Using power-law least-squares fits to thick-target measurements of X-ray bremsstrahlung and characteristic line emission, analytic expressions for spectra and emission efficiencies of X-rays produced by a Maxwellian electron distribution were calculated. These expressions are particularly useful for the analysis of X-ray spectra produced by hot electrons in laser-produced plasma. The effect of self-absorption on the analysis of these spectra is estimated. It is shown that both the spectral shape and the adsorption effects dictate that bremsstrahlung measurements of plasma temperature should be made at photon energies greater than kT.

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The x-ray bremsstrahlung from 4 to 50 keV emitted by laser-produced plasmas has been measured using a Bragg crystal spectrometer. Direct spectral information was obtained in contrast to earlier filter spectroscopy. Measurements were made with focal spot powers of 1016 W/cm2 of 1.06-μm radiation and 1014 W/cm2 of 10.6-μm radiation. A definite suprathermal electron component was observed.

Saturation gain-length product during short-wavelength plasma lasing Appl. Phys. Lett. 101, 081105 (2012) Laser induced avalanche ionization in gases or gas mixtures with resonantly enhanced multiphoton ionization or femtosecond laser pulse pre-ionization Phys. Plasmas 19, 083508 (2012) A new scheme for stigmatic x-ray imaging with large magnification Rev. Sci. Instrum. 83, 10E527 (2012) Additional information on Phys. Fluids

We have performed one-dimensional magnetohydrodynamic computer calculations of the formation and evolution of the solid-deuterium-fiber Z pinch. With use of a tabulated atomic data base and "cold-start" initial conditions, our computations show that current is carried by hot plasma which has been ablated from the solid fiber. The computations suggest that the experimentally observed instability growth may coincide with the complete ablation of the central fiber.

A new class of inertial fusion capsules is presented that combines multishell targets with laser direct drive at low intensity (2.8 × 10 14 W=cm 2 ) to achieve robust ignition. The targets consist of three concentric, heavy, metal shells, enclosing a volume of tens of μg of liquid deuterium-tritium fuel. Ignition is designed to occur well "upstream" from stagnation, with minimal pusher deceleration to mitigate interface Rayleigh-Taylor growth. Laser intensities below thresholds for laser plasma instability and cross beam energy transfer facilitate high hydrodynamic efficiency (∼10%). DOI: 10.1103/PhysRevLett.116.255003 A large convergence ratio and high implosion velocity have been the hallmarks of inertial fusion from its inception [1,2]. Target design has evolved over the past forty-plus years to culminate in the National Ignition Facility (NIF) ignition targets fired during the Ignition Campaign of 2009-2012. These targets sought to ignite a central hot spot formed by a small fraction of fuel that could be heated to ignition temperatures. Burn was then projected to propagate to the main fuel and produce high gain. A specific example (Fig. 107 of Ref.[2]) composed entirely of light materials is driven by 1.35 MJ of laser light. It required an implosion velocity u I ¼ 41 cm=μs and convergence ratio (initial capsule radius, R i divided by final radius R f ) of C ¼ 36 from a plastic and deuterium-tritium (DT) ice shell with an in-flight aspect ratio of 40. The predicted yield of 15 MJ from 180 μg of DT fuel corresponds to a burn fraction of 25%. Nearly perfect spherical symmetry was essential. The experimental results achieved to date on the NIF have underperformed predictions [3,4].A fundamentally different path to ignition is described in this Letter. A new class of targets capable of producing multi-megajoule yields from DT fuel masses of tens of μg, absorbed drive energies less than 2 MJ, and burn fractions exceeding 50% is defined. High gain is abandoned as a goal. Instead, we seek a mechanically robust implosion and large margin for ignition. The Revolver targets described here consist of three nested, spherical metal shells with buffer gas between the shells and a central volume filled with cryogenic liquid DT fuel. The baseline target is depicted in Fig. 1, which also shows the implosion diagram from a HYDRA [5] 1D simulation. Energy is absorbed by an ablator shell from a short laser pulse that leaves 70% of the ablator mass as payload to implode the target. The implosion is entirely mechanical, dominated by the metal shells. The metal multishell system is intended to be more robust hydrodynamically than a single plastic-DT ice shell. Ignition well upstream of stagnation is a key feature of the Revolver targets. This is controlled with a design parameter that allows for adjustment of the ignition margin.All the physics pieces we will assemble have long been known and studied. Metal pushers were first discussed in the literature by Kirkpatrick and co-workers [6,7], who showed the benefits of radiation t...

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can make an order-of-magnitude estimate of r using a classical hard-sphere model for the collisions where the rotons are assumed to be stationary, and the He^ quasiparticles move with a mean speed {v) = {^kT/m^''Y''^, Thenwhere r'Ms the mean collision frequency, n is the number density of atoms, and m^'^-^2,Zm^ is the effective mass of the He^ quasiparticle. Using a value ofa = 1.6xl0"^^ cm^ measured by Herzlinger and King,^ this expression becomes r(°K) = 5.7X, in satisfactory agreement with our results.