1. Project supported by JCHP-FFE, EC FP7 and Swedish Research Council
Development of Pellet Tracking Systems for PANDA and WASA
Hans Calén, Kjell Fransson, Carl-Johan Fridén, Björn Gålnander, Elin Hellbeck, Marek Jacewicz and Pascal Scheffels (Erasmus, Bochum) IFA & TSL, Uppsala University
Motivation, goals and challenges
Uppsala pellet test station, UPTS
Pellet Diagnostics with one Camera
Camera performance tests
Illumination
Two Synchronized Cameras
Pellet velocity (spread)
Time resolution and Camera efficiency
Tracking system design and simulations
Conclusion and Outlook
Results presented in Milestone report* for FP7 HadronPhysics2 WP19 (Futurejet), December (CM GSI 8/3 2010)
*) Design ideas for pellet tracking systems for PANDA and WASA
Project supported by JCHP-FFE, EC FP7 and Swedish Research Council

2. Goal: To know interaction point with a few 100 mm accuracy in 3d(xyz)
Method: Track pellets! and synchronize with time of interaction
Basis: Pellets F = < 30 mm, v ≈ 70 m/s, Dv/v = few %
Pellet stream F<10mm, intensity 10-20k plts/s
Possible pellet tracking detector positions m from int. point
Need: Pellet detection accuracy ≤ 50mm (xyz) and < 2ms in time
at pellet generator (and maybe detectors also at pellet dump)
Idea: - Use laser and line-scan (linear CCD) camera for pellet detection. z1 x1 z2 x2
zip
xip
Pellet generator
Challenges:
Detection efficiency
Position and Time resolution
Handle pellet velocity spread
Data processing
Calibration, alignment, control
Interaction point

3. Uppsala Pellet Test Station, UPTS
Two Cameras Aviiva M2 CL linear CCD pixels 14 x 14 mm - max line rate ~ 90 kHz? - lens: f=50 mm, work dist. = 240 mm pixel size  40 x 40 mm tot. coverage: +/- 8 mm, DOF: few mm
Laser beam with a line profile - type: Lasiris MFL 35 mW, SNF 50 mW
- profile: 50 mm(y) x 15 (3) mm(x) at work distance = 185 mm matched to camera with f=50 mm lens
Ongoing activities April-June 2010:
- Pellet diagnostics with single camera
- Understand camera performance - Improve light yield from pellets - Develop synchronized r/o for 2 cameras - Time and position correlation studies
- Prepare tracking chamber with two measurement levels
Laser LS-camera

4. UPTS control & monitoring
CCD camera monitors
Droplet chamber
Vacuum injection capillary (VIC) exit
At LS-cameras
LS-camera ctrl & monitoring

5. UPTS control Frequency generator and amplifier for the transducer
Control of valves and pumps
Vacuum display
Temperature control
Control of hydrogen and carrier gas

6. Pellet beam diagnostics with one LS camera
0.5 mm
Beam profile
Time between pellets
Pellet “width”
Study of pellet beam fluctuations on different time scales
0.1 s bins “vibrations”
>0.5 s bins slower movement
Used e.g. in optimization of pressure and temperature regulation.
Position Fit values
0.5 s
0.1 s
~1 min

7. Camera tests with thin wire illuminated by LED powered by pulse generator
cameras
LED
wire
Used for check of camera performance for different cycle and integration times and different LED pulse lengths, amplitudes and frequencies.
Synchronization tests with two cameras

8. CCD camera cycle specification:
- Maximum line rate 98 kHz, found ~90 kHz …
Integration time > 5 ms??, can be shorter …
- r/o time ~9 ms - Dead time between integration and r/o ~1 ms
- Pxl pedestal widths and signal resolution (~10 for 12bit r/o) - Signal stability
Linearity vs LED pulse length (ok) and amplitude (?)
Splitting of signals between lines
and between pxls (x-talk)
- Interference effects in camera cycle
Improper operation for cycles shorter than ~14 ms (>72 kHz)
- “Small” interference effects if integration and r/o overlaps

9. Camera tests with LED
Some pixel signal amplitudes for different cases Max signal peak seen if LED pulse length different from integration time.
No peak if they are equal (lower right plot).
Spectra are well reproduced by simulations (red) for 72 kHz line rate.
Lines between signals ….. LED at 9.2 kHz MC

