Micromegas TPC prototype results & Electronics Developments

Beijing, 5 February 2007

Micromegas TPC prototype results & Electronics Developments

Madhu DixitCarleton University & TRIUMF

On behalf of LC TPC collaboration

ILC tracking review - Beijing 5 February, 2007

Beijing, 5 February 2007 Madhu Dixit 2

•ILC tracker goal: r ≤ 100 m including stiff 90° 2 m drift tracks •Anode wire/cathode pad TPC resolution limited by ExB effects•Negligible ExB effects for Micro Pattern Gas Detectors (MPGD)•TESLA TPC TDR : 2 mm x 6 mm pads (1,500,000 channels) with GEMs or Micromegas •LC TPC R&D: 2 mm pads too wide with conventional readout

•For the GEM ~ 1 mm wide pads (~3,000,000 channels) •Even narrower pads would be needed for the Micromegas

•The new MPGD readout concept of charge dispersion can achieve good resolution with ~ 2 mm x 6 mm pads.•R&D summary - mainly on the Micromegas TPC readout option

Micro-Pattern Gas Detector development for the ILC TPC


Micromegas - a parallel plate gas avalanche detectorMicromesh supported by ~ 50 m pillars above anode


50 cm diameter Micromegas, 50 cm max. drift distance 1024 read out pads, Star TPC 20 MHz 10 bit digitizers

2 T superconducting magnet

Berkeley Orsay Saclay cosmic ray TPC tests

1 mm x 10 mm pads


4 Gev/c beam tests at KEK with standard readout

(2.3 mm x 6.3 mm pads)


MP TPC with Micromegas - standard readoutKEK PS 4 Gev/c hadron test beam (2.3 mm x 6.3 mm pads)

Resolution limited by pad width at high magnetic fields, worst at short drift distances


•Disperse track charge after gas gain to improve centroid determination with wide pads.•For the GEM, large transverse diffusion in the transfer & induction gaps provides a natural mechanism to disperse the charge.•No such mechanism for Micromegas•The GEM readout will still need ~ 1 mm wide pads to achieve ~ 100 m ILC resolution goal

Charge dispersion on a resistive anode - a mechanism to disperse the MPGD avalanche charge. It makes position sensing insensitive to pad width.The technique works for both the GEM and the Micromegas

Improving MPGD resolution without using narrower pads


•Modified MPGD anode with a high resistivity film bonded to a readout plane with an insulating spacer.•2-dimensional continuous RC network defined by material properties & geometry.•Point charge at r = 0 & t = 0 disperses with time.•Time dependent anode charge density sampled by readout pads.

€

∂ρ∂t

=1

RC

∂2ρ

∂r2+

1

r

∂ρ

∂r

⎡

⎣ ⎢

⎤

⎦ ⎥

€

⇒ ρ(r, t) =RC

2t

−r2RC

4 te

ρ(r,t) integral over pads

ρ(r) Q

mm ns

Charge dispersion in a MPGD with a resistive anode

Equation for surface charge density function on the 2-dim. continuous RC network:

M.S.Dixit et.al., Nucl. Instrum. Methods A518 (2004) 721.


Micromegas resistive anode readout structure

Drift Gap

MESHAmplification Gap

25 m Al/Si coated mylar

Surface resistivity ~1 M/

50 m pillars


•15 cm drift length with GEM or Micromegas readout •B=0•Ar+10% CO2 chosen to simulate low transverse diffusion in a magnetic field.•Aleph charge preamps. Rise= 40 ns, Fall = 2 s. •200 MHz FADCs rebinned to digitization effectively at 25 MHz.•60 tracking pads (2 x 6 mm2) + 2 trigger pads (24 x 6 mm2).

The GEM-TPC resolution was first measured with conventional direct charge TPC readout.

The resolution was next measured with a charge dispersion resistive anode readout with a double-GEM & with a Micromegas.

Cosmic ray TPC tests with MPGD charge dispersion readout


Charge dispersion pulses & pad response function (PRF)

•Non-standard variable pulse shape; both the rise time & pulse amplitude depend on track position. •The PRF is a measure of signal size as a function of track position relative to the pad.•We use pulse shape information to optimize the PRF.•The PRF can, in principle, be determined from simulation. •However, system RC non-uniformities & geometrical effects introduce bias in absolute position determination.•The position bias can be corrected by calibration. •PRF and bias determined empirically using a subset of data used for calibration. Remaining data used for resolution studies.


