the aleph time projection chamber
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17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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The Aleph Time Projection Chamber
The Aleph Time Projection Chamber
Ron Settles, MPI-Munich/DESY
TPC Symposium@LBNL17 October 2003
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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SummarySummary
TPC is a 3-D imaging chamber– Large volume, small amount of material.– Slow device (~50 s)
– 3-D ‘continuous’ tracking (xy 170 m, z 600 m for Aleph)
Review some of the main ingredients History
– First proposed in 1976 (PEP4-TPC)– Used in many experiments– Aleph as an example here– Now a well-established detection technique that is still in the
process of evolution…
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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OutlineOutline
Examples TPC principles of operation
– Drift velocity, Coordinates, dE/dx TPC hardware ingredients
– Field cage, gas system, wire chambers, gating, laser calibration system, electronics
The Aleph TPC From the drawing board to the gadget Performance Some ‘features’ (i.e. trouble shooting…) Conclusion
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Some TPC examplesSome TPC examples
TPC ReferencePEP4 PEP-PROPOSAL-004, Dec 1976TOPAZ Nucl. Instr. and Meth. A252 (1986) 423ALEPH Nucl. Instr. and Meth. A294 (1990) 121DELPHI Nucl. Instr. and Meth. A323 (1992) 209-212NA49 Nucl. Instr. and Meth. A430 (1999) 210STAR IEEE Trans. on Nucl. Sci. Vol. 44, No. 3 (1997)
Grand-daddy/mama of all TPCsSTAR FTPC, ALICE, LC, …
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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TPC principles of operationTPC principles of operation
A TPC contains:– Gas
E.g.: Ar + 10-20 % CH4
– E-fieldE ~ few x 100 V/cm
– B-fieldas large as possible to measure momentum,to limit electron diffusion
– Wire chamber (those days)to detect projected tracks
y
z
x
E
B electron drift
chargedtrack
wire chamber to detect projected tracks
gas volume with E & B fields
Now trying out new techniques--►
•
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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TPC Characteristics
– Only gas in active volume,small amount of material
– Long drift ( > 2 m ) therefore slow detector (~50 s)want no impurities in gasuniform E-fieldstrong & uniform B-field
– Track points recorded in 3-D(x, y, z)
– Particle Identification by dE/dx
– Large track densities possible
y
z
x
E
B drift
chargedtrack
0BE
•
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Drift velocity
22
2
)()()(
)(1 B
BBE
B
BEEvd
Drift of electrons in E- and B-fields (Langevin) mean drift time between collisions
me particle mobility
mceB cyclotron
frequency1)( Vd along E-field lines
1)( Vd along B-field lines
Typically ~5 cm/s for gases like Ar(90%) + CH4(10%)
Electrons tend to follow the magnetic field lines () >> 1
•
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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3-D coordinates
z
x
y
wire plane
track
projected track
– Z coordinate from drift time– X coordinate from wire number– Y coordinate?
» along wire direction» need cathode pads •
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Coordinate from cathode Pads
projected track
pads
drifting electrons
avalanche
y
x
y
z
– Measure Ai
– Invert equation to get y
)222)(( prwi
iyyAeA
Amplitude on ith pad
y avalanche position
iy position of center of ith pad
prw pad response width •
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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TPC Coordinates: Pad Response Width
Normalized PRW:
2
2
2ˆ
prw
Distance between pads
is a function of: •– the pad crossing angle
» spread in r
– the wire crossing angle » ExB effect, lorentz angle
– the drift distance» diffusion
2̂
22 tan~ˆ
cos)tan(tan~ˆ 22
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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TPC coordinate resolution
Same effects as for PRW are expected but statistics of • drifting electrons must be considered
zz
z
D
r
)(
cos)tan(tan
tan
),,(
2
222
22
2
0
2
electronics, calibration
angular pad effect (dominant for small momentum tracks)
angular wire effect
forward tracks -> longer pulses -> degrades resolution
)_(22 angledipzZ
“diffusion” term
(…disappears with new technologies…)
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Particle Identification by dE/dx
– Energy loss (dE/dx) depends on the particle velocity.
– The mass of the particle can be identified by measuring simultaneously momentum and dE/dx (ion pairs produced)
– Particle identification possible in the non-relativistic region (large ionization differences)
– Major problem is the large Landau fluctuations on a single dE/dx sample.
