J. Bruneau

Space and time resolved absorption spectroscopy of directly and indirectly driven expanding plasmas

Abstract We have extended the technique of absorption spectroscopy to study the ion charge distribution and the areal mass density variations of expanding laser-produced and radiationdriven plasmas. Specifically, we will present space and time-resolved absorption spectroscopy measurements for K and L -shell ions (Mg and Ge) in the 8–11 A spectral range. The nanosecond plasmas were created either by direct laser irradiance in the case of Mg (up to 10 13 W/cm 2 ) or by indirect x-ray heating (at a few 10 12 W/cm 2 x-ray irradiance). The ion population and areal mass of the expanding plasmas were deduced from the agreement between the experimental optical depths and the theoretical modelling of absorption derived from atomic data calculated either in a detailed configuration MCDF (Mg and Ge) or in a statistical UTA approach (Ge), both analysis being in good agreement. We will also present comparisons of the Mg and Ge data to space and time predictions of the hydrodynamical code CHIVAS.

Toroidal crystal spectrometer for time-resolved x-ray absorption diagnostic in dense plasmas

A toroidal crystal spectrometer was designed with the purpose of measuring the aluminum K-absorption edge shift, in the wavelength range around 7.9 A, in strongly compressed matter. The expected shift is about 100 mA (∼20 eV). The x rays reflected from the crystal are focused onto a streak camera slit of 16 mm high and 100 μm width, to obtain a time-resolved spectrum. High resolution and dispersion of about 1–16 A/mm on the detection window are obtained. A crystal with a toroidal surface is used to enhance the focusing power in the spatial dimension as in the spectral one. Numerical simulations are performed by means of one- and two-dimensional codes for the determination of the crystal characteristics like the dimension and the curvature radius with respect to the geometric constraints. Some experimental results are presented concerning the obtained spectra.

Effects of line focus width narrowing on amplification in Ne-like Se x-ray laser experiments

Ne-like Se X-ray laser experiments have been performed to examine the effects in line focus width narrowing on amplification in a collisional excitation scheme. Variation from 40 micrometers up to 180 micrometers has been investigated. Significant changes in temperature and ionization balance have been observed and explained from theoretical considerations.

Absorption spectroscopy of the K-shell Rydberg series in a Mg laser-produced plasma

The K-shell resonance and dielectronic satellite lines of Mg XI through Mg VIII have been observed in absorption in a near-LTE, radiatively-heated, laser-produced plasma. Measurements of the absorption of 1.3-1.7 keV X-rays from a Dy backlighter layer by 1-2, 1-3 and 1-4 transitions have been made with high spectral resolution. Radiative hydrocode simulations and detailed atomic physics calculations describe correctly the experimental results, except for the 1s2-1s2p resonance line of Mg XI which is always observed in emission. Resonance fluorescence resulting from a collisional-radiative cascade from the Mg XI 1s3p level photopumped by the strong 3d-4f transition arrays of Dy could be the source of the observed emission.

Three pumping schemes for soft X-ray lasers at λ ≈ 100 Å

Abstract In this paper we present X-UV gain measurements performed at nearly the same wavelength (≈ 100 A) using three different pumping schemes. The amplifying plasma was produced by the PHEBUS laser. A same diagnostic apparatus was kept in al cases providing a direct comparison of the experimental results.

Backlighters and the Megajoule laser

Backlighting is extensively used as a diagnostic tool in experiments relative to Inertial Confinement Fusion. Thus, beam and target nonuniformities effects on hydrodynamic instabilities growth and imprinting, shock propagation in solid materials and foil acceleration are studied in planar geometry. Spherical or cylindrical implosions measurements are relative to hydrodynamic instabilities, feedthrough and fuel-pusher mixing, in-flight aspect ratio, implosion velocity, symmetry and peak compression densities. With the laser mega-joule very high laser power and energy will be reached that will give access to new density and temperature domains. Correlatively, diagnostics survivability has to be considered taking the large X-ray, neutron and debris emissions into account. The X-ray induced shocks or neutron induced radioactivity will constitute limitations to measurements inside the target chamber. The experimental program on its route towards ignition and gain will anyway still require backlighters to optimize the targets parameters (the microballoon wall thickness, the ablator nature) and allow the adjustment of not well known quantities as opacities and equations of state.

Toroidal crystal spectrometer for dense plasma diagnostics

A toroidal crystal spectrometer was designed with the purpose of measuring the aluminum K-absorption edge shift, in the wavelength range around 7.9 angstroms, in highly compressed matter. The expected shift is about 100 mA (approximately 20 eV). The x-ray reflected from the crystal are focused onto a streak camera slit of 16 mm high and 100 micrometers width, to obtain a time resolved spectrum. High resolution value and dispersion of about 1 angstrom/16 mm on the detection window is hence required. A crystal with a toroidal surface is used to enhance the focusing power in the spatial dimension as in the spectral one. Numerical simulations are performed by means of 1D and 2D codes for the determination of the crystal characteristics like the dimension and the curvature radius with respect to the geometric constraints. Some results will be presented concerning the obtained spectra.

Measurement of x‐ray laser beam divergence with CADIX, a time‐resolved diagnostic tool using an insertable multilayer mirror

To study the x‐ray laser beam deflection and divergence due to the refraction within the plasma, a specific diagnostic called CADIX has been developed at the Centre d’Etudes de Limeil‐Valenton (CEL‐V). When the beam refraction analysis is required a multilayer mirror is inserted on the x‐ray laser output beam. It selects the lasing wavelengths and reflects them to an off‐axis streak camera which records x rays as a function of time and angle. A detailed description of the instrument is presented including multilayer mirror calibration at the LURE (Laboratoire pour L’Utilisation du Rayonnement Synchrotron, Orsay, France). An experimental measurement on neon‐like silver amplification is presented and analyzed with the response of the mirror. An important refraction effect is observed.