We present calculations for the field of view (FOV), image fluence, image monochromaticity, spectral acceptance, and image aberrations for spherical crystal microscopes, which are used as self-emission imaging or backlighter systems at large-scale high energy density physics facilities. Our analytic results are benchmarked with ray-tracing calculations as well as with experimental measurements from the 6.151 keV backlighter system at Sandia National Laboratories. The analytic expressions can be used for x-ray source positions anywhere between the Rowland circle and object plane. This enables quick optimization of the performance of proposed but untested, bent-crystal microscope systems to find the best compromise between FOV, image fluence, and spatial resolution for a particular application.
By magnetizing the fusion fuel in inertial confinement fusion (ICF) systems, the required stagnation pressure and density can be relaxed dramatically. This happens because the magnetic field insulates the hot fuel from the cold pusher and traps the charged fusion burn products. This trapping allows the burn products to deposit their energy in the fuel, facilitating plasma self-heating. Here, we report on a comprehensive theory of this trapping in a cylindrical DD plasma magnetized with a purely axial magnetic field. Using this theory, we are able to show that the secondary fusion reactions can be used to infer the magnetic field-radius product, BR, during fusion burn. This parameter, not ρR, is the primary confinement parameter in magnetized ICF. Using this method, we analyze data from recent Magnetized Liner Inertial Fusion experiments conducted on the Z machine at Sandia National Laboratories. We show that in these experiments BR ≈ 0.34(+0.14/-0.06) MG cm, a ∼ 14x increase in BR from the initial value, and confirming that the DD-fusion tritons are magnetized at stagnation. This is the first experimental verification of charged burn product magnetization facilitated by compression of an initial seed magnetic flux.
Magnetized Liner Inertial Fusion experiments performed at Sandia's Z facility have demonstrated significant thermonuclear fusion neutron yields (∼1012 DD neutrons) from multi-keV deuterium plasmas inertially confined by slow (∼10 cm/μs), stable, cylindrical implosions. Effective magnetic confinement of charged fusion reactants and products is signaled by high secondary DT neutron yields above 1010. Analysis of extensive power, imaging, and spectroscopic x-ray measurements provides a detailed picture of ∼3 keV temperatures, 0.3 g/cm3 densities, gradients, and mix in the fuel and liner over the 1-2 ns stagnation duration.
The magnetized liner inertial fusion concept [S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010)] utilizes a magnetic field and laser heating to relax the pressure requirements of inertial confinement fusion. The first experiments to test the concept [M. R. Gomez et al., Phys. Rev. Lett. 113, 155003 (2014)] were conducted utilizing the 19 MA, 100-ns Z machine, the 2.5-kJ, 1 TW Z Beamlet laser, and the 10-T Applied B-field on Z system. Despite an estimated implosion velocity of only 70-km/s in these experiments, electron and ion temperatures at stagnation were as high as 3-keV, and thermonuclear deuterium-deuterium neutron yields up to 2-×-1012 have been produced. X-ray emission from the fuel at stagnation had widths ranging from 50 to 110 μm over a roughly 80% of the axial extent of the target (6-8-mm) and lasted approximately 2-ns. X-ray yields from these experiments are consistent with a stagnation density of the hot fuel equal to 0.2-0.4-g/cm3. In these experiments, up to 5-×-1010 secondary deuterium-tritium neutrons were produced. Given that the areal density of the plasma was approximately 1-2-mg/cm2, this indicates the stagnation plasma was significantly magnetized, which is consistent with the anisotropy observed in the deuterium-tritium neutron spectra. Control experiments where the laser and/or magnetic field were not utilized failed to produce stagnation temperatures greater than 1-keV and primary deuterium-deuterium yields greater than 1010. An additional control experiment where the fuel contained a sufficient dopant fraction to substantially increase radiative losses also failed to produce a relevant stagnation temperature. The results of these experiments are consistent with a thermonuclear neutron source.
