Laser Doppler Vibrometer tests Goran Skoro UKNF Meeting 7-8 January 2010 Imperial College London UKNF Target Studies Web Page:

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

Energy deposition – current pulse Arbitrary units Time (  s) Fitted Measured 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: Current density is: Energy deposition ~ integral of j 2 Current pulse shape+ Lorentz force induced pressure wave

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

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

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

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

Tungsten Young’s modulus at room temperature Comments about literature data: -mostly tungsten sheets used - static (tension) techniques - dynamic techniques - no errors given 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) We have tungsten wires: manufactured in different way

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

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

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

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

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

Young’s modulus of tungsten as a function of temperature (0.5 mm diameter wire) Doesn’t depend on shock! 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! Radial oscillations Young’s modulus of tungsten as a function of temperature (0.75 mm diameter wire)

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

Conclusions * Note the different time scale 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: 1 st – LDV results (‘material’ journal – Journal of Nuclear Materials?) 2 nd – lifetime/fatigue tests, shock at the NuFact, etc… (NIM B ?)