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The dynamics of time evolution of quantum oscillator excitation by electromagnetic pulses is investigated theoretically for an arbitrary field amplitude in a pulse. We consider a harmonic oscillator without damping and excitation between stationary states. The general formula for the excitation of quantum states as a function of time is derived in terms of instantaneous energy of an associated classical oscillator in the field of an electromagnetic pulse. The derived expression is used in detailed analysis of the time dependence of the quantum oscillator excitation probability beyond the range of perturbation theory for various pulse parameters including total excitation from the ground state, excitation from excited states, and excitation spectra.

International audience; The theory of photoionization describing the interaction of x-ray free-electron laser (XFEL) pulses and high-harmonic-generated (HHG) radiation is generalized to ultrashort laser pulses, where the concept of the standard ionization probability per unit time in Fermi’s golden rule and in Einstein’s theory breaks down. Numerical calculations carried out in terms of a generalized photoionization probability for the total duration of pulses in the near-threshold regime demonstrate essentially nonlinear behavior, while absolute values may change by orders of magnitude for typical XFEL and HHG pulses. XFEL self-amplified spontaneous emission pulses are analyzed to reveal general features of photoionization for random and regular spikes: the dependences of the nonlinear photoionization probability on carrier frequency and spike duration are very similar, allowing an analytical expectation value approach that is valid even when there is only limited knowledge of random and regular parameters. Numerical simulations carried out for typical parameters demonstrate excellent agreement.

International audience; Novel phenomena and methods related to dielectronic capture and dielectronic recombination are studied for non-local thermodynamic equilibrium (LTE) plasmas and for applications to non-LTE ionization balance. It is demonstrated that multichannel autoionization and radiative decay strongly suppress higher-order contributions to the total dielectronic recombination rates, which are overestimated by standard approaches by orders of magnitude. Excited-state coupling of dielectronic capture is shown to be much more important than ground-state contributions, and electron collisional excitation is also identified as a mechanism driving effective dielectronic recombination. A theoretical description of the effect of angular-momentum-changing collisions on dielectronic recombination is developed from an atomic kinetic point of view and is visualized with a simple analytical model. The perturbation of the autoionizing states due to electric fields is discussed with respect to ionization potential depression and perturbation of symmetry properties of autoionization matrix elements. The first steps in the development of statistical methods are presented and are realized in the framework of a local plasma frequency approach. Finally, the impact of collisional–radiative processes and atomic population kinetics on dielectronic recombination is critically discussed, and simple analytical formulas are presented.

In this paper, we presented a model, describing transition scattering of ultrashort laser pulses (USLPs) in Maxwellian plasmas in terms of the full spectral-angular probability during the entire time of pulse action. We demonstrated that in the case of the USLP, probability dependence on pulse duration (τ-dependence) generally is a non-monotonic function. The main trends of the τ-dependence were defined. For quasi-elastic transition scattering, we derived analytical formulas of the full spectral-angular probability that describes non-monotonic areas of the τ-dependence with high accuracy. In the framework of the analytical approach, we established conditions, at which non-monotonic trends are realized, and assessed dynamics of local extremes at the variation of problem parameters. We compared τ-dependence, angular dependence of transition, and Thomson scattering probability and assessed limits of analytical approximations. The crucial similarities and differences of these two types of scattering were described.

International audience; On the basis of equations obtained in the framework of second-order quantum-mechanical perturbation theory, the standard approach to the calculation of scattering radiation probability is extended to the case of ultrashort laser pulses. We investigate the mechanism of the appearance of plasmon peaks in the spectrum of the plasma form factor for different parameters of the problem. For the case in which scattering on plasmons dominates over scattering on electron density fluctuations caused by chaotic thermal motion, we derive analytical expressions describing the scattering probability of ultrashort laser pulses on plasmons. Together with this, we obtain a simple expression connecting the frequency of scattered radiation and the energy transmitted from the incident pulse to plasmon, and vice versa. In considering the scattering probability, our emphasis is on the dependence on the pulse duration. We assess in detail the trends of this dependence for various relations between pulse carrier frequency and plasmon energy.

