Laboratory astroparticle physics

Abstract:

Dense titanium plasma has been heated to an electron temperature up to 1300 eV with a 100 TW, high intensity short-pulse laser. The experiments were conducted using Ti foils (5 μm thick) sandwiched between layers of either aluminum (1 or 2 μm thick) or plastic (2 μm thick) to prevent the effects of prepulse. Targets of two different sizes, i.e., 250 × 250 μm 2 and 1×1 mm2 were used. Spectral measurements of the Ti inner-shell emission, in the region between 4 and 5 keV, were taken from, the front-side (i.e., the laser illuminated side) of the target. The data show large shifts in the Kα emission from open-shell ions, suggesting bulk heating of the sample at near solid density, which was largest for reduced mass targets. Comparison with collisional radiative and 2D radiation hydrodynamics codes indicates a peak temperature of Te,peak= 1300 eV of solid titanium plasma in ∼0.2 μm thin layer. Higher bulk temperature (T e,bulk=100 eV) for aluminum tamped compared to CH tamped targets (Te,bulk=40 eV) was observed. A possible explanation for this difference is described whereby scattering due to the nuclear charge of the tamping material leads to modified electron transport behavior. © 2007 American Institute of Physics.

Abstract:

In this Letter we report on a near collective x-ray scattering experiment on shock-compressed targets. A highly coupled Al plasma was generated and probed by spectrally resolving an x-ray source forward scattered by the sample. A significant reduction in the intensity of the elastic scatter was observed, which we attribute to the formation of an incipient long-range order. This speculation is confirmed by x-ray scattering calculations accounting for both electron degeneracy and strong coupling effects. Measurements from rear side visible diagnostics are consistent with the plasma parameters inferred from x-ray scattering data. These results give the experimental evidence of the strongly coupled ionic dynamics in dense plasmas. © 2007 The American Physical Society.

Abstract:

We report spectrally resolved X-ray scattering data from shock compressed foils illustrating the feasibility of X-ray Thomson scattering experiment on a sub-kilo joule laser system. Sandwich targets consisting of CH/Al/CH were shock compressed using similar to 1 ns laser pulses. Separate 270 ps laser pulses were used to generate an intense source of Ti-He-alpha (1s(2)-1s2p(1)P) radiation which was used as a probing source of 4.75 keV photons. The spectrum of scattered photons was recorded at a scattering angle of 82 degrees with a CCD fitted spectrometer using a PET crystal in von-Hamos geometry. Although spectral resolution was used to separate the scatter from any background, the resolution was limited by source broadening. The relative level of scatter at different times in the sample history was measured by varying the delay between the shock driving beams and the back-lighter beams. We have compared the scatter spectra with simulations based on two different models of the L-shell bound-free contribution.

Abstract:

A novel wide angle spectrometer has been implemented with a highly oriented pyrolytic graphite crystal coupled to an image plate. This spectrometer has allowed us to look at the energy resolved spectrum of scattered x rays from a dense plasma over a wide range of angles (approximately 30 degrees ) in a single shot. Using this spectrometer we were able to observe the temporal evolution of the angular scatter cross section from a laser shocked foil. A spectrometer of this type may also be useful in investigations of x-ray line transfer from laser-plasmas experiments.

Abstract:

A first set of shock timing, 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. The experiments have demonstrated excellent agreement between measured and predicted laser-target coupling in foils and hohlraums, even when extended to a longer pulse regime unattainable at previous laser facilities, validated the predicted effects of beam smoothing oil intense laser beam propagation in long scale-length plasmas and begun to test 3D codes by extending the study of laser driven hydrodynamic jets to 3D geometries.