june 2-3, 2004 hapl meeting, ucla 1 progress on target survival presented by a.r. raffray other...
TRANSCRIPT
June 2-3, 2004HAPL meeting, UCLA
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Progress on Target Survival
Presented by A.R. Raffray
Other Contributors: B. Christensen, M. S. Tillack
UCSD
D. GoodinGeneral Atomics
HAPL MeetingUCLA
Los Angeles, CAJune 2-3, 2004
June 2-3, 2004HAPL meeting, UCLA
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Outline
• Benchmark analysis with U. Roch. LLE (D. Harding)- Purchase more advanced version of “DSMC”
- Number flux and heat flux analysis
- Effect of accommodation and sticking coefficients
• Modeling experimental results from LANL
(J. Hoffer/D. Geller)
DS2V was Purchased for Modeling the Thermal Loading from the Background Gas
Figure Above Shows the Temperature Field Around a Direct Drive Target.
• Xe flowing at 400 m/s in the positive x-dir. • 4000 K Xe stream temperature.
• 3.22x1021 m-3 Xe stream density.
• Sticking coefficient = 0.
• Target surface temperature = 18 K.
Capabilities:
• Axisymmetric flow.
• Adjustable sticking (condensation) coefficient.
• Adjustable accommodation coefficient.
Output:
• Heat flux, number flux, drag force,etc…
Injected Target Modeling:
• Simulated by flow over stationary target (hydrodynamic similarity).
• Could not find a correct way of modeling moving target in stationary gas with this version.
The Number Flux and Heat Flux at the Target ReachQuasi-Steady State in a Short Time
Figure Above Shows the Number Flux and Heat Flux Around a Direct Drive Target.
• Xe stream flowing at 400 m/s.
• 4000 K stream temperature.
• 3.22x1021 m-3 stream density.
• Sticking coefficient = 0.
• Target surface temperature = 18 K.
0.00E+00
5.00E+23
1.00E+24
1.50E+24
2.00E+24
2.50E+24
3.00E+24
3.50E+24
4.00E+24
4.50E+24
0.0E+00 1.0E-03 2.0E-03 3.0E-03 4.0E-03 5.0E-03 6.0E-03 7.0E-03
Position (m)
Number Flux (m
-2 s
-1)
t=2mst=2.4mst = 4mst=5.8ms
0.00E+00
2.00E+04
4.00E+04
6.00E+04
8.00E+04
1.00E+05
1.20E+05
1.40E+05
1.60E+05
0.00E+00 1.00E-03 2.00E-03 3.00E-03 4.00E-03 5.00E-03 6.00E-03 7.00E-03
Position (m)
Heat Flux (W/m^2)
t=2mst=2.4mst=4mst=5.8ms
June 2-3, 2004HAPL meeting, UCLA
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As the Stream Density Is Increased the Sticking Coefficient (sigma) Has a Greater Effect
• The number flux is not a function of the sticking coefficient (sigma) when the stream density is low.
• The number flux decreases with increasing sigma when the stream density is high.
• Kinetic theory and DS2V show good agreement (sigma=1, no shielding effect).
1.0E+20
1.0E+21
1.0E+22
1.0E+23
0.0E+00 1.0E-03 2.0E-03 3.0E-03 4.0E-03 5.0E-03 6.0E-03 7.0E-03
Position on Surface (m)
Number Flux (atoms/m
2s)
Log Scale T = 4000 K, sigma = 0T = 1300 K, sigma = 0T = 4000 K, sigma = 1T = 1300 K, sigma = 1Kinetic Theory, T = 4000 KKinetic Theory, T = 1300 K
1.0E+22
1.0E+23
1.0E+24
1.0E+25
0.0E+00 1.0E-03 2.0E-03 3.0E-03 4.0E-03 5.0E-03 6.0E-03 7.0E-03
Position on Surface (m)
Number Flux (atoms/m
2s)
Log ScaleT = 4000 K, sigma = 0T = 1300 K, sigma = 0T = 4000 K, sigma = 1T = 1300 K, sigma = 1Kinetic Theory, T = 4000 KKinetic Theory, T = 1300 K
Low Density Stream, n = 3.22x1019 m-3
High Density Stream, n = 3.22x1021 m-3
June 2-3, 2004HAPL meeting, UCLA
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1.0E+03
1.0E+04
1.0E+05
1.0E+06
0.0E+00 1.0E-03 2.0E-03 3.0E-03 4.0E-03 5.0E-03 6.0E-03 7.0E-03
Position on Surface (m)
Heat Flux (W/m
2) - Log Scale
T = 4000 K, sigma = 1, w/ Latent HeatT = 4000 K, sigma = 1T = 4000 K, sigma = 0T = 1300 K, sigma = 1, w/ Latent HeatT = 1300 K, sigma = 1T = 1300 K, sigma = 0
1.0E+00
1.0E+01
1.0E+02
1.0E+03
1.0E+04
0.0E+00 1.0E-03 2.0E-03 3.0E-03 4.0E-03 5.0E-03 6.0E-03 7.0E-03
Position on Surface (m)
Heat Flux (W/m
2)
Log ScaleT = 4000 K, sigma = 1, w/ Latent HeatT = 4000 K, sigma = 1T = 4000 K, sigma = 0T = 1300 K, sigma = 1, w/ Latent HeatT = 1300 K, sigma = 1T = 1300 K, sigma = 0
The Heat Flux is Significantly Affected by the Stream Density, Temperature, and Sticking Coefficient
• The effect of latent heat is not included in DS2V; needs to be included in post processing.
