Line Intensity Ratios in the EIS Range Sensitive to Electron Densities in 10⁷ K Plasmas

Abstract

Electron density variations during the rise, maximum, and decay phases of flaring plasmas at T simeq 10 MK are important quantities to be used to test flare models. To date, electron density values measured in solar flares are, with few exceptions, only lower limits. With the launch of the EUV Imaging Spectrometer (EIS) on Hinode, it has become possible for the first time to measure electron densities and their time evolution during flares. In this paper we discuss electron density diagnostics in the 10¹⁰-10¹³ cm^-3 range by means of intensity ratios of lines emitted by Ti, Cr, and Mn ions within the Hinode/EIS wavelength range.