FIRST TEST RESULTS FROM A MICROMEGAS LARGE TPC

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, Tsukuba P. Colas, Micromegas TPC tests 1

Introduction : resistive anode 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 sharing at low diffusion even with 1 mm 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°) 12/03/2009, Tsukuba D. Arogancia, K. Fujii et al. , to appear in NIM A P. Colas, Micromegas TPC tests 2

Introduction : resistive anode (2) One way to make charge sharing is to make a resistive anode (M. S. Dixit et. al. , NIM A 518 (2004) 721. ) This corresponds to adding a continuous RC circuit on top of the pad plane. Charge density obeys 2 D telegraph equation M. S. Dixit and A. Rankin NIM A 566 (2006) 281 SIMULATION MEASUREMENT Res. foil also provides anti-spark protection 12/03/2009, Tsukuba P. Colas, Micromegas TPC tests 3

Previous tests Micromegas TPC endplates have been tested in the past 1) Berkeley-Orsay-Saclay in cosmics, 2 T, 1000 channels (2002 -2004) 2) MP-TPC at KEK, 1 T, 380 channels (June 2005) 3) Carleton-Saclay chamber at KEK, 1 T, 128 channels with resistive anode (10/05) 4) Carleton-Saclay chamber at DESY 5 T in cosmics, 128 channels with r. a. Now test 1 panel in 1 T at DESY, 1726 channels (T 2 K electronics) 12/03/2009, Tsukuba P. Colas, Micromegas TPC tests 4

Previous results with resistive anodes KEK beam test, 2005 DESY 5 T cosmic test, 2007 50 micron resolution at short drift distance, with 2 mm pads (was obtained with an Al. Si cermet-coated mylar) 12/03/2009, Tsukuba P. Colas, Micromegas TPC tests 5

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 Test one Micromegas module at a time 12/03/2009, Tsukuba P. Colas, Micromegas TPC tests 6

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) RESULTS Other 2 ready/ in preparation : resistive ink and thin-layer deposit (N. Wyrsch, Neuchatel) 12/03/2009, Tsukuba P. Colas, Micromegas TPC tests 7

Detector and electronics - 24 x 72 pads of 3 x 7 mm² - AFTER-based electronics : low-noise (700 e-) pre-amplifiershaper, 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 Ge. V electrons) were taken at several z values by sliding the TPC in the magnet. Beam size was 4 mm rms. 12/03/2009, Tsukuba P. Colas, Micromegas TPC tests 8

12/03/2009, Tsukuba P. Colas, Micromegas TPC tests 9

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

Measured drift velocity (Edrift = 230 V/cm, 1002 mbar) : 7. 56 ± 0. 02 cm/µs Magboltz : 7. 548 ± 0. 003 pour Ar: CF 4: isobutane: H 2 O/95: 3: 2: 100 ppm Drift time (µs) B=0 data Z (mm) arbitrary origin 12/03/2009, Tsukuba P. Colas, Micromegas TPC tests 11

Displacement wrt vertical straight line (microns) B=0 data Pad line number Rms displacement: 9 microns DESY - 8 déc. 2009 TPC Analysis 12

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

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 c² fit, and fit simultaneously all lines to a circle in the xy plane 12/03/2009, Tsukuba P. Colas, Micromegas TPC tests xpad – xtrack (mm) 14

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? ) 12/03/2009, Tsukuba P. Colas, Micromegas TPC tests 15

There is a residual bias of up to 50 micron, with a periodicity of about 3 mm. Effect of the analysis? Or detector effect : pillars? Inhomogeneity of RC? 12/03/2009, Tsukuba P. Colas, Micromegas TPC tests 16

Resolution 46± 6 microns with 2. 7 -3. 2 mm pads Effective number of electrons 23. 3± 3. 0 consistent with expectations 12/03/2009, Tsukuba P. Colas, Micromegas TPC tests 17

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 3 mm 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, Tsukuba P. Colas, Micromegas TPC tests 18