10. Pellet illumination
Efficient tracking requires that the signals from (all) individual pellets should be clearly separable from background !
Pellets with v ~70 m/s  1 ms light pulse in 50 mm laser beam … difficult to get big enough signals for fully efficient detection.
How to get a stronger signal?
- Slower (or larger) pellets Maybe not desirable …
- Longer light pulses. Decrease camera magnification (use 25 mm lens) and increase laser line width Worsens resolution…
- Laser with higher intensity Didn’t find so far… - Optimize laser optics: 5º -> 1º fan angle Too narrow line profile ?
- Improve illumination geometry. More lasers ?
135°
45°
Spectra very sloping ….
Laser light speckle effect ?
Laser
Cameras
135°
45°
Signal amplitude

11. UPTS November 2009 Two-cameras setup
UPTS November 2009 Two-cameras setup. Synchronized measurement of x and z
Cameras A&B
laser beam exit
135 degrees illumination geometry

12. Two camera readout and synchronization
Camera links 120 Mbytes/s each
Framegrabbers: MatrixVision TitanCL PCI-board
NIM – Modules to generate synchronization signals for the line sweep of the cameras
DAQ Computer
Pulse generators:
for LEDs (for control and monitoring of camera synchronization)
for Camera cycle

13. Two camera synchronization with pellets
2d profile of the pellet beam
Line scans triggered from external pulse generator
Frames of 5000 lines each, analyzed in real time
Z coordinate
X coordinate
Lines between signals in camera A & B
Time
Same pellet seen by both cameras?
Frames out of synch

14. Control and monitoring of camera synchronization.
Time reference.
LS camera “picture” ( ≈ 500 lines ↔ 10 ms)
Use synchronized LEDs providing short light signals with low frequency (≈100 Hz)… to illuminate white screens placed at the vacuum window and at the edge of the field of view of the cameras. (Means also very out of focus).
Pellets
Synch lines

15. UPTS March 2010 Misc correlations between infos from the cameras …
pellet signal heights
measured pellet position
position – signal height
Laser
Cameras A B
Expected correlation between measured pellet positions (pixel signals from camera A. vs. camera B.).

16. Pellet velocity spread
WASA pellet generator
Pellet velocity spread
The pellets have very little spread in velocity and direction in the droplet chamber.
A significant spread in velocity and direction arise in connection with the injection into vacuum through the VIC (Vacuum Injection Capillary).
At WASA the time distribution of pellets at the interaction region, 2.4 m below the VIC, has turned out to be stochastic and this causes large variations in effective target thickness on a time scale from 10 microseconds to a few milliseconds.
At UPTS, already 0.3 m below the VIC, the pellet time distribution looks stochastic. Simulations show that this is expected for a velocity spread of a few percent.
For accurate pellet tracking the relative velocities must be measured with a precision better than 10-4 and for high efficiency the time and position measurement values must be correctly assigned to the individual pellets.
Simulation studies show how the measurement positions should be arranged for highest efficiency.
VIC
Fo = 1.4mm

17. Time between pellets --- pellet velocity spread (1)
Gauss upper and Exp lower curve 1. 2. 4. 3.
Time between pellets --- pellet velocity spread (1)
MC simulation
Case: 1) Short dist. / low vel. spread Gauss
2) Longer dist. / higher vel. spread Gauss (trunkated) 3) Longer dist. / higher vel. spread Gauss (tail) / Exp ? 4) Long dist. / high vel. spread Gauss (tail) / Exp !
sv/v=0.3%
sv/v=1% 4.
sv/v=2.5% 3. 2. 1.
sv/v=5%
Time between pellets
UPTS measurement 300 mm below VIC exit. f≈40kHz, p(H2) ≈ 400mbar, p(DC) ≈ 25mbar (total loss = camera deadtime illumination ineff. + lost pellets)
Curve = Exp w. slope  17 k/s
Time between pellets

18. Time between pellets --- pellet velocity spread (2)
At the ion beam region the distribution is stochastic even for a relative velocity spread of 1 ‰ !!!
Gauss upper and Exp lower curve
Time between pellets
sv/v=0.1%
sv/v=0.2%
sv/v=0.5% 2. 4. 3.
MC simulation 4. 3. 2.
MC shows that for a pellet rate of 10 k/s and velocity of 60 m/s there is a pellet in the region of a F=4mm ion beam only 50% of the time and that there is exactly one pellet 36% of the time … (in good agreement with expectations from the Poisson distribution).

