Laser Doppler Vibrometer tests

1. Laser Doppler Vibrometer tests GoranSkoro UKNF Target Studies Web Page: http://hepunx.rl.ac.uk/uknf/wp3/ UKNF Meeting 7-8 January 2010 Imperial College London

2. The Finite Element Simulations have been used to calculate equivalent beam power in a real target and to extract the corresponding lifetime. Tantalum wire – weak at high temperatures Tungsten – much better!!! Current pulse – wire tests at RAL

3. Energy deposition – current pulse Current pulse shape + Lorentz force induced pressure wave Fit: exponential and linear functions, then analytic solution for current density across the wire as a function of time For example, exponential rise of current: Energy deposition ~ integral of j2 Measured Fitted Current density is: Arbitrary units Time (ms)

4. Video camera to monitor laser beam position Hole in the wall – to monitor… Test wire - to illustrate a scale Tungsten wire at 2000 K Shock test Lab We are in other room …to measure temperature Remote control to change it Laser beam Laser beam Wire

5. 3 different decoders: VD-02 for longitudinal, DD-300 and VD-05 for radial oscillations Wire diameter [mm] - excluded Laser Doppler Vibrometer (LDV) Current < 10 kA Shock ~ NF target Freq. and Amp. range

6. Corresponding frequency spectrum Longitudinal oscillations Fundamental frequencies 0.5 mm diameter tungsten wire 4.5 cm length After error propagation: c – speed of sound l - wire length E – Young’s modulus r - density Laser beam Wire • Oscillations are complicated • Details not fully reproduced, but studies continuing

7. Our results for E vs. literature data? NuFact target will ‘oscillate’ in ~ this frequency range Longitudinal oscillations Next slide 0.3 mm diameter tungsten wire 3.9 cm length Shorter wire – higher frequency: Comparison between 2 different FFT algorithms. Laser beam Wire

8. Different results even for the ‘same’ samples • For example, • black points: 6 samples from the same manufacturer –> • 10% difference between Young’s modulus values • (sheets rolled from ingots which are pressed from powder and consolidated by sintering) Comments about literature data: • mostly tungsten sheets used • - static (tension) techniques • - dynamic techniques • - no errors given Tungsten Young’s modulus at room temperature We have tungsten wires: manufactured in different way

9. Different shape (as a function of time) – strongly depends on measurement’s position along the wire Peak displacement value – nice agreement between experiment and simulation Radial oscillations Radial displacement as a function of energy deposition (0.3 mm diameter wire) Hard to measure it for such a tiny wire! Better for 0.5 mm diameter wire (next slide) DD-300 decoder Frequency of radial oscillations f = 11.3 MHz (LS-DYNA) Wire length = 3.9 cm In experiment, we see it only here f = 11 MHz (crude estimate) Laser beam Wire

10. But, DD-300 is in saturation at higher temperatures (displacements outside the range) Frequency of radial oscillations as a function of energy deposition (0.5 mm diameter wire) Radial oscillations DD-300 decoder 2% difference Laser beam Wire In almost perfect agreement with expected value (from LS-DYNA)

11. Radial oscillations VD-05 DD-300 Frequency of radial oscillations as a function of temperature (0.5 mm diameter wire) Different decoder…

12. Radial oscillations 0.5 mm diameter wire VD-05 decoder Laser beam Wire • Details not fully reproduced • Frequency is OK! • Correct velocity is reproduced (level of stress is correct) • Lifetime results are valid

13. Radial oscillations 0.38 mm diameter wire VD-05 decoder per pulse 1000 pulses – no problem Then 1000 pulses at 3x higher stress than at NuFact, even higher… Laser beam Wire • wire is being stressed at above NF levels

14. If we know the frequency f, Poisson’s ratio , density , root of corresponding Bessel function  and wire radius r then: Radial oscillations Doesn’t depend on shock! Young’s modulus of tungsten as a function of temperature (0.5 mm diameter wire)

15. Radial oscillations Doesn’t depend on shock! Young’s modulus of tungsten as a function of temperature (0.75 mm diameter wire)

16. Bonus: Measurements of Young’s modulus of tungsten Young’s modulus remains high at high temperature & high stress! J.W. Davis, ITER Material Properties Handbook, 1997, Volume AM01-2111, Number 2, Page 1-7, Figure 2 E difference believed simply to be because different wire samples have different E Concern: low strength from static measuremts at high temp

17. Shock measurements: Measurements of tungsten properties: comparable with existing; LS-DYNA predictions: confirmed (details still being understood); oscillations are complicated, wire partially fixed to frame, frame also moves, etc Bottom line: Lifetime results are valid Wire is being stressed at above NuFact levels. Plans: Continue detailed studies; Repeat lifetime tests, but measure with LDV over time; Use beams and measure with LDV. Papers: 1st – LDV results (‘material’ journal – Journal of Nuclear Materials?) 2nd – lifetime/fatigue tests, shock at the NuFact, etc… (NIM B ?) Conclusions * Note the different time scale