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

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

3. Flange Timing (20 mm) Position Measurement window 40 mm 20 mm 22 mm 18 mm Lasers Lens Flange aperturesLens Photodiode Line scan camera Timing Position 45 mm 40 mm ~18 mm ~50 mm 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 How to get micron-level tracking accuracy (1)

4. Detector calibration is accomplished with target on translation stage - Flat field correction corrects for variability in laser intensity and camera response - Also accomplished automatically before each shot sequence How to get micron-level tracking accuracy (2) Flat field corrected data

5. We achieved tracking with high reliability on all three detector stations Air rifles were used to fire “surrogate targets” through the tracking stations - Previously achieved ~ 3  m tracking repeatability in stationary tests - Now working on in-flight - Modular development - using 4.5 mm BB’s (and pellets) - Up to 300 m/s with surrogate targets - Multiple shot capability - Installed back on main line Target “shadow” (raw data)

6. 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 = 3  ud -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)

7. Three Injection Paths Considered: Path 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 5 mm circle around chamber center Target trajectory Injection Path I Peak gas velocity approximately 300 m/s Path II Path III

8. Preliminary Results are Encouraging 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 Data point from previous example

9. Chamber gas also affects tracking accuracy The time between position measurements must be guided by measurement accuracy and acceleration uncertainty. Example: Position measurement uncertainty  X 0 = 10  m Acceleration uncertainty  a = 300 m/s 2 Initial velocity uncertainty  V 0 = 2  X 0/ 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 Chamber center Next to last measurement Final measurement  at 0.1 m interval; in-chamber tracking may be inadequate

10. “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. *Tracy McSheery Private Communications, 23 Jan 2004 - PhaseSpace Inc. Injector Discrete trackers Continuous tracker

11. A new concept for target tracking and driver alignment* *Mark Tillack and Ron Petzoldt Moving target PSD? Quad Driver beam Full or reduced power Removable mirrors? Tracking beam Beam combiner Alignment mirrors Beam and tracking final pointing mirror X, Y translation ,  angle Optical filter 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

12. Current PSD accuracy is not adequate for in-chamber tracking Hamamatsu S1881 PSD 22 mm Active area Zone A Zone B Resolution = 2.8 micron Zone A Position error = ±150 micron Zone B Position error = ±400 micron 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

13. We measured Young’s modulus for RF foam Simple measuring system Force (grams) vs Compression Linear part of measurements gives E = 0.25 MPa 105 mg/cm 3 RF foam Dimensions H = 6.1 mm W = 6.3 mm L = 7.4 mm 1-D estimates for compression of foam by accelerated target are given by: 0 50 100 150 200 250 300 350 400 450 00.511.522.5 Compression (mm) Force (gram) Similar measurements: 14 mg/cc TPX foam E= 0.11 MPa 100 mg/cc DVB foam E= 0.76 MPa RF foam sample Ansys calculations show 1.3  m compression RF foam and 0.4  m for DVB Acceleration Comp Comp.

14. Low modulus for DVB and RF foam will decrease buckle pressure (and increase fill time) Target Radius = 1950  m External PS membrane 1  m (2  m for PS foam calc) Buckle Pressure Calculations *Roark and Young, Formulas for Stress and Strain (1982) -Real Buckle Pressure ANSYS buckling model

15. Liquid surface tension during insulating foam drying could damage foam cells Options for drying insulating foam Freeze drying 1.Fill targets with DT gas. 2.Freeze DT. 3.Draw vacuum to sublimate DT gas from insulating foam. Alternate method 1.Fill targets with DT gas. 2.Supercritical evaporation from insulation to critical point (39.4 K, 1.77 MPa). 3.Continued drying with reduced pressure in insulation to prevent condensation. 4.Slightly higher pressure inside seal coat to allow condensation. Requires care to avoid shell rupture. Fill chamber Insulating foam Seal Coat Inner DT Burst pressure

16. 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 Open cell foam DT gas radius r 1 Beta decay heat causes temperature drop across insulating foam during layering

17. Small non-concentricities cause changes in outer DT temperature A B A< B Offset = (B-A)/2 Nominal foam thickness = 150  m Nominal DT thickness = 450  m 012345 0 500 1000 1500 2000 2500 3000 3500 4000  T (  K) Offset (  m) DT outer surface temperature difference vs foam offset (assumes uniform outer foam temperature)

18. A small non-concentricity of the foam layer results in a much greater DT layer non-concentricity 00.40.81.21.62 0 2 4 6 8 10 Offset of the foam (  m) =(B-A)/2 DT Offset (  m) =(C-D)/2 The DT is repositioned during Beta layering to maintain a uniform inner surface temperature k(DT) = 330 mW/mK k(foam) = 26 mW/mK A B C D Conclusion: DT offset requirement is unknown but expect foam non-concentricity must be < 1%

19. Summary and Conclusions I.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 II.Tracking/Beam Steering Interface - A new concept for Tracking/Steering alignment is under consideration III.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