UNCLASSIFIED

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

UCRL-CONF-230794 UNCLASSIFIED

Fabry Perot / PDV Comparison

51st Annual FUZE Conference

May 24, 2007

Ralph Hodgin, Chadd May, Roy Hanks, Don Hansen,

Tony Whitworth

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Ralph Hodgin

Objective: will PDV measure the fast pulses seen with exploding bridge flyers

Each test fired under same conditionsChange probes for Fabry-Perot & PDV1-2 shots for each setup

Parylene & Spun Kapton

All Shots into LiF under vacuum

0.3 uF Fireset

Six shots with PDV

Compare Fabry-Perot to PDV

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Ralph Hodgin

What is a Slapper

SubstrateGold

Dielectric Flyer

Exploding Foil (al or cu)

Barrel

Target

SubstrateBridge MaterialFlyer MaterialBarrel LengthTarget

H.E.LIF

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Ralph Hodgin

How do you fire a Slapper?

Exploding Foil

FlyerBarrel

high current

V Target

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Ralph Hodgin

General Layout of Two-Beam Fabry-Perot System for Diagnostic Measurements on Slapper Initiators

m m+1

Slit

Target Slow Cavity

Pulsed Nd:YAG

Fast CavityFast Camera Down to 30ns Sweep Window

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Ralph Hodgin

Fabry-Perot in HEAF

Room Size

2 Fabry-Perot

2 Streak Cameras

Yag Laser

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Ralph Hodgin

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

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Ralph Hodgin

Fabry Results limited by the Cavity

.5ns max resolution

PDV may solve this problem

The Fill-Time of the Fabry-Perot Cavity may Filter Sub-Nanosecond Data – PDV may be a Solution

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

0 1 2 3 4

Par

ticle

vel

ocity

(km

/s)

Measured wave profileCalculated wave profile

Experimental and calculated velocity wave profiles

into LiF for a 50um flight distance.

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Ralph Hodgin

What is PDV (Photonic Doppler Velocimeter)

High speed detectors measure the difference in frequency, ‘the Beat’, between the original signal and Doppler-shifted return signal.

Laser

Detector

Probe

MovingSurface

Portion of Original Signal

Doppler-shifted light

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Ralph Hodgin

PDV Beat

PDV Raw Data Output

The ‘beat’ frequency is Proportional to Velocity

Expanded view

40G sample digitizer25ps/point1550 nm laser wavelength

Ted Strand

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Ralph Hodgin

Fabry-Perot Measurements Conducted in Vacuum Provide Information on Slapper’s Pulse Duration and Equation of State

Working in a vacuum eliminatesthe air cushion and the air flashat impact.

Probe for Fabry or PDV

Fabry-Perot and PDV Setup

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Ralph Hodgin

Simulation of a 60.0um Parylene-C Flyer into LiF with Strong Shock Shows Stepped-Top as Seen with Fast Fabry-Perot Diagnostic

0

2

4

6

8

10

12

14

0.1 0.11 0.12 0.13 0.14 0.15

Time (us)

Pres

sure

(GP

a)

For thick flyers (>40um) a shock wave builds in flyer materialShock causes a second jump in Up in LiF as shown here

Front Surface Velocity of 68.8um Flyer

Impact into LIF

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Ralph Hodgin

68.6um Parylene - Fabry

Complex Return

Front & Rear flyer surface producing separate returns

Multiple Returns are easily seen with fabry perot

Transparent material

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Ralph Hodgin

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…

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Ralph Hodgin

68.8u Parylene Flyer

6ns fft window

3ns fft window

Raw Fabry-Perot Data

PDV Spectrograph with 3ns window

Reanalyzed with a

6ns FFT window

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Ralph Hodgin

Comparison for 68.6um Parylene-C Flyer

All PDV shots used a 3.2ns FFT WindowShould try faster window for pressure pulseOne of several methods for data analysis

The ‘step’ on the pressure pulse seen on both

Fabry-Perot and PDV4ns fid

Preliminary PDV/Fabry Comparison

0

0.5

1

1.5

2

2.5

3

3.5

4

-0.05 0 0.05 0.1 0.15 0.2

Time (us)

Vel

oict

y (m

m/u

s)

PDV with 3ns FFT Window Shot 1PDV with 3ns FFT Window Shot 1PDV with 3ns FFT window Shot 2PDV with 3ns FFT Window Shot 2Fabry VelocityFabry Up

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Ralph Hodgin

50.4u Paralyne Flyer Spectograph & Fabry-Perot

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Ralph Hodgin

PDV/Fabry-Perot Comparison 50.4um Parylene-C

PDV/Fabry Comparison 50.4u Parylene Flyer

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0.24 0.26 0.28 0.3 0.32 0.34 0.36 0.38 0.4

Time (us)

Velo

city

(mm

/us)

PDV # 1

PDV #1

PDV #2

PDV #2

Fabry #1

Fabry #1

Fabry #2

Fabry#2

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Ralph Hodgin

12.3u Spun Kapton Flyer

1880

Thin flyers produce a very narrow pulse on impact

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Ralph Hodgin

12.3um Flyer Fabry to PDV Comparison Shot

PDV 3ns window did see the pulse Same Velocity profile 12.3 um Parylene-C Flyer into LiF

0

1

2

3

4

5

6

-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)

Vel

ocity

(mm

/us)

FabryFabryPDV #1PDV #1PDV #2PDV #2

12.3 um Parylene-C Flyer into LiF

0

0.5

1

1.5

2

2.5

0.06 0.065 0.07 0.075 0.08

Time (us)

Velo

city

(mm

/us) Fabry

PDV #2

PDV #2

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Ralph Hodgin

12.3um Flyer Fabry to PDV Comparison Shot

PDV – Hand Read of the pulse found 5 data points on this 1.2ns impact pulse

12.3um Parylene

0

0.5

1

1.5

2

2.5

0.063 0.065 0.067

Time

Par

tical

Vel

ocity 1889 pulse

Hand ReadFP-1881

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Ralph Hodgin

Conclusions

Fabry-PerotGraphic – instantly see the velocity/time dataComplex returns easily seenSpeed limited by the fabry cavity (.5ns)Expensive, Room size

PDVMust be analyzed to see the dataComplex returns are seen with additional analysisSpeed limited only by the recording digitizerPortable, less expensive