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Title: Design and Fabrication of Opacity Targets for the National Ignition Facility

Abstract

Accurate models for opacity of partially ionized atoms are important for modeling and understanding stellar interiors and other high-energy-density phenomena such as inertial confinement fusion. Lawrence Livermore National Laboratory is leading a multilaboratory effort to conduct experiments on the National Ignition Facility (NIF) to try to reproduce recent opacity tests at the Sandia National Laboratory Z-facility. Since 2015, the NIF effort has evolved several hohlraum designs that consist of multiple pieces joined together. The target also has three components attached to the main stalk over a long distance with high tolerances that have resulted in several design iterations. The target has made use of rapid prototyped features to attach a capsule and collimator under the hohlraum while avoiding interference with the beams. Here, this paper discusses the evolution of the hohlraum and overall target design and the challenges involved with fabricating and assembling these targets.

Authors:
 [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1];  [1];  [1];  [1]; ORCiD logo [1];  [2];  [3]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  2. General Atomics, San Diego, CA (United States)
  3. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1416284
Report Number(s):
LA-UR-17-26125
Journal ID: ISSN 1536-1055
Grant/Contract Number:
AC52-06NA25396; AC52‐07NA27344; NA0001808
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Fusion Science and Technology
Additional Journal Information:
Journal Name: Fusion Science and Technology; Journal ID: ISSN 1536-1055
Publisher:
American Nuclear Society
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Opacity; solar interior; target fabrication

Citation Formats

Cardenas, Tana, Schmidt, Derek William, Dodd, Evan S., Perry, Theodore Sonne, Capelli, Deanna, Quintana, Theresa E., Oertel, John A., Peterson, Dominic S., Giraldez, Emilio, and Heeter, Robert F. Design and Fabrication of Opacity Targets for the National Ignition Facility. United States: N. p., 2017. Web. doi:10.1080/15361055.2017.1389559.
Cardenas, Tana, Schmidt, Derek William, Dodd, Evan S., Perry, Theodore Sonne, Capelli, Deanna, Quintana, Theresa E., Oertel, John A., Peterson, Dominic S., Giraldez, Emilio, & Heeter, Robert F. Design and Fabrication of Opacity Targets for the National Ignition Facility. United States. doi:10.1080/15361055.2017.1389559.
Cardenas, Tana, Schmidt, Derek William, Dodd, Evan S., Perry, Theodore Sonne, Capelli, Deanna, Quintana, Theresa E., Oertel, John A., Peterson, Dominic S., Giraldez, Emilio, and Heeter, Robert F. 2017. "Design and Fabrication of Opacity Targets for the National Ignition Facility". United States. doi:10.1080/15361055.2017.1389559.
@article{osti_1416284,
title = {Design and Fabrication of Opacity Targets for the National Ignition Facility},
author = {Cardenas, Tana and Schmidt, Derek William and Dodd, Evan S. and Perry, Theodore Sonne and Capelli, Deanna and Quintana, Theresa E. and Oertel, John A. and Peterson, Dominic S. and Giraldez, Emilio and Heeter, Robert F.},
abstractNote = {Accurate models for opacity of partially ionized atoms are important for modeling and understanding stellar interiors and other high-energy-density phenomena such as inertial confinement fusion. Lawrence Livermore National Laboratory is leading a multilaboratory effort to conduct experiments on the National Ignition Facility (NIF) to try to reproduce recent opacity tests at the Sandia National Laboratory Z-facility. Since 2015, the NIF effort has evolved several hohlraum designs that consist of multiple pieces joined together. The target also has three components attached to the main stalk over a long distance with high tolerances that have resulted in several design iterations. The target has made use of rapid prototyped features to attach a capsule and collimator under the hohlraum while avoiding interference with the beams. Here, this paper discusses the evolution of the hohlraum and overall target design and the challenges involved with fabricating and assembling these targets.},
doi = {10.1080/15361055.2017.1389559},
journal = {Fusion Science and Technology},
number = ,
volume = ,
place = {United States},
year = 2017,
month =
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on December 22, 2018
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  • Accurate models of X-ray absorption and re-emission in partly stripped ions are necessary to calculate the structure of stars, the performance of hohlraums for inertial confinement fusion and many other systems in high-energy-density plasma physics. Despite theoretical progress, a persistent discrepancy exists with recent experiments at the Sandia Z facility studying iron in conditions characteristic of the solar radiative–convective transition region. The increased iron opacity measured at Z could help resolve a longstanding issue with the standard solar model, but requires a radical departure for opacity theory. To replicate the Z measurements, an opacity experiment has been designed for the National Facility (NIF). The design uses established techniques scaled to NIF. A laser-heated hohlraum will produce X-ray-heated uniform iron plasmas in local thermodynamic equilibrium (LTE) at temperaturesmore » $${\geqslant}150$$ eV and electron densities$${\geqslant}7\times 10^{21}~\text{cm}^{-3}$$. The iron will be probed using continuum X-rays emitted in a$${\sim}200$$ ps,$${\sim}200~\unicode[STIX]{x03BC}\text{m}$$diameter source from a 2 mm diameter polystyrene (CH) capsule implosion. In this design,$2/3$$of the NIF beams deliver 500 kJ to the$${\sim}6$$ mm diameter hohlraum, and the remaining$$1/3$directly drive the CH capsule with 200 kJ. Calculations indicate this capsule backlighter should outshine the iron sample, delivering a point-projection transmission opacity measurement to a time-integrated X-ray spectrometer viewing down the hohlraum axis. Preliminary experiments to develop the backlighter and hohlraum are underway, informing simulated measurements to guide the final design.« less
  • Several targets are described that in simulations give yields of 1--30 MJ when indirectly driven by 0.9--2 MJ of 0.35 {mu}m laser light. The article describes the targets, the modeling that was used to design them, and the modeling done to set specifications for the laser system in the proposed National Ignition Facility. Capsules with beryllium or polystyrene ablators are enclosed in gold hohlraums. All the designs utilize a cryogenic fuel layer; it is very difficult to achieve ignition at this scale with a noncryogenic capsule. It is necessary to use multiple bands of illumination in the hohlraum to achievemore » sufficiently uniform x-ray irradiation, and to use a low-{ital Z} gas fill in the hohlraum to reduce filling of the hohlraum with gold plasma. Critical issues are hohlraum design and optimization, Rayleigh--Taylor instability modeling, and laser--plasma interactions.« less
  • 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 techniquesmore » 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 sensitivity of the margin to characteristics of the experiment. The formalism is used to estimate probability of ignition. The ignition experiment will be preceded with an experimental campaign that determines features of the design that cannot be defined with simulations alone. The requirements for this campaign are summarized. Requirements are summarized for the laser and target fabrication.« less