[en] The plasma conditions in isochorically heated beryllium are measured by x-ray Thomson scattering in the collective regime with a Cl Ly-α x-ray source at 2.96 keV. In addition to the down-shifted plasmon shape which provides electron density and temperature information, an up-shifted plasmon signal is observed allowing a model independent determination of the plasma temperature from the detailed balance relation

[en] We are developing a target platform that utilizes short-pulse (10 ps) generated hot electrons (∼1 MeV) to isochorically heat solid density beryllium up to several 10 eV. X-ray Thomson scattering is employed to characterize the plasma conditions. X-rays from a Cl Ly-α line source at 2.96 keV are scattered off the plasma in forward direction where the inelastically scattered signal is sensitive to plasma oscillations. Besides Landau-damping the strong energy down-shifted plasmon signal is also broadened by collisions which, in turn, allows to infer the collision rate and thus the conductivity in these plasmas. Recently, we demonstrated that from the ratio of the energy up-shifted to the down-shifted plasmon signals the plasma temperature can be inferred from the detailed balance relation which is based on first principles. Thus from the Plasmon shift and detailed balance we will be able to consistently determine plasma density and temperature, and relate this to the collisionality inferred from the Plasmon broadening. A precise knowledge of the collisionality in the parameter regime we are aiming at with these experiments is important to correctly model the conditions encountered during capsule implosions at the National Ignition Facility.

[en] The ionization of silver clusters exposed to pairs of intense femtosecond laser pulses strongly depends on the optical delay. Enhanced production of a certain atomic charge state z is obtained by a z-dependent delay. This may open a possible route to control the excitation process and populate specific charge states. The optimum pulse separation which maximizes the generation of highly ionized species varies by more than one order of magnitude when the mean size of the clusters increases from N-bar = 80 to N-bar = 22000. Semiclassical Vlasov simulations applied to a model system reveal the importance of the initial ionic motion in the ionization process. (authors)

[en] A high contrast 12.6 keV Kr Kα source has been demonstrated on the petawatt-class Titan laser facility. The contrast ratio (Kα to continuum) is 65, with a competitive ultra short pulse laser to x-ray conversion efficiency of 10^-5. Filtered shadowgraphy indicates that the Kr Kα and Kβ x-rays are emitted from a roughly 1 x 2 mm emission volume, making this source suitable for area backlighting and scattering. Spectral calculations indicate a typical bulk electron temperature of 50-70 eV (i.e. mean ionization state 13-16), based on the observed ratio of Kα to Kβ. Kr gas jets provide a debris-free high energy Kα source for time-resolved diagnosis of dense matter

[en] We present measurements of the chlorine K-alpha emission from reduced mass targets, irradiated with ultra-high intensity laser pulses. Chlorinated plastic targets with diameters down to 50 micrometers and mass of a few 10^-8 g were irradiated with up to 7 J of laser energy focused to intensities of several 10¹⁹ W/cm². The conversion of laser energy to K-alpha radiation is measured, as well as high resolution spectra that allow observation of line shifts, indicating isochoric heating of the target up to 18 eV. A zero-dimensional 2-temperature equilibration model, combined with electron impact K-shell ionization and post processed spectra from collisional radiative calculations reproduces the observed K-alpha yields and line shifts, and shows the importance of target expansion due to the hot electron pressure

[en] The experiment in this work was preformed at the Titan laser facility (S1) where a short pulse beam at a wavelength of 1053nm delivered up to 350J in 0.5 to 20 ps and a long pulse beam at 527nm, 2ω frequency provided energies up to 450J in 1 to 6 ns. Long pulse shaping in this experiment, similar to future capabilities at NIF, was primarily a 4ns long foot with an intensity of 1 x 10¹³ W/cm², followed by a 2ns long peak with an intensity of 3 x 10¹³ W/cm². A ∼ 600 um phase plate was used on the long pulse beam to moderate non-uniformities in the intensity profile. An illustration of the Thomson scattering setup for this experiment is provided in Fig. 1 of the main text. A nearly mono-energetic scattering source of ΔE/E ∼ 0.3% in the 4.5 keV Ti K-alpha line was produced via intense short-pulse laser irradiation of 1.9 x 3 x 0.01 mm Ti foils, creating energetic keV electrons in the process (S2, S3). The nearly isotropic source emission (S4) is produced in the cold solid density bulk of the foil from electron K shell ionization of neutral or weakly ionized atoms, with an emission size on the order of the laser focal spot. By optimizing the laser intensity and pulse width to 4.4 x 10¹⁶ W cm^-2, a total of 2.3 x 10¹³ x-ray photons have been produced into 4π. This value corresponds to a conversion efficiency of laser energy into Ti K-alpha x-ray energy of 5 x 10^-5, see Fig. S1. These sources provide ∼10 ps x-ray pulses as measured experimentally (S5)

[en] Spectrally resolved Thomson scattering using ultra-fast K-α x-rays has measured the compression and heating of shocked compressed matter. The evolution and coalescence of two shock waves traveling through a solid density LiH target were characterized by the elastic scattering component. The density and temperature at shock coalescence, 2.2 eV and 1.7 x 10²³cm^-3, were determined from the plasmon frequency shift and the relative intensity of the elastic and inelastic scattering features in the collective scattering regime. The observation of plasmon scattering at coalescence indicates a transition to the dense metallic state in LiH. The density and temperature regimes accessed in these experiments are relevant for inertial confinement fusion experiments and for the study of planetary formation

[en] We have developed accurate x-ray scattering techniques to measure the physical properties of dense plasmas. Temperature and density are inferred from inelastic x-ray scattering data whose interpretation is model-independent for low to moderately coupled systems. Specifically, the spectral shape of the non-collective Compton scattering spectrum directly reflects the electron velocity distribution. In partially Fermi degenerate systems that have been investigated experimentally in laser shock-compressed beryllium, the Compton scattering spectrum provides the Fermi energy and hence the electron density. We show that forward scattering spectra that observe collective plasmon oscillations yield densities in agreement with Compton scattering. In addition, electron temperatures inferred from the dispersion of the plasmon feature are consistent with the ion temperature sensitive elastic scattering feature. Hence, theoretical models of the static ion-ion structure factor and consequently the equation of state of dense matter can be directly tested.

[en] We have fielded a multi-pinhole, hard x-ray (> 100 keV) imager to measure the spatially-resolved bremsstrahlung emission from energetic electrons slowing in a plastic ablator shell during indirectly driven implosions at the National Ignition Facility. These electrons are generated in laser plasma interactions, and are a source of preheat to the deuterium-tritium fuel that could limit the compressibility required for ignition and burn. Our hard x-ray imaging measurements allow to set an upper limit to the DT fuel preheat, which we find is acceptable in current capsule implosions on the NIF.

[en] We propose a collective Thomson scattering experiment at the VUV free electron laser facility at DESY (FLASH) which aims to diagnose warm dense matter at near-solid density. The plasma region of interest marks the transition from an ideal plasma to a correlated and degenerate many-particle system and is of current interest, e.g. in ICF experiments or laboratory astrophysics. Plasma diagnostic of such plasmas is a longstanding issue. The collective electron plasma mode (plasmon) is revealed in a pump-probe scattering experiment using the high-brilliant radiation to probe the plasma. The distinctive scattering features allow to infer basic plasma properties. For plasmas in thermal equilibrium the electron density and temperature is determined from scattering off the plasmon mode