Search

Attosecond pulses created by high-order harmonic generation in gases often exhibit strong chromatic aberrations, arising from the broad bandwidth and wavelength-dependent nonlinear light-matter interaction. When the driving laser intensity varies spatially, as for Gaussian driving beams, the apparent source position of the harmonics differs significantly from one order to the next, thus affecting the achievable intensity and duration of the attosecond pulses when they are focused on a target. We show that these chromatic aberrations can be reduced by spatially shaping the fundamental beam to generate high-order harmonics with a driver having a flat-top profile inside the gas medium. By measuring both the intensity profile and wavefront for each harmonic in a plane, we access the extreme ultra-violet (XUV) beam properties and investigate these properties near focus. We observe that controlling chromatic aberrations by flat-top spatial shaping strongly reduces the variation of the XUV spectrum on the beam axis during propagation and, in return, the longitudinal sensitivity of both the temporal profiles and the temporal shifts of the focused attosecond pulses., 12 pages, 8 figures + supplementary material: 10 pages, 13 figures

International audience; Recent experiments in gas-phase molecules have shown the versatility of using attosecond pulse trains combined with IR femtosecond pulses to track and control excitation and ionization yields on the attosecond timescale. The interplay between electron and nuclear motions drives the light-induced transitions favoring specific reaction paths, so that the time delay between the pulses can be used as the tracking parameter or as a control knob to manipulate the molecular dynamics. Here, we present ab initio simulations on the hydrogen molecule to demonstrate that by filtering the high harmonics in an attosecond pulse train one can quench or enhance specific quantum paths thus dictating the outcome of the reaction. It is then possible to discriminate the dominant sequential processes in two-photon ionization, as for example molecular excitation followed by ionization or the other way around. More interestingly, frequency filters can be employed to steer the one- and two-photon yields to favor electron emission in a specific direction.

The high brilliance of ultrashort X-ray pulses recently generated in free electron lasers will soon open the way to the investigation of non-linear processes that still remain inaccessible due to the smallness of the corresponding cross sections. One of them is stimulated Compton scattering from molecules. In this work, we investigate stimulated Compton scattering from fixed-in-space H2 molecules in the few-hundred eV photon energy range, where both dipole and non-dipole transitions are important. We show that the interference between dipole and non-dipole transitions leads to pronounced asymmetries in the electron angular distributions. These asymmetries strongly depend on molecular orientation, to the point that they can lead to electron emission in either the forward or the backward directions with respect to the propagation axis, or in both directions, or even in the orthogonal direction. This is in contrast with Compton scattering from free electrons or atomic targets. X-ray free electron lasers provide high brightness sources that permit the study of low-cross section phenomena, such as Compton scattering from atoms and molecules. Here, the angular distribution of electrons after stimulated Compton scattering from molecular hydrogen are simulated, revealing the influence of dipole and non-dipole transitions.

International audience; Controlling the wavefront of an extreme ultraviolet (XUV) high-order harmonic beam during the generation process offers the capability of modifying the beam properties without resorting to any XUV optics. By characterizing the XUV intensity profile and wavefront, we quantitatively retrieve both the size and the position of the waist of each harmonic generated in an argon jet. We show that optics-free focusing can occur under specific generating conditions leading to XUV focii of micrometer size. We also demonstrate that each focus is located at distinct longitudinal positions. Using this remarkable XUV wavefront control combined with near focus spatial selection, we experimentally demonstrate efficient and adjustable spectral filtering of the XUV beam, along with a strong rejection of the fundamental beam, without using any XUV optics. The experimental results are compared with simulations providing the impact of the filtering on the temporal profile of the XUV field. It shows that the attosecond structure is preserved and that the beam is more homogeneous after the filtering, thereby reducing the longitudinal focii shift. This is a major step to achieve high XUV intensity and probing ultrafast processes with an improved resolution.

