X-ray plasma diagnostics

Abstract

Results and methods are given for the investigation of hot laboratory and astrophysical plasmas parameters in a soft X-ray region 1 = 1-40 A. Line spectra of multiply charged ions are usually studied exper~mentally, and relative Intensities of spectral lines are measured. Achievements of modern physics of electronion collisions and theoretical spectroscopy make it possible to obtain for transient plasma the electronic temperature, density, ionization stage, and to investigate time and spatial distributions of these parameters. Introduction. X-ray spectroscopy of high temperature plasmas, as a new direction in plasma physics, has been developed recently by efforts of many scientists in different laboratories. This field deals mainly with line spectra of multiply charged ions in the spectrum region 1-40 A, and more hard adjacent continuous component is of interest. From physical point of view the X-ray plasma spectroscopy has the following background. In a case of ions with a high charge Z is> 1 any excitation decays mainly due to radiation. Other channels, both collisions and autoionization exist being well controlled corrections in comparison with radiative one. It leads to simple and understandable connections between spectral line intensities and mechanism of spectra formation. Modern physics of electronic and atomic collisions provides sufficient and accurate methods for calculations of cross sections and rate coefficients involving multiply charged ions. Theoretical spectroscopy has also reliable methods for classification and calculations of spectral lines in the X-ray region. Simultaneously, experimental technique has been developed with appropriate spectral, time and spatial resolution. It is worth noting that in the most of important cases low density astrophysical plasmas (electron density N, 5 1014 ~ m ~ ) and laboratory plasmas (N, 5 1020-1023 cmP3) are optically thin for the X-ray radiation. It helps much for interpretation of experimental results, and theoretical analysis. Therefore, the X-ray plasma spectroscopy contains three important parts : new sources and measurement methods of highly charged ion spectral data + physics of electronic and atomic collisions + theoretical spectroscopy of ions. For plasma physics the X-ray spectroscopy provides new and effective methods of contactless plasma diagnostics. It is essential that X-ray spectroscopy methods are equally valid for investigation both of astrophysical (active regions and Solar flares) and laboratory plasmas. At the present time this field has many hundreds of original papers and just few review publications. Among the latter papers [l-61 contain some systematization and extended list of references to earlier works. 1. Plasma parameters obtained from X-ray spectra. Multiply charged heavy ions are small impurities (much less than 1 %) in astrophysical plasmas and in stationary laboratory sources (Tokamak, Stellarator, etc.). Inertial plasmas produced by laser or electronic beams, plasmas of exploding wires and low-inductance sparks may be chemically homogeneous or consist of few heavy elements. X-ray spectroscopy provides universal diagnostic methods valid for all the cases mentioned. It is important to underline that plasma parameters can be obtained with the help of relative intensities of spectral lines, and one can avoid absolute flux calibration. Still absolute measurements provide the additional information (emission measure, etc.). Plasma parameters and types of spectral line used for the determination of them are listed in table I.