The radial dependence of the free electron density within the ion sphere radius in finite temperature dense plasmas shows characteristic scaling laws that permit us to derive analytical plasma screening potentials. A generalized analytical approach is developed which shows good agreement with self-consistent quantum mechanical calculations. It is empirically discovered that anomalous strong scaling in the analytical model provides agreement with data obtained in a regime where the lattice structure still prevails.

Advanced X-ray spectroscopic methods provide unique and critical data to study matter under extreme environmental conditions induced by high-intensity and high-energy lasers. The aim of this paper is to contribute to a contemporary discussion of the role of X-ray spectroscopy in the investigation of radiative properties of strongly coupled, highly correlated, and frequently weakly emissive plasma systems formed in matter irradiated by sub-petawatt and petawatt class lasers. After reviewing the properties of different X-ray crystal spectrometers, high-resolution X-ray diagnostic methods are surveyed with respect to their potential to study plasma-induced and externally induced radiation fields, suprathermal electrons, and strong electromagnetic field effects. Atomic physics in dense plasmas is reviewed with emphasis on non-Maxwellian non-LTE atomic kinetics, quasi-stationary and highly-transient conditions, hollow ion X-ray emission, and field-perturbed atoms and ions. Finally, we discuss the role of X-ray free electron lasers with respect to supplementary investigations of matter under extreme conditions via the use of controlled high-intensity radiation fields.Advanced X-ray spectroscopic methods provide unique and critical data to study matter under extreme environmental conditions induced by high-intensity and high-energy lasers. The aim of this paper is to contribute to a contemporary discussion of the role of X-ray spectroscopy in the investigation of radiative properties of strongly coupled, highly correlated, and frequently weakly emissive plasma systems formed in matter irradiated by sub-petawatt and petawatt class lasers. After reviewing the properties of different X-ray crystal spectrometers, high-resolution X-ray diagnostic methods are surveyed with respect to their potential to study plasma-induced and externally induced radiation fields, suprathermal electrons, and strong electromagnetic field effects. Atomic physics in dense plasmas is reviewed with emphasis on non-Maxwellian non-LTE atomic kinetics, quasi-stationary and highly-transient conditions, hollow ion X-ray emission, and field-perturbed atoms and ions. Finally, we discuss the role of X-ray...

Statistical models combined with the local plasma frequency approach applied to the atomic electron density are employed to study the photoionization cross-section for complex atoms. It is demonstrated that the Thomas–Fermi atom provides surprisingly good overall agreement even for complex outer-shell configurations, where quantum mechanical approaches that include electron correlations are exceedingly difficult. Quantum mechanical photoionization calculations are studied with respect to energy and nl quantum number for hydrogen-like and non-hydrogen-like atoms and ions. A generalized scaled photoionization model (GSPM) based on the simultaneous introduction of effective charges for non-H-like energies and scaling charges for the reduced energy scale allows the development of analytical formulas for all states nl. Explicit expressions for nl = 1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d, 4f, and 5s are obtained. Application to H-like and non-H-like atoms and ions and to neutral atoms demonstrates the universality of the scaled analytical approach including inner-shell photoionization. Likewise, GSPM describes the near-threshold behavior and high-energy asymptotes well. Finally, we discuss the various models and the correspondence principle along with experimental data and with respect to a good compromise between generality and precision. The results are also relevant to large-scale integrated light–matter interaction simulations, e.g., X-ray free-electron laser interactions with matter or photoionization driven by a broadband radiation field such as Planckian radiation.

The standard approach to calculate the Thomson scattering probability is reconsidered for the case of ultrashort incident laser pulses (USLPs). We established a new model for the interaction of USLP with plasmas that is based on Fermi's equivalent photon conception to calculate the spectral-angular differential Thomson scattering probability. The simulations demonstrate that the scattering probability for USLP is a non-monotonic function of pulse duration in contrast to the standard long-pulse model showing linear dependence. An analytical approach is developed to study the nonlinear behavior of the scattering probability as a function of pulse duration and other parameters.

