1. The ALICE TPC C. Garabatos, GSI
Description, tasks
A challenging design
optimise the drift gas
Construction
Readout chambers
Field Cage
Electronics
Cooling
Laser system
Outlook

2. C. Garabatos, GSI Darmstadt
TPC
|| < 0.9 (full length tracks)
845 < r < 2466 mm
2 ´ 2500 mm drift
88 m3
readout pads
Vienna 2004
C. Garabatos, GSI Darmstadt

3. C. Garabatos, GSI Darmstadt
Layout
Inner and Outer
Containment Vessels
(150 mm, CO2)
Central electrode
100 kV
Suspended field
defining strips
400 V/cm
Endplates housing
2 ´ 2 ´ 18 chambers
Vienna 2004
C. Garabatos, GSI Darmstadt

4. Challenging requirements for the gas
High
Multiplicities
High Rate
(200 Hz)
Momentum
Resolution
dE/dx
Resolution
Occupancy
2 track res.
Field
Distortions
Drift speed
(max. HV)
Multiple
Scattering
Signal/
Noise
Argon
CO2
Hydrocarbons
Neon
CF4
Small pads:
4 ´ 7.5 mm2
Neutrons
Ageing
Flammability ?
???
Gain:
2 ´ 104
Concentration:
90-10
Vienna 2004
C. Garabatos, GSI Darmstadt

5. Characteristics of the gas Ne-CO2 [90-10]
Non saturated drift velocity (as with Ar):
strong dependence of Vd on everything
Very 'sensitive' Townsend coefficients:
strong dependence of Gain on everything
(Everything: T, P, E, composition, purity, ...)
Poor stability: tendency to undergo self-sustained glow discharges due to minor imperfections in chamber construction
Is there any other quencher out there?
Vienna 2004
C. Garabatos, GSI Darmstadt

6. C. Garabatos, GSI Darmstadt
Yes: add Nitrogen
5% lower drift velocity or ~5% higher drift field
Vienna 2004
C. Garabatos, GSI Darmstadt

7. Drift velocity changes of no N2 vs. N2
Ne-CO2-N2
Temperature
+0.37 % / K
+0.34 % / K
Pressure
-0.15 % / mbar
CO2 concentration
-7.6 % / %CO2
-6.4 % / %CO2
N2 contamination
-1 % / %N2
... and same diffusion coefficients, same electron absorption.
Vienna 2004
C. Garabatos, GSI Darmstadt

8. C. Garabatos, GSI Darmstadt
Gain changes of N2 vs. no N2
90-10
Temperature
+0.9 % / K
? % / K
Pressure
-0.34 % / mbar
? % / mbar
CO2 concentration
+67, -20 % / %CO2
+17, -14 % / %CO2
N2 contamination
+34 % / %N2
+6.3 % / %N2
Vienna 2004
C. Garabatos, GSI Darmstadt

9. N2 vs. no N2: Stability Instantaneous maximum gain
Operating
gain
Vienna 2004
C. Garabatos, GSI Darmstadt

10. C. Garabatos, GSI Darmstadt
Why N2 helps with Neon: quenching (by ionisation) of Neon excited states in the avalanche
Vienna 2004
C. Garabatos, GSI Darmstadt

11. C. Garabatos, GSI Darmstadt
Chamber gain
PCmonte simulations (S. Biagi) with Penning transfer, and measurements
Vienna 2004
C. Garabatos, GSI Darmstadt

12. Readout Chamber Production
About 2/3 of the –not that conventional– wire chambers assembled and thoroughly tested
Material ageing tests
End of production/testing: Spring 2004
Vienna 2004
C. Garabatos, GSI Darmstadt

13. The Field Cage vessels with field-shaping strips
Macrolon rods
to support the strips
(à la NA49)
to supply the HV
and degrade it along
to distribute the gas
(radially in/out)
to distribute laser tracks
(à la STAR)
Suspended Al-mylar strips
Stretched Al-mylar central
electrode
Endplates to hold ROCs
Mechanical precision:
~200 mm
Ready for gas and volts: summer 2004
Vienna 2004
C. Garabatos, GSI Darmstadt