» 60% for 4 cm track» 120% for 4 mm track
2)1(
2ln
1 22
2
22
J
mv
A
ZKz
dx
dE
Energy loss (Bethe-Bloch)
m mass of electron
vz, charge and velocity of incident particle
J mean ionization energy density effect term
•
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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TPC ingredients (Aleph example)TPC ingredients (Aleph example)
Wire chambers – Gating– Cooling– Mechanics
Field cage Gas system Laser system Electronics
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Wire Chambers
3 planes of wires •– gating grid– cathode plane (Frisch
grid)– sense and field wire
plane
– cathode and field wires at zero potential
pad size– various sizes & densities– typically few cm2
gas gain– typically 3-5x103
pad plane
field wire
sense wire
gating grid
Drift region
cathode plane
V=0
x
z
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Wire Chambers: ALEPH
36 sectors, 3 types •– no gaps extend full radius
wires– gating spaced 2 mm – cathode spaced 1 mm – sense & field spaced 2 mm, interleaved
pads– 6.2 mm x 30 mm– ~1200 per sector– total 41004 pads
readoutpads and wires •
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Gating
Problem: Build-up of space charge in the drift region by ions.
– Grid of wires to prevent positive ions from entering the drift region
“Gating grid” is either in the open or closed state
– Dipole fields render the gate opaque •
Operating modes:– Switching mode (Aleph)– Diode mode
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Cooling, Mechanics
Terribly mundane but terribly important (everything is important)
Cooling:– Combined air and water cooling to completely
insulate the gas volume Mechanics:
– 25% X_0 for sectors, preamps, cooling (but before cables)
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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E-field produced by a Field Cage
HV
Ewires at ground potential
planar HV electrode
potential strips encircle gas volume
– chain of precision resistors with small current flowing provides uniform voltage drop in z direction
– non uniformity due to finite spacing of strips falls exponentially into active volume
z
y
•
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Field cage: ALEPH example
Dimensionscylinder 4.7 x 1.8 m
Drift length2x2.2 m
Electric field110 V/cm
E-field toleranceV < 6V
Electrodescopper strips (35 m & 19 m thickness, 10.1 mm pitch, 1.5 mm gap) on Kapton
Insulatorwound Mylar foil (75m)
Resistor chains2.004 M (0.2%)
Nucl. Instr. and Meth. A294 (1990) 121
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Laser Calibration System
PurposeMeasurement of drift velocity Determination of E- and B-field distortions
Drift velocity Laser system ∂(v_drift) ~ 1‰
Hookup tracks to Vdet ∂(v_drift)~a few times 0.01‰ …used after Vdet installation
ExB Distortions Laser used only in early days to get firstcorrections. After, tracks (mostly μ pairs from Z decays) used exclusively (read on…)
Laser tracks in the ALEPH TPC
•
•
•
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Gas system
Properties:Drift velocity (~5cm/s)Gas amplification (~7000)Signal attenuation my electron attachment (<1%/m)
Parameters to control and monitor:Mixture quality (change in amplification)O2 (electron attachment, attenuation)
H2O (change in drift velocity, attenuation)
Other contaminants (attenuation)
Typical mixtures: Ar91%+CH49%, Ar90%+CH45%+CO25%
Operation at atmospheric pressure
•
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Influence of Gas Parameters (*)
Parameterchange
Drif t velocity, vd Eff ect on gasamplifi cation, A
Signal ettenuation byelectron attachment
0.1% CH4 0.4 % -2.5% f or A = 1x104
10 ppm O2 Negligible up to 100 ppm Negligible up to 100 ppm 0.15%/ m of drif t
10 ppm H2O 0.5 % Negligible at 100 ppm < 0.03% / m of drif t
1 mbar Negligible if at max. -(0.5%-0.7%)
(*) from ALEPH handbook (1995)
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Electronics: from pad to storageTPC pad
amp
FADC
zerosuppression
featureextraction
DAQ
Pre-amplifiercharge sensitive, mounted on wire chamber
Shaping amplifier:pole/zero compensation. Typical FWHM ~200ns
Flash ADC:8-9 bit resolution. 10 MHz. 512 time buckets
Multi-event buffer
Digital data processing: zero-suppression.
