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VISAR & Vibrometer results

VISAR & Vibrometer results. Goran Skoro (University of Sheffield) UK Neutrino Factory Meeting Lancaster, April 2009. 02. Part I: VISAR. Idea was to measure the VISAR signal and to extract the longitudinal oscillations of the pulsed wire.

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VISAR & Vibrometer results

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  1. VISAR & Vibrometer results Goran Skoro (University of Sheffield) UK Neutrino Factory Meeting Lancaster, April 2009

  2. 02 Part I: VISAR

  3. Idea was to measure the VISAR signal and to extract the longitudinal oscillations of the pulsed wire VISAR tests have been performed with 0.3 mm diameter tungsten wire Analysis shown on the following slides will try to address this problem VISAR signal obtained for the very first time - nice agreement with simulations results - Two characteristic results (shots 3 and 5) shown on the left* VISAR tests But, noise is an issue here!!! VISAR signal Yellow – Current pulse VISAR signal VISAR signal Current pulse Current pulse VISAR signal 3 * Note the different time scale Green, Purple – VISAR signal (2 channels) 5 Laser beam Wire 03

  4. FFT method (MATLAB) has been used – from time to frequency domain - Dominant signal frequency clearly seen in frequency spectrum (noise - negligible) We need this region too in order to describe the wire motion properly (noise ~ signal) Frequency analysis of the VISAR signal 3 Current pulse VISAR signal VISAR signal ~ 16ms ~ 60 kHz 04

  5. Real effect (friction of wire’s end) or noise? Compare with previous plot – looks like a noise (here: not enough data points for noise) Dominant signal frequency (not so clearly) seen in frequency spectrum FFT method (MATLAB) has been used – from time to frequency domain - Frequency analysis of the VISAR signal Really powerful method; we need more data from VISAR 5 Current pulse VISAR signal VISAR signal ~ 60 kHz ~ 16ms ~ 8ms ~ 125 kHz 05

  6. Frequency analysis of the VISAR signal - Filtering A few examples how we can filter the data Filter set 2 2 Filter set 1 1 06

  7. Dominant frequency that corresponds to longitudinal motion of the wire is clearly present in both frequency spectra Frequency analysis of the VISAR signal and LS-DYNA results shot 3 ~ 60 kHz ~ 60 kHz 07

  8. New tests have been performed with a shorter wire But, interesting ‘coincidence’ in frequency spectrum… VISAR tests with a shorter wire A few characteristic results First conclusion: no signal here! Current pulse VISAR signal VISAR signal Difference between green and purple VISAR signal VISAR signal Current pulse VISAR signal VISAR signal Difference between green and purple Current pulse Difference between green and purple Laser beam Wire 08

  9. FFT analysis of each shot – no signal seen (expected, if we look at previous slide) But, by averaging the frequency spectra, the ‘structure’ starting to appear exactly at the right position We could expect to see this dominant frequency (~ 80 kHz) Frequency analysis of the VISAR signal averaged Tests with a shorter wire Experiment Small statistics – so we can say it’s a coincidence (but will be interesting to collect more data) 09

  10. The measurements have been performed at different temperatures as a function of applied current. First wire has bent during the test at 1750 C. Only single shot at this temperature has been recorded (shown on the left) Each temperature (and current value) – between 5 and 20 shots (FFT analysis of each shot then averaging) Wire has been replaced and measurements continued – excellent consistency between two sets of data! VISAR tests have been performed with 0.5 mm diameter tungsten wire More than 130 shots have been taken between 17 and 19 March Scripts* have been written for a quick analysis of such a large ammount of data VISAR tests – data collection *Particular thanks to Jelena Ilic for her help. VISAR signal VISAR signal 1750 C Difference between green and purple Current pulse Laser beam Wire 10

