23 March 2005International TPC R&D Meeting Berkeley 1 Readout of a TPC using the Medipix2 CMOS pixel...
-
Upload
mabel-parker -
Category
Documents
-
view
214 -
download
0
Transcript of 23 March 2005International TPC R&D Meeting Berkeley 1 Readout of a TPC using the Medipix2 CMOS pixel...
23 March 2005 International TPC R&D Meeting Berkeley
1
Readout of a TPC using the Medipix2 CMOS pixel sensor
(detection of single electrons on a direct pixel segmented anode)
Jan Timmermans
NIKHEF - Amsterdam
23 March 2005 International TPC R&D Meeting Berkeley
2
NIKHEF Auke-Pieter Colijn Arno AartsAlessandro Fornaini Maximilien
ChefdevilleHarry van der Graaf Sipho van der PuttenPeter KluitJan TimmermansJan Visschers
Saclay CEA DAPNIA Paul ColasYannis GiomatarisArnaud Giganon
Univ. Twente/Mesa+ Jurriaan Schmitz
CERN/Medipix Constm Erik HeijneXavie LlopartMichael Campbell
23 March 2005 International TPC R&D Meeting Berkeley
3
Goals• Gas multiplication GEM or Micromegas foil(s)• Charge collection with granularity matching
primary ionisation cluster spread• Needs sufficiently low diffusion gas• dE/dx using cluster counting?
( M. Hauschild)
• Proof of principle based on existing Medipix2 readout chip
23 March 2005 International TPC R&D Meeting Berkeley
4
Our GEM-equipped TPCWe have constructed a small test TPC equipped with three GEM foils whichcan be read out by means of the MEDIPIX2 CMOS pixel sensor.The GEM foils were obtained from the CERN/Sauli/GEM group;hole-to-hole distance (hexagonal geometry): 140 µm, hole diameter 85 µm,fiducial surface 100 mm x 100 mm, thickness 50 µm.The drift volume (vol. 100x100x100 mm3) is surrounded by square wire loops,spaced 6.3 mm, put at decreasing potential. Three GEM foils are placed 7.4 mmbehind the plane of the bottom wire loop; the distance between GEM foils is 1.6 mm.The anode plane, at ground potential, is 6.6 mm below the third GEM foil.
23 March 2005 International TPC R&D Meeting Berkeley
5
DriftSpace
GEM foils
MediPix CMOS pixel sensorBrass spacer blockPrinted circuit boardAluminium base plate
Medipix2: 256 x 256 pixels
55 m x 55 m
area 14 x 14 mm2
each pixel: low-noise preamp,
discriminator, two threshold DAC,
13-bit counter, communication logic
Drift length: 100 mmDistance between GEMs: 1.6/2.6 mmDistance bottom GEM/MEDIPIX: 6.6 mm
23 March 2005 International TPC R&D Meeting Berkeley
6
First events, recorded on March 29, 2003!Drift space irradiated with 55Fe quanta
Not immediately understood. Now we do: conversion source ~0.3 mm, defocussing GEM ~0.5 mm, diffusion in driftspace ~1.5 mm
Ar/CH4 90/10
23 March 2005 International TPC R&D Meeting Berkeley
7
exposed 0.01 s exposed 2 s exposed 2 s
exposed 0.1 s 90Sr source; exposed 0.01 s
Fiducial field:14 x 14 mm2
Collected ionisationin 14 x 14 x 100 mm3
during exposure time
Feb 9, 2004
Ar/Isobutane 95/5
23 March 2005 International TPC R&D Meeting Berkeley
8
MediPix2 pixel sensorBrass spacer blockPrinted circuit boardAluminum base plate
Micromegas
Cathode (drift) plane
55Fe
Baseplate
Drift space: 15 mm
With Paul Colas & Ioannis Giomataris:MediPix2 & Micromegas
Very strong E-field above (CMOS) MediPix!
