FIRST TEST RESULTS FROM A MICROMEGAS LARGE TPC

PROTOTYPEP. Colas (CEA Saclay), on behalf of the LC-TPC collaboration

Micromegas with resistive anode: previous resultsThe Large PrototypeMicromegas panelsDataDrift velocity measurementPad response functionResolution

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Introduction : resistive anode

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D. Arogancia, K. Fujii et al., to appear in NIM A

LC-TPC goal is 200 measurement points on a track, with <130 micron resolution

With Micromegas, signal spread is equal to the avalanche size, 12-14 microns : not enough charge sha-ring at low diffusion even with 1mm pads.Need to share the charge between neighbouring pads to make a barycentre possible and improve resolution.

Also charge sharing saves number of channels ($, W, X°)

Introduction : resistive anode (2)

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One way to make charge sharing is to make a resistive anode (M.S.Dixit et.al., NIM A518 (2004) 721.) This corresponds to adding a continuous RC circuit on top of the pad plane. Charge density obeys 2D telegraph equation

t

1

RC

2r2

1

r

r

(r, t)RC2t

r2RC4 te

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

SIMULATION

MEASUREMENT

Res. foil also provides anti-spark protection

Previous testsMicromegas TPC endplates have been tested in the past1) Berkeley-Orsay-Saclay in cosmics, 2T, 1000 channels (2002-2004)2) MP-TPC at KEK, 1T, 380 channels (June 2005)3) Carleton-Saclay chamber at KEK, 1T, 128 channels with resistive anode

(10/05)

4) Carleton-Saclay chamber at DESY 5T in cosmics, 128 channels with r.a. Now test 1 panel in 1 T at DESY, 1726 channels (T2K electronics)

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Previous results with resistive anodes

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KEK beam test, 2005 DESY 5T cosmic test, 2007

50 micron resolution at short drift distance, with 2mm pads

(was obtained with an AlSi cermet-coated mylar)

eff

dx N

zC

220

The EUDET setupat DESY

See talk by K. Dehmelt

PCMag magnet from KEKCosmic trigger hodoscope from Saclay-KEK-INRBeam trigger from NikhefDummy modules from BonnField cage, gas from DESYEndplate from Cornell

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Test one Micromegas module at a time

12/03/2009, Tsukuba P. Colas, Micromegas TPC tests

Two panels have been tested at DESY

Both in ‘bulk’ technology

One with standard pads, one with resistive anode (Carbon-loaded kapton)

Improved resistive anode 75 micron kapton + 25 micron C-loaded kapton (CERN)

Other 2 ready/ in preparation : resistive ink and thin-layer deposit (N. Wyrsch, Neuchatel)

RESULTS

7

Detector and electronics

- 24x72 pads of 3x7 mm²- AFTER-based electronics : low-noise (700 e-) pre-amplifier-

shaper, 100 ns to 2 µs tunable peaking time, full wave sampling by SCA, frequency tunable from 1 to 100 MHz (most data at 25 MHz), 12 bit ADC (rms pedestals 4 to 6 channels)

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

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1012/03/2009, Tsukuba P. Colas, Micromegas TPC tests10

• Peaking time: 1 μs• Frequency sampling: 100 MHz

Cosmic ray data sample

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0

1

2

3

4

5

6

7

8

0 100 200 300 400 500 600

Z (mm) arbitrary origin

Drif

t tim

e (µ

s)

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

Magboltz : 7.548 ± 0.003 pour Ar:CF4:isobutane:H2O/95:3:2:100ppm

B=0 data

DESY - 8 déc. 2009 TPC Analysis 12

y = 13,884x - 165,42

-200

-150

-100

-50

0

50

100

150

200

0 4 8 12 16 20 24Dis

plac

emen

t w

rt v

ertic

al s

trai

ght

line

(mic

rons

)

Pad line numberRms displacement: 9 microns

B=0 data

13

Magboltz 59 m/nsMagboltz 76 m/ns

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B=1T data for several peaking time settings200 ns, 500 ns, 1 µs, 2µs

Edrift = 220 V/cm Edrift = 140 V/cm

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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 spreading over 2-3 pads(use data with 500 ns shaping)

Then fit x(cluster) using this shape with a ² fit, and fit simultaneously all lines to a circle in the xy plane

xpad – xtrack (mm)

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RESIDUALS (z=10 cm)

Do not use lines 0-4 and 19-23 for the time being (non gaussian residuals, magnetic field inhomogeneous for some z positions?)

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

Effect of the analysis?Or detector effect : pillars? Inhomogeneity of RC?

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Resolution 46±6 microns with 2.7-3.2 mm padsEffective number of electrons 23.3±3.0 consistent with expectations

eff

dx N

zC 2

20

CONCLUSION• Excellent start for the Micromegas

TPC tests within the EUDET facility. Smooth data taking

• First analysis results confirm excellent resolution at small distance:

50 microns 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

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