Felix Dietrich | AWLC14 | 14.05.2014 |

Stress simulation in the ILC positron target with ANSYS

Felix Dietrich (TH-Wildau), Sabine Riemann, Friedrich Staufenbiel (DESY)

Felix Dietrich | AWLC14 | 14.05.2014 | page 2

Outline

> Alternative source

> Goal of the studies

> Model

> Implementation into ANSYS

> Temperature calculation

> Results

> Summary

> Next steps

Felix Dietrich | AWLC14 | 14.05.2014 | page 3

Alternative source

> Suggested by T. Omori et al., see also NIMA672 (2012) 52

> Uses beam (“conventional” source) of 6GeV

> Target: Tungsten

> 300Hz scheme Stretch ILC bunch train (~1ms) to 63ms

lower peak heat load

Stacking of in the damping ring

> ILC time structure achieved by extraction scheme from damping ring

> Benchmark from SLC target: Peak Energy Deposition Density (PEDD) should not exceed 29J/g

> Electron beam parameters are selected accordingly

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Goal of the studies

> Beam parameters are given ( ~29J/g peak energy deposition @SLC)

> How is the dynamic stress evolving in the target with 300Hz scheme in the tungsten target

> Target lifetime depend on static and dynamic stress

• Energy deposition within fraction of a nanosecond instantaneous temperature rise

• Reaction of material within milliseconds

Stress dynamics

> Benchmark: SLC target But SLC number of positrons per second was about 50 times lower than at ILC

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Model

> Model 1– Modified SLC target Fe – ring & Ag – coat & W – core

Radius for beam line @ target = 10.75cm

> Model 2– cylinder with diameter corresponding to beam spot size

W – Layer & Ag – Layer

Beam spot radius =0.8cm

Radius of the whole model is r=2.2cm

> Parameters for both models Particle shower has been calculated with FLUKA

Average energy deposition in the target:

35kW without silver layer49kW with silver layer

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Implementation into ANSYS

> Mesh Mesh size is related to time steps

is given = velocity of sound =5180 m/s

Model 1 : 22124 elements

Model 2 : 9419 elements

Elements: Hexagonal elements

> Time structure 1st attempt: Every bunch is calculated. the length of one bunch is 250ps

2nd attempt: Linear rise of the temperature in one mini train

> Calculation & Results Model 1: first Calculations could be done. But there is still some work to do.

Model 2: works well, needs less computing time

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Temperature calculation

> With good mesh, the temperature change resulting from energy deposition by each bunch shows regular behavior with negligible numerical errors

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Temperature rise: 1st attempt

> The temperature increases per bunch by 1.6K

> The graph shows the temperature rise for the first triplet

0,0 0,2 0,4 0,6 0,8 1,0 1,2

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ture

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time[µs]

max. temperatur

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Results: Stress evolution – Model 2

> The Picture shows the equivalent stress (von-Mises) at diferent positions in the Material

> The Picture was taken at: 1.0205 µs

(t=5ns first bunch of mini train)

> Deformation is scaled by 730 for visualization; max. surface displacement is about 8µm

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Result: Short time – Model 2

0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 1,10

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4003rd mini Train

2nd mini Train

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ss[M

Pa]

time[µs]

stress max (von Mises)

stress z=1,4cm stress z=1,375cm stress z=1,35cm stress z=1,325cm stress z=1,3cm stress z=1,25cm stress z=1,2cm stress z=1,15cm stress z=1,1cm stress z=1,05cm stress z=0,9cm

1st mini Train

> Results are calculated for 1µs

> Red line shows max. stress at any given point at one time

> The other lines are calculated an the center of the disc at different depth (1.4cm equals the surface; 0.9cm equals a depth of 0.5cm)

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Result: Conclusion short time

> Max. temperature rise by one triplet is T=210°C within ~1ms

> Heat dispersion into the target body within microseconds is negligible temperature of the target body is 22°C

> Max. stress after one triplet 377MPa

> Every mini train adds a different stress load First mini train +225MPa

Second mini train +110MPa

Third mini train +37MPa

> Max. stress by one triplet is below fatigue stress limit 377MPa<520MPa

Felix Dietrich | AWLC14 | 14.05.2014 | page 12

0,0 0,5 1,0 1,5 2,0 2,5 3,00

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4503rd mini Train

2nd mini Train1st mini Train

stre

ss[M

Pa]

time[µs]

stress max (von Mises)

stress z=1,4cm stress z=1,375cm stress z=1,35cm stress z=1,325cm stress z=1,3cm stress z=1,25cm stress z=1,2cm stress z=1,15cm stress z=1,1cm stress z=1,05cm stress z=0,9cm

Results: Long time

> First attempt 2 µs pause

> Same configuration like the first graph

> Results arepreliminary

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Temperature rise: 2nd attempt

> The temperature rises linearly over the whole mini train

> That saves computing time

0,0 0,2 0,4 0,6 0,8 1,0 1,2

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time[µs]

max. temperatur

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Results for 2nd attemept: Model 1

> Results are calculated for 3µs

> Max. stress is about 400MPa

> Results are preliminary

0,0 0,5 1,0 1,5 2,0 2,5 3,00

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2nd mini train3rd mini train

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ss[M

Pa]

time[µs]

max_stress stress z=1.4cm stress z=1.375cm stress z=1.35cm stress z=1.325cm stress z=1.3cm stress z=1.25cm stress z=1.2cm stress z=1.15cm stress z=1.1cm stress z=1.05cm stress z=0.9cm

1st mini train

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Results for 2nd attempt: Model 2

> Results are calculated for 3µs

> Max. sress is about 420MPa

> Results arepreliminary

0,0 0,5 1,0 1,5 2,0 2,5 3,00

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ss[M

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time[µs]

max_stress stress z=1.4cm stress z=1.375cm stress z=1.35cm stress z=1.325cm stress z=1.3cm stress z=1.25cm stress z=1.2cm stress z=1.15cm stress z=1.1cm stress z=1.05cm stress z=0.9cm

3rd mini train2nd mini train

1st mini train

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Summary

> Maximum dynamic stress per triplet is about 377MPa (fatigue stress limit is 520MPa)

> longer time Stress rise up to 425MPa for both attempts

> Load cycles per year at one spot : cycles

> With target rotation the number of load cycles at the same beam spot volume can be kept below

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Next steps

> Simulations of a longer period: Few triplets

Include target rotation

Check whether interferences of stress waves are possible

> Degradation of material is expected due to irradiationevaluation of dynamic load has to be repeated with modified parameters

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Addition

0,0 0,2 0,4 0,6 0,8 1,00

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400 stress(z=0,014m) stress(z=0,0135m) stress(z=0,013m) stress(z=0,0125m) stress(z=0,012m) stress(z=0,0115m) stress(z=0,011m)

stre

ss [M

Pa]

time [µs]

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Addition

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Addition

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stress_max longtime stress_max shorttime