S1
23 March 2005 International TPC R&D Meeting Berkeley
9
MediPix modified by MESA+, Univ. of Twente, The Netherlands
Pixel Pitch: 55 x 55 μm2
Bump Bond pad: 25 μm octagonal75 % surface: passivation SiNNew Pixel Pad: 45 x 45 μm2
Insulating surface was 75 %Reduced to 20 %
23 March 2005 International TPC R&D Meeting Berkeley
10
23 March 2005 International TPC R&D Meeting Berkeley
11
23 March 2005 International TPC R&D Meeting Berkeley
12
We always knew, but never saw: the conversion of 55Fe quanta in Ar gas
No source, 1sNo source, 1s5555Fe, 1sFe, 1s
5555Fe, 10sFe, 10s
Friday 13 (!) Feb 2004: signals from a 55Fe source (220 e- per photon); 300 m x 500 m clouds as expected
14 mm
The Medipix CMOS chip facesan electric field of 350 V/50 μm
= 7 kV/mm !!
Ar/Isobutane 95/5
23 March 2005 International TPC R&D Meeting Berkeley
13
New trial: March 30 - April 2, 2004try to see single electrons from cosmic muons (MIPs)
•New Medipix
•New Micromegas (holds >500 V over 50 m in …..)
•He/Isobutane 80/20 (gas gain 10,000 – 20,000)
•Pixel preamp threshold: ~3000 e-
•Required gain: 5,000 – 10,000
….. it works !
23 March 2005 International TPC R&D Meeting Berkeley
14
23 March 2005 International TPC R&D Meeting Berkeley
15
He/Isobutane80/20Modified MediPix
31 March 2004
23 March 2005 International TPC R&D Meeting Berkeley
16
He/Isobutane80/20Modified MediPix
31 March 2004
23 March 2005 International TPC R&D Meeting Berkeley
17
He/Isobutane80/20Non ModifiedMediPix
Amaricium Source
1 April 2004
23 March 2005 International TPC R&D Meeting Berkeley
18
He/Isobutane80/20Modified MediPix
31 March 2004
23 March 2005 International TPC R&D Meeting Berkeley
19
He/Isobutane80/20Modified MediPix
31 March 2004
23 March 2005 International TPC R&D Meeting Berkeley
20
Example of a track reconstructed
This track:
•#hits = 24
•#clusters = 11
•length (3d) = 16.8 mm
•1.4 e-/mm; 0.65 cl./mm On average:•1.8 e-/mm; 0.5 cl./mm
23 March 2005 International TPC R&D Meeting Berkeley
21
Detection of single electrons using MediPix2/Micromegas assembly as Direct Pixel Segmented Anode
• NIM A540 (2005) 295 (physics/0409048)
• #pixels hit/mm track length = 1.83
• #clusters/mm track length = 0.52
• Single electron efficiency 0.9
• Moire effects: mismatch in pixel and hole pitch: 60/(60-55) = 12 pixels repetition
23 March 2005 International TPC R&D Meeting Berkeley
22
Non Modified Modified
Explanation for Moire effect: pitch Micromegas holes: 60 μm pitch MediPix pixels: 55 μm
Periodic position of hole w.r.t. pixel: repeats after 12 pixels!
Modified
Non Modified
InGrid: perfect alignment of pixels and grid holes!Small pad: small capacitance!
23 March 2005 International TPC R&D Meeting Berkeley
24
Recent work (with new Micromegas and new MediPix):
•Threshold studies (equalisation)
•Implementation external trigger (needed new Medipix software and interface box); it works!
•New data taking: much lower single electron efficiency (not yet understood)
•Kept MediPix chip alive for about 4 weeks!