Poster session III (Tu4A); International audience; We experimentally characterize XUV intensity profiles and wavefronts, and demonstrate XUV beams focusing without resorting any optics. We use this coherent effect to spectrally filter group of harmonics. Simulations show possible control of attosecond temporal structure.

Synopsis We present a theoretical study on H2 photionization taking into account coupled electron-nuclear motion and non-dipole effects. In the first part we study the effects of harmonic filtering in a pump-probe scheme using attosecond train pulses (ATP) in dipole approximation. In the second part we investigate nondipole effects in XUV and soft X-ray regimes.

Controlling generation of XUV high-order harmonic beams provides focusing of attosecond pulses without any XUV optics., By experimentally studying high-order harmonic beams generated in gases, we show how the spatial characteristics of these ultrashort extreme-ultraviolet (XUV) beams can be finely controlled when a single fundamental beam generates harmonics in a thin gas medium. We demonstrate that these XUV beams can be emitted as converging beams and thereby get focused after generation. We study this optics-less focusing using a spatially chirped beam that acts as a probe located inside the harmonic generation medium. We analyze the XUV beam evolution with an analytical model and obtain very good agreement with experimental measurements. The XUV foci sizes and positions vary strongly with the harmonic order, and the XUV waist can be located at arbitrarily large distances from the generating medium. We discuss how intense XUV fields can be obtained with optics-less focusing and how the order-dependent XUV beam characteristics are compatible with broadband XUV irradiation and attosecond science.

The many-body quantum nature of molecules determines their static and dynamic properties, but remains the main obstacle in their accurate description. Ultrashort extreme ultraviolet pulses offer a means to reveal molecular dynamics at ultrashort timescales. Here, we report the use of time-resolved electron-momentum imaging combined with extreme ultraviolet attosecond pulses to study highly excited organic molecules. We measure relaxation timescales that increase with the state energy. High-level quantum calculations show these dynamics are intrinsic to the time-dependent many-body molecular wavefunction, in which multi-electronic and non-Born−Oppenheimer effects are fully entangled. Hints of coherent vibronic dynamics, which persist despite the molecular complexity and high-energy excitation, are also observed. These results offer opportunities to understand the molecular dynamics of highly excited species involved in radiation damage and astrochemistry, and the role of quantum mechanical effects in these contexts., The many-body quantum nature of molecules determines their static and dynamic properties, but remains the main obstacle in their accurate description. Here, the authors employ ultrafast spectroscopic methods to explore the dynamics of highly excited organic molecules, revealing many-body effects and hints of coherent vibronic dynamics which persist despite their molecular complexity.

We investigate the harmonic generation induced by the interaction of a laser field with a solid target. The harmonic spectra is composed of the contribution of two processes interpreted as interband and intraband transitions. The interband process corresponds to the recombination from an upper band, populated during the laser interaction, to a lower band. The intraband process originates from nonlinear processes of the current in individual bands. In this Letter, we develop a theory based on Wannier states and reveal in depth the underlying physics of intraband dynamics. In particular, this approach highlights the determinant role of transitions between different lattice wells. Furthermore, our approach provides quantitative predictions concerning high-order harmonic energy cutoffs, harmonic yields, and emission times.

Les sources attosecondes sont maintenant une realite. Elles ont ouvert le domaine de l’attoscience et permettent l’etude de dynamiques ultrarapides a des echelles de temps attoseconde et, en particulier, l’etude de dynamiques electroniques. Ces sources XUV ultracourtes sont aussi coherentes et ont de nombreuses caracteristiques similaires au laser. Cet article presente le principe physique de leurs generations, leurs controles et leurs utilisations et montre ainsi comment la physique non-lineaire induite par laser femtoseconde intense permet aujourd’hui le developpement de l’attophysique.

International audience

The effect of fluctuations of the electron temperature on the population kinetics of a reduced atomic system is investigated in the case of a low density plasma, where the coronal approximation can be used. An exponential correlation function is assumed for the electron temperature fluctuations. A resonance of the average population as a function of the correlation time is observed and analyzed.

