UCRL-CONF-230794 Fabry Perot / PDV Comparison 51 st Annual FUZE Conference May 24, 2007, Chadd May, Roy Hanks, Don Hansen, Tony Whitworth This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48
Compare Fabry-Perot to PDV Objective: will PDV measure the fast pulses seen with exploding bridge flyers Each test fired under same conditions Change probes for Fabry-Perot & PDV 1-2 shots for each setup Parylene & Spun Kapton All Shots into LiF under vacuum 0.3 uf Fireset Six shots with PDV Page 2
What is a Slapper Substrate Bridge Material Flyer Material Barrel Length Target H.E. LIF Target Barrel Exploding Foil (al or cu) Dielectric Flyer Gold Substrate Page 3
How do you fire a Slapper? V Target Barrel Flyer Exploding Foil high current Page 4
General Layout of Two-Beam Fabry-Perot System for Diagnostic Measurements on Slapper Initiators Target Slow Cavity Slit m m+1 Pulsed Nd:YAG Fast Cavity Fast Camera Down to 30ns Sweep Window Page 5
Fabry-Perot in HEAF Room Size 2 Fabry-Perot 2 Streak Cameras Yag Laser Page 6
Photonic Doppler Velocimeter (PDV) Portable system rack mount Doppler Velocimetry Greater than 5 mm/µsec velocity Limited by bandwidth only Room Size Doppler Velocimetry Velocity and Pulse width limited by the Fabry Cavity Page 7
The Fill-Time of the Fabry-Perot Cavity may Filter Sub- Nanosecond Data PDV may be a Solution Fabry Results limited by the Cavity.5ns max resolution Experimental and calculated velocity wave profiles into LiF for a 50um flight distance. PDV may solve this problem P article velocity (km/s) 1.80 1.60 1.40 1.20 1.00 0.80 0.60 0.40 0.20 Measured wave profile Calculated wave profile 0.00 0 1 2 3 4 Page 8
What is PDV (Photonic Doppler Velocimeter) Laser Portion of Original Signal Probe Detector Doppler-shifted light Moving Surface High speed detectors measure the difference in frequency, the Beat, between the original signal and Doppler-shifted return signal. Page 9
PDV Beat PDV Raw Data Output The beat frequency is Proportional to Velocity Expanded view 40G sample digitizer 25ps/point 1550 nm laser wavelength Ted Strand Page 10
Fabry-Perot Measurements Conducted in Vacuum Provide Information on Slapper s Pulse Duration and Equation of State Probe for Fabry or PDV Working in a vacuum eliminates the air cushion and the air flash at impact. Fabry-Perot and PDV Setup Page 11
Simulation of a 60.0um Parylene-C Flyer into LiF with Strong Shock Shows Stepped-Top as Seen with Fast Fabry-Perot Diagnostic Pressure (GPa) 14 12 10 8 6 4 For thick flyers (>40um) a shock wave builds in flyer material Shock causes a second jump in Up in LiF as shown here 2 0 0.1 0.11 0.12 0.13 0.14 0.15 Time (us) Impact into LIF Front Surface Velocity of 68.8um Flyer Page 12
68.6um Parylene - Fabry Complex Return Front & Rear flyer surface producing separate returns Multiple Returns are easily seen with fabry perot Transparent material Page 13
The 60um Parylene-C Flyer Impact Irregularity Two pressure pulses were measured with Fast Fabry-Perot System Originally we believed that the flyer may have spalled After witnessing this effect in other thick flyers we hypothesize that the second step is the result of a strong shock in the thick flyer Page 14
68.8u Parylene Flyer PDV Spectrograph with 3ns window Raw Fabry-Perot Data 3ns fft window Reanalyzed with a 6ns FFT window 6ns fft window Page 15
Comparison for 68.6um Parylene-C Flyer All PDV shots used a 3.2ns FFT Window Should try faster window for pressure pulse One of several methods for data analysis Veloicty (mm/us) 4 3.5 3 2.5 2 1.5 1 0.5 Preliminary PDV/Fabry Comparison PDV with 3ns FFT Window Shot 1 PDV with 3ns FFT Window Shot 1 PDV with 3ns FFT window Shot 2 PDV with 3ns FFT Window Shot 2 Fabry Velocity Fabry Up 0-0.05 0 0.05 0.1 0.15 0.2 Time (us) The step on the pressure pulse seen on both Fabry-Perot and PDV 4ns fid Page 16
50.4u Paralyne Flyer Spectograph & Fabry-Perot Page 17
PDV/Fabry-Perot Comparison 50.4um Parylene-C PDV/Fabry Com parison 50.4u Parylene Flyer Velocity (mm/us) 4.5 4 3.5 3 2.5 2 1.5 PDV # 1 PDV #1 PDV #2 PDV #2 Fabry #1 Fabry #1 Fabry #2 Fabry#2 1 0.5 0 0.24 0.26 0.28 0.3 0.32 0.34 0.36 0.38 0.4 Time (us) Page 18
12.3u Spun Kapton Flyer 1880 Thin flyers produce a very narrow pulse on impact Page 19
12.3um Flyer Fabry to PDV Comparison Shot PDV 3ns window did see the pulse Same Velocity profile 6 12.3 um Parylene-C Flyer into LiF 5 Fabry 12.3 um Parylene-C Flyer into LiF Velocity (mm/us) 4 3 2 Fabry PDV #1 PDV #1 PDV #2 PDV #2 2.5 1 Velocity (mm/us) 2 1.5 1 Fabry PDV #2 PDV #2 0-0.04-0.02 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 Time (us) 0.5 0 0.06 0.065 0.07 0.075 0.08 Time (us) Page 20
12.3um Flyer Fabry to PDV Comparison Shot PDV Hand Read of the pulse found 5 data points on this 1.2ns impact pulse 2.5 12.3um Parylene Partical Velocity 2 1.5 1 0.5 0 0.063 0.065 0.067 Time 1889 pulse Hand Read FP-1881 Page 21
Conclusions Fabry-Perot PDV Graphic instantly see the velocity/time data Complex returns easily seen Speed limited by the fabry cavity (.5ns) Expensive, Room size Must be analyzed to see the data Complex returns are seen with additional analysis Speed limited only by the recording digitizer Portable, less expensive Page 22