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

The Aleph Time Projection Chamber

Ron Settles, MPI-Munich/DESY

TPC Symposium@LBNL17 October 2003

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…

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

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, …

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

B electron drift

chargedtrack

wire chamber to detect projected tracks

gas volume with E & B fields

Now trying out new techniques--►

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

B drift

chargedtrack

Drift velocity

)()()(

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

3-D coordinates

wire plane

projected track

– Z coordinate from drift time– X coordinate from wire number– Y coordinate?

» along wire direction» need cathode pads •

Coordinate from cathode Pads

projected track

drifting electrons

avalanche

– 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 •

TPC Coordinates: Pad Response Width

Normalized 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

22 tan~ˆ

cos)tan(tan~ˆ 22

TPC coordinate resolution

Same effects as for PRW are expected but statistics of • drifting electrons must be considered

cos)tan(tan

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…)

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

Energy loss (Bethe-Bloch)

m mass of electron

vz, charge and velocity of incident particle

J mean ionization energy density effect term

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

Wire chambers – Gating– Cooling– Mechanics

Field cage Gas system Laser system Electronics

Wire Chambers

3 planes of wires •– gating grid– cathode plane (Frisch

grid)– sense and field wire

– 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

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 •

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

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)

E-field produced by a Field Cage

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

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

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

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

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)

Electronics: from pad to storageTPC pad

zerosuppression

featureextraction

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

Analog Electronics

ALEPH analog electronics chain

–Large number of channels O(105)–Large channel densities–Integration in wire chamber–Power dissipation–Low noise

More details about Aleph…More details about Aleph…

Wire Chambers: ALEPH

Long pads for better coordinate precision

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

count)…

From TPC90…↑

…as usual, lots of meetings…↓

From the drawing board to the gadget…

A Detector with TPC

you end up with-----------►

…where…

Thanks to many people… (and to Pere Mato and Werner Wiedenmann for help on these slides)

…you need a few cables, cooling, etc…

It finally started working…

ALEPH Event, early days…

And towards the end…

Coordinate Resolution(1): ALEPH TPC

Coordinate Resolution(2): ALEPH TPC

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)

But, there were ‘FEATURES’…

Werner’s talk contains many details, see alephwww.mppmu.mpg.de/~settles/tpc • here a few examples…

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

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

Examples from Werner’s slides…

e.g. (see Werner’s slides…)

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

e.g., disconnected gating grids

e.g., field-cage shorts

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

σ ~ 0.54E-03

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

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…

Extra slides on LCTPC

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…

LDCLDC

GLDGLD

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

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

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

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?

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

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

MWPCMWPC

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

GEM and MicromegasGEM and Micromegas

S1/S2 ~ Eamplif / Edrift

Due to the high value of wt and the low grid transparency, does it work in a magnetic field? -> Simulations in Aachen

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

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

JECCEE inner diameter : 850 mm　 effective length: 1 m

KEK Beam Line

We have conducted a series of beam experiments at KEK PS.

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

SW spacing 2 mm

SW - Pads 1 mm

2 (2.3) mm×6 (6.3) mm

[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

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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