Pulse charge and time estimates
Data acquisition and recording system
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Analog Electronics
ALEPH analog electronics chain
–Large number of channels O(105)–Large channel densities–Integration in wire chamber–Power dissipation–Low noise
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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More details about Aleph…More details about Aleph…
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Wire Chambers: ALEPH
Long pads for better coordinate precision
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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After 3 man-centuries(or more, depending on how you
count)…
From TPC90…↑
…as usual, lots of meetings…↓
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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From the drawing board to the gadget…
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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A Detector with TPC
you end up with-----------►
…where…
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Thanks to many people… (and to Pere Mato and Werner Wiedenmann for help on these slides)
…you need a few cables, cooling, etc…
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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It finally started working…
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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ALEPH Event, early days…
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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And towards the end…
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Coordinate Resolution(1): ALEPH TPC
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Coordinate Resolution(2): ALEPH TPC
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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dE/dx: Results
Good dE/dx resolution requires
long track lengthlarge number of samples/trackgood calibration, no noise, ...
ALEPH resolutionup to 334 wire samples/tracktruncated (60%) mean of samples4.5% (330 samples)
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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But, there were ‘FEATURES’…
Werner’s talk contains many details, see alephwww.mppmu.mpg.de/~settles/tpc • here a few examples…
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Historical Development (1)
LEP start-up: 1989-1990– Failure of magnet compensating power supplies in 1989 required
development of field-corrections methods» derived from 2 special laser runs (B on/off)» correction methods described in NIM A306(1991)446
– Later, high statistics Z->μμ events give main calibration sample LEP 1: 1991-1994
– VDET 1 becomes operational in 1991– Development of common alignment procedures for all three tracking
detectors– Incidents affect large portions of collected statistics and require
correction methods based directly on data» 1991-1993, seven shorts on field cage affect 24% of data» 1994, disconnected gating grids on 2 sectors affect 20% of data
– All data finally recuperated with data-based correction methods
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Historical Development (2)
LEP 1/2: 1994-1996– Tracking-upgrade program (LEP 1 data reprocessed)
» Improved coordinate determination requires better understanding of systematic effects
» Combined calculations for field and alignment distortions, reevaluation of B-field map
– All methods for distortion corrections now based directly on data– Development of “few”-parameter correction models to cope with
drastically reduced calibration samples at LEP 2 LEP 2: 1995-2000
– New VDET with larger acceptance– Calibrations@Z at beginning of run periods have limited statistics– Frequent beam losses cause charge-up effects and new FC shorts
» Superimposed distortions» Short-corrections with Z -> μμ;time-dep. effects tracked with
hadrons
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Examples from Werner’s slides…
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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e.g. (see Werner’s slides…)
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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e.g., non-linear F.C. potential
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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e.g., disconnected gating grids
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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e.g., field-cage shorts
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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(N.B., design your detector to be easily accessible…)
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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σ ~ 0.54E-03
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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the bottom line (e.g., momentum resolution)
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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ConclusionConclusion
We’d better learn from these past lessons so that the new TPC will evolve to a much better main tracker for the future LC its performance will then improve by an order of magnitude relative to that at Lep…
