Showing papers by "R. E. Olson published in 2011"

Point design targets, specifications, and requirements for the 2010 ignition campaign on the National Ignition Facility

Abstract: Point design targets have been specified for the initial ignition campaign on the National Ignition Facility [G. H. Miller, E. I. Moses, and C. R. Wuest, Opt. Eng. 443, 2841 (2004)]. The targets contain D-T fusion fuel in an ablator of either CH with Ge doping, or Be with Cu. These shells are imploded in a U or Au hohlraum with a peak radiation temperature set between 270 and 300 eV. Considerations determining the point design include laser-plasma interactions, hydrodynamic instabilities, laser operations, and target fabrication. Simulations were used to evaluate choices, and to define requirements and specifications. Simulation techniques and their experimental validation are summarized. Simulations were used to estimate the sensitivity of target performance to uncertainties and variations in experimental conditions. A formalism is described that evaluates margin for ignition, summarized in a parameter the Ignition Threshold Factor (ITF). Uncertainty and shot-to-shot variability in ITF are evaluated, and...

Capsule implosion optimization during the indirect-drive National Ignition Campaign

Abstract: Capsule performance optimization campaigns will be conducted at the National Ignition Facility [G. H. Miller, E. I. Moses, and C. R. Wuest, Nucl. Fusion 44, 228 (2004)] to substantially increase the probability of ignition. The campaigns will experimentally correct for residual uncertainties in the implosion and hohlraum physics used in our radiation-hydrodynamic computational models using a variety of ignition capsule surrogates before proceeding to cryogenic-layered implosions and ignition experiments. The quantitative goals and technique options and down selections for the tuning campaigns are first explained. The computationally derived sensitivities to key laser and target parameters are compared to simple analytic models to gain further insight into the physics of the tuning techniques. The results of the validation of the tuning techniques at the OMEGA facility [J. M. Soures et al., Phys. Plasmas 3, 2108 (1996)] under scaled hohlraum and capsule conditions relevant to the ignition design are shown ...

Demonstration of ignition radiation temperatures in indirect-drive inertial confinement fusion hohlraums.

Abstract: We demonstrate the hohlraum radiation temperature and symmetry required for ignition-scale inertial confinement fusion capsule implosions. Cryogenic gas-filled hohlraums with 2.2 mm-diameter capsules are heated with unprecedented laser energies of 1.2 MJ delivered by 192 ultraviolet laser beams on the National Ignition Facility. Laser backscatter measurements show that these hohlraums absorb 87% to 91% of the incident laser power resulting in peak radiation temperatures of T(RAD)=300 eV and a symmetric implosion to a 100 μm diameter hot core.

Progress towards ignition on the National Ignition Facility

Abstract: The National Ignition Facility at Lawrence Livermore National Laboratory was formally dedicated in May 2009. The hohlraum energetics campaign with all 192 beams began shortly thereafter and ran until early December 2009. These experiments explored hohlraum-operating regimes in preparation for experiments with layered cryogenic targets. The hohlraum energetic series culminated with an experiment that irradiated an ignition scale hohlraum with 1 MJ. The results demonstrated the ability to produce a 285 eV radiation environment in an ignition scale hohlraum while meeting ignition requirements for symmetry, backscatter and hot electron production. Complementary scaling experiments indicate that with ~1.3 MJ, the capsule drive temperature will reach 300 eV, the point design temperature for the first ignition campaign. Preparation for cryo-layered implosions included installation of a variety of nuclear diagnostics, cryogenic layering target positioner, advanced optics and facility modifications needed for tritium operations and for routine operation at laser energy greater than 1.3 MJ. The first cyro-layered experiment was carried out on 29 September 2010. The main purpose of this shot was to demonstrate the ability to integrate all of the laser, target and diagnostic capability needed for a successful cryo-layered experiment. This paper discusses the ignition point design as well as findings and conclusions from the hohlraum energetics campaign carried out in 2009. It also provides a brief summary of the initial cryo-layered implosion.