  11. Frequencies seen in spectra: ~ 20 kHz; ~ 40 kHz; ~ 60 kHz; ~ 80 kHz; ~ 100 kHz; ~ 140 kHz (weak). We expect* to see 80 kHz as a result of wire thermal expansion What about the others? Answer (part I): 20, 60, 100, 140 kHz are the fundamental frequencies of the wire vibrations Peak current = 7.5 kA except for T = 850 C where it was 8.1 kA VISAR tests – Results (Part I) - as a function of temperature - C (for tungsten) ~ 4 km/s L (wire full length) ~ 5 cm f0 = 20 kHz, f1 = 60 kHz, f2 = 100 kHz, f3 = 140 kHz… *See: FFT_Visar_ver2.ppt (Slide 9) 11

  12. Legend: 1 = ff (1st harmonic) 2 = ff (2nd harmonic) 3 = ff (3rd harmonic) 4 = ff (4th harmonic) b = bending frequency Arrow = 80 kHz (thermal expansion) Only the magnitude of the 80 kHz spectral structure increases with increasing current!!! VISAR tests – Results (Part III) - as a function of current (for T = 1100 C) - 12

  13. Legend: 1 = ff (1st harmonic) 2 = ff (2nd harmonic) 3 = ff (3rd harmonic) 4 = ff (4th harmonic) b = bending frequency Arrow = 80 kHz (thermal expansion) Again, higher current –> higher magnitude of the 80 kHz spectral structure!!! VISAR tests – Results (Part IV) - as a function of current (for T = 1300 C) - 80 kHz thermal expansion 13

  14. r - density; n – Poisson’s ratio; l – length of wire (heated part) P R E L I M I N A R Y - Young’s modulus of tungsten wire - VISAR tests Errors estimated from the widths of the characteristic spectral ‘line’. f – measured frequency 14

  15. 15 Part II: Vibrometer

  16. Laser Doppler Vibrometer tests have been performed with 0.5 mm diameter tungsten wire Only a few shots taken - shown on the left and below* Vibrometer tests But, noise is an issue here!!! Velocity “Displacement” Yellow – Current pulse Green, Purple – “Displacement”, Velocity * Note the different time scale 6 Current pulse Velocity 5 Current pulse “Displacement” Velocity 4 Current pulse “Displacement” Laser beam Wire 16

  17. FFT method (MATLAB) has been used to analyse velocity signal – here: short time scale - Frequency analysis of the Vibrometer signal Current pulse (and reflections) Radial oscillations of the wire We expect to see radial oscillations ~ 1ms ~ 1 MHz ~ 160 ns ~ 6 MHz 6 Current pulse “Displacement” Velocity 17

  18. FFT method (MATLAB) has been used to analyse velocity signal – here: medium time scale - Expected frequency of longitudinal oscillations should be in this region (even lower) Very noisy here – is the previous results (see slide 3) in this frequency range realistic? Frequency analysis of the Vibrometer signal We ‘see’ radial oscillations of the wire We expect to see ‘longitudinal oscillations’ ~ 150 -300 kHz ~ 6 MHz 4 Current pulse “Displacement” Velocity 18

  19. FFT method (MATLAB) has been used to analyse velocity signal – here: long time scale - We expect to see violin modes of wire oscillations Frequency analysis of the Vibrometer signal They are here 5 Current pulse “Displacement” Velocity 19

  20. Velocity decoder VD02 has been used to extract the surface velocity of the wire - but it’s upper frequency limit is 1.5 MHz - Frequency analysis of the Vibrometer signal - Filtering What is ‘wrong’ with these pictures? 6 MHz signal seen in both frequency spectra To answer this question we need a decoder which works in higher frequency regime (DD300) ~ 6 MHz ~ 6 MHz 20

  21. Frequency analysis of the Vibrometer signal and LS-DYNA results Radial oscillations of the wire!!! VISAR – noisy but a decent level of information can be extracted (FFT, filtering, …) Vibrometer has been purchased (just arrived to RAL) More results soon… ~ 6 MHz ~ 6 MHz 21

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