GEM & Micromegas track Pad Response Functions Ar+10%CO2 2x6 mm2 pads

GEM PRFs Micromegas PRFs

Micromegas PRF narrower due to higher resistivity anode & smaller diffusion than in GEM after avalanche gain.

The pad response function (PRF) amplitude for longer drift distances is lower due to Z dependent normalization.


PRF[x,Γ(z),Δ(z),a,b] =(1+ a2x

2 + a4x4 )

(1+b2x2 +b4x

4 )

a2 a4 b2 & b4 can be written down in terms of Γ and Δ & two scale parameters a & b.

Track PRFs with GEM & Micromegas readout

The PRFs are not Gaussian.The PRF depends on track position relative to the pad.

PRF = PRF(x,z)PRF can be characterized by FWHM Γ(z) & base width Δ(z).PRFs determined from the data parameterized by a ratio of two symmetric 4th order polynomials.


Track fit using the the PRF

Determine x0 & by minimizing 2

for the entire event

2 mm

6 mm

Track at: xtrack= x0+ tan() yrow

16

2

2 ∑∑=

⎟⎟⎠

⎞⎜⎜⎝

⎛

∂−

=rows padsi i

ii

APRFA

Definitions:

- residual: xrow-xtrack

- bias: mean of xrow-xtrack = f(xtrack)

- resolution: standard deviation of residuals


Bias corrections for the GEM & for Micromegas

GEM Micromegas

2x6 mm2 pads

Initial bias Initial bias

Remaining bias after correction

2x6 mm2 pads

Remaining bias after correction


Transverse resolution (B=0) - Cosmic Rays Ar+10%CO2

R.K.Carnegie et.al., NIM A538 (2005) 372

K. Boudjemline et.al., NIM A - in press

€

02 +

CD2

Nez

A. Bellerive et al, LCWS 2005, Stanford

Compared to conventional readout, charge dispersion gives better resolution for the GEM and the Micromegas.


Track display - Ar+5%iC4H10 KEK 4 GeV/c hadrons Micromegas 2 mm x 6 mm pads B = 1 T

Zdrift = 15.3 cmmain pulse


Pad Response Function / Ar+5%iC4H10

Micromegas+Carleton TPC 2 x 6 mm2 pads, B = 1 T

xtrack – xpad / mm

norm

aliz

ed a

mpl

itude

0 < z < 0.5 cm 0 .5 < z < 1 cm 1 < z < 1.5 cm 1.5 < z < 2 cm 2 < z < 2.5 cm 2.5 < z < 3 cm

3 < z < 3.5 cm 3.5 < z < 4 cm 4 < z < 4.5 cm 4.5 < z < 5 cm 5 < z < 5.5 cm 5.5 < z < 6 cm


4 pads / ±4 mm

30 z regions / 0.5 cm step


Pad Response Function Ar+5%iC4H10



xtrack – xpad / mm

norm

aliz

ed a

mpl

itude

4 pads / ±4 mm

PRF parameters•a = b = 0

Δ = base width = 7.3 mm

Γ = FWHM = f(z)The parameters depend on TPC gas & operational details


Bias for central rows / Ar+5%iC4H10 B = 1 T

xtrack / mm (± 14 mm)

Res

idua

l / m

m (

± 0.

15 m

m)

bias before bias after

± 20 m

correction

row 4

row 5

row 6


Extrapolate to B = 4T Use DTr = 25 µm/cm Resolution (2x6 mm2 pads) Tr 100 m (2.5 m drift)

KEK beam test - Transverse resolution Ar+5%iC4H10

E=70V/cm DTr = 125 µm/cm (Magboltz) @ B= 1T

€

x = σ 02 +

Cd2 ⋅z

Neff

4 GeV/c + beam ~ 0°, ~ 0°

0= (52±1) mm

Neff = 220 (stat.)

