Thesis Defense Presentation

1
Progress on Target Tracking Engagement
Demonstration
Presented by Lane Carlson1 M. Tillack1, T.
Lorentz1, J. Spalding1, D. Turnbull1 N.
Alexander2, G. Flint2, D. Goodin2, R.
Petzoldt2 (1UCSD, 2General Atomics) HAPL Project
Review PPPL, Princeton, NJ December 12-13, 2006
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Omnipresent Target Engagement Requirement

• Final Key Requirement
• 20 µm engagement accuracy in (x,y,z) at 20 m
  (10-6)

• All individual tracking and engagement components
  have been operated successfully.
• All components necessary for a glint-only
  hit-on-the-fly demo have been integrated and are
  operational.

3
Current tabletop target engagement demo is
complete with one simulated driver beam
Glint laser now in operation
Poisson fringe counting systems not used in
glint-only demo
4
Hit-on-the-fly experiment has demonstrated
engagement on moving target

• Update time of Poisson spot centroiding algorithm
  down from 10 ms to 3.5 ms in software.
• Fringes off falling target counted over 3 mm.
• Using crossing sensors, the timing triggering
  system triggers all necessary lasers/components
  on-the-fly.
• Engaged moving targets with a simulated driver
  beam by using the glint return signal to steer a
  fast steering mirror.
• Verification system has been used to measure
  error in target engagement.
• 150 µm range
• 6 µm resolution

5
A range of tracking/engagement scenarios call for
different requirements
Example 1 no in-chamber gas, glint provides
final mirror steering
Example 2 in-flight, pre-steering corrections
by Poisson, fringe counter
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1 Transverse Target Tracking Using Poisson Spot
Centroid
7
Reduced region of interest (ROI) technique
further improves update time

• Update time reduced from 10 ms to 3.5 ms by
  implementing a dynamic ROI in software.
• Number of pixels to process is reduced from 307k
  to 10k.

• The smaller ROI assumes the target will not move
  more than a few pixels between frames.
• ROI is recalculated each frame to follow the
  Poisson spot centroid.

30x less pixels
4mm sphere on translation stage
8
New centroiding algorithm implements dynamic ROI

• Target position update time 3.5 ms (5 µm 1?)
• Closing in on goal of 1-2 ms

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2 Axial Target Tracking Using Interferometic
Fringe Counting
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Fringe counting has been demonstrated over 3 mm

• Lower-noise photo-detector
• Higher-power laser (60 mW)
• gt Fringes off falling target counted over 3 mm

Similar intensities
Target releasing from vacuum needle
Mini drop tower setup
Free-falling target
5 ms/div
5 V/div
time
Signal processing required to obtain countable
signal
20 µs/div
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3 Crossing Sensors Axial Position Prediction
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Crossing sensors real-time operating system
compute predicted target location on-the-fly

• Last time Established crossing sensors to be
  sufficiently precise (45 µm 1?) to trigger glint
  laser.
• Overview of Timing Sequence
• Timing sequence initiated by target crossing C1.
• C2 crossing yields target velocity.
• Velocity info used to trigger alignment beam,
  glint laser, verification camera, and driver beam.

? Timing and triggering system fully operational
for our demo

• Disparity between predicted and actual target
  location is detected by PSD and corrected by
  steering mirror

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4 Glint System
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All necessary components have been integrated for
glint-only target engagement demo
Glint laser - final component of hit-on-the-fly
demo has been installed
Pulsed diode laser (simulated driver)
New Wave 35 mJ, 1064 nm glint laser
Simulated wedged dichroic mirror
Optics In Motion fast steering mirror
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Wedged dichroic mirror compensates for
glint/chamber center offset
1 cm
Verification camera
Simulated wedged dichroic mirror
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We have engaged moving targets with a simulated
driver beam

• Last time we used a simulated glint return from a
  stationary target to steer a mirror.
• Now, we have used the real glint return signal
  from a moving target (5 m/s) to steer a simulated
  driver beam to engage the target.

Targets fully engaged 20 of the time (in 150 µm
verification range)
150 µm diam. verification beamlets
20
40
40
outside range
outside range
150 µm verification range
But does not meet the 20 µm spec yet
Snapshots of engaged targets
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Effort to improve engagement accuracy to 20 µm
must address minimize all uncertainties
PSD signal with ground-looping

• Errors uncertainties from every subsystem
  contribute to engagement accuracy.
• We are working to understand errors and to
  address each one.
• Air fluctuations, sensor noise, bandwidth
  limitations, response times

Erratic 50 mV signal translates to significant
mirror steering! (100s microns)
? Resolved by plugging all electrical components
into same circuit

• Error contributions to engagement accuracy
• Reading glint return
• (PSD, LabView) 100s µm
• Air fluctuations 20 µm
• Verification camera 12 µm
• Mirror pointing 6 µm

• Most dominant uncertainty so far is deciphering
  the glint return on PSD

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Glint return is used to make one final steering
mirror correction depending on PSD reading

• Glint return on PSD gives targets final
  position.
• LabView reads PSD signal, then calculates
  steering gain to give FSM.
• LabView loop time is 50 20 µs due to
  non-deterministic operating system.

Steering signal to FSM X-axis

• Inconsistent voltage readings grossly and falsely
  steer the mirror.

Glint return on PSD X
2V/div
Glint return on PSD Y
Glint laser q-switch
19
Peak-hold circuit picks off PSD voltage more
consistently than software

• Peak-hold circuit holds the peak voltage until
  LabView can read it.
• Also researching other ways to read glint
  (photo-diode, quad-cell)

Signal held by peak det. (not mirror command)
Rise time may also influence reading consistency
gt More work must be done on glint return
characterization, PSD response, error/noise
reduction.
2V/div
Glint returns on PSD
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5 Engagement Verification for Hit-on-the-fly
Demo
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Applet post-processes snapshot to verify target
engagement accuracy
target
beamlets
PSD

• Applet computes light centroid of obscured and
  un-obscured beamlets.

• Resolution of 6 µm, 150 µm range

imaginary target shadow
No target
Target offset to the right 100 µm
Target equally eclipsing beamlets
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Summary of progress plans
1 Moving target engaged by simulated driver
beam2 Transverse Tracking System Using Poisson
Spot Progress Improved update time to 3.5 ms
using dynamic ROI Plans Implement into system
to help pre-steer mirror 3 Axial Tracking
Triggering Prediction Progress Faithfully
triggering glint, simulated driver beam
verification camera. Also, fringes off
moving target counted over 3 mm 4 Glint
System Progress Glinted target steered FSM
to engage in-flight target Plans Better
characterize glint return PSD response to meet
20 µm goal5 Target Engagement Verification
Progress Engagement verification resolution of
6 µm, 150 µm range Future Goals to
Consider - increase speed capability to couple
with a 50 m/s injector - add more driver
beamlines at different angles.