International audience; We present a simple upgrade of a time-resolved attosecond extreme ultraviolet and infrared (XUV-IR) setup designed to perform time-resolved or spectrally resolved studies of a target under similar experimental conditions. A flat XUV grating inserted in the path of an attosecond pulse train obtained via high order harmonic generation in gases is used either in the zeroth order of diffraction to follow attosecond dynamics or in the first order of diffraction to study the target spectral response with a temporally stretched single harmonic. Electron momentum measurement is performed with a velocity map imaging spectrometer, and the 10 W femtosecond laser system operating at 5 kHz provides an XUV photon flux compatible with rapid acquisition in both the monochromatic and broadband configurations. The change of experimental configuration between broadband and monochro-matic sources is rapid and performed in situ. We present the experimental implementation applied to krypton atoms and detail the capabilities and limits of this approach when an XUV grating with constant groove density is used with a converging XUV beam.

We prove Strichartz estimates on general flat $d$-torus for arbitrary $d$. Using these estimates, we prove local wellposedness for the cubic nonlinear Schrodinger equations in appropriate Sobolev spaces. In dimensions $2$ and $3$, we prove polynomial bounds on the possible growth of Sobolev norms of smooth solutions.

The discovery of an overlooked but apparently ubiquitous spike in the mid-infrared photoelectron spectra of molecular and atomic gases suggests that we don’t know as much as we thought we did about the ionization of matter in strong fields.

Going from a diatomic to a polyatomic linear or non-linear molecule, the description of molecular frame photoemission in photoionization of molecules involves a function of increasing complexity. Using the electron-ion Vector Correlation method, which provides the emission velocity vectors of the emitted charged particles in a dissociative photoionization reaction, generally gives access to Recoil Frame Photoelectron Angular Distributions (RFPADs). We report results for site selected inner-shell photoionization of the N2O molecule induced by elliptically polarized light, where the primary ionization reaction leads to the production of several fragmentation channels. Ion fragment kinetic energy release distributions as well as RFPADs are reported for selected two ion-channels containing the complete parent molecule. Experimental results are compared with recent multi-channel Schwinger configuration interaction (MCSCI) ab initio calculations at the level of the RFPADs. The link with the original computed molecular frame photoelectron angular distributions (MFPADs) is discussed.

Probing electronic wave functions of polyatomic molecules is one of the major challenges in high-harmonic spectroscopy. The extremely nonlinear nature of the laser-molecule interaction couples the multiple degrees of freedom of the probed system. We combine two-dimensional control of the electron trajectories and vibrational control of the molecules to disentangle the two main steps in high-harmonic generation-ionization and recombination. We introduce a new measurement scheme, frequency-resolved optomolecular gating, which resolves the temporal amplitude and phase of the harmonic emission from excited molecules. Focusing on the study of vibrational motion in N_{2}O_{4}, we show that such advanced schemes provide a unique insight into the structural and dynamical properties of the underlying mechanism.

We introduce a new method for probing electronic dynamics in polyatomic molecules using high harmonic generation spectroscopy. Using a two-colour pump-probe scheme, we resolve the temporal amplitude and phase of harmonic emission from vibrationally excited molecules.

We investigate the role of excited states in High-order Harmonic Generation by studying the spectral, spatial and temporal characteristics of the radiation produced near the ionization threshold of argon by few-cycle laser pulses. We show that the population of excited states can lead either to direct XUV emission through Free Induction Decay or to the generation of high-order harmonics through ionization from these states and recombination to the ground state. By using the attosecond lighthouse technique, we demonstrate that the high-harmonic emission from excited states is temporally delayed by a few femtoseconds compared to the usual harmonics, leading to a strong nonadiabatic spectral redshift., Comment: Accepted at Physical Review Letters

