Advanced Line-Shape Calculations and their Use in the Determination of 'Isotropic' Magnetic Fields in Pulsed Plasmas

摘要

Summary form only given. Measurements of magnetic fields are central in many studies of equilibrium and transient laboratory plasmas. Known diagnostic methods are based on detecting an anisotropy in either the emitted radiation (the Zeeman/Paschen-Back effect) or the dispersion properties of the medium (the Faraday rotation). Consequently, these techniques can not be used in situations where the magnetic field has various directions in the region viewed by the diagnostic system or if its direction varies during the time of observation, as is often the case in e.g. laser-produced or pinch plasmas. Moreover, magnetic fields with amplitudes that vary in time or in space pose additional problems in the applicability of the traditional methods. In order to overcome these difficulties, a new spectroscopic approach for measurements of magnetic fields with such configurations in plasmas has been proposed and experimentally verified. The technique is based on the spectroscopic analysis of line-shapes of different fine-structure components of the same atomic multiplet that undergo different splitting under the magnetic field. Furthermore, this technique allows for accurate magnetic field detection in the presence of other rather dominating broadening mechanisms in plasma (the Stark and the Doppler effects). In order to obtain accurate results, especially in the case of Stark-dominated spectra, this technique requires detailed line-shape analysis. To this end, use is made of a new method for the calculation of the spectral line broadening in plasma. The idea of the method is to numerically simulate the motion of the interacting plasma particles (both ions and electrons) and use the resulting time-dependent field to obtain the evolution of the emitter system. This approach allows for addition of external electric and/or magnetic fields in a fully consistent manner, thus providing a powerful tool for investigating spectral line profiles in plasma under the simultaneous influence- of magnetic and electric fields.