19. Time between pellets --- pellets in the ion beam (1)
For 10k/s & sv /v = 1% :
50% of the time
70 % of the time
0.7 pellets
1.4 pellets
How often are there pellets in the ion beam ? How often are there exactly one pellet candidate in “(hadronic) events” ?
What is the average number of pellets in the ion beam ? What is the average number of pellet candidates in “(hadronic) events” ?

20. Time between pellets --- pellets in ion beam (2)
Number of pellets in ion beam vs time (during 5 ms) for different pellet generation frequencies (5-20 k/s):
MC results for pellet v=60 m/s, sv /v=1% and ion beam F=4mm.
= average over time = average in “events”
0.34
1.41
1.80
0.73
1.04
1.16
1.37
1.54
f = 5 k/s
f = 20 k/s
f = 15 k/s
f = 10 k/s

21. Time between pellets --- pellets in ion beam (3)
Number of pellets in ion beam vs time (during 5 ms) for different pellet generation frequencies (10 & 20 k/s) and sv /v (0.1 & 1%):
MC results for pellet v=60 m/s and ion beam F=4mm.
= average over time = average in “events”
0.71
1.41
1.80
0.73
1.43
1.23
1.37
1.68
f = 10 k/s sv /v=0.1%
f = 20 k/s sv /v=1%
f = 20 k/s sv /v=0.1%
f = 10 k/s sv /v=1%

22. Time between pellets --- pellets in ion beam (4)
Number of pellets in “ion beam” ( ms interval) vs time (during 5 ms) for a pellet rate around 15 k/s:
MC result with pellet rate=15k/s, pellet velocity v=60 m/s, sv /v=1% and ion beam F=4mm.
UPTS measurement result with a pellet rate ≈ 17 k/s … .. seen by the LS-cameras.
1.04
1.54
MC f = 15 k/s
UPTS data
Time [20ms]

23. Synchronized LS cameras at two levels
UPTS April/May 2010
Droplet chamber
VIC exit
Laser
Camera Up
Synchronized LS cameras at two levels
Distance ≈ 30cm
Laser
Camera Lo

24. Pellet velocity estimate at UPTS May 2010
Steering of the pellet stream close to the VIC wall introduced a disturbance that broadened the angular distribution. In this distribution one can make cuts ….
Synchronized LS cameras at two levels
Laser
Camera Up
At VIC exit
Distance ≈ 30 cm
Laser
Camera Lo
30 cm below
Measured pellet position (z)
… which is helpful in studies of pellet signal correlations … (in particular when the total pellet rate is high)

25. … that can be used to get a hook on pellet velocity distributions …
Pellet velocity estimate at UPTS May 2010
… that can be used to get a hook on pellet velocity distributions …
Pellet generation conditions fdroplet ≈ 50kHz p(H2) ≈ 400mbar, p(droplet.ch.) ≈ 25mbar droplet velocity 25 m/s pellet diameter micron (guess )
DT (lower-upper) for all combinations of pellet time signals
MC simulation
Time difference
Time difference
A big fraction of the pellets have a velocity v ≈ 80 m/s
with velocity spread sv /v ≈ 1%.
60m/s Velocity m/s

26. Time resolution, efficiency & measurement dead time
With two specially designed cameras (having 3 ms period time), measuring the same coordinate at the same y-level and synchronized with their cycles shifted half a period time one would have a time bin of ms i.e. s ≈ 0.25 ms which is in the region of the final goal for PANDA.
With such an arrangement one would also get rid of inefficiencies due to the camera cycle dead times.
With the present camera performance of 14 ms period and 10 ms exposure time one would get s ≈ 1.5 ms which could give an interaction position vertical (y) coordinate s ≈ 1.5 mm i.e. what could be useful for WASA …. A
Laser(s)
Cameras B
Camera A
Camera B
1 cycle = 3 µs
0.5 µs
1 µs
exp 1
exp 2
… strong / many enough to give full detection possibility.