Micromegas TPC 2 x 6 mm2 pads

•Transverse diffusion strongly suppressed at high B fields.Examples (4 T):DTr~ 25 m/cm (Ar/CH4 91/9) Aleph TPC gas ~ 20 m/cm (Ar/CF4 97/3)


5 T cosmic tests of charge dispersion at DESY COSMo (Carleton, Orsay, Saclay, Montreal) Micromegas

TPC

~ 50 m av. resolution over 15 cm (diffusion negligible)100 m over 2 meters appears feasible

Preliminary

Preliminary

Nov-Dec, 2006

DTr= 19 m/cm, 2 x 6 mm2 pads


Gain ~ 4700Gain ~ 4700 Gain ~ 2300Gain ~ 2300

Sample cosmic ray tracks - data taken at high & at low gains (B = Sample cosmic ray tracks - data taken at high & at low gains (B = 0.5 T)0.5 T)

The effect of lower gain on resolution

1

2

3

4


Gain ~ 4700 B=0.5 T

The resolution and 0 still good at low gain

Gain ~ 2300 B=0.5 T

COSMo TPC transverse resolution - Cosmic rays DESY magnet


Gain dependence on B field for Ar+5%C4H10

Micromegas gain constant to within ~ 0.5% up to 5 Tesla


Micromegas gain with a resistive anode Micromegas gain with a resistive anode Argon/Isobutane 90/10

Resistive anode suppresses sparking & improves Micromegas HV stability


Simulating the charge dispersion phenomenon

•The charge dispersion equation describe the time evolution of a point like charge deposited on the MPGD resistive anode at t = 0. •No standard pulse shape. For improved understanding & to compare to experiment, one must include the effects of:

•Longitudinal & transverse diffusion in the gas.

•Intrinsic rise time Trise of the detector charge pulse.

•The effect of preamplifier rise and fall times tr & tf.

•And for particle tracks, the effects of primary ionization clustering.

M.S.Dixit and A. Rankin, Nucl. Instrum. Methods A566 (2006) 281.


Charge dispersion signals for the GEM readoutSimulation vs. measurement for Ar+10%CO2 (2 x 6 mm2 pads) Collimated ~ 50 m 4.5 keV x-ray spot on pad centre.

Simulated primary pulse is normalized to the data.

Difference = induced signals (MPGD '99, Orsay & LCWS 2000) were not included in simulation).

Primary pulse normalization used for the simulated secondary pulse


GEM TPC charge dispersion simulation (B=0) Cosmic ray track, Z = 67 mm Ar+10%CO2

Centre pulse used for normalization - no other free parameters.

2x6 mm2 pads

Simulation

Data


Micromegas gas gain measurements at Saclay

100

1000

10000

100000

50 55 60 65 70 75 80 85 90 95 100

Mesh bias (kV/cm/atm)

Gain

Iso : 1%

Iso : 2%

Iso : 3%

Iso : 4%

Iso : 5%

CF4 : 3%, Iso : 1%

CF4 : 3%, Iso : 2%

CF4 : 3%, Iso : 3%

CH4 : 6.5%

CH4 : 8%

CH4 : 9%

CH4 : 10%

CH4 : 8%, CF4 : 3%

CH4 : 8%, CF4 : 5%

CH4 : 8%, CF4: 10%

CH4 : 10%, CF4 : 3%

CH4 : 5%, CO2 : 3%

CH4 : 10%, CO2 : 10%

CO2 : 10%

CO2 : 20%

CO2 : 30%

CO2 : 10%, Iso 2%

CO2 : 10%, Iso 5%

CO2 : 10%, Iso 10%

CF4 : 3%, CO2 : 1%

CF4 : 3%, CO2 : 3%

CF4 : 3%, CO2 : 5%

Iso : 2%, CH4 : 10%

Iso : 5%, CH4 : 10%

Iso : 10%, CH4 : 10%

Ethane 10%

Ethane 5%

Ethane 3.5%

Ethane 2%

Ethane 3.5% - CO210%Ethane 3.5% - CF4 3%

Ethane 3.5% - CF410%Ethane 3.5% - Iso 2%

Mixtures of gases containing argon

iC4H10

Gaz froids: CO2, CH4

C2H6

Mesh : 50 m gap of 10x10 size

(David Attie, EUDET Meeting, Munich 18 October, 2006)


Bulk Micromegas obtained by lamination of a woven grid on an anode with two photo-imageable films. The pillars hold the mesh on the whole surface: no frame needed.

New development: Bulk Micromegas (2004)I. Giomataris et al., CERN-Saclay collaboration, NIM A 560 (2006).


