Target InjectionPositioning Update

1
Target Injection/Positioning Update

• Presented by Ron Petzoldt
• Neil Alexander1, Jason Bousquet1, Amy Bozek1,
  Lane Carlson2, Dan Frey1, Jonathan Hares3, Dan
  Goodin1, Jeremy Stromsoe2, and Emanuil
  Valmianski2
• HAPL Project Review
• PPPL, Princeton New Jersey
• Dec 12-13, 2006

• General Atomics
• UCSD
• Kentech Instruments, UK

2
Why would we consider target steering for HAPL?
Log scale
gt100X

• Improved placement accuracy (lt1 mm) might allow
  beam steering based on glint only (Lane Carlson)
• For FTF - Target steering to lt20 µm with 0.5 m
  standoff may allow no beam steering for
  non-reprated operation

improved accuracy (with in-flight steering)
reduces beam steering requirements
3
Recent progress in target positioning

• Converted to two-axis steering
• Achieved 50 µm placement accuracy in X and Y
• Improved position measurement stability From 10
  µm to 5 µm
• Measured target charge
• Started vacuum chamber and automatic loading
  design
• Started modeling electrostatic accelerator

4
Two-dimensional in-flight target steering
achieved with dropped targets
Mirror
Laser
Target release
10 cm, 0.14 s
Target charging
90 cm, 0.31s
3 kV steering electrodes
50 cm, 0.10 s
Target charge measurement
Camera
Key parameters Target charge (up to -0.8 nC),
Target mass (270 mg), 4 mm diameter Peak velocity
(5.4 m/s), Steering field range (120 kV/m)
5
Target charge is measured to verify effectiveness
of charging method
Target charged with -5 kV electrode
Target
-
Conducting tube
V

-
R 1 M?
Charge is drawn onto tube through 1 M?
oscilloscope resistance Standard deviation of
target charge is currently 12 Signal also
indicates when target is near end of fall
6
Steering improves placement accuracy from 500 to
50 µm in X and Y
No steer
No steer
?X Final 52 µm
?Y Final 45 µm
?X Exiting Electrodes 25 µm
?Y Exiting Electrodes 22 µm
50 µm/0.5 m 100 µrad (corresponds to 1 mm at 10
m)
7
Further improvement will come from reducing error
sources

• Error sources (magnitudes of some contributors
  not yet known)
• Position measurement stability 5 µm
• Position measurement accuracy vs spot size and
  shape 5-10 µm
• Target interaction with air
• Electric field variation with position
• Position measurement vibration was reduced with
  better structural system and beam tubes
• Added mass reduced mirror vibration by
  increasing inertia
• Beam tubes reduced effect of air currents
• Typical position measurement standard deviation
  reduced from 10 µm to 5 µm X and Y with 4 m
  standoff

8
We calculated non-uniform electric fields and
will use results to improve steering algorithm

• Important to align tracking system with
  electrodes
• Steering has thus far assumed uniform field
• (field is rather uniform for few hundred micron
  target movement)
• We are ready to modify electrode potential for
  desired field
• based on target position (improve algorithm)

9
We will improve our optics to improve position
measurement
2.5 mm

• Typical tracking Poisson spot image is imperfect
• Not very round or uniform
• Superimposed interference patterns
• Improved mirrors, windows and filters will help

10
Operation in vacuum will eventually be required
for HAPL or FTF operations
Started design of an experimental setup to do
this in vacuum.
Interlocked Plexiglas housing
See-through cast acrylic vacuum chamber
Cast acrylic vacuum spoolpiece for later
expansion to add accelerator
80/20 internal tower

• Using ASME BPV Code
• Section VIII, Division 1, Parts UG-34 and UG-37,
  and Mandatory Appendix 2
• Section II, Subpart 3, Figure G

11
Automatic target loading will be necessary to
avoid returning to atmospheric pressure with each
shot
Vacuum Enclosure
Shell Loader
Drum Servo
Rotating Shell Tray
Drum Shell Feeder
Shell Catcher
Shell
Tray Servo
12
Preliminary modeling for an electrostatic
accelerator shows a lens effect between
electrodes
2 Phase
3 Phase
5 Phase
Symmetry axis
Equipotential Spacing 0.1 V
Equipotential Spacing 0.025 V
Equipotential Spacing 0.05 V

• An electrostatic accelerator is part of the
  plan for demonstrating high-speed steering for
  the FTF (not necessarily IFE)
• Additional phases reduce lens effect in
  accelerator

13
Summary of injection/positioning progress

• 2D in-flight target steering has been achieved
• Real-time trajectory corrections based on
  position measurement (v5 m/s)
• Placement accuracy improved to 50 ?m (1? at 0.5
  m standoff X and Y, a 270 mg surrogate-target in
  air)
• Placement accuracy 23 ?m exiting electrodes
• Better accuracy is expected from improved optics
  and steering algorithm
• For FTF - demonstrate this for a lightweight (1
  mg) target in vacuum at 50 m/s
• Designs for vacuum operation and electrostatic
  acceleration have begun