Analysis of the National Ignition Facility ignition hohlraum energetics experiments

Abstract. Experiments conducted at the National Ignition Facility using shaped laser pulses with more than 1 MJ of energy have demonstrated the ability to control the implosion symmetry under ignition conditions. To achieve thermonuclear ignition, the low mode asymmetries must be small to minimize the size of the hotspot. The symmetry tuning experiments use symmetry capsules, "symcaps", which replace the DT fuel with an equivalent mass of CH to emulate the hydrodynamic behavior of an ignition capsule. The x-ray selfemission signature from gas inside the capsule during the peak compression correlates with the surrounding hotspot shape. By tuning the shape of the self-emission, the capsule implosion symmetry can be made to be "round." In the experimental results presented here, we utilized crossbeam energy transfer [S. H. Glenzer, et al., Science 327, 1228] to change the ratio of the inner to outer cone power inside the hohlraum targets on the NIF. Variations in the ratio of the inner cone to outer cone power affect the radiation pattern incident on the capsule modifying the implosion symmetry.

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Symmetry tuning with megajoule laser pulses at the National Ignition Facility

Kline

Meezan

Callahan

et al. 2013

“…Tabular opacities and equation of state are used for the ablator and DT fuel. The input laser sources are adjusted to account for the backscattered energy and the crossbeam energy transfer that occurs in the hohlraum plasma [7,8]. The Monte Carlo particle transport package was used to generate realistic neutron spectra for simulated neutron diagnostics.…”

Section: Introductionmentioning

confidence: 99%

Towards an integrated model of the NIC layered implosions

Jones

Callahan

Cerjan

et al. 2013

Abstract.A detailed simulation-based model of the June 2011 National Ignition Campaign (NIC) cryogenic DT experiments is presented. The model is based on integrated hohlraum-capsule simulations that utilize the best available models for the hohlraum wall, ablator, and DT equations of state and opacities. The calculated radiation drive was adjusted by changing the input laser power to match the experimentally measured shock speeds, shock merger times, peak implosion velocity, and bangtime. The crossbeam energy transfer model was tuned to match the measured time-dependent symmetry. Mid-mode mix was included by directly modeling the ablator and ice surface perturbations up to mode 60. Simulated experimental values were extracted from the simulation and compared against the experiment. The model adjustments brought much of the simulated data into closer agreement with the experiment, with the notable exception of the measured yields, which were 15-40% of the calculated yields.

“…Implosion velocities and the rocket-model-associated ablator mass remaining are measured using backlit x-ray radiography of the capsule limb [7] and can be adjusted using the peak power level, ablator thickness and dopant choice. Implosion symmetry is inferred from the soft x-ray reemission limb uniformity of a surrogate high Z sphere at early time ("Reemit") [8] and from core x-ray self-emission at pole and equator views at bangtime [9,10], and optimized using a combination a e-mail: landen1@llnl.gov This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.…”

Section: Introduction To Tuning Parameters and Platformsmentioning

confidence: 99%

Ignition tuning for the National Ignition Campaign

Landen

Edwards

Haan

et al. 2013

Self Cite

Abstract. The overall goal of the indirect-drive inertial confinement fusion [1] tuning campaigns [2] is to maximize the probability of ignition by experimentally correcting for likely residual uncertainties in the implosion and hohlraum physics [3] used in our radiation-hydrodynamic computational models, and by checking for and resolving unexpected shot-to-shot variability in performance [4]. This has been started successfully using a variety of surrogate capsules that set key laser, hohlraum and capsule parameters to maximize ignition capsule implosion velocity, while minimizing fuel adiabat, core shape asymmetry and ablator-fuel mix.