X-ray free electron laser (XFEL) interaction with solids has been simulated to resolve simultaneously variable XFEL photon energy and x-ray spectral distribution of the target emission (2D-maps). It is discovered that the highly transient charge state distribution exhibits a characteristic target response due to the action of the sharply rising radiation field. Finally, we identify advantageous features for studies of dense plasma effects of two K-shell vacancy hollow ion x-ray emission excited via resonance excitation. These features and characteristics permit the global study of dense plasma effects via the simulation of the time-integrated joint distribution of pumped and fluorescence energies. It is shown that the simulation of these specific 2D-maps offers a global vision of the complex interplay between different processes or phenomena such as photoionization, resonance excitation, or ionization potential depression.

Radiative emission of fast electrons in collision with an “ion-sphere” electron distribution in dense plasmas is under consideration. The electron structure of the ion sphere is calculated ab initio using self-consistent solution of both bound and free electron distribution inside the sphere. Two radiation channels are included: emission of the colliding electron itself in static potential (conventional or static Bremsstrahlung) and the emission of “ion sphere” medium due to its polarization by the colliding electron (polarization Bremsstrahlung). The last one is calculated in the frame of local plasma density approximation. Interference between conventional and polarization Bremsstrahlung is taken into account. It is shown that spectral cross section of the process has characteristic features depending on plasma density and ionization stage of plasma ions. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Finite-temperature dense plasma relativistic atomic structure calculations are employed to study the energy eigenvalues and transition probabilities related to the 1s3l fine structure levels of He-like ions. We discovered a particular response of the level structure that is distinctly different from simple nuclear charge screening effects that exists also for atoms and ions in vacuum as Z decreases. It is demonstrated that characteristic level crossings are driven by the free electron screening due to a particular dependence on the quantum numbers of each level of the 1s3l-configuration. Levels with large l shift stronger to the continuum than levels with small l whereas spin dependent dense plasma effects are relatively small. As a result, the known energy level fine structure in vacuum is subject to characteristic changes (level crossings, level order). Numerical calculations performed for a wide range of density, temperature and different chemical elements indicate that induced level crossings and change in level order are general characteristics of dense plasma effects.

A novel target configuration for equation of state measurements using intense ion beams is proposed. It is based on a stack consisting of several thin foils which expand quasi-statically when heated with the ion beam. The merging of the single foils causes a sharp increase of the expansion velocity. Together with the known energy deposition of the ion beam this allows direct determination of equation of state data. The parameters of the stack target were optimized with hydrodynamic calculations. Finally, a simple analytical model to predict the expansion velocity was developed.

Opacity measurements in warm dense matter (WDM) provide a valuable benchmark for the diverging theoretical models in this regime. Heating of thin foils with intense heavy-ion beams allows one to create isolated samples of warm dense matter suitable for experimental determination of frequency-dependent opacities. A prerequisite for the measurements is the isothermal expansion of the heated foil. Hydrodynamic simulations predict that this condition is fulfilled. The analysis shows that existing ion-beam accelerators are capable to contribute to this field of research.

Simulations of the helium radiative properties carried out with the recently developed multi-level meta-stable resolved collisional-radiative code SOPHIA discovered new unique emission lines to analyze optically thick divertor plasmas relevant for ITER. The comparison of their time dependent line emission obtained from the NAGDIS-II plasma simulator experiments with time dependent temperature probe measurements shows a strong correlation. This indicates that line intensity fluctuations can be transformed to the important quantities of density and temperature fluctuations. A transformation method based on integral line intensity ratios which can be recorded with high time resolution is discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We present our numerical calculations of dielectronic recombination rate coefficients which are spin dependent (2lnl-1snl 1 L, 1snl 3 L) and develop scaling relations which are converging for all spin (S), angular (L) and main (n) quantum numbers. The influence of atomic data inaccuracies, spin dependent channelling of dielectronic recombination rates and collisions on the atomic/ionic fractions is discussed.