We report new (e,2e) and (e,3e) experiments for ionization of argon under unexplored kinematics characterized by large energy transfer to the target and where the two 'atomic' electrons carry the same kinetic energy. This opens the possibility of competition and interference between direct 3p-outer shell double ionization (DI) and indirect DI via an Auger emission from the 2p shell. The (e,2e) results are found to be in reasonably good agreement with state-of-the-art theoretical models for 2p-single ionization. The importance of the other competing processes, namely direct 3p-DI and/or Auger relaxation, not included in the models is highlighted. The measured (e,3e) angular correlation pattern displays a rich structure, partly resulting from final state interactions where the outgoing electrons tend to minimize their Coulomb repulsion. The rapprochement with the (e,2e) results allows the assignment of some of the observed peaks to given ionization mechanisms, either the two-step 2 direct 3p-DI, or a 2p-single ionization followed by an Auger emission.

A new step for complete experiments in photoionization (PI) of linear molecules is achieved when the electron-ion vector correlation method, based on imaging and time-of-flight resolved electron-ion coincidence techniques, is combined with the use of elliptically polarized light. The molecular frame photoelectron angular distributions (MFPADs), as well as the s1 and s2 Stokes parameters characterizing the polarization state of the light, can be derived from a single experiment performed with undefined elliptically polarized light. Using this method, we report and discuss MFPADs for site selective K-shell ionization of the NO and N2O linear molecules in the region of the N 1s and O 1s shape resonances. A large molecular frame circular dichroism is observed, well predicted by the multi-channel Schwinger configuration interaction calculations reported for PI of NO. We also present recent experimental results for PI of non-linear molecules like CH3Cl measured above the Cl 2p and C 1s ionization thresholds: the recoil frame photoelectron angular distributions (RFPADs) obtained by the vector correlation method may be influenced both by the molecular frame photoemission pattern and the fragmentation process.

We investigate the theoretical problem of the photoelectron cutoff change in periodical structures induced by an infrared laser field. We use a one-dimensional Kronig-Penney potential including a finite number of wells, and the analysis is fulfilled by resolving the time-dependent Schrödinger equation. The electron spectra, calculated for an increasing number of wells, clearly show that a plateau quickly appears as the periodic nature of the potential builds up, even at a moderate intensity (10 TW/cm(2)). Varying the intensity from 10 to 30 TW/cm(2) we observe a net increase of both the yield and accessible energy range of the ionization spectrum. In order to gain insight into the dynamics of the system at these intensities, we use an analytical approach, based on exact solutions of the full Hamiltonian in a periodic potential. We show that the population transfers efficiently from lower to upper bands when the Bloch and laser frequencies become comparable. The model leads to a quantitative prediction of the intensity range where ionization enters the nonperturbative regime. Moreover, it reveals the physics underlying the increase of the photoelectron energy cutoff at moderate intensities, as observed experimentally.

We gratefully acknowledge fruitful discussions with Dr. A. Palacios. This work was accomplished with an allocation of computer time from Mare Nostrum BSC and CCCUAM and was partially supported by European Research Council Advanced Grant No. XCHEM 290853, MINECO Project No. FIS2013-42002-R, ERA-Chemistry Project No. PIM2010EEC-00751, European Grant No. MC-ITN CORINF, European COST Action XLIC CM1204, and the CAM project NANOFRONTMAG. H.B. acknowledges support for mobility from ITN CORINF and is grateful for the hospitality of the Universidad Autonoma de Madrid. R.E.F.S. acknowledges FCT - Fundacao para a Ciencia e Tecnologia, Portugal, Grant No. SFRH/BD/84053/2012

We study the electron impact double ionization of argon in the case where two, or else, three of the outgoing electrons (one scattered and two ejected) have the same energy. Each electron in the final (continuum) state is described by a Coulomb wave and account is taken for the interaction between these three electrons. We also include exactly all the exchange effects for the first time. The results of our model are compared to the recent experiments of Catoire et al (2004, Photonic, Electronic and Atomic Collisions ed R Schuch et al (Phys. Scr. T110 228–32); 2005, Electron and Photon Impact Ionization and Related Topics ed B Piraux (Bristol: Institute of Physics) p 53).

