C. Mossé

Experimental results on line shifts from dense plasmas

Abstract The dynamics of the implosion of a deuterium-filled microsphere has been investigated via the detailed analysis of the Ar XVII 1s 2 –1s3p 1 P line shape. Ar is doped into the deuterium core for diagnostic purposes. For the analysis calculations of Ar XVII 1–3 line shape including lithium-like dielectronic satellites were compared with time-resolved data. Three fitting parameters were used: (a) electron temperature, (b) electron density, and (c) relative shift of the wavelength axis between calculation and data. The temporal evolution of the core electron temperature and density were derived, and the shot-to-shot formation of the core plasma was shown to be reliable and reproducible. We report on the wavelength shift of the Ar XVII 1s 2 –1s3p 1 P line shape between electron densities of 10 23 – 10 24 cm −3 , results indicate a systematic red shift with increasing density.

Spectroscopic line shape measurements at high densities

Abstract A comprehensive spectroscopic investigation of plasmas at extreme conditions produced by indirectly driven inertially confined implosions is described. In these experiments argon is doped into the gas filled core of implosion targets and the Ar K-shell emission is used to make time resolved measurements of electron density and electron temperature. The electron density is derived from the Stark broadened Ar XVII 1s 2 -1s3p line shape, the electron temperature is derived from the line intensity ratio of the Ar XVII ls 2 -ls3p transition and the lithium-like dielectronic satellites 2121′, 2131′ lying on the low energy side of the resonance line. We give examples of the experimental data and compare the extracted time histories of electron density and electron temperature with simple radiation hydrodynamic simulations, where broad agreement is found. Detailed line shape measurements of the Ar XVII 1s 2 -1s3p transition are presented and the absence of an intensity dip at line center in the experiment results is discussed. The validity of the quasi-static ion approximation for these plasma conditions is tested by varying the mass of the fill gas in the core. Results from deuterium, deuterated methane, and nitrogen filled implosions are presented and indicate ion dynamic effects are not responsible for the line center discrepancy. We discuss other possibilities including spatial gradients in the core affecting measurements of the intrinsic line shape.

Ground work supporting the codes based upon the frequency fluctuation model

The development of the frequency fluctuation model (FFM) had two strong motivations. First, there was interest to model line shapes accounting for ion dynamics and second the inclusion of higher order radiative processes in plasmas was considered important for future development. The FFM relies on the hypothesis that the emitter-plasma system behaves approximately like a pseudo-molecule embedded into a thermal bath. As a result, the pseudo-system can be considered to have internal states connected to each others by collisions with the bath. This simple starting point has been translated into a powerful renormalization process, called FFM, resulting, a few years ago, in a fast line shape code called Pim Pam Poum (PPP) and more recently into a code for the computation of radiative redistribution. The authors present a few of the milestones in this evolution.

X-RAY LASER PHOTOPUMPED RESONANCE FLUORESCENCE

Abstract A calculation of the resonance fluorescence spectrum of the 146.526 A 3d-2p transition of fluorine-like magnesium photopumped by the 146.515 A zirconium X-ray laser line is discussed in connection with an experimental measurement in a hot, dense laser produced plasma. The calculation of the fluorescence spectral profile is based on a recent extension of the Frequency Fluctuation Model (FFM) that enables the computation of radiative redistribution and other higher order radiative processes. The discussion of the photopumping experiment includes an analysis of the optimal plasma conditions and the associated characteristics of the redistributed radiation with specific reference to the experimental feasibility. The potential information to be acquired in the comparison of the computational and experimental results also will be considered.

An analytical model for the Ly α redistribution function in conditions of tokamak edge plasmas

Radiation redistribution is investigated for applications to magnetic fusion studies. An analytical model, suitable for Monte Carlo simulations of radiative transfer, is developed for the redistribution function of the resonance line of hydrogen isotopes. The model retains Zeeman and Stark effects in the atoms rest frame and in the impact approximation. The Zeeman effect is shown to play a major role on redistribution. Discussions are given on consequences of the Doppler effect in the laboratory frame.

Electric micro fields in simulated two component plasmas.

The statistical properties of local electric fields in an classical plasma are investigated by molecular dynamics (MD) simulation. Two‐component plasma simulations of neutral hydrogen, protons and electrons for intermediate plasma coupling conditions, typically Ne≈1018cm−3, Te≈1eV, have been carried out. These simulations appear as a possible and very useful way to generate relevant microfield sample‐sets appropriate for ion emitter lineshape simulations for plasma spectroscopy and to provide guidance for line shape modeling.

Experiments on hot and dense laser-produced plasmas

Plasmas generated by irradiating targets with ∼20 kJ of laser energy are routinely created in inertial confinement fusion research. X-ray spectroscopy provides one of the few methods for diagnosing the electron temperature and electron density. For example, electron densities approaching 1024 cm−3 have been diagnosed by spectral linewidths. However, the accuracy of the spectroscopic diagnostics depends the population kinetics, the radiative transfer, and the line shape calculations. Analysis for the complex line transitions has recently been improved and accelerated by the use of a database where detailed calculations can be accessed rapidly and interactively. Examples of data from Xe and Ar doped targets demonstrate the current analytic methods. First we will illustrate complications that arise from the presence of a multitude of underlying spectral lines. Then, we will consider the Ar He-like 1s2(1S0)−1s3p(1P0) transition where ion dynamic effects may affect the profile. Here, the plasma conditions are ...

Improved Frequency Fluctuation Model for Spectral Line Shape Calculations in Fusion Plasmas

A very fast method to calculate spectral line shapes emitted by plasmas accounting for charge particle dynamics and effects of an external magnetic field is proposed. This method relies on a new formulation of the Frequency Fluctuation Model (FFM), which yields to an expression of the dynamic line profile as a functional of the static distribution function of frequencies. This highly efficient formalism, not limited to hydrogen‐like systems, allows to calculate pure Stark and Stark‐Zeeman line shapes for a wide range of density, temperature and magnetic field values, which is of importance in plasma physics and astrophysics. Various applications of this method are presented for conditions related to fusion plasmas.

MD and FFM Electron Broadening for Warm and Dense Hydrogen Plasmas

Direct integration of the semi‐classical evolution equation based on Molecular Dynamics simulations (MD) and the Frequency Fluctuation Model (FFM) have long been used to synthesize spectra accounting for ion dynamics. Cross comparisons of these approaches generally show results in good agreement. Recently, interest in low temperature (Te ∼ 1eV) and high density (Ne ∼ 1018 cm−3) hydrogen plasma spectroscopy has motivated extended applications of FFM. Arising discrepancies were found to originate in electron collision operators suggesting an improper use of impact approximations for warm and dense plasma conditions. In order to clarify this point, new useful cross comparisons between MD and FFM have been carried out for electron broadening.

Frequency fluctuation model survey

Developed since the late eighties the frequency fluctuation model line shape code (today called PPP, formerly PimPamPoum) is recognized as a flexible fast and accurate state of the art plasma spectroscopy tool altogether with a powerful link between charge dynamics theory in hot and dense matter and spectroscopy.