FIRST TEST RESULTS FROM A MICROMEGAS LARGE TPC PROTOTYPE P. Colas (CEA Saclay), on behalf of the LC-TPC collaboration Micromegas with resistive anode: previous results The Large Prototype Micromegas panels Data Drift velocity measurement Pad response function Resolution 12/03/2009, Tsukuba1P. Colas, Micromegas TPC tests

Introduction : resistive anode 12/03/2009, TsukubaP. Colas, Micromegas TPC tests2 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, 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) 12/03/2009, TsukubaP. Colas, Micromegas TPC tests3 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 M.S.Dixit and A. Rankin NIM A566 (2006) 281 SIMULATION MEASUREMENT Res. foil also provides anti-spark protection

Previous tests Micromegas TPC endplates have been tested in the past 1) Berkeley-Orsay-Saclay in cosmics, 2T, 1000 channels ( ) 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) 12/03/2009, TsukubaP. Colas, Micromegas TPC tests4

Previous results with resistive anodes 12/03/2009, TsukubaP. Colas, Micromegas TPC tests5 KEK beam test, 2005DESY 5T cosmic test, micron resolution at short drift distance, with 2mm pads (was obtained with an AlSi cermet-coated mylar)

The EUDET setup at DESY See talk by K. Dehmelt PCMag magnet from KEK Cosmic trigger hodoscope from Saclay-KEK-INR Beam trigger from Nikhef Dummy modules from Bonn Field cage, gas from DESY Endplate from Cornell 12/03/2009, Tsukuba6P. Colas, Micromegas TPC tests Test one Micromegas module at a time

12/03/2009, TsukubaP. 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. 12/03/2009, TsukubaP. Colas, Micromegas TPC tests8

12/03/2009, TsukubaP. Colas, Micromegas TPC tests9

10 12/03/2009, TsukubaP. Colas, Micromegas TPC tests 10 Peaking time: 1 μs Frequency sampling: 100 MHz Cosmic ray data sample

12/03/2009, TsukubaP. Colas, Micromegas TPC tests11 Z (mm) arbitrary origin Drift time (µs) Measured drift velocity (Edrift = 230 V/cm, 1002 mbar) : 7.56 ± 0.02 cm/µs Magboltz : ± pour Ar:CF4:isobutane:H2O/95:3:2:100ppm B=0 data

DESY - 8 déc. 2009TPC Analysis12 Displacement wrt vertical straight line (microns) Pad line number Rms displacement: 9 microns B=0 data

13 Magboltz 59  m/ns Magboltz 76  m/ns 12/03/2009, TsukubaP. Colas, Micromegas TPC tests B=1T data for several peaking time settings 200 ns, 500 ns, 1 µs, 2µs Edrift = 220 V/cmEdrift = 140 V/cm

12/03/2009, TsukubaP. Colas, Micromegas TPC tests14 Determination of the Pad Response Function Fraction of the row charge on a pad vs x pad – x track (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 x pad – x track (mm)

12/03/2009, TsukubaP. Colas, Micromegas TPC tests15 RESIDUALS (z=10 cm) Do not use lines 0-4 and for the time being (non gaussian residuals, magnetic field inhomogeneous for some z positions?)

12/03/2009, TsukubaP. Colas, Micromegas TPC tests16 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?

12/03/2009, TsukubaP. Colas, Micromegas TPC tests17 Resolution 46±6 microns with mm pads Effective number of electrons 23.3±3.0 consistent with expectations

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 12/03/2009, TsukubaP. Colas, Micromegas TPC tests18