We report new coplanar (e, 2e) measurements for ionization of He and Ar under kinematics characterized by large energy transfer and close to minimum momentum transfer from the projectile to the target. These kinematics have remained rather unexplored to date due to the smallness of the corresponding cross sections. They could be investigated here thanks to the high sensitivity of our multi-collection spectrometer. The experimental results are used as a sensitive test of state-of-the-art available theoretical models for multi-electron atoms, namely the BBK and a hybrid DWBA+R-matrix (close coupling) models. An overall satisfactory agreement with experiment is obtained for the hybrid DWBA results for both targets. However, a close inspection of the remaining discrepancies calls for further refinement of the theory.

A complete analysis of our recent (e, 3e) experiments on helium at 601 eV incident energy (Lahmam-Bennani et al 2003 Phys. Rev. A 67 010701) is conducted by using an approximate 6C model which accounts for the interaction between all four particles (the scattered electron, the two ejected electrons and the nucleus) in the final state. An accurate wavefunction for the initial state is also used. The agreement between experiments and theory is not always good even though most peaks and dips can be explained. Comparison is also made with the results of the first Born-BBK approximation as well as with approximate second Born results.

We consider the interaction of hydrogen-like atoms with a strong laser field and show that the strong field approximation and all its variants may be grouped into a set of families of approximation schemes. This is done by introducing an ansatz describing the electron wave packet as the sum of the initial state wave function times a phase factor and a function which is the perturbative solution in the Coulomb potential of an inhomogeneous time-dependent Schr\"odinger equation. It is the phase factor that characterizes a given family. In each of these families, the velocity and length gauge version of the approximation scheme lead to the same results at each order in the Coulomb potential. By contrast, irrespective of the gauge, approximation schemes belonging to different families give different results. Furthermore, this new formulation of the strong field approximations allows us to gain deeper insight into the validity of the strong field approximation schemes. In particular, we address two important questions: the role of the Coulomb potential in the output channel and the convergence of the perturbative series in the Coulomb potential. In all the physical situations we consider here, our results are compared to those obtained by solving numerically the time-dependent Schr\"odinger equation., Comment: 19 pages, 9 figures, submitted for publication

International audience; XUV induced dynamics in molecules is still largely unexplored while experimental and theoretical tools are becoming available in several labs. In this work, we present a compact XUV beamline designed to induce and probe femtosecond and attosecond dynamics in gas samples (from atoms to complex molecular species). The induced processes are studied with time-resolved photoelectron or/and photoion imaging. The characterization of the performances of the experimental setup is presented. We show experimental results obtained in naphthalene molecule showing femtosecond and attosecond time-resolved photoelectron imaging experiments allowing electron wavepacket phase measurements.

A novel approach to the modeling of atomic populations in turbulent plasmas is applied to ionization–recombination balance calculations. Fluctuations of the fluid parameters are retained using a time-dependent statistical approach, suitable for cases where the turbulence characteristic times are of the same order as or smaller than the typical atomic relaxation times. We show that the populations are sensitive to the shape of the autocorrelation function of the fluctuations. An illustration is proposed through an ideal two-level system forced by non-Markovian temperature fluctuations.

In lithium-wall-conditioned tokamaks, the line radiation due to the intrinsic impurities (Li/Li + /Li ++ ) plays a significant role on the power balance. Calculations of the radiation losses are usually performed using a stationary collisional–radiative model, assuming constant values for the plasma parameters ( N e , T e ,…). Such an approach is not suitable for turbulent plasmas where the various parameters are time-dependent. This is critical especially for the edge region, where the fluctuation rates can reach several tens of percents [e.g. J.A. Boedo, J. Nucl. Mater. 390–391 (2009) 29–37]. In this work, the role of turbulence on the radiated power is investigated with a statistical formalism. A special emphasis is devoted to the role of temperature fluctuations, successively for low-frequency fluctuations and in the general case where the characteristic turbulence frequencies can be comparable to the collisional and radiative rates.