• By neglecting the latent heat the “shielding” effect of a non-condensing gas (sigma = 0) is seen.
• Virtually no “shielding” for the low density stream.
• Significant “shielding” for the high density stream.
• The rapid change in heat flux with position suggests that the average max. heat flux could be reduced by tumbling the target.
Low Density Stream, n = 3.22x1019 m-3
High Density Stream, n = 3.22x1021 m-3
June 2-3, 2004HAPL meeting, UCLA
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Conclusions from DS2V Study• Simulate injected target situation by flow over stationary target
(hydrodynamic similarity)
• The number flux and heat flux at the target reach quasi-steady state in a relatively short time
(no need to run longer except if outside conditions (gas) change)
• The effect of latent heat is not included in DS2V; needs to be included in post processing.
• “Shielding” effect dependent on sticking coefficient for high density gas - Virtually no “shielding” for the low density stream (~1 mTorr).
- Significant “shielding” for the high density stream ( q’’ reduced by a factor of 2 or more when sigma changes from 1 to 0 for example case at ~100 mTorr)
• Experimental determination of the sticking coefficient is needed (U. Roch.)
• The accommodation coefficient should also be determined if the sticking coefficient is found to be significantly less than one.
June 2-3, 2004HAPL meeting, UCLA
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Initial Modeling of Direct Heating Experiments at LANL (J. Hoffer/D. Geller)
epoxy layercoil
4.00 mm Ø
1 mm Ø
8.00 mm Ø
• 1-D spherical numerical model.
• Constant heat flux.
• Initial temperature = 18 K.
• DT thickness = 400 m.
June 2-3, 2004HAPL meeting, UCLA
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The Time to Triple Point, as Predicted by the Two Numerical Models, is Generally Consistent with
Experimental Results
1
10
100
1000
0 0.5 1 1.5 2 2.5
Input Heat Flux (W/cm 2)
Time to Triple Point (ms) - Log Scale
Experimental
ANSYS
1-D Spherical Model
June 2-3, 2004HAPL meeting, UCLA
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There are Large Differences in the Melt Layer Thickness Results
0
20
40
60
80
100
120
140
0 20 40 60 80 100 120
Time (ms)
Melt Layer (mm)
Experimental
ANSYS
1-D Spherical Model
June 2-3, 2004HAPL meeting, UCLA
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Summary• Encouraging that melting time seems to be predicted quite accurately,
• Some question marks on melt layer thickness experimental and modeling results
• Modeling these experimental results can be improved:
- Create 1-D cylindrical model.
- Allow for variable heat flux (for melt layer computations)
- Code optimization: meshing, time-steps, assumed temperature range over which melting occurs
- Modeling experimental set-up
• Experimental uncertainties need to be better understood
- Measurement; how to specify melt layer boundary
- Heat flux changes when melting starts
• Working with our LANL colleagues on how to produce experimental results more amenable for our model and on how to improve model to simulate a wider range of experimental conditions
June 2-3, 2004HAPL meeting, UCLA
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• Brian has completed his MS Thesis on this - a summary of which will be submitted for journal publication
• Thesis defense next week
• His results has shed much light on the different processes affecting target survival
• He has included recommendation on future work (2-D or quasi 2-D modeling + experiments)
• We have identified a new student to continue this work as from the Fall (after the “Olympics”!)
Please Refer to Brian Christensen’s Poster for More Details on our 1-D Target Thermomechanics Modeling
(Including Phase Change) and DS2V Modeling