Design of a spectrometer for opacity experiments at the National Ignition Facility

Presentation (PDF Available) · August 2015with 65 Reads
DOI: 10.13140/RG.2.2.19439.64163
SPIE Optics and Photonics, San Diego, CA, DOI:10.13140/RG.2.2.19439.64163
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Managed and Operated by National Security Technologies, LLC
Nevada National Security Site
Design of a spectrometer for opacity experiments at the National Ignition Facility : 8/13/2015
Design of a spectrometer for opacity experiments at
the National Ignition Facility
P.W. Ross1, M.F. Ahmed3, J.E. Bailey2, G.S. Dunham2, J.A.
Emig3, M.J. Haugh1, R.F. Heeter3, E.J. Huffman1, J.A.
Koch1, D.A. Liedahl3, Y.P. Opachich1, T.S. Perry4, M.B.
Schneider3, G.F. Stone3
1National Security Technologies, LLC
2Sandia National Laboratories
3Lawrence Livermore National Laboratory
4Los Alamos National Laboratory
This work was done by National Security Technologies, LLC, under Contract No. DE-AC52-
06NA25946 with the U.S. Department of Energy. DOE/NV/25946--[insert 4-digit STIP number].
DOE/NV/25946--xxxx
Managed and Operated by National Security Technologies, LLC
Nevada National Security Site
Design of a spectrometer for opacity experiments at the National Ignition Facility : 8/13/2015
Background The Solar Opacity Discrepancy
Opacity by stellar matter has long
been known to affect the internal
temperature profiles of stars
Increasingly precise observations of
the photosphere have repeatedly
led to revisions in the model for the
sun’s interior composition
Reductions of 30-50% in
inferred carbon, nitrogen, and
oxygen since 2004.
New models disagree with
helioseismic observations when
standard opacity models are
used.
Managed and Operated by National Security Technologies, LLC
Nevada National Security Site
Design of a spectrometer for opacity experiments at the National Ignition Facility : 8/13/2015
Iron Opacity Experiments at Z
Iron is responsible for ¼ of the opacity at the radiation/convection
zone boundary
Opacity measurements would need to be larger than models by nearly
30%.
Until Z experiments were performed, opacity models had “never
been validated through measurements made for solar conditions”
(Basu, et al.)
Solar-relevant conditions: 1-2 x 106K, 1017-1018 cm-3
Z experiments have been performed at a variety of solar-relevant
conditions to measure the opacity of iron.
Managed and Operated by National Security Technologies, LLC
Nevada National Security Site
Design of a spectrometer for opacity experiments at the National Ignition Facility : 8/13/2015
Opacity Experiments at Z (continued)
As the sample increases in temperature and pressure, the discrepancy with
the model increases (Bailey, et al., Nature 2015.)
Z- data in red. Model in blue
Managed and Operated by National Security Technologies, LLC
Nevada National Security Site
Design of a spectrometer for opacity experiments at the National Ignition Facility : 8/13/2015
NSTec Spectrometer to be used in a 5-lab collaboration (LANL, LLNL,
SNL, NSTec, LLE) for a stewardship Opacity Platform using NIF
Sandia data disagree w/ models; major
implications for understanding of stars.
NIF is only place to replicate the
experiment.
Temperatures: 1-2.5 x 106 K, 1021-
1022 cm-3
Opacity
Hohlraum
with sample
CH Capsule
Backlighter
X-ray Shield
w/ Aperture
Polar DIM w/ Spectrometer
Being designed by NSTec
NSTec Opacity Spectrometer
Managed and Operated by National Security Technologies, LLC
Nevada National Security Site
Design of a spectrometer for opacity experiments at the National Ignition Facility : 8/13/2015
NIF Opacity Platform – Confirm Z opacity
measurements on an independent platform
Iron target is heated using a laser-
driven hohlraum (can achieve
temperatures > 2 x 106K)
When the target is heated to a
plasma, the backlighter is imploded,
creating a broadband X-ray flash
Simultaneously measure density
with an orthogonal view of the target
Spectrometer must cover desired
spectral range
Spectral range determined by
crystal choice
Minimum range dictated by Cr lines,
oxygen absorption
Maximum range dictated by
necessary spectral range (Al K-shell
through Ly-beta at 2048 eV, for
temperature diagnostic)
~20 mm
~10 mm
~2 mm
~600 mm
Backlighter
Spectrometer
hohlraum
Iron sample
Managed and Operated by National Security Technologies, LLC
Nevada National Security Site
Design of a spectrometer for opacity experiments at the National Ignition Facility : 8/13/2015
Description of the NIF Opacity X-Ray Spectrometer (OpSpec)
The OpSpec is a crystal spectrometer snout
designed to be fielded on a DIM in NIF. (Self-
contained snout)
Time-integrated X-ray spectroscopy will be
performed on NIF with OpSpec. (Time-
resolved opacity measurements using a
pulsed backlighter X-ray flash of ~500 ps)
7
OpSpec Design Specifications
Dispersion
Element 2x Curved Bragg Crystals (possible option for
a reflection grating)
Spectral
Coverage
0.54 2.1 keV photon energy (extendable
using other dispersion elements e.g. PET vs.