A large international effort is nowadays devoted to increase the energy of the extreme ultraviolet pulses by using high-peak power ultrashort fundamental pulses (Terawatt level). Using such fundamental pulses brings specific constraints that need to be addressed. Here we study high-order harmonic generation in gases with 10 fs pulses at Terawatt peak power and demonstrate that extreme ultraviolet beams can be highly structured and complex in various conditions. We use a single-shot spatially resolved spectral detection and demonstrate direct observation of the spatio-temporal coupling occurring in the generating medium. Clear and reproducible complex spatio-spectral structures are observed in the far field. Similar structures are reproduced with simulations and we show that they are intimately associated to the high nonlinearity of high-order harmonic generation. Those findings are of prime importance for the generation of high-energy attosecond pulses and reveal important issues for their applications.

We present an extension of the resolvent-operator method (ROM), originally designed for atomic systems, to extract differential photoelectron spectra (in photoelectron- and nuclear-kinetic energy) for diatomic molecules interacting with strong, ultrashort laser fields in the single active electron approximation. The method is applied to the study of H2+ photodissociation and photoionization by femtosecond laser pulses in the XUV-IR frequency range. In particular, the method is tested (i) in the perturbative regime, for few-photon absorption and bound-bound electronic transitions, and (ii) in the strong-field regime, in which multiphoton absorption and tunneling are present. In the latter case, we show how the differential ROM allows one to track the transition between both regimes. We also analyze isotopic effects by comparing the dynamics of H2+ and D2+ ionization for different pulses. © 2014 American Physical Society., This work was accomplished with an allocation of computer time from Mare Nostrum BSC and CCC-UAM and was partially supported by the MICINN Projects No. FIS2010- 15127 and No. CSD 2007-00010, ERA-Chemistry Project No. PIM2010EEC-00751, the European grants No. MC-ITN CORINF and No. MC-RG ATTOTREND, the European COST Action No. CM0702, and European Research Council Advanced Grant No. XCHEM 290853. R.E.F.S. acknowledges a Ph.D. contract from ITN CORINF and Grant No. SFRH/BD/84053/2012 from the Portuguese government. P.R. acknowledges a Juan de la Cierva contract grant from the Spanish MICINN

The population balance of atoms or ions in an edge plasma is calculated in the presence of fluctuating density or temperature. We have used a stochastic model taking advantage of the knowledge of the plasma parameter statistical properties, and assuming a stepwise constant stochastic process for the fluctuating variable. The model is applied to simplified atomic systems such as three level hydrogen atoms or the ionization balance of carbon affected by electronic temperature or density fluctuations obeying a gamma PDF, and an exponential waiting time distribution.

We present a theoretical study of H2+ ionization under strong IR femtosecond pulses by using a method designed to extract correlated (2D) photoelectron and proton kinetic energy spectra. The results show two distinct ionization mechanisms—tunnel and multiphoton ionization—in which electrons and nuclei do not share the energy from the field in the same way. Electrons produced in multiphoton ionization share part of their energy with the nuclei, an effect that shows up in the 2D spectra in the form of energy-conservation fringes similar to those observed in weak-field ionization of diatomic molecules. In contrast, tunneling electrons lead to fringes whose position does not depend on the proton kinetic energy. At high intensity, the two processes coexist and the 2D plots show a very rich behavior, suggesting that the correlation between electron and nuclear dynamics in strong field ionization is more complex than one would have anticipated, This work was accomplished with an allocation of computer time from Mare Nostrum BSC and CCC-UAM, and was partially supported by the MICINN Projects No. FIS2010-15127, No. ACI2008-0777, and No. CSD 2007-00010, the ERA-Chemistry Project No. PIM2010EEC-00751, the European Grants No. MCITN CORINF and No. MC-RG ATTOTREND, the European COST Action CM0702, and the Advanced Grant of the European Research Council, Grant No. XCHEM 290853. R. E. F. S. acknowledges a Ph.D. contract from ITN CORINF. P. R. acknowledges a Juan de la Cierva contract grant from MICINN

