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Title: Asymmetric-shell ignition capsule design to tune the low-mode asymmetry during the peak drive

Abstract

The low-mode radiation flux asymmetry in the hohlraum is a main source of performance degradation in the National Ignition Facility (NIF) implosion experiments. To counteract the deleterious effects of the large positive P2 flux asymmetry during the peak drive, this paper develops a new tuning method called asymmetric-shell ignition capsule design which adopts the intentionally asymmetric CH ablator layer or deuterium-tritium (DT) ice layer. A series of two-dimensional implosion simulations have been performed, and the results show that the intentionally asymmetric DT ice layer can significantly improve the fuel ρR symmetry, hot spot shape, hot spot internal energy, and the final neutron yield compared to the spherical capsule. This indicates that the DT asymmetric-shell capsule design is an effective tuning method, while the CH ablator asymmetric-shell capsule could not correct the fuel ρR asymmetry, and it is not as effective as the DT asymmetric-shell capsule design.

Authors:
; ; ; ; ; ; ; ;  [1]
  1. Institute of Applied Physics and Computational Mathematics, Beijing 100088 (China)
Publication Date:
OSTI Identifier:
22599914
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 23; Journal Issue: 8; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ASYMMETRY; CAPSULES; COMPARATIVE EVALUATIONS; DESIGN; DEUTERIUM; FUELS; HOT SPOTS; IMPLOSIONS; LAYERS; NEUTRONS; PEAKS; RADIATION FLUX; SHELLS; SPHERICAL CONFIGURATION; THERMONUCLEAR IGNITION; TRITIUM; TWO-DIMENSIONAL CALCULATIONS; US NATIONAL IGNITION FACILITY

Citation Formats

Gu, Jianfa, E-mail: gu-jianfa@iapcm.ac.cn, Dai, Zhensheng, E-mail: dai-zhensheng@iapcm.ac.cn, Song, Peng, Zou, Shiyang, Ye, Wenhua, Zheng, Wudi, Gu, Peijun, Wang, Jianguo, and Zhu, Shaoping. Asymmetric-shell ignition capsule design to tune the low-mode asymmetry during the peak drive. United States: N. p., 2016. Web. doi:10.1063/1.4960658.
Gu, Jianfa, E-mail: gu-jianfa@iapcm.ac.cn, Dai, Zhensheng, E-mail: dai-zhensheng@iapcm.ac.cn, Song, Peng, Zou, Shiyang, Ye, Wenhua, Zheng, Wudi, Gu, Peijun, Wang, Jianguo, & Zhu, Shaoping. Asymmetric-shell ignition capsule design to tune the low-mode asymmetry during the peak drive. United States. doi:10.1063/1.4960658.
Gu, Jianfa, E-mail: gu-jianfa@iapcm.ac.cn, Dai, Zhensheng, E-mail: dai-zhensheng@iapcm.ac.cn, Song, Peng, Zou, Shiyang, Ye, Wenhua, Zheng, Wudi, Gu, Peijun, Wang, Jianguo, and Zhu, Shaoping. 2016. "Asymmetric-shell ignition capsule design to tune the low-mode asymmetry during the peak drive". United States. doi:10.1063/1.4960658.
@article{osti_22599914,
title = {Asymmetric-shell ignition capsule design to tune the low-mode asymmetry during the peak drive},
author = {Gu, Jianfa, E-mail: gu-jianfa@iapcm.ac.cn and Dai, Zhensheng, E-mail: dai-zhensheng@iapcm.ac.cn and Song, Peng and Zou, Shiyang and Ye, Wenhua and Zheng, Wudi and Gu, Peijun and Wang, Jianguo and Zhu, Shaoping},
abstractNote = {The low-mode radiation flux asymmetry in the hohlraum is a main source of performance degradation in the National Ignition Facility (NIF) implosion experiments. To counteract the deleterious effects of the large positive P2 flux asymmetry during the peak drive, this paper develops a new tuning method called asymmetric-shell ignition capsule design which adopts the intentionally asymmetric CH ablator layer or deuterium-tritium (DT) ice layer. A series of two-dimensional implosion simulations have been performed, and the results show that the intentionally asymmetric DT ice layer can significantly improve the fuel ρR symmetry, hot spot shape, hot spot internal energy, and the final neutron yield compared to the spherical capsule. This indicates that the DT asymmetric-shell capsule design is an effective tuning method, while the CH ablator asymmetric-shell capsule could not correct the fuel ρR asymmetry, and it is not as effective as the DT asymmetric-shell capsule design.},
doi = {10.1063/1.4960658},
journal = {Physics of Plasmas},
number = 8,
volume = 23,
place = {United States},
year = 2016,
month = 8
}
  • In the deuterium-tritium inertial confinement fusion implosion experiments on the National Ignition Facility, the hot spot and the surrounding main fuel layer show obvious P2 asymmetries. This may be caused by the large positive P2 radiation flux asymmetry during the peak pulse resulting form the poor propagation of the inner laser beam in the gas-filled hohlraum. The symmetry evolution of ignition capsule implosions is investigated by applying P2 radiation flux asymmetries during different time intervals. A series of two-dimensional simulation results show that a positive P2 flux asymmetry during the peak pulse results in a positive P2 shell ρR asymmetry;more » while an early time positive P2 flux asymmetry causes a negative P2 in the fuel ρR shape. The opposite evolution behavior of shell ρR asymmetry is used to develop a new tuning method to correct the radiation flux asymmetry during the peak pulse by adding a compensating same-phased P2 drive asymmetry during the early time. The significant improvements of the shell ρR symmetry, hot spot shape, hot spot internal energy, and neutron yield indicate that the tuning method is quite effective. The similar tuning method can also be used to control the early time drive asymmetries.« less
  • Here, indirect drive experiments at the National Ignition Facility are designed to achieve fusion by imploding a fuel capsule with x rays from a laser-driven hohlraum. Previous experiments have been unable to determine whether a deficit in measured ablator implosion velocity relative to simulations is due to inadequate models of the hohlraum or ablator physics. ViewFactor experiments allow for the first time a direct measure of the x-ray drive from the capsule point of view. The experiments show a 15%–25% deficit relative to simulations and thus explain nearly all of the disagreement with the velocity data. In addition, the datamore » from this open geometry provide much greater constraints on a predictive model of laser-driven hohlraum performance than the nominal ignition target.« less
  • 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 analyticmore » 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 to meet the required sensitivity and accuracy. A roll-up of all expected random and systematic uncertainties in setting the key ignition laser and target parameters due to residual measurement, calibration, cross-coupling, surrogacy, and scale-up errors has been derived that meets the required budget. Finally, we show how the tuning precision will be improved after a number of shots and iterations to meet an acceptable level of residual uncertainty.« less
  • Mode 1 radiation drive asymmetry (pole-to-pole imbalance) at significant levels can have a large impact on inertial confinement fusion implosions at the National Ignition Facility (NIF). This asymmetry distorts the cold confining shell and drives a high-speed jet through the hot spot. The perturbed hot spot shows increased residual kinetic energy and reduced internal energy, and it achieves reduced pressure and neutron yield. The altered implosion physics manifests itself in observable diagnostic signatures, especially the neutron spectrum which can be used to measure the neutron-weighted flow velocity, apparent ion temperature, and neutron downscattering. Numerical simulations of implosions with mode 1more » asymmetry show that the resultant simulated diagnostic signatures are moved toward the values observed in many NIF experiments. The diagnostic output can also be used to build a set of integrated implosion performance metrics. The metrics indicate that P{sub 1} has a significant impact on implosion performance and must be carefully controlled in NIF implosions.« less