High-energy short-pulse lasers are pushing the limits of plasma-based particle acceleration, x-ray generation, and high-harmonic generation by creating strong electromagnetic fields at the laser focus where electrons are being accelerated to relativistic velocities. Understanding the relativistic electron dynamics is key for an accurate interpretation of measurements. We present a unified and self-consistent modeling approach in quantitative agreement with measurements and differing trends across multiple target types acquired from two separate laser systems, which differ only in their nanosecond to picosecond-scale rising edge. Insights from high-fidelity modeling of laser-plasma interaction demonstrate that the ps-scale, orders of magnitude weaker rising edge of the main pulse measurably alters target evolution and relativistic electron generation compared to idealized pulse shapes. This can lead for instance to the experimentally observed difference between 45-MeV and 75-MeV maximum energy protons for two nominally identical laser shots, due to ps-scale prepulse variations. Our results show that the realistic inclusion of temporal laser pulse profiles in modeling efforts is required if predictive capability and extrapolation are sought for future target and laser designs or for other relativistic laser ion acceleration schemes.
The standard approaches to inertial confinement fusion (ICF) rely on implosion velocities greater than 300 km/s and spherical convergence to achieve the high fuel temperatures (T > 4 keV) and areal densities (ρr > 0.3 g/cm2) required for ignition1. Such high velocities are achieved by heating the outside surface of a spherical capsuleeither directly with a large number of laser beams (Direct Drive) or with x-rays generated within a hohlraum (Indirect Drive). A much more energetically efficient approach is to use the magnetic pressure generated by a pulsed power machine to directly drive an implosion. In this approach 5-10% of the stored energy can be converted to the implosion of a metal tube generally referred to as a “liner”. However, the implosion velocity is not very high 70-100 km/s and the convergence is cylindrical (rather than spherical) making it more difficult to achieve the high temperatures and areal densities needed for ignition.
The data described in this document consist of image files of shadowgraphs of astrophysically relevant laser driven blast waves. Supporting files include Mathematica notebooks containing design calculations, tabulated experimental data and notes, and relevant publications from the open research literature. The data was obtained on the Z-Beamlet laser from July to September 2014. Selected images and calculations will be published as part of a PhD dissertation and in associated publications in the open research literature, with Sandia credited as appropriate. The authors are not aware of any restrictions that could affect the release of the data.
This Letter presents results from the first fully integrated experiments testing the magnetized liner inertial fusion concept [S.A. Slutz et al., Phys. Plasmas 17, 056303 (2010)], in which a cylinder of deuterium gas with a preimposed axial magnetic field of 10 T is heated by Z beamlet, a 2.5 kJ, 1 TW laser, and magnetically imploded by a 19 MA current with 100 ns rise time on the Z facility. Despite a predicted peak implosion velocity of only 70 km/s, the fuel reaches a stagnation temperature of approximately 3 keV, with Te ≈ Ti, and produces up to 2e12 thermonuclear DD neutrons. In this study, X-ray emission indicates a hot fuel region with full width at half maximum ranging from 60 to 120 μm over a 6 mm height and lasting approximately 2 ns. The number of secondary deuterium-tritium neutrons observed was greater than 1010, indicating significant fuel magnetization given that the estimated radial areal density of the plasma is only 2 mg/cm2.
Laser-driven proton radiography provides electromagnetic field mapping with high spatiotemporal resolution, and has been applied to many laser-driven High Energy Density Physics (HEDP) experiments. Our report addresses key questions about the feasibility of ion radiography at the Z-Accelerator (%E2%80%9CZ%E2%80%9D), concerning laser configuration, hardware, and radiation background. Charged particle tracking revealed that radiography at Z requires GeV scale protons, which is out of reach for existing and near-future laser systems. However, it might be possible to perform proton deflectometry to detect magnetic flux compression in the fringe field region of a magnetized liner inertial fusion experiment. Experiments with the Z-Petawatt laser to enhance proton yield and energy showed an unexpected scaling with target thickness. Full-scale, 3D radiation-hydrodynamics simulations, coupled to fully explicit and kinetic 2D particle-in-cell simulations running for over 10 ps, explain the scaling by a complex interplay of laser prepulse, preplasma, and ps-scale temporal rising edge of the laser.