Gianluca Gregori

Abstract:

We present collective x-ray scattering (CXS) measurements using a chlorine He-alpha x-ray source pumped with less than 200 J of laser energy. The experimental scattering spectra show plasmon resonances from shocked and radiatively heated samples. These experiments use only 10(12) x-ray photons at the sample of which 10(-5) have been scattered and detected with a highly efficient curved crystal spectrometer. Our results demonstrate that x-ray scattering is a viable technique on smaller laser facilities, making CXS measurements accessible to a broad scientific community. (c) 2006 American Institute of Physics.

Abstract:

Short pulse (< 100 fs) tunable X-ray and VUV laser sources, based on the free electron laser (FEL) concept, will be a watershed for high energy density research in several areas. These new 4 th generation light sources will have extremely high fields and short wavelength (∼.1 nm) with peak spectral brightness -photons/(s/mrad 2/mm 2/0.1% bandwidth- 10 10 greater than 3 rd generation light sources. We briefly discuss several applications: the creation of warm dense matter (WDM), probing of near solid density plasmas, and laser-plasma spectroscopy of ions in plasmas. The study of dense plasmas has been severely hampered by the fact that laser-based probes that can directly access the matter in this regime have been unavailable and these new 4 th generation sources will remove these restrictions. Finally, we present the plans for a user-oriented set of facilities that will incorporate high-energy, intense short-pulse, and x-ray lasers at the first x-ray FEL, the LCLS to be opened at SLAC in 2009.

Abstract:

We propose a modified x-ray form factor that describes the scattering cross section in warm dense matter valid for both the plasma and the solid (crystalline) state. Our model accounts for the effect of lattice correlations on the electron-electron dynamic structure, as well as provides a smooth transition between the solid and the plasma scattering cross sections. In addition, we generalize the expression of the dynamic structure in the case of a two-temperature system (with different electron and ion temperatures). This work provides a unified description of the x-ray scattering processes in warm and dense matter, as the one encountered in inertial confinement fusion, laboratory astrophysics, material science, and high-energy density physics and it can be used to verify temperature relaxation mechanisms in such environments.

Abstract:

We experimentally demonstrate that application of laser smoothing schemes including smoothing by spectral dispersion (SSD) and polarization smoothing (PS) increases the intensity range for efficient coupling of frequency doubled (527 nm) laser light to a long scalelength plasma with n(e)/n(cr) = 0.14 and T-e = 2 keV.

Abstract:

The Fast Ignition Program in the United States has enjoyed increased funding in various forms from the Office of Fusion Energy Sciences of the Department of Energy. The program encompasses experiments on large laser facilities at various world-wide locations, and benefits enormously from collaborations with many international scientists. The program includes exploratory work in cone-target design and implosion dynamics, high electron current transport measurements in normal density materials, development of diagnostics for heating measurements, generation of protons from shaped targets, theoretical work on high gain target designs, and extensive modeling development using PIC and hybrid codes.