The chlorine Heαradiation of polyvinyl chloride (PVC) was investigated with respect to X-ray scattering experiments on dense plasmas. The X-ray source was a laser-produced plasma that was observed with a highly reflective highly oriented pyrolytic graphite (HOPG) crystal spectrometer as it is used in current x-ray scattering experiments on dense plasmas. The underlying dielectronic satellites of Heαcannot be resolved, therefore the plasma was observed at the same time with a focusing spectrometer with spatial resolution. To reconstruct the spectrum a simple model to calculate the spectral line emission based on dielectronic recombination and inner shell excitation of helium- and lithium-like ions was used. The analysis shows that chlorine dielectronic satellite emission is intense compared to Heαin laser-produced chlorine plasmas with a temperature of 300 eV in this wavelength range of Δλ = 0.07 Å (ΔE= 43 eV). The method proposed in this paper allows deducing experimentally the role of the underlying dielectronic satellites in the scatter spectrum measured with a HOPG crystal spectrometer. It is shown that the dielectronic satellites can be neglected when the scattering is measured with low spectral resolution in the non-collective regime. They are of major importance in the collective scatter regime where a high spectral resolution is necessary.

High-current discharge channels are ideally suited for the focusing and transport of intense charged particle beams. The azimuthal magnetic field provides a strong focusing force, which acts symmetrically towards the discharge axis. A sufficiently dense and hot plasma can also neutralize the beam current and space charge of very intense ion beams, relevant to a number of future applications. In this paper we present experiments on high-current discharge channels designed for the transport of heavy ion beams. A spectroscopic method is introduced, which allows us to determine both the plasma temperature and density in hydrogen–nitrogen plasmas, from comparisons of the measurements with computer calculations. The temperature is derived from a comparison of experimentally obtained relative nitrogen-line intensities with a collisional radiative rate modelling of the nitrogen plasma. The electron density is determined by a detailed line shape analysis of the Stark-broadened hydrogen Balmer lines.

Ion-beam transport in space charge neutralizing discharge channels has been proposed for the final focus and chamber transport in a heavy-ion fusion reactor. A driver scenario with two-sided target illumination requires a system of two intersecting discharges to transport beams of the same charge from opposite sides towards the fusion target. In this article we report on experiments on the creation of free-standing, intersecting high-current discharge channels. The discharges are initiated in ammonia gas (NH3) in a metallic chamber by two perpendicular CO2-laser beams, which resonantly heat and subsequently rarefy the gas along the laser paths before the breakdown. These low density channels guide the discharges along the predefined paths and also around the 90° angles without any mechanical guiding structures. In this way stable X-, T-, and L-shaped discharges with currents in excess of 40 kA, at pressures of a few mbar were created with a total length of 110 cm. An 11.4 A MeV 58Ni+12 beam from the UNILA...

We have observed photons in the visible light range emitted from slow (2.0 keV/amu) highly charged Ar6+ ions which have captured one electron and transmitted through a Ni microcapillary target. Observed lines were identified by comparing with an ab initio calculation based on the multi-configuration Hartree-Fock method. (C) 2003 Elsevier Science B.V. All rights reserved.

A new technique for X-ray spectromicroscopy of fast heavy ion radiation during the ion interaction with stopping media is presented using focusing spectrometers with spatial resolution. Spherically bent crystals of quartz and mica with small curvature radii, R=150 mm, and large apertures were used as dispersive elements in experiments on fast Ni ions with energies of 5.9 and 11.2 MeV/u which are being stopped in different media: Ar gas, SiO2-aerogels and solid quartz. Spectrally high (λ/Δλ=1000–3000) and spatially high (up to 10–100 μm) resolved Kα-satellite spectra of Ni projectiles as well as of the ionized stopping media were observed.

Satellite lines caused by radiative transitions from the Rydberg autoionization states of a Li-like Mg X ion in a plasma heated by radiation from a XeCl and a Nd laser are identified for the first time, and their wavelengths are measured precisely. Comparison of the experimental data with the atomic structures calculated by the method of relativistic perturbation theory shows that the accuracy of calculations of the energy of autoionization states is rather high even without the use of any semiempirical corrections and is of the order of 0.06%. The experimentally measured wavelengths can be used for a semiempirical estimate of the value of the leading order of perturbation theory among the orders that were neglected in calculations. It is shown that the simulation of the population kinetics of Rydberg autoionization states of Li-like ions in a dense plasma should take into account all possible channels of dielectronic capture, in particular, from the excited states of a He-like ion. The precision experimental wavelengths obtained for satellites of the Hes and Heγ lines of the Mg XI ion make possible to use these satellites as reference lines in studies of complicated spectra of multielectron ions.

