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