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Operational Experience and Hazards of Photon Doppler Velocimetry as an Alternative to VISAR

Operational Experience and Hazards of Photon Doppler Velocimetry as an Alternative to VISAR. David B. Holtkamp Hydrodynamic & X-Ray Physics This is not going to be a “Physics” talk… At least not much… Mostly gadgets, examples, and stuff…. Acknowledgements.

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Operational Experience and Hazards of Photon Doppler Velocimetry as an Alternative to VISAR

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  1. 7/15/2008 Page 1

  2. Operational Experience and Hazards of Photon Doppler Velocimetry as an Alternative to VISAR David B. Holtkamp Hydrodynamic & X-Ray Physics This is not going to be a “Physics” talk… At least not much… Mostly gadgets, examples, and stuff… 7/15/2008 Page 2

  3. Acknowledgements • Ted Strand (LLNL) – it is a tribute to the quality of his advice that our first generation PDV worked the first time we turned it on • LANL Colleagues – Pat Rodriguez, Benjie Stone, Lenny Tabaka (P-22), Brian Jensen, Paulo Rigg (DE-9), Matt Briggs, Will Hemsing, Mike Shinas (HX-3) • NSTec Colleagues – Doug DeVore, Araceli Diaz, Adam Iverson, Vince Romero, Mike Rutkowski, Jason Young • STL (Santa Barbara) – Bruce Marshall 7/15/2008 Page 3

  4. Why do we need velocimetry? • Shock waves create conditions of pressure and strain that are well beyond the limits of conventional velocity sensors • Velocities of shocked surfaces move at 1-20 km/s • In the past we used long pulse (or CW) lasers at visible wavelengths in Fabry Perot or VISAR systems Courtesy http://www.dtra.mil/newsservices/photo_library/oe/CS/CS-3.cfm 7/15/2008 Page 4

  5. What is PDV? • Photon Doppler Velocimetry • Direct detection of difference beat signal between unshifted & Doppler shifted light • First used for fluid flow measurements (1964-65)* • Recent improved methods developed by Ted Strand and co-workers at LLNL (1999-2008)** • Los Alamos systems developed & refined 2004-08 • Y. Yeh and H. Z. Cummins, Appl. Phys. Lett. V. 4, no. 10, p. 176 (1964); & J. W. Foreman, E. W. George, R. D. Lewis, Appl. Phys. Lett. v. 7, no. 4, p. 77 (1965); Wayne Willhite at China Lake (unpublished).** Oliver T. Strand, Leon V. Berzins, David R. Goosman, William W. Kuhlow, Paul R. Sargis,and Tony L. Whitworth, LLNL Report UCRL-CONF-206034, 26th Int. Conf. on High-speed Photography and Photonics, Alexandria, VA September 19-24, 2004; O.T. Strand, D. R. Goosman, C. Martinez, T. L. Whitworth, and W. W. Kuhlow, “Compact system for high-speed velocimetry using heterodyne techniques,” Rev. Sci. Inst.77, 083108 (2006). 7/15/2008 Page 5

  6. Features of PDV • Small, portable systems are fast to set up • Class IV lasers, but nearly eye safe (1550 nm) • Absolute accuracy demonstrated to ± 0.1% (or better) • Demonstrated long tracking distances under less than ideal conditions • Probe geometry flexible over a wide range of distances and probe geometries • Single bare fiber per point (< 10 or 20 mm) • Lensed probes (< 100 mm) • Coupled with conventional lens optic (< 30 m (!) or more) • Velocity range from ~few mm/s to > 14 km/s with current systems; long record lengths (> 1 ms); self triggerable 7/15/2008 Page 6

  7. What is PDV? (Reprise) • Direct detection of interference between unshifted and Doppler shifted light • PDV is Ted’s original name; he’s also suggested Heterodyne Velocimeter (“Het-V”) but it wasn’t as catchy…it’s really a homodyne velocimeter (usually) • Basically - a very fast Michelson Interferometer Michelson Interferometer 7/15/2008 Page 7

  8. Michelson Interferometer • Distance can be measured by moving the mirror and counting fringes • The distance of travel d is associated with m fringes byd = m /2 7/15/2008 Page 8

  9. Beat of Shifted & Unshifted Frequencies • If we know unshifted (f1) frequency, and beat frequency, then we can infer shifted (f2) frequency 7/15/2008 Page 9

  10. Beat frequency = fb = fd – f0 = 2 (v/c)f0 @ 1550 nm and v = 1 mm/µs Illustration from Ted Strand f0 = 193414.49 GHzfd = 193415.78 GHz fb = 1.29 GHz V = λ/2 x F V(mm/µs) = 0.775 x F (GHz) “Baby Pictures” • Single channel shown (2 watt laser can support ~4 pts) – typically 200-500 mW each P-22 Single Point PDV (Oct 2004) 7/15/2008 Page 10

  11. Krakatau Installation 4 Channel Optic & Detector Boxes 5 W Lasers • 12 point system (10 used) with two 5 W lasers & recording 7/15/2008 Page 11

  12. Unicorn Installation • 8 channels (2 x 4 point systems) • 2 lasers (not shown) • 4 scopes (2 voltage coverages per channel) 7/15/2008 Page 12

  13. “Handheld” PDV • Miniature PDV • 12 V @ < 1 A • Ready < 100 ms after power on • Multimode fiber • Up to 5 km/s • Analog downlink for recording on ground • Patent pending 7/15/2008 Page 13

  14. VISAR Xmit & Rcv PDV Xmit & Rcv Asay Foil Foil First Data at Santa Barbara (2004) • 3 shots with bare fiber in tube + bare fiber VISAR alongside • 2 mm standoff from polished or ball rolled surface VISAR Bare Fiber PDV Bare Fiber 7/15/2008 Page 14

  15. Ball Rolled Surface (2004) • Blue is raw signal, green is high passed digitally • Note that raw signal is > ± ~100 mV 7/15/2008 Page 15

  16. Raw PDV Signal (2004) • Shock break out to << 1 ns • Elastic precursor evident • Can use various methods to estimate velocity “fast” when SNR is good 7/15/2008 Page 16

  17. Bare Fiber + Ball Rolled Surface ~2.6 GHz • 1024 running FFT with 50% overlap • Note SNR is ~40dB in places (less elsewhere) • VISAR also shows impact of debris on bare fibers between 5 and 5.5 µs 7/15/2008 Page 17

  18. SNR @ 1 Time • Picked a point near 4 µs • SNR  104:1 in frequency/velocity domain 7/15/2008 Page 18

  19. Oz & Lightpath Probes Oz Optics Probes • Trying to standardize on bare fiber (& Lightpath) probe tube diameters, length, etc for multiple users 7/15/2008 Page 19

  20. Summary • PDV is being used at LLNL, LANL, SNL, Universities, commercial (?) • Likely to replace VISAR in most applications • Intrinsically safer than high power visible laser velocimetry approaches (high MPE) • However: • Hazardous conditions exist at probes (when exposed) • Distance between laser systems and probes (and high power fiber connections) require interlocks to prevent accidental exposure 7/15/2008 Page 20

  21. PDV is the up and coming method for velocimetrybecause it really works great If you do dynamic experiments at your lab – expect to see one soon! 7/15/2008 Page 21

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