The X-ray spectral distribution of swift heavy Ti and Ni ions (11 MeV/u) observed inside aerogels (ρ = 0.1 g/cm3) and dense solids (quartz, ρ = 2.23 g/cm3) indicates a strong presence of simultaneous 3–5 charge states with one K-hole. We show that the theoretical analysis can be split into two tasks: first, the treatment of complex autoionizing states together with the originating spectral distribution, and, second, a charge-state distribution model. Involving the generalized line profile function theory, we discuss attempts to couple charge-state distributions.

By means of spatially resolved high-resolution X-ray spectroscopy, we have investigated the generation of fast ions at various laser installations with different flux densities and laser wavelengths. It is demonstrated that the fast ion generation in laser-produced plasma can be achieved for a very low level of the averaged laser intensity on the target. The time-of-flight mass spectrometry ion diagnostics and X-ray spectrographs give very close results for the energy distribution of the thermal ion component. For higher energies, however, we found significant differences: the spatially resolved high-resolution spectrographs expose the presence of suprathermal ions, while the time-of-flight method does not. Suprathermal ion energies Eion plotted as a function of the qλ2 parameter show a large scatter far above the experimental errors. The cause of these large scatters is attributed to a strong nonuniformity of the laser intensity distribution in the focal spot. The analysis by means of hydrodynamics and spectral simulations show that the X-ray emission spectrum is a complex convolution from different parts of the plasma with strongly different electron density and temperature. It is shown that the highly resolved Li-like satellite spectrum near Heαcontains significant distortions even for very low hot electron fractions. Non-Maxwellian spectroscopy allows determination of both the hot electron fraction and the bulk electron temperature.

The satellite structure accompanying the Al Lyα emission from plasma regions close to the surface of the laser-irradiated targets is studied. In spectra produced at constant laser energy but variable pulse duration we identify the situations where the resonance line is suppressed and only the emission from long-wavelength satellites is observed. The experimental data are compared with results of calculations based on two-dimensional hydrodynamics and multilevel collisional-radiative codes. Simulations indicate that these spectra originate from cold dense plasma created inside the crater several tens of micrometers under the surface of the solid target.

A study on the interaction of a 10 TW, 60 fs, Ti–Sapphire laser with a high-density long-scale pulsed nitrogen gas jet is reported. Experimental data on the laser propagation are analyzed with the help of a ray-tracing model. The plasma dynamics is investigated by means of time-resolved shadowgraphy and time-integrated high-resolution x-ray spectroscopy. Shadowgrams show that the plasma does not expand during the first 55 ps, while x-ray spectra exhibit an unusual continuum-like structure attributed to hollow atoms produced by charge exchange process between bare nuclei expelled from the plasma and molecules of the surrounding gas. The interpretation of the results is supported by particle-in-cell simulations. The question of x-ray lasing is also examined using a hydrodynamic code to simulate the long lasting regime of recombination.

The high current upgrade of the accelerator facilities at GSI Darmstadt, Germany, has created possibilities for a new class of experiments with heavy ion beams. Intense pulses of heavy ions can rapidly heat converter targets to high temperatures. The hydrodynamic response of these converters, the temperature development and the emitted radiation are investigated experimentally. Moreover, measurements are compared to numerical simulations. In addition, the expansion of the converters can be employed to compress cryogenic solid hydrogen that is located next to the converters for fundamental research on the equation of state of hydrogen at high pressures. Due to the long range of the ions in the converters rather large volumes of hydrogen can be compressed homogeneously, allowing for high precision in the diagnostics. Various geometries for planar or radial compression are under discussion. With a 300 MeV/u 40Ar18+ beam of 2×1010 particles and 400 μm radius (HWHM), delivered within a pulse of 300 ns width (FWHM), lead targets were brought to hydrodynamic expansion and collision. Maximum expansion velocities were 570 m/s. The numerical simulations yielded maximum temperatures of 0.17 eV and maximum pressures of 2.8 GPa in direct heating.

