17 october 2003tpc symposium@lbnl aleph tpc ron settles, mpi-munich/desy1 the aleph time projection...

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


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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…


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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


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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, …


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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--►

•


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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

•


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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

•


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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 •


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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 •


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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


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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…)


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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

•


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TPC ingredients (Aleph example)TPC ingredients (Aleph example)

Wire chambers – Gating– Cooling– Mechanics

Field cage Gas system Laser system Electronics


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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


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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 •


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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


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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)


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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

•


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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


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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

•

•

•


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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

•


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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)


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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


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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


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More details about Aleph…More details about Aleph…


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Wire Chambers: ALEPH

Long pads for better coordinate precision


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After 3 man-centuries(or more, depending on how you

count)…

From TPC90…↑

…as usual, lots of meetings…↓


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From the drawing board to the gadget…


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A Detector with TPC

you end up with-----------►

…where…


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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…


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It finally started working…


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ALEPH Event, early days…


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And towards the end…


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Coordinate Resolution(1): ALEPH TPC


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Coordinate Resolution(2): ALEPH TPC


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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)


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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…


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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


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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


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Examples from Werner’s slides…


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44


45


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e.g. (see Werner’s slides…)


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e.g., non-linear F.C. potential


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e.g., disconnected gating grids


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e.g., field-cage shorts


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(N.B., design your detector to be easily accessible…)


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σ ~ 0.54E-03


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the bottom line (e.g., momentum resolution)


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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…


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Extra slides on LCTPC


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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…


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LDCLDC


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GLDGLD

TPC


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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


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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


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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


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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?


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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


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MPI-Munich prototype for Wires, Gem and Micromegas test in 5T at Desyand in 1T in beam at Kek


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MWPCMWPC

Very


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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


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GEM and MicromegasGEM and Micromegas

S1/S2 ~ Eamplif / Edrift

S1

S2


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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


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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


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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.


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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

17 october 2003tpc symposium@lbnl aleph tpc ron settles, mpi-munich/desy1 the aleph time projection...

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