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Extra slides on LCTPC
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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GoalTo design and build an ultra-high performance
Time Projection Chamber
…as central tracker for the LC detector …where excellent vertex, momentum and jet energy precision are wanted…
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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LDCLDC
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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GLDGLD
TPC
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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The basic idea…
Cost-effective way of instrumenting a large volume With continuous tracking and a minimum of material Want the largest possible granularity -- i.e. ~ 2 .109 voxels -- the best possible σpoint resolution -- the best possible 2-track resolution
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Why…
High granularity to ensure robust operation in presence of large backgrounds
Continuous tracking to ensure good momentum-measuring precision and >98% pattern-recognition eff. in jets
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Size: Effective volume = 4.1 m (diameter) × 4.6 m (full length)
Spatial resolution
r -φ : 100 – 200 μ m z: ≲ 1 mm
Two-track resolving power
r -φ : ≲ 2 mm z: ≲ 10 mm
Number of coordinate samples per track: ∼ 250
Momentum resolution (TPC alone)
δ Pt / Pt ∼ 10⁻⁴ Pt [GeV/c] for high momentum tracks
Particle identification capability: dE/dx ∼ 4%
ILC-TPCA Large, High precision, High 3-D granularity Time Projection Chamber operated under a high magnetic field of 3 – 4 T
Unprecedented requirements to TPC especially for granularity
→ use of micro pattern gas detector (MPGD) as a readout device
performance tests using prototypes
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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LCTPC/LP Groups (16 August 06) Americas
CarletonMontreal VictoriaCornellIndianaLBNLMIT
PurdueYale
EuropeEuropeLAL OrsayLAL Orsay IPN OrsayIPN Orsay
SaclaySaclayAachenAachenBonnBonnDESYDESY
UHamburgUHamburgFreiburgFreiburgKarlsruheKarlsruhe
MPI-MunichMPI-MunichRostockRostockSiegenSiegenNIKHEFNIKHEF
UMM KrakowUMM KrakowBucharestBucharest
NovosibirskNovosibirskPNPI StPetersburgPNPI StPetersburg
LundLundCERNCERN
AsiaAsiaTsinghuaTsinghua
CDC:CDC:HiroshimaHiroshima
KEKKEKKinki UKinki USagaSaga
KogakuinKogakuinTokyo UA&TTokyo UA&T
U TokyoU TokyoU TsukubaU Tsukuba
Minadano SU-IITMinadano SU-IIT
…Other groups interested?
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Examples of Prototype TPCs
Carleton, Aachen, Cornell/Purdue,Desy(n.s.) for B=0or1T studies
Saclay, Victoria, Desy (fit in 2-5T magnets)
Karlsruhe, MPI/Asia, Aachen built test TPCs for magnets (not shown), other groups built small special-study chambers
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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MPI-Munich prototype for Wires, Gem and Micromegas test in 5T at Desyand in 1T in beam at Kek
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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MWPCMWPC
Very
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Replace ‘sensor (wire) gitter’ previous slide by either GEM or Micromegas:Replace ‘sensor (wire) gitter’ previous slide by either GEM or Micromegas:
VeryGEM: Two copper perforated foils separated by an insulator
The multiplication takes place in the holes.
Usually used in 2 or 3 stages
Micromegas : a micromeshsustained by 50-100 m - high insulating pillars. The multiplication takes place between the anode and the meshOne stage
200 m
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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GEM and MicromegasGEM and Micromegas
S1/S2 ~ Eamplif / Edrift
S1
S2
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Due to the high value of wt and the low grid transparency, does it work in a magnetic field? -> Simulations in Aachen
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Prototype TPC
Field cage maximum drift length: 260 mm typical cathode H.V. : - 6 kV
Readout plane effective area: 100 mm×100 mm MWPC GEMs (3-stage) or MicroMEGAS
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Experimental setup
Beam: mostly 4 GeV/c pions (0.5-4 GeV/c hadrons & electrons) Magnet: super conducting solenoid
without return yoke (max field: 1.2 T)
TPC in JACCEE magnet
Beam
JECCEE inner diameter : 850 mm effective length: 1 m
KEK Beam Line
We have conducted a series of beam experiments at KEK PS.
17 October 2003 TPC Symposium@LBNL ALEPH TPC Ron Settles, MPI-Munich/DESY
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Readout scheme and Gas
ALEPH TPC Electronics : charge sensitive preamp. + shaper amp. (shaping time = 500 ns) + digitizer (time bucket = 80 nsec)
Readout Device Pads: 32 pads ×12 pad rows
Width (pitch)× Length (pitch)
Gas (1 atm.)
Drift field
MWPC
SW spacing 2 mm
SW - Pads 1 mm
2 (2.3) mm×6 (6.3) mm
TDR
[Ar- 4CH (5%)- 2CO (2%)]
220 V/cm
GEM (triple stage)
CERN Standard
transfer gaps 1.5 mm
induction gap 1.0 mm
1.17 (1.27) mm×6 (6.3) mm
staggered
TDR
220 V/cm
Ar – methane (5%)
100 V/cm
MicroMEGAS
50-μm mesh
50-μm gap
2 (2.3) mm×6 (6.3) mm
Ar - isobutane (5%)
220 V/cm
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