The influence of a highly energetic electron beam on the electron distribution function (e.d.f.) in a hot dense plasma is investigated by solving the Boltzmann equation analytically. A plateau is obtained in the tail of the e.d.f. over an energy range between the excitation threshold and an energy value half that of the monoenergetic electrons. The importance of this plateau is discussed for a dense He-like argon plasma.

New types of space resolved X-ray spectra produced in light matter experiments with high intensity lasers have been investigated experimentally and theoretically. This type of spectra is characterised by the disappearance of distinct resonance line emission and the appearance of very broad emission structures due to the dielectronic satellite transitions associated to the resonance lines. Atomic data calculations have shown, that rather exotic states with K-shell vacancies are involved. For quantitative spectra interpretation we developed a model for dielectronic satellite accumulation (DSA-model) in cold dense optically thick plasmas which are tested by rigorous comparison with space resolved spectra from ns-lasers. In experiments with laser intensities up to 10 19 W/cm 2 focused into nitrogen gas targets, hollow ion configurations are observed by means of soft X-ray spectroscopy. It is shown that transitions in hollow ions can be used for plasma diagnostic. The determination of the electron temperature in the long lasting recombining regime is demonstrated. In Light-matter interaction experiments with extremely high contrast (up to 10 10 ) short pulse (400 fs) lasers electron densities of n e ≈3×10 23 cm −3 at temperatures between kT e =200–300 eV have been determined by means of spectral simulations developed previously for ns-laser produced plasmas. Expansion velocities are determined analysing asymmetric optically thick line emission. Further, the results are checked by observing the spectral windows involving the region about the He α -line and the region from the He β -line to the He-like continuum. Finally, plasmas of solid density are characteristic in experiments with heavy ion beams heating massive targets. We report the first spectroscopic investigations in plasmas of this type with results on solid neon heated by Ar-ions. A spectroscopic method for the determination of the electron temperature in extreme optically thick plasmas is developed.

The unique combination of an intense heavy ion beam and a high-energy Nd:glass laser system at Gesellschaft f Schwerionenforschung (GSI-Darmstadt) facilitates pioneering beam-plasma interaction experiments and thus allows to address basic physics issues associated with heavy ion-driven inertial fusion. The deposition power of the intense heavy ion beam from the synchrotron has recently been increased to 1 kJ/g. The hydrodynamic response of solid targets was measured. A comparison with detailed numerical simulations attributes the target response to a pressure pulse of 3 GPa at a maximum temperature of 2500 K. Beam plasma interaction experiments to measure the stopping power of laser plasmas for heavy ion beams have been performed and show an increased energy loss for Ni ions in a 60 eV dense carbon plasma. Subsequently performed time-resolved charge-state measurements indicate that the increased stopping power can partially be attributed to a high charge state of the beam ions traversing the plasma. Improved plasma diagnostic by high-resolution spectroscopy revealed the unexpected existence of He-like resonance and intercombination lines (Heaa 1s2p 3 P1‐1s 2 and Yaa 1s2p 3 P1‐1s 2 ) of fluorine even for a modest laser intensity of 5 · 10 11 W/cm 2 . ” 2000 Elsevier Science B.V. All rights reserved.

At the synchrotron SIS of GSI (Gesellschaft fur Schwerionenforschung, Darmstadt, Germany) the energy deposition of intense heavy ion beams in solid targets can be employed to create dense plasmas by isochoric heating and quasi-adiabatic compression. Typical beam parameters are 2.10 10 Ar 18+ ions of 300 MeV/u. The stored beam energy of ca. 40 J is deposited in the solid state targets within 250 ns, leading to a specific energy deposition of about 1 kJ/g. Target materials are rare gas crystals, metals especially lead and solid hydrogen or deuterium. Diagnostic tools are high speed and fast shutter, intensified cameras, pressure sensors and spectroscopes. With this experimental setup it was for the first time possible to record the heavy ion beam induced hydrodynamic motion of lead and the emission in the visible range of neon. Though experimental details are different, both in lead and in neon initial pressure values of 0.1-0.3 GPa and temperature of ca. 0.1 eV were measured. Combining the respective properties of lead and hydrogen in compound targets and with the improved beam parameters after the intensity upgrade at SIS we intend to join the experimental activities to produce metallic hydrogen.

