Target Tracking, TrackingBeam Steering Interface, and Target Fabrication Progress - PowerPoint PPT Presentation

Title: Target Tracking, TrackingBeam Steering Interface, and Target Fabrication Progress


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Target Tracking, Tracking/Beam Steering
Interface, and Target Fabrication Progress
presented by Ron Petzoldt HAPL Project
Review Atlanta, Georgia February 5-6, 2004
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Outline

• Target Tracking
• - Experimental system progress
• - Effect of chamber gas pressure on target
  placement and tracking
• Tracking/Beam Steering Interface
• - A new concept for Tracking/Steering alignment
• Target Fabrication
• - Insulating foam

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How to get micron-level tracking accuracy (1)
Timing (20 mm)
Position Measurement window 40 mm
22 mm
20 mm
18 mm
Timing
Flange
Photodiode
Line scan camera
Lens
Flange apertures
Lens
Lasers
A 4 mm diameter target will decrease the
photodiode current more than 10 (trigger) over a
range of 13 to 14 mm. The line scan camera sees
both sides of the target over similar range.
The functional span is about 6 mm
Position
40 mm
18 mm
45 mm
50 mm
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How to get micron-level tracking accuracy (2)
Detector calibration is accomplished with target
on translation stage
Flat field corrected data
- Flat field correction corrects for
variability in laser intensity and camera
response - Also accomplished automatically
before each shot sequence
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We achieved tracking with high reliability on all
three detector stations
- Previously achieved 3 ?m tracking
repeatability in stationary tests - Now working
on in-flight - Modular development - using 4.5
mm BBs (and pellets)
Target shadow (raw data)
Air rifles were used to fire surrogate targets
through the tracking stations
- Up to 300 m/s with surrogate targets - Multiple
shot capability - Installed back on main line
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We have calculated the displacement of the target
due to chamber gas velocity

• Output from SPARTAN code was used to estimate the
  deflection of a target injected 100 ms after a
  target explosion
• These preliminary calculations are conservative
  and results should be considered mostly as
  illustrative.
• - Stokes law assumed
• F 3pmud
• - Chamber gas velocity based on initial SPARTAN
  code results which did not include radiation
  effects
• Target displacement calculated as a function of
  injection velocity and gas imparted acceleration
• Three target trajectory paths considered

(from Z. Dragojlovic, UCSD)
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Three Injection Paths ConsideredPath I

• Example results for target at 600 m/s
• 50 mTorr Xe
• 0.1 s after microexplosion
• Target within 5 mm of center
• Other paths had much less deflection

Injection Path I
Target trajectory
Path II
Path III
5 mm circle around chamber center
Peak gas velocity approximately 300 m/s
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Preliminary Results are Encouraging
Data point from previous example
Depending on the injection path, injection
velocity of 100-600 m/s required tomaintain
displacement within 5 mm These results are
preliminary and need to be confirmed based on
updated chamber gas velocity profiles The force
imparted on the target by gas flow also needs to
be better assessed.
? Preliminary results indicate proper chamber
design can minimize target displacement
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Chamber gas also affects tracking accuracy
The time between position measurements must be
guided by measurement accuracy and acceleration
uncertainty. Example Position measurement
uncertainty ?X0 10 ?m Acceleration
uncertainty ?a 300 m/s2 Initial velocity
uncertainty ?V0 2 ?X0/t ?at/2 Time
measurement uncertainty ?t 0 (very
small) Position measurement interval t
250 ?s 4 kHz or 0.1 m at 400 m/s
0.1 m
0.1 m
Chamber center
Next to last measurement
Final measurement
? at 0.1 m interval in-chamber tracking may be
inadequate
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Continuous tracking with extremely fast beam
steering response could improve accuracy

• Mirrors would be continuously aligned with
  target tracking measurements.
• Alignment actuators would have to be closely
  spaced because material
• - sound speed (5100 m/s for aluminum)and damping
  
• will limit steering response time.
• Continuous tracking requires 10 ?m accuracy at
  10 kHz at 10 m distance
• - 100 ?m accuracy (10 ?m resolution) achieved
  commercially at 480 Hz
• from 2 m with 2 m (56 degree) field of view
  (accuracy scales with FOV)
• Discrete trackers could acquire the target,
  reduce the required field of view,
• and hand off to continuous tracking system.

