Three-Dimensional Modeling of Cross-Beam Energy Transfer ...
Transcript of Three-Dimensional Modeling of Cross-Beam Energy Transfer ...
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D. H. EdgellUniversity of RochesterLaboratory for Laser Energetics
Three-Dimensional Modeling of Cross-Beam Energy Transfer and Its Mitigation in Symmetric Implosions on OMEGA
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1.40
1.42
1.44
1.46
1.44 TW/sr!0.16% 0.76 TW/sr!2.0%
0.72
0.74
0.76
0.78
No CBET TW/sr CBET TW/sr
47th Annual AnomalousAbsorption Conference
Florence, OR11–16 June 2017
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Cross-beam energy transfer (CBET) modeling suggests that 3-D effects may be important for symmetric direct drive
Summary
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• CBET between beams at angles of 40° to 110° are most significant
• Non-axially symmetric details of the absorption profile can increase the absorption rms (root mean square) over the target surface by an order of magnitude
• The total absorption and rms asymmetry can be greatly improved over a standard symmetric implosion by wavelength separating
the three OMEGA beam legs
D. H. Edgell et al., “Mitigation of Cross-Beam Energy Transfer in Symmetric Implosions on OMEGA Using Wavelength Detuning,” to be published in Physics of Plasmas.
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Collaborators
R. K. Follett, I. V. Igumenshev, J. F. Myatt, J. G. Shaw, and D. H. Froula
University of RochesterLaboratory for Laser Energetics
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Three-dimensional modeling uses a geometric optics ray-based model using the coronal plasma taken from hydrodynamic code
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–500
x (nm)
–1000
–500
0
500
1000
y (n
m)
0 500
0.6
0.8
1.0
0.4
0.2
0.0
6810
s (nm)
u (n
m)
–500–1000
–10001000
1000
0
0
0 500
×1013
420
ne /nc
ShadowCaustic
rmin
Turningpoint
Turningpoint
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CBET is calculated in each beamlet cell for crossings with all other beamlets
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• Both intrabeam and interbeam crossings
• Beamlet intensities at crossings are determined using
– inverse bremsstrahlung absorption
– intensity law of geometric optics
– CBET at crossings using a 3-D extension of Randall’s quasi-slab model fluid model*
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~IAW = ~1 – ~2
kIAW = k1 – k2< < <
IAW: ion-acoustic wave*C. J. Randall, J. R. Albritton, and J. J. Thomson, Phys. Fluids 24, 1474 (1981).
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The model is in good agreement with LPSE* calculations of CBET in a simple geometry
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×10
14 W
/cm
2Inte
nsi
ty o
ut
Po
lari
zati
on
co
sin
e
Beam 1
0
2
4
6
8
0
2
4
6
8
–30 –20 –10 0
Beam profile (nm) Beam profile (nm)
0.4
0.5
0.6
0.7
0.8
10 20 30
–40 –20 0
OES
y (nm)
x (n
m)
–40
–20
0
20
40
400
1
2
3
4
5
6
20
Bea
m 1
Beam 2
Beam 2
–30 –20 –10 0 10 20 30
LPSEBEAMER
*R. K. Follett et al., ThP-2, this conference.J. F. Myatt et al., Phys. Plasmas 24, 056308 (2017).
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u (n
m)
×108
–400
v (nm)
0
Nearest neighbor
400
3
2
1
0
–400
0
400
TW/sr
Absorptionwith CBET
0.78
0.76
0.74
0.72
–s
+srnc /4
rMach 1
TargetplasmaTargetplasma
Impactparameter
Turning points = 0
Turning points = 0
rmin
rmin
To display 3-D calculations on 2-D slides we use integrated images and surface maps
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dEabss/
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Two-beam modeling shows that CBET exchange is strongest for beams that are at angles between 40-110°
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Angle between beams (°)
84
88
92
90
86
94
Las
er a
bso
rpti
on
(%)
0 6030 90 150120
Beams at anglesgreater than 150°are essentiallydecoupled
180
Two-beam CBETOne-beam self-CBETNo CBET
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CBET adds non-axisymmetric features to the beams’ absorption profile that depend on their 3-D orientation
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0 400
0
No CBET ×108
Beams at 90°
v (nm)
u (n
m)
–400
–400
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0 400
×108
v (nm)–400
–1.0
–0.5
0.0
0.5
1.0
0 400
CBET ×108
v (nm)–400
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5400
dEabss/ dECBET
s/ dEabs
s/
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For the OMEGA symmetric geometry, profile features are the sum of interactions between 60 beams
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–400
v (nm)
–400
0
400
u (n
m)
0 400
2
1
–1
0
–2
–400
v (nm)
0 400
16
12
8
4
0
×108 ×107
dECBETs/ dEabs
s/
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CBET can increase the absorption nonuniformity of a symmetric implosion by an order of magnitude
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The nonuniformity is not simply caused by 1-D CBET from inside to outside of beam profile.
, , dE r rabs i {^ h#
dEabss/
No CBET
Absorptionsurface maps
Absorptionprofiles
×108
0.51.01.52.02.53.03.5
1.40
1.42
1.44
1.46
CBET ×107
2
6
10
14
18 18
0.72
0.74
0.76
0.78
CBET(axiSym averaged) ×107
2
6
10
14
0.73
0.75
0.77
0.79
1.44 TW/sr!0.16% TW/sr 0.76 TW/sr!2.0% TW/sr 0.76 TW/sr!0.13% TW/sr
–400
v (nm)
–400
0
400
u (n
m)
0 400 –400
v (nm)
0 400 –400
v (nm)
0 400
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The nonuniformity originates from the subtle non-axially symmetric details of the absorption profile
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TW/sr
0.72
0.74
0.76
0.78
No CBET CBET
Single-beam pattern
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Wavelength shifting a single OMEGA beam provides insight into multicolor CBET mitigation
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–30 –20 –10 0
Ab
sorb
ed p
ow
er (
TW)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Dm (Å)
10 20 30
Shifted beamUnshifted beamsSelf-CBET limit
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Breaking cadence: Wavelength shifting the three OMEGA beamline legs to mitigate CBET
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There is a “sweet spot” around Dm = 10 Å, where the absorbed power is maximum and the nonuniformity is near minimum.
Dm (Å)
0.0
0.1
0.2
0.3
0.4
Ab
sorb
ed p
ow
er (
TW)
0 20 10
Dm (Å)
00
2
4
6
8
Ab
sorp
tio
n r
ms (%
)
3020
Leg 1Leg 2Leg 3AverageSelf-CBET limit
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Summary/Conclusions
Cross-beam energy transfer (CBET) modeling suggests that 3-D effects may be important for symmetric direct drive
• CBET between beams at angles of 40° to 110° are most significant
• Non-axially symmetric details of the absorption profile can increase the absorption rms (root mean square) over the target surface by an order of magnitude
• The total absorption and rms asymmetry can be greatly improved over a standard symmetric implosion by wavelength separating
the three OMEGA beam legs
D. H. Edgell et al., “Mitigation of Cross-Beam Energy Transfer in Symmetric Implosions on OMEGA Using Wavelength Detuning,” to be published in Physics of Plasmas.