The radiation emission of the He lines 1s3p 3 P1 1s2 1 S0 +h and 1s3p 1 P1 1s2 1 S0 +h in dense optically thick and non-Maxwellian plasmas is found to be sensitive to higher multipole orders both for the radiation transitions and the collisional excitation cross sections. It is demonstrated that magnetic dipole and even quadrupole radiation transitions influence not only the absolute radiation line emission but also their qualitative evolution in dense plasmas. The proposed radiation model describes the He emission for low- and high-density plasmas and enables diagnostics under typical conditions of both magnetic and inertial fusion plasmas.

A new approach for investigation of the generation of fast ions and hot electrons inside the same plasma volume in laser-produced plasmas is proposed. It is based on the spectroscopic observation of line radiation from singly and doubly excited levels with simultaneous high spectral and spatial resolution. The experimental results demonstrate the observation of fast ions from highly charged target material inside the plasma volume and suggest that the generally accepted scaling relations are seriously invalid under certain conditions. Even at rather modest intensities ions with energies of several MeV are observed.

For the first time registration of high-resolution soft x-ray emission and atomic data calculations of hollow-atom dielectronic satellite spectra of highly charged nitrogen have been performed. Double-electron charge-exchange processes from excited states are proposed for the formation of autoionizing levels in high-intensity laser-produced plasmas, when field-ionized ions penetrate into the residual gas. Good agreement is found between theory and experiment. Plasma spectroscopy with hollow ions is proposed and a temperature diagnostic for laser-produced plasmas in the long-lasting recombining regime is developed.

On the basis of experimental and theoretical investigations it is demonstrated for the first time that in cold dense optically thick laser-produced plasmas, created near the target surface, the capture into the He-like ground state is negligible for line formation and that observed high-intensity -Rydberg satellite intensities are correlated with highly populated He-like excited states . X-ray emission spectra with simultaneous high spectral and spatial resolution provide a direct verification of the proposed excitation mechanism. Atomic data calculations for all configurations with n = 3 - 6 have been carried out and were employed in spectral modelling. Taking into account the proposed excitation channels, excellent overall agreement is found. Successful cross-checks with the spectral interval near the -line are demonstrated. The spectral modelling is proposed for sensitive density (electron density, excited state population) and temperature diagnostics near the target surface.

A hydrodynamic model of the interaction of a short, intense laser pulse with moderate-density gases is constructed. The model systematically takes into account both tunneling-ionization processes and the relativistic motion of the electrons that are produced by the ionization of the gas in the relativistically strong field of the pulse. X-ray spectroscopy data agree well with the proposed theory.

Nonthermal excitation of atomic states by suprathermal electrons was observed for the first time within inertial confinement fusion hohlraum plasmas. The nonthermal excitation process results in the simultaneous emission of the Ly-{alpha} transition and the K -shell satellite series (lithiumlike through carbonlike) which were observed on temporally resolved x-ray emission spectra. A quantitative analysis with a time-dependent collisional-radiative non-Maxwellian model shows that these spectra can be used to obtain temporally and spatially resolved measurements of the suprathermal electron fraction in indirectly driven inertial confinement fusion targets. {copyright} {ital 1998} {ital The American Physical Society}

A new method for the determination of hot electrons in high-temperature plasmas is proposed. The presence of hot electrons leads not only to a balance shift of the ion abundance but also to a qualitative distortion. In experiments the distortion is observable through the emission of H-like and the series satellites of Li- to F-like ions. The wide range of application is demonstrated and holds even for optically thick plasmas. Transient numerical calculations are carried out for typical parameters of fusion plasmas.