Applications of a Rayleigh-Taylor model to direct-drive laser fusion.

This paper presents a simple physics-based model for the interpretation of key metrics in laser direct drive. The only input parameters required are target scale, in-flight aspect ratio, and beam-to-target radius, and the importance of each has been quantified with a tailored set of cryogenic implosion experiments. These analyses lead to compact and accurate predictions of the fusion yield and areal density as a function of hydrodynamic stability, and they suggest new ways to take advantage of direct drive.

Optimization Methodology of Polar Direct-Drive Illumination for the National Ignition Facility.

Improved laser illumination uniformity drives shocks and implosions to create more extreme high energy density environments. Predominantly, the geometry of experiments that can be performed is dictated by the layout of beams at laser facilities, limiting interfacility and multiscale investigations. This Letter presents the first automated, algorithmic approach for generating illumination configurations for high energy density experiments.

Partition of Omega-like facility into two configurations of 24 and 36 laser beams to improve implosion performance.

An Omega-like beam configuration is considered where the 60-beam layout can be separated into two independent sub-configurations with 24 and 36 laser beams, each minimizing direct drive illumination non-uniformity. Two different laser focal spot profiles, one associated with each configuration, are proposed to apply the zooming technique in order to increase the laser-target coupling efficiency. This approach is used by 1D hydrodynamics simulations of the implosion of a direct-drive capsule characterized by a relatively large aspect ratio A = 7 and an optimized laser pulse shape delivering a maximum of 30 TW and 30 kJ, with different temporal pulse shapes in each of the two sets of beams.

The Scattered Light Time-history Diagnostic suite at the National Ignition Facility.

The Scattered Light Time-history Diagnostic (SLTD) is being implemented at the National Ignition Facility (NIF) to greatly expand the angular coverage of absolute scattered-light measurements for direct- and indirect-drive inertial confinement fusion (ICF) experiments. The SLTD array will ultimately consist of 15 units mounted at a variety of polar and azimuthal angles on the NIF target chamber, complementing the existing NIF backscatter suite. Each SLTD unit collects and diffuses scattered light onto a set of three optical fibers, which transport the light to filtered photodiodes to measure scattered light in different wavelength bands: stimulated Brillouin scattering (350 nm-352 nm), stimulated Raman scattering (430 nm-760 nm), and ω/2 (695 nm-745 nm).

Saturn-ring proton backlighters for the National Ignition Facility.

Proton radiography is a well-established technique for measuring electromagnetic fields in high-energy-density plasmas. Fusion reactions producing monoenergetic particles, such as DHe, are commonly used as a source, produced by a capsule implosion. Using smaller capsules for radiography applications is advantageous as the source size decreases, but on the National Ignition Facility (NIF), this can introduce complications from increasing blow-by light, since the phase plate focal spot size is much larger than the capsules.

Developing a high-flux, high-energy continuum backlighter for extended x-ray absorption fine structure measurements at the National Ignition Facility.

Extended X-ray absorption fine structure (EXAFS) spectroscopy is a powerful tool for characterization of matter in the high energy density regime. An EXAFS platform is currently being developed on the National Ignition Facility. Development of a suitable X-ray backlighter involves minimizing the temporal duration and source size while maximizing spectral smoothness and brightness.

Capsule implosions for continuum x-ray backlighting of opacity samples at the National Ignition Facility.

Direct drive implosions of plastic capsules have been performed at the National Ignition Facility to provide a broad-spectrum (500-2000 eV) X-ray continuum source for X-ray transmission spectroscopy. The source was developed for the high-temperature plasma opacity experimental platform. Initial experiments using 2.

X-ray source development for EXAFS measurements on the National Ignition Facility.

Extended X-ray absorption Fine Structure (EXAFS) measurements require a bright, spectrally smooth, and broad-band x-ray source. In a laser facility, such an x-ray source can be generated by a laser-driven capsule implosion. In order to optimize the x-ray emission, different capsule types and laser irradiations have been tested at the National Ignition Facility (NIF).

X-ray self-emission imaging used to diagnose 3-D nonuniformities in direct-drive ICF implosions.

As hydrodynamics codes develop to increase understanding of three-dimensional (3-D) effects in inertial confinement fusion implosions, diagnostics must adapt to evaluate their predictive accuracy. A 3-D radiation postprocessor was developed to investigate the use of soft x-ray self-emission images of an imploding target to measure the size of nonuniformities on the target surface. Synthetic self-emission images calculated from 3-D simulations showed a narrow ring of emission outside the ablation surface of the target.

Publisher's Note: Demonstration of Fuel Hot-Spot Pressure in Excess of 50 Gbar for Direct-Drive, Layered Deuterium-Tritium Implosions on OMEGA [Phys. Rev. Lett. 117, 025001 (2016)].

This corrects the article DOI: 10.1103/PhysRevLett.117.

Demonstration of Fuel Hot-Spot Pressure in Excess of 50 Gbar for Direct-Drive, Layered Deuterium-Tritium Implosions on OMEGA.

A record fuel hot-spot pressure P_{hs}=56±7  Gbar was inferred from x-ray and nuclear diagnostics for direct-drive inertial confinement fusion cryogenic, layered deuterium-tritium implosions on the 60-beam, 30-kJ, 351-nm OMEGA Laser System. When hydrodynamically scaled to the energy of the National Ignition Facility, these implosions achieved a Lawson parameter ∼60% of the value required for ignition [A. Bose et al.