X-ray ablation rates in inertial confinement fusion capsule materials

Abstract: X-ray ablation rates have been measured in beryllium, copper-doped beryllium, germanium-doped plastic (Ge-doped CH), and diamondlike high density carbon (HDC) for radiation temperatures T in the range of 160–260 eV. In beryllium, the measured ablation rates range from 3 to 12 mg/cm2/ns; in Ge-doped CH, the ablation rates range from 2 to 6 mg/cm2/ns; and for HDC, the rates range from 2 to 9 mg/cm2/ns. The ablation rates follow an approximate T3 dependence and, for T below 230 eV, the beryllium ablation rates are significantly higher than HDC and Ge-doped CH. The corresponding implied ablation pressures are in the range of 20–160 Mbar, scaling as T3.5. The results are found to be well predicted by computational simulations using the physics packages and computational techniques employed in the design of indirect-drive inertial confinement fusion capsules. An iterative rocket model has been developed and used to compare the ablation rate data set to spherical indirect-drive capsule implosion experiments and ...

Observation of high soft x-ray drive in large-scale hohlraums at the National Ignition Facility.

Abstract: The first soft x-ray radiation flux measurements from hohlraums using both a 96 and a 192 beam configuration at the National Ignition Facility have shown high x-ray conversion efficiencies of {approx}85%-90%. These experiments employed gold vacuum hohlraums, 6.4 mm long and 3.55 mm in diameter, heated with laser energies between 150-635 kJ. The hohlraums reached radiation temperatures of up to 340 eV. These hohlraums for the first time reached coronal plasma conditions sufficient for two-electron processes and coronal heat conduction to be important for determining the radiation drive.

Shock Timing experiments on the National Ignition Facility

Abstract: Capsule implosions on the National Ignition Facility (NIF) [Lindl et al., Phys. Plasmas 11, 339 (2004)] are underway with the goal of compressing deuterium-tritium (DT) fuel to a sufficiently high areal density (ρR) to sustain a self-propagating burn wave required for fusion power gain greater than unity. These implosions are driven with a carefully tailored sequence of four shock waves that must be timed to very high precision in order to keep the DT fuel on a low adiabat. Initial experiments to measure the strength and relative timing of these shocks have been conducted on NIF in a specially designed surrogate target platform known as the keyhole target. This target geometry and the associated diagnostics are described in detail. The initial data are presented and compared with numerical simulations. As the primary goal of these experiments is to assess and minimize the adiabat in related DT implosions, a methodology is described for quantifying the adiabat from the shock velocity measurements. Results are contrasted between early experiments that exhibited very poor shock timing and subsequent experiments where a modified target geometry demonstrated significant improvement.

Shock timing on the National Ignition Facility: First Experiments

Abstract: An experimental campaign to tune the initial shock compression sequence of capsule implosions on the National Ignition Facility (NIF) was initiated in late 2010. The experiments use a NIF ignition-scale hohlraum and capsule that employs a reentrant cone to provide optical access to the shocks as they propagate in the liquid deuterium-filled capsule interior. The strength and timing of the shock sequence is diagnosed with velocity interferometry that provides target performance data used to set the pulse shape for ignition capsule implosions that follow. From the start, these measurements yielded significant new information on target performance, leading to improvements in the target design. We describe the results and interpretation of the initial tuning experiments.

Hohlraum Designs for High Velocity Implosions on NIF

Abstract: In this paper, we compare experimental shock and capsule trajectories to design calculations using the radiation-hydrodynamics code HYDRA. The measured trajectories from surrogate ignition targets are consistent with reducing the x-ray flux on the capsule by about 85%. A new method of extracting the radiation temperature as seen by the capsule from x-ray intensity and image data shows that about half of the apparent 15% flux deficit in the data with respect to the simulations can be explained by HYDRA overestimating the x-ray flux on the capsule. The National Ignition Campaign (NIC) point-design target is designed to reach a peak fuel-layer velocity of 370 km/s by ablating 90% of its plastic (CH) ablator. The 192-beam National Ignition Facility laser drives a gold hohlraum to a radiation temperature (T{sub RAD}) of 300 eV with a 20 ns-long, 420 TW, 1.3 MJ laser pulse. The hohlraum x-rays couple to the CH ablator in order to apply the required pressure to the outside of the capsule. In this paper, we compare experimental measurements of the hohlraum T{sub RAD} and the implosion trajectory with design calculations using the code hydra. The measured radial positions of the leading shock wave and the unablated shell are consistent with simulations in which the x-ray flux on the capsule is artificially reduced by 85%. We describe a new method of inferring the T{sub RAD} seen by the capsule from time-dependent x-ray intensity data and static x-ray images. This analysis shows that hydra overestimates the x-ray flux incident on the capsule by {approx}8%.