In this work we consider the theoretical treatment of the interaction of a laser pulse with an atom and focus on the methodology used to extract the quantity that is observed experimentally, i.e., the electron probability density. We solve the time-dependent Schr\"odinger equation (TDSE) using two techniques: the spectral method, which makes use of an expansion of the wave function onto the field-free atomic eigenstates, and the wave-function method, where the TDSE is numerically solved on a grid. In this work we show that the electron probability density can be extracted from the final wave function, obtained by the wave-function method, by using the resolvent technique with a proper choice of the energy resolution. The advantage of this approach is that it does not require the calculation of the field-free atomic eigenstates. As an illustration of this method we compare the spectral and wave-function methods in the case of atomic hydrogen interacting with a linearly polarized mid-IR laser pulse. The comparison shows excellent agreement.

The population balance of atoms and ions in a tokamak edge plasma is calculated in the presence of density and temperature fluctuations. We apply a stochastic model to simplified atomic systems and examine the sensitivity of the energy level populations to the statistical properties of the fluctuations.

One-photon single ionization of molecules has been at the focus of several discussions concerning the reconstruction of observables obtained with ultrashort pulses from those obtained from continuous wave radiation (and vice versa). A related controversy on the conditions and observables that allow for coherent control in one-photon processes has been recently revisited (Science 2006, 313, 1257; J. Chem. Phys. 2010, 133, 151101). Our benchmark to investigate these issues is photoionization of the hydrogen molecule, where the autoionization events are the time-dependent processes in field-free evolution that could serve as a target for coherent control. We show that the variation of one-photon ionization probabilities with pulse duration are solely due to spectral effects and thus cannot be coherently controlled. We then discuss for which observables and under which conditions phase control of autoionization dynamics is possible.

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.

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 used to describe turbulent fluctuations. This model incorporates several important known features of Scrape-off-Layer turbulence, and has been implemented in the EIRENE Monte Carlo code. The effect of fluctuations on the neutral density, ionisation source and Balmer α radial profiles are investigated. Two important control parameters are identified, namely the ratio of the neutral mean free path to the size of turbulent structures, and the ratio of recycling time scales to the turbulent times.

We address a model for atomic population kinetics in fluctuating plasmas. An analytical expression for the ensemble-average populations is obtained in terms of two statistical functions that can be retrieved experimentally, namely the probability density function and the autocorrelation of the plasma fluid fields. This expression, allowing for very fast calculations, is of great interest to thoroughly analyze the radiative properties of fluctuating plasmas. Two limits, where the fluctuations are either faster or slower than the atomic relaxation time scales, are discussed in detail. Finally, an application to atomic hydrogen is presented.

We present approaches using stochastic processes for the calculation of line broadening in plasmas. The derivation of model microfield methods (MMM) based on analytic formulations is recalled, as well as an approach using a simulation of the stochastic process. We discuss the possibility of an improvement of the stochastic process by comparing our first results to ab initio particle simulations coupled to a numerical integration of the emitters Schrödinger equation.

In this work we address the effect of plasma turbulence on atomic levels population. The plasma turbulence is considered in Collisional Radiative Modeling through fluctuations of macroscopic quantities such as the electron temperature and/or density. This study focuses on the effect of the Probability Density Function of the electron temperature on the average level populations, in the case where the turbulence frequency is either larger or smaller than any atomic time scales. Then we study the effect of the introduction of a non-Maxwellian Velocity Distribution Function using a -function.

Stark broadening of atomic lines in plasmas is calculated by modelling the plasma stochastic electric field using the CTRW approach [1,2]. This allows retaining non Markovian terms in the Schrodinger equation averaged over the electric field fluctuations. As an application we consider a special case of a non separable CTRW process, the so called Kangaroo process [3]. An analytic expression for the line profile is presented for arbitrary waiting time distribution functions. A preliminary application to the hydrogen Lyman α line is discussed.