Note: A monoenergetic proton backlighter for the National Ignition Facility.

A monoenergetic, isotropic proton source suitable for proton radiography applications has been demonstrated at the National Ignition Facility (NIF). A deuterium and helium-3 gas-filled glass capsule was imploded with 39 kJ of laser energy from 24 of NIF's 192 beams. Spectral, spatial, and temporal measurements of the 15-MeV proton product of the (3)He(d,p)(4)He nuclear reaction reveal a bright (10(10) protons/sphere), monoenergetic (ΔE/E = 4%) spectrum with a compact size (80 μm) and isotropic emission (∼13% proton fluence variation and <0.

Channeling of multikilojoule high-intensity laser beams in an inhomogeneous plasma.

Channeling experiments were performed that demonstrate the transport of high-intensity (>10(18)W/cm(2)), multikilojoule laser light through a millimeter-sized, inhomogeneous (∼300-μm density scale length) laser-produced plasma up to overcritical density, which is an important step forward for the fast-ignition concept. The background plasma density and the density depression inside the channel were characterized with a novel optical probe system. The channel progression velocity was measured, which agrees well with theoretical predictions based on large scale particle-in-cell simulations, confirming scaling laws for the required channeling laser energy and laser pulse duration, which are important parameters for future integrated fast-ignition channeling experiments.

Mass-ablation-rate measurements in direct-drive cryogenic implosions using x-ray self-emission images.

A technique to measure the mass ablation rate in direct-drive inertial confinement fusion implosions using a pinhole x-ray framing camera is presented. In target designs consisting of two layers of different materials, two x-ray self-emission peaks from the coronal plasma were measured once the laser burned through the higher-Z outer layer. The location of the inner peak is related to the position of the ablation front and the location of the outer peak corresponds to the position of the interface of the two layers in the plasma.

Optical diagnostic suite (schlieren, interferometry, and grid image refractometry) on OMEGA EP using a 10-ps, 263-nm probe beam.

A 10-ps, 263-nm (4ω) laser is being built to probe plasmas produced on the OMEGA EP [J. H. Kelly, L.

Saturation of the two-plasmon decay instability in long-scale-length plasmas relevant to direct-drive inertial confinement fusion.

Measurements of the hot-electron generation by the two-plasmon-decay instability are made in plasmas relevant to direct-drive inertial confinement fusion. Density-scale lengths of 400 μm at n(cr)/4 in planar CH targets allowed the two-plasmon-decay instability to be driven to saturation for vacuum intensities above ~3.5×10(14) W cm(-2).

High-power, kilojoule class laser channeling in millimeter-scale underdense plasma.

Experiments were performed using the Omega EP laser, operating at 740 J of energy in 8 ps (90 TW), which provides extreme conditions relevant to fast ignition studies. A carbon and hydrogen plasma plume was used as the underdense target and the interaction of the laser pulse propagating and channeling through the plasma was imaged using proton radiography. The early time expansion, channel evolution, filamentation, and self-correction of the channel was measured on a single shot via this method.

Scaling hot-electron generation to high-power, kilojoule-class laser-solid interactions.

Thin-foil targets were irradiated with high-power (1 ≤ P(L) ≤ 210 TW), 10-ps pulses focused to intensities of I>10(18) W/cm(2) and studied with K-photon spectroscopy. Comparing the energy emitted in K photons to target-heating calculations shows a laser-energy-coupling efficiency to hot electrons of η(L-e) = 20 ± 10%. Time-resolved x-ray emission measurements suggest that laser energy is coupled to hot electrons over the entire duration of the incident laser drive.

High-areal-density fuel assembly in direct-drive cryogenic implosions.

The first observation of ignition-relevant areal-density deuterium from implosions of capsules with cryogenic fuel layers at ignition-relevant adiabats is reported. The experiments were performed on the 60-beam, 30-kJUV OMEGA Laser System [T. R.

Self-interference patterns and their application to inertial-fusion target characterization.

The sphericity and wall-thickness uniformity requirements of direct-drive inertial-fusion targets are of the order of less than 1%. These shells display self-interference patterns (SIP's) when irradiated with a spatially incoherent, narrow-bandwidth light source and viewed with a compound microscope. These patterns are distinct concentric fringes when the target is uniform, whereas faint, distorted, or discontinuous fringes indicate a nonuniform target.

Demonstration of the dual-tripler scheme for increased-bandwidth third-harmonic generation.

The dual-tripler scheme for enhancing the bandwidth of third-harmonic generation proposed by Eimerl et al. [Opt. Lett.

The saturn target for polar direct drive on the national ignition facility.

A new target design concept is proposed for direct-drive implosions while the National Ignition Facility is in its initial, indirect-drive configuration. It differs from earlier "polar-direct-drive" designs by adding a low-Z ring around the capsule equator. Refraction in the plasma formed around this ring permits time-dependent tuning of the capsule drive uniformity.

Multibeam effects on fast-electron generation from two-plasmon-decay instability.

Experiments with multiple laser beams have been carried out in both spherical and planar geometry to study two-plasmon-decay instability, the predominant source of suprathermal electrons in direct-drive inertial confinement fusion experiments. These electrons are observed using the hard x rays generated through electron-target interactions. The experiments show for the first time that the total overlapped intensity governs the scaling of the suprathermal-electron generation regardless of the number of overlapped beams, in contrast to conventional theories that are based on the single-beam approximation.