Showing papers by "Siegfried Glenzer published in 2005"

Experimental characterization of a strongly coupled solid density plasma generated in a short-pulse laser target interaction

Abstract: We have measured high resolution copper Kα spectra from a picosecond high intensity laser produced plasma By fitting the shape of the experimental spectra with a self-consistent-field model which includes all the relevant line shifts from multiply ionized atoms, we are able to infer time and spatially averaged electron temperatures (Te) and ionization state (Z) in the foil Our results show increasing values for Te and Z when the overall mass of the target is reduced In particular, we measure temperatures in excess of 200 eV with Z ∼ 13-14 For these conditions the ion-ion coupling constant is Γii ∼ 8-9, thus suggesting the achievement of a strongly coupled plasma regime (© 2005 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim)

Integrated laser–target interaction experiments on the RAL petawatt laser

Abstract: We review a recent experimental campaign to study the interaction physics of petawatt laser pulses incident at relativistic intensities on solid targets. The campaign was performed on the 500 J sub-picosecond petawatt laser at the Rutherford Appleton Laboratory. An extensive suite of optical, x-ray, and particle diagnostics was employed to characterise the processes of laser absorption, electron generation and transport, thermal and K-alpha x-ray generation, and proton acceleration.

Radiation-Driven Hydrodynamics of High-Z Hohlraums on the National Ignition Facility

Abstract: The first hohlraum experiments on the National Ignition Facility (NIF) using the initial four laser beams tested radiation temperature limits imposed by plasma filling. For a variety of hohlraum sizes and pulse lengths, the measured x-ray flux shows signatures of filling that coincide with hard x-ray emission from plasma streaming out of the hohlraum. These observations agree with hydrodynamic simulations and with an analytical model that includes hydrodynamic and coronal radiative losses. The modeling predicts radiation temperature limits with full NIF (1.8 MJ), greater, and of longer duration than required for ignition hohlraums.

Supersonic propagation of ionization waves in an underdense, laser-produced plasma

Abstract: A laser-driven supersonic ionization wave propagating through a millimeter-scale plasma of subcritical density up to 2–3keV electron temperatures was observed. Propagation velocities initially ten times the sound speed were measured by means of time-resolved x-ray imaging diagnostics. The measured ionization wave trajectory is modeled analytically and by a two-dimensional radiation-hydrodynamics code. The comparison to the modeling suggests that nonlocal heat transport effects may contribute to the attenuation of the heat-wave propagation.

Measurement of the dispersion of thermal ion-acoustic fluctuations in high-temperature laser plasmas using multiple-wavelength Thomson scattering.

Abstract: The dispersion of ion-acoustic fluctuations has been measured using a novel technique that employed multiple color Thomson scattering to measure the frequency spectrum for two separate thermal ion-acoustic fluctuations with significantly different wave vectors. The plasma fluctuations are shown to become dispersive with increasing electron temperature. They demonstrate that this technique allows a time resolved local measurement of electron density and temperature in inertial confinement fusion plasmas.

First laser–plasma interaction and hohlraum experiments on the National Ignition Facility

Abstract: Recently the first laser–plasma interaction and hohlraum experiments have been performed at the National Ignition Facility (NIF) in support of indirect drive inertial confinement fusion designs. The effects of laser beam smoothing by spectral dispersion and polarization smoothing on the intense (2 × 1015 W cm−2) beam propagation in gas-filled tubes has been studied at up to 7 mm plasma scales as found in indirect drive gas filled ignition hohlraum designs. These experiments have shown the expected full propagation without filamentation and beam break up when using full laser smoothing. In addition, vacuum hohlraums have been irradiated with laser powers up to 6 TW, 1–9 ns pulse lengths and energies up to 17 kJ to activate several diagnostics, to study the hohlraum radiation temperature scaling with the laser power and hohlraum size, and to make contact with hohlraum experiments performed at the Nova and Omega laser facilities. Subsequently, novel long laser pulse hohlraum experiments have tested models of hohlraum plasma filling and long pulse hohlraum radiation production. The validity of the plasma filling assessment using in analytical models and radiation hydrodynamics calculations with the code LASNEX has been proven in these studies. The comparison of these results with modelling will be discussed.

The First Experiments on the National Ignition Facility

Abstract: A first set of laser-plasma interaction, hohlraum energetics and hydrodynamic experiments have been performed using the first 4 beams of the National Ignition Facility (NIF), in support of indirect drive Inertial Confinement Fusion (ICF) and High Energy Density Physics (HEDP). In parallel, a robust set of optical and x-ray spectrometers, interferometer, calorimeters and imagers have been activated. The experiments have been undertaken with laser powers and energies of up to 8 TW and 17 kJ in flattop and shaped 1-9 ns pulses focused with various beam smoothing options.

X-ray flux and x-ray burnthrough experiments on reduced-scale targets at the NIF and OMEGA lasers

Abstract: An experimental campaign to maximize radiation drive in small-scale hohlraums has been carried out at the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory (Livermore, CA USA) and at the OMEGA laser at the Laboratory for Laser Energetics (Rochester, NY USA) The small-scale hohlraums, laser energy, laser pulse, and diagnostics were similar at both facilities but the geometries were very different The NIF experiments used on-axis laser beams whereas the OMEGA experiments used 19 beams in three beam cones In the cases when the lasers coupled well and produced similar radiation drive, images of x-ray burnthrough and laser deposition indicate the pattern of plasma filling is very different

Coupling of High Power Lasers to Small, Hot Targets at the National Ignition Facility

Abstract: Summary form only given. An experimental campaign to study radiation drive in small-scale halfraums has been carried out using the first four beams of the National Ignition Facility (NIF) at the Lawerence Livermore National Laboratory (Livermore, CA). The targets fill with plasma so quickly that, late in time, most of the laser energy is deposited at the laser entrance hole. Experiments have shown the effect of laser beam conditioning, laser power, and target size on hohlraum performance. The experimental results on X-radiation drive, laser backscatter, hard X-rays, hard X-ray imaging, and X-ray burnthrough are discussed

Laser-beam propagation in high temperature hohlraum plasmas

Abstract: The authors have developed a new target platform to study propagation and backscatter of a frequency-doubled (2{omega}) laser beam through large-scale length plasmas at ignition-design densities, intensities and temperatures above 3 keV The plasma is created by heating a gas filled hohlraum target with 37 heater beams that deliver a total energy of up to 15 kJ in a 1 ns square pulse They measure a factor of two higher temperatures than in open geometry gasbag targets investigated earlier This new temperature regime with a measured beam transmission of up to 80% suggests we can expect good laser coupling into ignition hohlraums at the National Ignition Facility (NIF) using 2{omega} light