KAP crystal)
Resolving Power E /E >500 (>700 from 0.8 to 1.5 keV)
Data Collection Time-integrated X-ray film or Image Plate
(CMOS detector in future)
NIF Usage All DIMs (initially on Polar DIM).
Preliminary OpSpec
Design
Managed and Operated by National Security Technologies, LLC
Nevada National Security Site
Design of a spectrometer for opacity experiments at the National Ignition Facility : 8/13/2015
OpSpec Uses a Bragg Crystal with Film to measure the Opacity
of a NIF Heated Sample using a backlighter as a source
8
Crystal
TALIS
Envelope
Film
Source
DIM
Clearance
Film length required: 173x70 mm active area
Distance from source to crystal: >600 mm
Point-projection spectroscopy
Managed and Operated by National Security Technologies, LLC
Nevada National Security Site
Design of a spectrometer for opacity experiments at the National Ignition Facility : 8/13/2015
-9-
A
B
CD
E
A. Opacity region (data of interest)
B. Penumbra
C. Source (unattenuated)
D. Self-emission
E. Background
Ray tracing the NIF Opacity platform allows us to
simultaneously make data and background
measurements
Managed and Operated by National Security Technologies, LLC
Nevada National Security Site
Design of a spectrometer for opacity experiments at the National Ignition Facility : 8/13/2015
OpSpec Resolving power meets design parameters
of > 800 over the energy range 540 eV to 2100 eV
10
OpSpec Design Parameters
Film Length 173 mm
Resolving Power >800
Crystal KAP
Crystal Radius 75 mm
Calculations assume a source size of 300 µm and a
source-to-crystal distance of 600 mm.
Detector resolution is assumed to be 20 µm.
Crystal resolving power is from Henke’s tables.
Managed and Operated by National Security Technologies, LLC
Nevada National Security Site
Design of a spectrometer for opacity experiments at the National Ignition Facility : 8/13/2015
KAP crystal chosen for relatively featureless reflectivity
over the energy range of interest
Energy band of interest
KAP was chosen due to the RAP features near 2 keV.
Managed and Operated by National Security Technologies, LLC
Nevada National Security Site
Design of a spectrometer for opacity experiments at the National Ignition Facility : 8/13/2015
Detector medium Low-energy X-ray sensitive film
Kodak 2492 RAR film
Calibrated by Henke in 1984
Grain resolution: 20 µm
Can also use image plate (100 µm resolution, may
become limiting factor on OpSpec Resolving power)
May create handling issues
The filters need to be light-tight to the film to prevent data loss upon
removal from spectrometer
Using 2 crystals and 2 pieces of film per shot
Necessary to simultaneously measure (on each piece of film):
Film background
Self-emission
Source emission
Sample transmission (opacity)
Managed and Operated by National Security Technologies, LLC
Nevada National Security Site
Design of a spectrometer for opacity experiments at the National Ignition Facility : 8/13/2015
Design Status
Complete:
Housing Design
Crystal Mounts
Mounting Flange
Remaining Issues:
Filters (delicate, sub-micron)
Filter mounts
Film pack (light tight)
Managed and Operated by National Security Technologies, LLC
Nevada National Security Site
Design of a spectrometer for opacity experiments at the National Ignition Facility : 8/13/2015
Future Work / Schedule
Design finished: Mid August
NIF design reviews: August -September
Necessary to ensure OpSpec does not cause facility problems
August -December: Procurement
December January: Fabrication
January: Deliver to NIF
February: 1st shot on NIF
Opacity Platform Schedule:
Current work: Backlighter development
FY16: Hohlraum development
FY17: 1st Opacity Measurements
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