27. System design simulations
At PANDA & WASA two sections of the target pipe, one at the gene- rator and one at the dump are planned for tracking equipment.
The length of the sections are 40 cm (Panda) and 27 cm (Wasa). Simulations are used to determine the optimal use and they are also needed in the development of tracking algorithms. By the simulations one should also be able to investigate the following questions:
- What is the number of pellets in the interacting region at a certain time ? How good information can one get from the tracking system on this ?
- What are the effectiveness in tracking and the quality of the tracking information (on event by event basis) ?
- How accurate is the reconstruction of the interaction position ? The measurement accuracy and efficiency, the alignment of the system and the performance of the tracking algorithm are important factors.
PTR section – Interaction region ≈ 2 meters

28. Pellet tracking Step-by-Step
A: Determine mean velocity (v0) & spread in the pellet stream
B.1: Determine “roughly” time, position, direction and velocity of a pellet candidate using v0.
At the 1st levels in the upper tracking section.
B.2: Extrapolate pellet track to the other measurement positions and pick up matching information. Improve velocity determination.
It takes ≈100 ms for a pellet to pass all measurement points.
B.3: Use all info (including geometrical constraints like point of exit from the VIC) to reconstruct the final track Determine the time and path for passage through the interaction region.
It takes ≈100 ms for a pellet to pass the interaction region.
B.4: Store info for all pellets, sorted by the time of passage through the interaction region Put a time stamp from the experiment clock used for interaction events.
A common time scale is needed for matching with the experiment DAQ.
C: For each interaction event, process (offline) the pellet info stored and check pellet candidates responsible for the interaction and if possible make use of the position information.

29. Tracking step B.1:
Initial determination of velocity for the individual pellets
Efficiency (%)
The measurements at the 1st levels are crucial … … for catching a pellet and determine its velocity correctly.
For a pellet rate of 10k/s an “efficiency” > 90% is obtained for a velocity spread of 1% and a distance of 50 mm between the measurement points.
For 100 mm distance the efficiency has dropped to 85%.
Pellet rate (k/s)
Pellet rate (k/s)

30. UPTS tracking chamber in preparation
Will be placed below a skimmer.
For operation with 2-4 cameras + with check possibilities using the existing upper levels at the pellet generator …..
Two levels for LS-camera measurements separated by 80 mm.
Masih Noor, CAI (Center for Accelerator and Instrument Development), Uppsala University
UPTS bottom floor (with the old PANDA vacuum test structure)

31. Design idea: PANDA upper pellet tracking section
Four levels for LS-camera measurements - Distance for velocity determination 60 – 260 mm.
- Distance for direction determination 200 mm (…internally… one can use VIC exit also).
Total height 400 mm. Space requirement radially: rmax = 500 mm.
Camera
Laser
Level for additional monitoring (alignment)
Masih Noor, CAI (Center for Accelerator and Instrument Development), Uppsala University

32. Multi camera readout and synchronization
Adapter cards (1 per camera)
Camera links 120 Mbytes/s each
Optical links 2 Gbytes/s for 16 links
Convert data to optical links
Synchronize all cameras
16 optical receivers 1.6 Gbits/s 64 Mbyte of DDR ram 8 Mbyte of Flash rom USB, Ethernet VME-64x or LVD –bus readout Pellet identification and storage with time stamp
Experiment triggers stored with timestamp
Experiment trigger
Timestamp to DAQ
A few Mbyte/s output data rate for 16 cameras
Up to 16 cameras
Virtex5-FXT data processing board

33. Pellet target mode for tracking
A pellet position accuracy in the interaction region of s(x), s(z) = 0.15 mm and s (y) ≤ 1.5 mm* should be obtained from the optical pellet tracking system.
There should be a high (> 50% **) probability to have exactly one pellet in the accelerator beam region at the same time and there should be useful tracking information available for > 75% of the interaction events. This puts a lower limit on the average distance between pellets and on the acc. beam vertical diameter and an upper limit on the acceptable velocity spread.
- The pellet size must be big enough to have efficient pellet detection. Here only pellets of hydrogen are considered. Since pellets of other elements have different optical properties and must have half size for the same target thickness it is not clear how well they can be detected. _____________________________________________________________________ (+) Pellet diameter ≥ 20 mm *** (+) Pellet frequency ≤ 10k plt/s Average pellet velocity ≈ 60 m/s (+) Total spread in pellet relative velocity ≤ +/- 5 % **** (+) Average distance between pellets ≥ 4 mm Effective target thickness ≤ 1.5 × 1015 at./cm Pellet stream diameter ≈ 3 mm (+) Accelerator beam vertical diameter ≥ 3.5 mm (s ≥ 1 mm) (+) Average number of pellets in acc. beam ≈ 0.7 _____________________________________________________________________ *) With a dedicated (specially designed) CCD chip also a s (y) around 0.15 mm can be reached. **) Design value. Could be increased by further development of pellet generation. ***) Might go to smaller pellet size if additional improvements in pellet detection will allow. ****) Present design goal.