Advantages of Bulk Micromegas•Large surfaces at low cost (1000 € for a 34cm x 36cm detector)

•Almost no dead area•Very robust (robust mesh held everywhere)•Insensitive to dust (the mesh is dust-tight down to 30 µ)

•Good/excellent uniformity of the gap•Can be segmented and repaired

New bulk development: excellent resolution and stability

(KEK test Jan.07, 55Fe with no collimation)

pillar


Bulk Micromegas is cut with a 2 mm border

Bulk Micromegas development for T2K

Fully engineered projectMinimum dead space between panels ~ 8 mm


•T2K will have 3 TPCs•72 Micromegas modules •Total area ~ 9 m2

•124416 readout channels

Large panel Micromegas for T2K TPCs


Electronics

•Development for LP TPC based on ALICE TPC ALTRO digitizing electronics.•TPC requirements: highest flexibility in terms of pad geometry and shape of pad panels. •Design for 1 x 4 mm2 pads •Proposal: 32 channels modules, where each channel corresponds to an area of around 4 mm2.•2000 channels of 40 MHz ALTRO chips available. •Plans to acquire more channels - up to 10,000 for LP TPC tests.

3815 November 2006 Luciano Musa / CERN

anode wire

pad plane

drift region88s

PASA ADC DigitalCircuit

RAM

8 CHIPS (16 CH / CHIP) 8 CHIPS (16 CH / CHIP)

CUSTOM IC(CMOS 0.35m) CUSTOM IC (CMOS 0.25m )

DETECTOR Front End Card (128 CHANNELS)

557 568 PADS (3200 CH / RCU)

gat

ing

gri

d ALTRO

RCU

Front End and Readout Electronics

Captoncable

CustomBackplane

power consumption < 40 mW / channel

power consumption < 40 mW / channel

L1: 6.5s 1 KHz

L2: < 100 s 200 Hz

1 MIP = 4.8 fC

S/N = 30 : 1

DYNAMIC = 30 MIP

CSA SEMI-GAUSS. SHAPER

GAIN = 12 mV / fCFWHM = 190 ns

10 BIT

10 MHz

• LINEARIZATION

• BASELINE CORR.

• TAIL CANCELL.

• ZERO SUPPR.

MULTI-EVENT

MEMORY

Alice TPC


PASA designed for wire chamber pulses with long ion tails

Semi-Gaussian output pulse with ~200 ns integration produced for the digitizer. (base width ~ 450 ns)

Tail cancellation and shaping

Time (s)

Wire TPC charge pulse

PASA

0 2 4 6 8 10


PASA preamplifier-shaper not suitable for MPGD-TPC readout

(ns)0 200 400 600 800 1000

With 2 s charge preamp decay time

Charge pulse rise times will be much longer for ILC TPC tracks (dominated by charge collection). •Up to ~ 500 ns to collect the charge due to longitudinal diffusion and track angles.•ILC TPC resolution near statistical limit of diffusion.•Must collect over 90% of electrons for best resolution.•No optimum shaping time to achieve both good single hit and 2-track resolution•Better to digitize charge pulse directly without shaping.

GEM charge pulse - point x ray source


New preamp design to replace PASALuciano Musa


Table1. Specifications of the Programmable Charge Amplifier (PCA)

Conversion Gain Programmable in the range 10-30 mV/fC (see fig. 2)

Dynamics (Max Signal / noise) ~ 2000

Peaking Time Programmable in the range 30-100ns (see fig. 3)

Signal Polarity Programmable for positive and negative pulses

Power consumption < 8mW / channel (<1mW in standby mode)

Nr. Channels 32

Area 0.2 mm2/channel

Technology CMOS 130nm

Programmable gain Programmable peaking & decay times

Luciano Musa


Leif Jonsson Eudet meeting - Munich Nov. 2006


Summary•MPGD-TPC has difficulty achieving good resolution with wide pads •With charge dispersion, the charge can be dispersed in a controlled way. Wide pads can be used without sacrificing resolution. Charge dispersion works both for the GEM and the Micromegas.•At 5 T, an average ~ 50 m resolution has been demonstrated with 2 x 6 mm2 readout pads for drift distances up to 15 cm. •Electronics development on track•The ILC-TPC resolution goal, ~100 m for all tracks, appears feasible.

Micromegas TPC prototype results & Electronics Developments

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