david attié — on behalf of the lc-tpc collaboration —

[email protected] Astrophysics Detector Workshop – Nice – November 18th, 2008

1

David Attié— on behalf of the LC-TPC Collaboration —

Micromegas TPC Micromegas TPC Large Prototype Large Prototype

beam testsbeam tests

TILC09 – Tsukuba – April 17-21, 2009

Outline

[email protected] TILC09 – Tsukuba – April 18th, 2009 2

• Introduction, solutions for ILC-TPC

• Micromegas with resistive anode

– description

– previous results

• The Large Prototype (LP)

• Micromegas panels in the LP

– drift velocity

– pad response function

– resolution

• Conclusion

How to improve the spatial resolution?


• Need for ILC: measure 200 track points with a transverse resolution ~ 100 μm

example of track separation with 1 mm x 6 mm pad size: 1,2 × 106 channels of electronics z=0 > 250 μm amplification avalanche over one pad

• Spatial resolution σxy:

limited by the pad size (0 ~ width/√12)

charge distribution narrow (RMSavalanche ~ 15 μm)

1. Decrease the pad size: narrowed strips, pixels+ single electron efficiency – need to identify the electron clusters

2. Spread charge over several pads: resistive anode+ reduce number of channels, cost and budget+ protect the electronics– limit the track separation– need offline computing – time resolution is affected 2. Resistive anode

Simulation for the ILC-TPC55 m

1. Pixels

Micromegas


Micromegas

Best technology for gaseous detector readout: Micro Pattern Gaseous Detector

• more robust than wires

• no E×B effect

• better ageing properties

• easier to manufacture

• fast signal & high gain

• low ion backdrift

• MICROMEsh GAseous StructureY. Giomataris et al., NIM A 376 (1996) 29

• metallic micromesh (typical pitch 50μm)

• sustained by 50-100 μm pillars • simplicity

• single stage of amplification

• fast and natural ion collection

• discharges non destructive

~50 µm

~50 kV/cm

cathode

~1 kV/cm

Resistive anode


(r,t) integrate over pads

(r)

r (mm)

Q(t)

t (ns)

M.S.Dixit et.al., NIM A518 (2004) 721

• One way to make charge sharing is to make a resistive anode

• Equivalent to adding a continuous RC circuit on top of the pad plane.

• Charge density ρ(r,t) obeys 2D telegraph equation:

rρ

rrρ

tρ

RC ∂

∂

∂

∂

∂

∂ 112

2

et

RCtrρ t

RCr4

2

2),(

R R R R R R R R

C C C C C C C

Rp RpRp

Current generators

Pad amplifiers

Signal pickup pads

Resistiv

e fo

il

Resistive anode


M.S.Dixit and A. Rankin NIM A566 (2006) 281

2 x 6 mm2 pads

(r,t) integrate over pads

(r)

r (mm)

Q(t)

t (ns)

SimulationData

Micromegas with resistive anode


• TPC COSMo (Carleton-Orsay-Saclay-Montreal) at DESY in 2006+ Micromegas 10 x 10 cm² (gap 50 μm)+ resistive anode used to spread charge over

126 pads (7x18) of 2x6 mm²15 cm drift space

• 25 µm mylar with Cermet (Al-Si) of 1 M/□ glued onto the pads with 50 µm thick dry adhesive

5 T magnet at DESY + TPC COSMo

Micromegas

TPC COSMo

Resistive foil

Glue

pads

PCB

mesh

Resistive anode

Spatial resolution at 0.5T


• B = 0.5T, resolution fitted by where

• Resolution 0 ( at z = 0) ~ 50 µm still good at low gain (will minimize ion feedback)

• Mean of Neff = 27 (value measured before ~ 22)

Gain = 4700 Gain = 2500

Neff=25.2±2.1 Neff=28.8±2.2

x 02 Cd2 zNeff

0 = 1/40 of pad pitch

2

/1/1 NNeff

Spatial resolution at 5T


• Analysis: - Curved track fit- EP < 2 GeV

- || < 0.05 (~3°)

Ar Iso (95:5)

B = 5T

Ar Iso (95:5)

B = 5T

50 m

~ 50 µm independent of the drift distance

Extrapolate to B = 4T with T2K gas for 2x6 mm2 pads:

• DTr = 23.3 μm/cm, • Neff ~ 27,• 2 m drift distance,

Resolution of Tr 80 m will be possible !!!

