R. Stamm

On the role of ion dynamics in the stark broadening of hydrogen lines

Abstract A review and critical discussion of previous treatments of ion dynamics in hydrogen-line broadening by plasmas is followed by the description of a computer simulation of ion motion for the Lyman-β line of hydrogen. The profile of Ly-β is calculated for the static ion case as well as for three dynamic emitter-perturber couples, namely H-H + , H-Ar + , and D-Ar + . Our results, which show an important effect due to ion dynamics, are compared with a recent experimental result and with theoretical results obtained by the model microfield method.

Transport of neutral particles in turbulent scrape-off layer plasmas

The effect of turbulence on the transport of neutral species (atom, molecules) in plasmas is investigated. A stochastic model relying on a multivariate gamma distribution is introduced to describe turbulent fluctuations, and implemented in EIRENE. The effects of fluctuations on the neutral density and ionization source radial profiles are investigated. The role of temperature fluctuations is discussed in detail. Calculations with ITER scrape-off layer parameters are presented, and two distinct regimes with respect to the effects of temperature fluctuations are identified, depending on the far SOL mean temperature. Finally, the influence of fluctuations on impurity contamination is discussed.

ASPECTS OF PLASMA SPECTROSCOPY : RECENT ADVANCES

Abstract Two important recent developments in Stark broadening are presented in this work: The first describes the Frequency Separation Technique (FST), which is motivated by the standard electron-ion separation and has important applications in that, coupled to any of a variety of methods capable of treating the intermediate ion-dynamical regime, (but not capable of treating ion impact), presents a unified and practical solution to the ion-dynamical problem. That is, this technique allows the relaxation of the quasistatic approximation. The second describes recent improvements that allow the accurate calculation of electron impact widths.

Effects of radiator motion on plasma-broadened hydrogen lyman-β

Abstract For the hydrogen line L-β, broadening in an Ar + -plasma ( N e = 7.2 × 10 16 cm −3 , T = 12,200 K ) has been investigated with the help of a computer simulation of ion broadening taking full account of radiator motion. The anisotropy in Stark broadening for a moving radiator is found to be negligible under these conditions, but Stark profiles depend markedly on the radiator speed. The final line profile (including Stark and Doppler broadening) is nearly the same as the profile obtained by convolution of the Doppler profile with the Stark profile for radiators at rest and fictitious ions with the reduced mass of the atom-ion pair.

Effects of turbulent fluctuations with prescribed statistics on passive neutral particle transport in plasmas

This work addresses the transport of neutral particles (atoms, molecules) in magnetized fusion plasmas, in the presence of density fluctuations with given statistics. The latter are described by a multivariate gamma distribution. The geometry is a 2D slab and turbulence is assumed to be statistically homogeneous. The average neutral density and ionization source, which are the quantities relevant for integrated simulations and diagnostic applications, are calculated analytically in the scattering free case. The boundary conditions and the ratio of the turbulence correlation length to the neutral mean free path are identified as the main control parameters in the problem. The non-trivial relationship between the average neutral density and the ionization source is investigated. Monte Carlo calculations including scattering are then presented, and the main trends obtained in the scattering free case are shown to be conserved.

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.

Narrowing of Doppler spectral line shapes by correlated ion and electron temperature fluctuations

The influence of low-frequency temperature fluctuations on Doppler line shapes is investigated. It is shown that the line profile can be strongly narrowed if the fluctuations of ion and electron temperatures are correlated. This result shows that the widely used model retaining only velocity fluctuations in the analysis of Doppler lines might lead to misleading conclusions about turbulence level.

Influence of hot electrons on radiative properties of a helium plasma

We have studied anomalous line intensities in space resolved helium plasmas in different configurations of the MISTRAL-B plasma divertor simulator experiment. Spectral simulations show that the different experimental configurations differ from one another by the hot electron fraction which drives the observed anomalous large emission of the singlet line 1s2s 1S–1s5p 1P compared with the triplet lines 1s2p 3P–1snd 3D. Theoretical spectra analyses carried out with the recently developed non-Maxwellian SOPHIA code are in good agreement with the data and allowed one to identify non-Maxwellian signatures. Independently performed Langmuir probe measurements are in good agreement with the spectroscopic analysis.