34. Status and Conclusions June 2010
Camera performance basically understood ….
Synchronized operation with two cameras works !
Illumination/detection conditions good … but should be improved
Desired transverse (x,z) position resolution reachable with present cameras. Solution for good time ( y position) resolution and high camera efficiency exists
Clear indication that pellet velocity spread sv /v ≤ 1% can be obtained  Effective pellet tracking possible !!!
Preparation of a first prototype PTR system for UPTS in progress:
- Tracking chamber with two levels of pellet detection
LS-cameras with lasers - New readout system
Ready for design & preparation of tracking systems with more LS-cameras.
Preparing simulations for the design of a full scale system for PANDA

35. Plan for
Continuation of basic performance studies/optimizations at UPTS LS-camera cycle, synchronization, calibration Illumination conditions Alignment cameras – lasers Analysis procedures
Continuation of studies of pellet stream properties at UPTS Time and position distributions Correlation studies, velocity measurement procedures Analysis procedures
Continuation of simulation studies connected to basic LS-camera performance and to pellet stream properties.
Preparation of a first prototype PTR system at a section to be placed below the pellet stream collimator at UPTS for measurements of pellet target parameters dt, dx, dz Tracking chamber with two levels of pellet detection
- Camera synchronization system (with LED signal monitoring) Development of a multi-camera readout system prototype (i-face, FPGA)
Begin preparations for a simplified tracking system based on at least 4 LS-cameras (that could be tested at WASA).
Start simulations for the design of a full scale system (PANDA).

36. Outlook
Plan for :
Prepare a (2dim) tracking system based on at least 4 LS-cameras for WASA.
Full scale system for PANDA: Finish full performance simulations of possible tracking system configurations and algorithms using realistic pellet stream parameters Finish design of the full scale system (with up to 16 LS-cameras) including mechanics, detectors*, lasers, readout, software etc.
*) Try to find faster/dedicated CCD-chip/LS-camera for improved time resolution
Plan for :
Prepare full scale system for PANDA: System readout and synchronization hardware (interface, FPGA) Readout software (including FPGA firmware) LED signal monitoring system Systems for camera and laser alignment (h-w, s-w) Control and analysis software
- Prepare one, of two planned, tracking sections for PANDA and test it at UPTS.

37. Resources needed for the pellet tracking systems 2011-2014
(The costs given below are based on more or less rough estimates).
UPTS operation: present “total” Cost ≈ 22 k€/y (FP7, SRC grants)
PTR UPTS: camera system. Cost ≈ 21 k€ + design, tests etc (FFE, FP7, SRC grants/applications)
Equipment: additional std diagnostics 2.5k€, laser w holder 3k€, r/o system, adapters+opt.links 5k€, FPGA card 5k€, monitoring system 5k€
PTR for WASA/PANDA prototype: 6 camera system. Cost ≈ 65k€ + design, tests etc (FFE, SRC applications)
Equipment: tracking chamber 10k€, cameras w holders 30k€, lasers w holders 9€ r/o system, adapters+opt.links 6k€, FPGA card 5k€, monitoring system 5k€
PTR for PANDA 16 camera system. Cost ≈ 275k€ + design, tests etc (Equipm, FFE, FP7 applications)
Equipment: tracking chambers 2x15k€, cameras w holders 20x5.6k€, laser sw holders 20x3k€, synch. LED system 10k€, alignm.system 5k€ r/o system, adapters+opt.links 11k€, FPGA card 5k€, monitoring system 12k€
Misc: system tests at upts 20k€, transport+installation 10k€ el.nics design & tests 2 my, mechanics design 0.5 my.
______________________________________________________________________________________________
Applications
SRC operation UPTS, PTR UPTS, PTR WASA
JCHP-FFE researcher PTR WASA, PTR PANDA
FP7 HP operation UPTS, PTR UPTS, PTR WASA, PTR PANDA (pers., consum., travel)