ILC-TPC Large Prototype


• Built by the collaboration

• Financed by EUDET

• Sharing out :

- magnet : KEK, Japon

- field cage : DESY, Allemagne

- trigger : Saclay, France

- endplate : Cornell, USA

- Micromegas : Saclay, France

- GEM : Saga, Japon

- TimePix pixel : F, D, NLc



• Endplate ø = 80 cm of 7 interchangeable panels of 23 cm:

– Micromegas – GEMs– Pixels (TimePix + GEM or Microgemgas)

80 cm

24 rows x 72 columns <pad size> ~ 3x7 mm2

Bulk Micromegas panels tested at DESY


• Two panels were successively mounted in the Large Prototype and 1T magnet - standard anode- resistive anode (carbon loaded kapton) with a resistivity ~ 5-6 MΩ/□

• Two other resistive technology are planned to be tested:- resistive ink (~1-2 MΩ/□) ready for next beam tests in May- a-Si thin-layer deposit (N. Wyrsch, Neuchatel) in preparation

Standard bulk Micromegas module Carbon loaded kapton Micromegas module

Beam test conditions


• Bulk Micromegas detector: 1726 (24x72) pads of ~3x7 mm²

• AFTER-based electronics (72 channels/chip): – low-noise (700 e-) pre-amplifier-shaper– 100 ns to 2 µs tunable peaking time– full wave sampling by SCA

• Beam data (5 GeV electrons) were taken at several z values by sliding the TPC in the magnet. Beam size was 4 mm rms.

– frequency tunable from 1 to 100 MHz (most data at 25 MHz)

– 12 bit ADC (rms pedestals 4 to 6 channels)

5 GeV e- beam data in T2K gas


• Frequency sampling: 25 MHz• T2K gas: Ar/CF4/iso-C4H10 (95:5:3)• B = 1T • Peaking time: 500 ns

Pad signals: beam data sample


• RUN 284

• B = 1T

• T2K gas

• Peaking time: 100 ns

• Frequency: 25 MHz

Pad signals: cosmic-ray data sample


• RUN 294

• B = 1T

• T2K gas

• Peaking time: 1 μs

• Frequency: 100 MHz

Systematics


Dis

plac

emen

t / v

ertic

al s

trai

ght l

ine

(μm

)

Pad line number rms displacement: ~9

microns

B = 0T

Drift velocity measurement


• Measured drift velocity (Edrift = 230 V/cm, 1002 mbar): 7.56 ± 0.02

cm/μs

• Magboltz: 7.548 ± 0.003 for Ar/CF4/iso-C4H10/H2O (95:3:2:100ppm)

B = 0T

Drift Velocity vs. Peaking Time


Edrift = 220 V/cm

VdMagboltz = 76 m/ns

• B=1T data

• For several peaking time settings: 200 ns, 500 ns, 1 µs,

2µs Edrift = 140 V/cm

VdMagboltz = 59 m/ns

Z (cm)Z (cm)

Tim

e b

ins

Tim

e b

ins

Determination of the Pad Response Function


• Fraction of the row charge on a pad vs xpad – xtrack

(normalized to central pad charge)

Clearly shows charge spreadingover 2-3 pads(use data with 500 ns shaping)

• Then fit x(cluster) using thisshape with a χ² fit, and fit simultaneously all linesto a circle in the xy plane

xpad – xtrack (mm)

Pad pitch

Residuals (z=10 cm)


• Lines 0-4 and 19-23 removed for the time being(non gaussian residuals, magnetic field inhomogeneous for some z positions?)

row 5 row 6 row 7

row 8 row 9 row 10

Residuals (z=10 cm)


• There is a residual bias of up to 50 micron, with a periodicity of about 3mm.

• Unknown origin:

– Effect of the analysis?

– Or detector effect:

pillars?

Inhomogeneity of RC?

row 6

row 7

row 8

Spatial resolution at 1T


• Resolution (z=0): σ0 = 46±6 microns with 2.7-3.2 mm pads

• Effective number of electrons: Neff = 23.3±3.0 consistent with expectations

eff

2d2

0x N

zCσσ

Further tests for Micromegas


In 2008 with one detector module In 2009 with 7 detector modules.

Com

pact

the e

lect

ron

ics

wit

hposs

ibili

ty t

o b

ypass

shapin

gR

esi

tive t

ech

nolo

gy c

hoic

e

4 chipsWire bonded

Front End-Mezzanine

Conclusions


• Excellent start for the Micromegas TPC tests within the EUDET facility. Smooth data taking.

• First analysis results confirm excellent resolution at small distance:50 μm for 3mm pads

• Expect even better results with new (bypassed shaper) AFTER chips

• Plans are to test several resistive layer fabrication, then go to 7 modules with integrated electronics

Backup slides


david attié — on behalf of the lc-tpc collaboration —

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