F. B. Rosmej

High energy heavy ion jets emerging from laser plasma generated by long pulse laser beams from the NHELIX laser system at GSI

High energy heavy ions were generated in laser produced plasma at moderate laser energy, with a large focal spot size of 0.5 mm diameter. The laser beam was provided by the 10 GW GSI-NHELIX laser systems, and the ions were observed spectroscopically in status nascendi with high spatial and spectral resolution. Due to the focal geometry, plasma jet was formed, containing high energy heavy ions. The velocity distribution was measured via an observation of Doppler shifted characteristic transition lines. The observed energy of up to 3 MeV of F-ions deviates by an order of magnitude from the well-known Gitomer ~Gitomer et al., 1986! scaling, and agrees with the higher energies of relativistic self focusing.

Plasma physics with intense laser and ion beams

The unique combination of an intense heavy ion beam and a high-energy Nd:glass laser system at Gesellschaft fx7f 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.

X-ray radiation from ions with K-shell vacancies

Abstract 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.

Charge-exchange-induced formation of hollow atoms in high-intensity laser-produced plasmas

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.

Line formation of high-intensity -Rydberg dielectronic satellites in dense laser-produced plasmas

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.

X-ray spectromicroscopy of fast heavy ions and target radiation

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 ¼ 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 (l=Dl ¼ 100023000) and spatially high (up to 10–100mm) resolved Ka-satellite spectra of Ni projectiles as well as of the ionized stopping media were observed. r 2002 Elsevier Science B.V. All rights reserved.

The generation of fast particles in plasmas created by laser pulses with different wavelengths

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 Heβ emission in dense non-Maxwellian plasmas

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.

High-resolution x-ray imaging spectroscopy diagnostic of hollow ions in dense plasmas

Abstract The formation of hollow ions in dense Z-pinch and laser produced plasmas is investigated by means of high-resolution X-ray spectroscopy and atomic data calculations. Dense plasma effects are found to result in highly populated excited states which open up excitation channels not accessible in low-density plasma sources. This makes fs-laser radiation interacting with matter an important tool for modern atomic physics investigations.

Observation of MeV ions in long-pulse, large-scale laser-produced 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.