Discrete trackers
Injector
Continuous tracker
Tracy McSheery Private Communications, 23 Jan
2004 - PhaseSpace Inc.
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A new concept for target tracking and driver
alignment
A method must be developed to ensure a common
reference for driver beams and target tracking
One concept is to somehow measure where beams
actually hit the targets This new concept uses
common optics for driver and tracking Requires
separate tracking for each driver beam
PSD?
Driver beam Full or reduced power
Optical filter
Moving target
?, ? angle
Tracking beam
Removable mirrors?
X, Y translation
Beam and tracking final pointing mirror
Beam combiner
Alignment mirrors
Quad
Quad
Mark Tillack and Ron Petzoldt
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Current PSD accuracy is not adequate for
in-chamber tracking
22 mm
Resolution 2.8 micron Zone A Position error
150 micron Zone B Position error 400 micron
22 mm
Zone A
Zone B
Active area
Hamamatsu S1881 PSD
Voltage rise time is 3 ?s which is also too long
for high-speed tracking (the target moves 0.4
mm/?s)
Conclusion An alternative sensor would probably
be needed to perform the PSD function
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We measured Youngs modulus for RF foam
105 mg/cm3 RF foam Dimensions H 6.1 mm W 6.3
mm L 7.4 mm
RF foam sample
Force (grams) vs Compression
450
400
350
300
Force (gram)
Linear part of measurements gives E 0.25 MPa
250
200
150
Similar measurements 14 mg/cc TPX foam E 0.11
MPa 100 mg/cc DVB foam E 0.76 MPa
100
50
Simple measuring system
0
0
0.5
1
1.5
2
2.5
Compression (mm)
1-D estimates for compression of foam by
accelerated target are given by
Comp
Ansys calculations show 1.3 ?m compression RF
foam and 0.4 ?m for DVB
Acceleration
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Low modulus for DVB and RF foam will decrease
buckle pressure (and increase fill time)
Buckle Pressure Calculations
Target Radius 1950 ?m External PS membrane 1 ?m
(2 ?m for PS foam calc)
ANSYS buckling model
Roark and Young, Formulas for Stress and Strain
(1982) -Real Buckle Pressure
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Liquid surface tension during insulating foam
drying could damage foam cells
Fill chamber

• Options for drying insulating foam
• Freeze drying
• Fill targets with DT gas.
• Freeze DT.
• Draw vacuum to sublimate DT gas from insulating
  foam.
• Alternate method
• Fill targets with DT gas.
• Supercritical evaporation from insulation to
  critical point
• (39.4 K, 1.77 MPa).
• Continued drying with reduced pressure in
  insulation to prevent condensation.
• Slightly higher pressure inside seal coat to
  allow condensation. Requires care to avoid shell
  rupture.

Insulating foam
Seal Coat
Inner DT
Burst pressure
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Insulating foam must be very concentric with
target to achieve uniform DT layer thickness
He gas greatly increases thermal conductivity in
insulating foam
DT Fuel
Permeation boundary
DT gas radius r1
Open cell foam
Beta decay heat causes temperature drop across
insulating foam during layering
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Small non-concentricities cause changes in outer
DT temperature
Alt B Offset (B-A)/2 Nominal foam thickness
150 ?m Nominal DT thickness 450 ?m
A
DT outer surface temperature difference vs foam
offset (assumes uniform outer foam temperature)
4000
3500
3000
B
2500
?T (?K)
2000
1500
1000
500
0
Offset (?m)
0
1
2
3
4
5
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A small non-concentricity of the foam layer
results in a much greater DT layer
non-concentricity
The DT is repositioned during Beta layering to
maintain a uniform inner surface temperature
k(DT) 330 mW/mK k(foam) 26 mW/mK
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A
C
8
DT Offset (?m) (C-D)/2
6
4
D
2
B
0
0
0.4
0.8
1.2
1.6
2
Offset of the foam (?m) (B-A)/2
Conclusion DT offset requirement is unknown but
expect foam non-concentricity must be lt 1
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Summary and Conclusions

• Target Tracking
• - Tracking station reliable operation was
  developed offline
• - Detectors are ready of online operation
• - Preliminary calculations indicate that proper
  chamber design and injection path selection can
  minimize gas induced target displacement
• Tracking/Beam Steering Interface
• - A new concept for Tracking/Steering alignment
  is under consideration
• Target Fabrication
• - Low measured DVB and RF foam strength would
  increase fill time
• - Insulating foam thickness must be very uniform
  
• Next step Focus on online target tracking