ABSTRACT
Backlit-pinhole radiography uses a pinhole placed between an x-ray source and a sample. The backlit-multi-pinhole design uses two pinholes on the same substrate, which are separated by a wall, to create two radiographic images projected along similar axes. The wall, a 100-µm thick titanium foil, prevents x-rays generated near one pinhole from exiting the other pinhole. First results indicate that the multi-pinhole target can create two independent radiographs along similar axes. The images are recorded 2 ns apart. Details of our multi-pinhole design and our first results are discussed.
ABSTRACT
This paper examines the experimental requirements to observe two shock fronts driven by a single x-ray source in systems with a sharp absorption edge. We consider systems where the peak of the x-ray radiation drive coincides with the K-edge of the carbon, which occurs at a photon energy of 284 eV, causing photons to be deposited in two regions. The low-energy photons (E < 284 eV) penetrate further and drive the main shock, while the higher-energy photons (E > 284 eV) are absorbed in the ablated plasma. These higher-energy photons create an ionization front, which then produces a second shock, termed an edge-shock. Using a different radiation-hydrodynamics code and different opacity and equation of state tables, we replicate the previous work and build upon them to explore the conditions required to form the edge shock. We find that having the material K-edge coincide with the spectral domain of the radiation source is necessary but not sufficient on its own to drive the edge-shock.
ABSTRACT
Foams are a common material for high-energy-density physics experiments because of low, tunable densities, and being machinable. Simulating these experiments can be difficult because the equation of state is largely unknown for shocked foams. The focus of this experiment was to develop an x-ray scattering platform for measuring the equation of state of shocked foams on OMEGA EP. The foam used in this experiment is resorcinol formaldehyde with an initial density of 0.34 g/cm3. One long-pulse (10 ns) beam drives a shock into the foam, while the remaining three UV beams with a 2 ns square pulse irradiate a nickel foil to create the x-ray backlighter. The primary diagnostic for this platform, the imaging x-ray Thomson spectrometer, spectrally resolves the scattered x-ray beam while imaging in one spatial dimension. Ray tracing analysis of the density profile gives a compression of 3 ± 1 with a shock speed of 39 ± 6 km/s. Analysis of the scattered x-ray spectra gives an upper bound temperature of 20 eV.
ABSTRACT
The visible matter in the universe is turbulent and magnetized. Turbulence in galaxy clusters is produced by mergers and by jets of the central galaxies and believed responsible for the amplification of magnetic fields. We report on experiments looking at the collision of two laser-produced plasma clouds, mimicking, in the laboratory, a cluster merger event. By measuring the spectrum of the density fluctuations, we infer developed, Kolmogorov-like turbulence. From spectral line broadening, we estimate a level of turbulence consistent with turbulent heating balancing radiative cooling, as it likely does in galaxy clusters. We show that the magnetic field is amplified by turbulent motions, reaching a nonlinear regime that is a precursor to turbulent dynamo. Thus, our experiment provides a promising platform for understanding the structure of turbulence and the amplification of magnetic fields in the universe.
Subject(s)
Astronomical Phenomena , Galaxies , Magnetic Fields , Models, Theoretical , Computer Simulation , Lasers , Solar System , Spectrum Analysis , Temperature , ThermodynamicsABSTRACT
Past decades significantly advanced our understanding of Rayleigh-Taylor (RT) mixing. We briefly review recent theoretical results and numerical modelling approaches and compare them with state-of-the-art experiments focusing the reader's attention on qualitative properties of RT mixing.
