Role of Plasma Spectroscopy in Understanding Plasma Processes on the Sun

Abstract

Emission spectroscopic methods are very useful in determining the plasma parameters such as electron density, electron temperature, chemical abundances and energy levels of atoms and ions. A knowledge of the above mentioned parameters and collision cross sections provides an insight into various plasma processes on the Sun. As one passes from photosphere to chromosphere and corona the temperature as well as the electron density changes drastically (Te ~4500 − 2×1060K; n e ~ 108 − 1013 cm−3) (1). Hence the solar spectrum.excited by different mechanisms and different equilibrium conditions, extends from vacuum ultraviolet to visible and infrared regions. For example the spectrum in the region between 3000−1300Å is produced by the upper photosphere and lower chromosphere. In this region the temperature is in the range of 6000-10000 K. This region is characterised by several emission and absorption Lines superimposed over continuum. Below 1600Å consists of emissions from highly ionised atomic species originating from chromosphere and corona (2).A correct interpretation of the spectral features is possible only after understanding the influence of various factors on spectral line shapes and intensities. They are 1) damping by collisions with neutral atoms; 2) collisions by charged particles leading to linear and quadratic Stark effects on atomic lines of hydrogen and helium; 3)thermal Doppler broadening 4) Doppler broadening or shift due to microturbulent velocity field.