10.1134/S1063773720010028 Keywords: solar transition region, electron density diagnostics, non-Maxwellian distribution.
INTRODUCTION
Ultraviolet (EUV) lines emitted from the solar transition region, which may provide important sources for plasma diagnostics. In the solar atmospheric plasma especially in the transition region, the electron density varies sharply, thus, distribution of the electron density could not be described by the Boltzmann distribution. Meanwhile, frequent collisions occur between ions and electrons in the solar transition region. Thus, for accurate spectral diagnostics of the solar atmospheric plasma, the collisional excitation and de-excitation model should be used for the solar atmospheric plasma diagnostic. This model has been used widely in the solar atmospheric plasma diagnostics in recent years, especially in the solar transition region (Warren and Hassler 1999; He et al. 2016). In the solar atmosphere plasma diagnostics by the collision excitation and de-excitation model, the Maxwellian distribution of electron velocity is often assumed before. However, non-Maxwellian distribution of the electron velocity has been found recently (Rousseldupre 1980). The actual distribution is close to the Maxwellian distribution at low energy while has a power-law distribution at high energy, which can be modeled by the κ distribution. For example, Si III lines are used for temperature and electron density diagnostics for the solar atmospheric plasma, however, results indicate that different ratios cannot yield consistent results if the Maxwellian distribution is assumed. Consistency in terms of temperature
Diagnostics of the solar atmospheric plasma has been an interesting subject for several decades. By use of the observed line rati
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