14. FEC (Front End Card) - 128 CHANNELS (CLOSE TO THE READOUT PLANE)
Front-end Electronics: Architecture
anode
wire
pad
plane
drift region
88ms
L1: 5ms
200 Hz
DETECTOR
570132
PADS
gating grid
cathodes
PASA
ADC
Digital
Circuit
(ALTRO)
RAM
8 CHIPS x
16 CH / CHIP
CUSTOM IC
(CMOS 0.35mm)
CUSTOM IC (CMOS 0.25mm )
FEC (Front End Card) CHANNELS
(CLOSE TO THE READOUT PLANE)
L2: < 100 ms
200 Hz
DDL
(4096 CH / DDL)
Power
consumption:
< 40 mW / channel
CSA
SEMI-GAUSS. SHAPER
1 MIP = 4.8 fC
S/N = 30 : 1
DYNAMIC = 30 MIP
BASELINE CORR.
TAIL CANCELL.
ZERO SUPPR.
10 BIT
< 10 MHz
MULTI-EVENT
MEMORY
GAIN = 12 mV / fC
FWHM = 190 ns
Vienna 2004
C. Garabatos, GSI Darmstadt

15. ALTRO: digital tail cancellation and baseline restoration
Cosmic ray event
in prototype FC
Vienna 2004
C. Garabatos, GSI Darmstadt

16. Electronics production status
PASA chips (18000 produced), end of production: March 04
ALTRO (digital chip): chips produced by March 04
FEC 4800 boards (50 produced). Production finished Oct. 04.
Automatic (robot) tests running: 1200 chips/day
Vienna 2004
C. Garabatos, GSI Darmstadt

17. Cooling: Temperature Stabilization and Homogeneity
Very challenging: we aim at T  0.1 K in the whole volume
Thermal screens towards TRD (outer) and ITS (inner)
Water-cooling of Readout Chamber Al bodies and pad planes
Water cooling of FEE boards (total power 27 kW)
All leakless (P < Patm) cooling systems
>400 temperature probes
HV resistor rod: 4 x 8 W
water-cooled
removable
electrolysis, corrosion
... all under control
Vienna 2004
C. Garabatos, GSI Darmstadt

18. C. Garabatos, GSI Darmstadt
Laser System
Rays perpendicular
to beam axis
Effective ray  ~1mm
2 x 4 z-planes
Strategic boundary crossings
Additional signal from central electrode
Vienna 2004
C. Garabatos, GSI Darmstadt

19. Performance simulations
> 97 % dN/dy = 8000
Magnetic field 0.5 T
dp/p (100 GeV) vs dN/dy:
16%  9% at dN/dy=2000
dp/p
dE/dx resolution:
5.3 – 6.8 % depending on multiplicity
Vienna 2004
C. Garabatos, GSI Darmstadt

20. Space resolution from cosmic ray data
PRELIMINARY
Resolution in bend direction
Resolution in drift direction
Vienna 2004
C. Garabatos, GSI Darmstadt

21. C. Garabatos, GSI Darmstadt
Summary
A challenging, large TPC is thoroughly being constructed for ALICE
High multiplicities, high occupancy, high gain à Optimised gas:
Ne-CO2-N2 [ ]
(If you can't beat her, join her)
Outlook:
Dec Aug. 05: Full TPC assembly in surface
2006: TPC Installation underground
2007 START OF LHC
Vienna 2004
C. Garabatos, GSI Darmstadt

22. ALICE TPC Collaborators
T. Alt, Y. Andres, T. Anticic, D. Antonczyk, H. Appelshäuser, J. Bächler, J. Bartke, J. Belikov, N. Bialas, U. Bonnes, R. Bramm, P. Braun-Munzinger, R. Campagnolo, P. Christakoglou, E. Connor, H. Daues, C. Engster, Y. Foka, F. Formenti, A. Förster, U. Frankenfeld, J.J. Gaardhøje, C. Garabatos, P. Glässel, C. Gregory, H.A. Gustafsson, J. Hehner, H. Helstrup, M. Hoch, M. Ivanov, R. Janik, K. Kadija, R. Keidel, W. Klempt, E. Kornaś, M. Kowalski, S. Lang, J. Lien, V. Lindenstruth, C. Loizides, L. Lucan, P. Malzacher, T. Meyer, D. Miskowiec, B. Mota, L. Musa, B.S. Nielsen, H. Oeschler, A. Oskarsson, L. Osterman, A. Petridis, M. Pikna, S. Popescu, S. Radomski, R. Renfordt, J.P. Revol, D. Röhrich, G. Rüschmann, K. Safarik, A. Sandoval, H.R. Schmidt, K.E. Schwarz, B. Sitar, H.K. Soltveit, J. Stachel, T.M. Steinbeck, H. Stelzer, E. Stenlund, R. Stock, P. Strmen, T. Susa, I. Szarka, H. Tilsner, G. Tsiledakis, K. Ullaland, M. Vassiliou, A. Vestbo, D. Vranic, J. Westergaard, A. Wiebalck, B. Windelband
Vienna 2004
C. Garabatos, GSI Darmstadt

23. C. Garabatos, GSI Darmstadt
Additional slides
Vienna 2004
C. Garabatos, GSI Darmstadt

24. Absorption cross-section of quenchers
Vienna 2004
C. Garabatos, GSI Darmstadt

25. C. Garabatos, GSI Darmstadt
Unprecedented gain?
Vienna 2004
C. Garabatos, GSI Darmstadt

26. TPC test facility measurements
rms noise statistics, mean 700 e
Cosmics tracks
pad #
time bin
time bin
Vienna 2004
C. Garabatos, GSI Darmstadt

27. Field Cage: Central Electrode
6m wide mylar foil, glued from 3 sheets
Vienna 2004
C. Garabatos, GSI Darmstadt

28. ALICE TPC READOUT CHIP – Principle
10- bit
20 MSPS
11- bit CA2
arithmetic
18- bit CA2
arithmetic
11- bit
arithmetic
10-bit
arithmetic
40-bit
format
40-bit
format
SAMPLING CLOCK up to 20 MHz (5.7 MHz used)
READOUT CLOCK 40 MHz
16 ADCs and Digital Filter channels in one chip
Algorithms and parameters reconfigurable
Vienna 2004
C. Garabatos, GSI Darmstadt

29. Field Cage Outer Containment Vessel
Vienna 2004
C. Garabatos, GSI Darmstadt

30. Readout Chamber Wire Geometry
gate wires
cathodes
anodes
pads
Vienna 2004
C. Garabatos, GSI Darmstadt

31. C. Garabatos, GSI Darmstadt
Pad Plane
optimized pad sizes
4 x 7.5 mm
6 x 10 mm
6 x 15 mm
segmented: IROC and OROC
total pads
Vienna 2004
C. Garabatos, GSI Darmstadt

32. Outer chamber test status
Vienna 2004
C. Garabatos, GSI Darmstadt

33. C. Garabatos, GSI Darmstadt
Tightness
Vienna 2004
C. Garabatos, GSI Darmstadt

34. C. Garabatos, GSI Darmstadt
Gain curve
Vienna 2004
C. Garabatos, GSI Darmstadt

35. C. Garabatos, GSI Darmstadt
Gain uniformity test
Vienna 2004
C. Garabatos, GSI Darmstadt

36. C. Garabatos, GSI Darmstadt
Long-term test
Vienna 2004
C. Garabatos, GSI Darmstadt

37. C. Garabatos, GSI Darmstadt
Ageing tests
Tested many assembly materials:
Glues:
Araldit 2012, 2013, dp190, 116
Tedlar foil
Vacuum grease
Lithelen
Apiezon
Stesalit-like insulator
Vienna 2004
C. Garabatos, GSI Darmstadt

38. Rate of ageing in ALICE with P10
Vienna 2004
C. Garabatos, GSI Darmstadt

39. Ageing predictions with P10
Vienna 2004
C. Garabatos, GSI Darmstadt

40. Challenging requirements
High multiplicities (dN/dy = 8000 originally)
High occupancy ð Small pads (down to 4 ´ 7.5 mm2)
E (and E ´ B) distortions in drift volume ð No Argon
Momentum resolution goal dp/p  1%
low multiple scattering gas ð No Argon
Event rate (up to 200 Hz)
100 ms max. drift time but 100 kV max ð Not much quencher allowed
Good particle ID through dE/dx
signal/noise, uniformity ð High enough gain
Vienna 2004
C. Garabatos, GSI Darmstadt

41. C. Garabatos, GSI Darmstadt
The gas: what is left
Noble gas cannot be Argon
Positive ions too slow, Multiple scattering
Noble gas must be Neon
Quencher cannot be a hydrocarbon
Flammability, Ageing, Slow proton production
Quencher cannot be CF4 (not well understood)
Quencher must be CO2
Composition not different from [90-10] (Vd=2.8 cm/ms)
Low primary ionisation + small pads:
Unprecedented high gain: 2 ´ 104 (for TPCs)
Vienna 2004
C. Garabatos, GSI Darmstadt

42. Front End Card connection and cooling
FEC in cooled
Cu sandwich
Flexible cables
to PASA input
Extra structure
(Service Support Wheel)
to hold weight of electronics
Vienna 2004
C. Garabatos, GSI Darmstadt

43. FEE Components Assembly
Readout and Control
Backplane
(300 MB /sec)
25 Front End Cards
Power Connector
PASA
Readout Partition (3200 channels)
ALTRO
Vienna 2004
C. Garabatos, GSI Darmstadt