23 March 200523 March 2005 International TPC R&D Meeting BerkelInternational TPC R&D Meeting Berkeleyey
2525
Integrate GEM/Micromegas and pixel sensor
‘GEM’ ‘Micromegas’
By ‘wafer post processing’
InGrid
23 March 2005 International TPC R&D Meeting Berkeley
26
Wafer dia.: 100 mm
30 fields with variety of pillar geometry
First trials with pillars look OK
Had some problems with ‘Micromegas’ grid(holes closed with very thin layer)
First ‘good’ Ingrid in Feb. 2005
Reached 170V before breakdown(after that 80V with 4.6μA current)
New design: -thicker grid layer (few microns) -larger spacing between fields -could be ready in few weeks
23 March 2005 International TPC R&D Meeting Berkeley
27
INGRID: some first trials
Various pitches, shapes
By ‘wafer post processing’at MESA+, Univ. of Twente
pads
pillars
grid foils
23 March 2005 International TPC R&D Meeting Berkeley
28
23 March 2005 International TPC R&D Meeting Berkeley
29
with pillars
with walls
23 March 2005 International TPC R&D Meeting Berkeley
30
TimePix1•Distribute clock to full 256x256 pixel matrix (100-160MHz)
•Enable counting by first hit after ‘shutter’ opens, until ‘shutter’ closes (common stop)
•Dynamic range 214 x 10 ns = 160 μs
•(for the time being) no zero-suppress to remain fully compatible with Medipix2
•Shaping time ~200 ns, might be reduced for TimePix
•Extra static discharge protection for the front-end will be considered
•Keep same chip-size, pixel-size, readout protocol
•Can be done in 5-6 months (if done by MediPix2 designers)
23 March 2005 International TPC R&D Meeting Berkeley
31
Further Tests and Developments
• Investigate possible use of CMS (or Atlas) frontend pixel chip
• Ageing tests for….• GOSSIP: very thin gas/pixel detectors as Vertex
Detector (LHC/ILC) (TIMEPIX2 with ~1 ns resolution)• Chip tiling: large(r) detector surfaces (2x2, 2x4 chips)• Through Si connectivity: avoiding bonding wires• Fast readout technology
(~5 Gb/s)
23 March 2005 International TPC R&D Meeting Berkeley
32
•MediPix designed at CERN
•4-chip tiling, serial readout and interface: NIKHEF
•20 keV X-ray source at CERN
•Readout single chips 20 frames/sec
•New exp. software 70 frames/sec
•Next version chip several 103 frames/s
23 March 2005 International TPC R&D Meeting Berkeley
33
Backup slides
23 March 2005 International TPC R&D Meeting Berkeley
34
Top Drifter 5700 V
Bottom Drifter 3473 V
Top GEM 1 2813 V
Bottom GEM 1 2462 V
Top GEM 2 1876 V
Bottom GEM 2 1524 V
Top GEM 3 938 V
Bottom GEM 3 586 V
In the base plate of the chamber, a hole was cut out for the MEDIPIX2 chip: its pixel surfacewas flush with the (anode plane) base plateplane. The MEDIPIX2 chip contains 256 x 256square pixels with pitch 55 µm x 55 µm givinga total fiducial sensitive area of14.08 mm x 14.08 mm. Each pixel is equippedwith a low-noise charge preamp, discriminator,two threshold DACs, a 13-bit counter andcommunication logic.Since a triggering system had not beenimplemented, we operated the MEDIPIX2sensor by enabling the counters manually,and stop the counting after a pre-set timeinterval (0.1 - 10 s). After that, the counts ofeach pixel are read out.
Drift length: 100 mmDistance between GEMs: 1.6/2.6 mmDistance bottom GEM/MEDIPIX: 6.6 mm
23 March 2005 International TPC R&D Meeting Berkeley
35
Eff = e-n/G
n: threshold setting (#e-)G: Gas amplification
Single electron efficiency
0.00
0.20
0.40
0.60
0.80
1.00
0 1000 2000 3000 4000
Threshold setting (number of electrons)
Eff
icie
ncy
(-)
G=500
G=1000
g=2000
g=4000
g=8000
Expon. (G=500)
Expon. (G=1000)
Expon. (g=2000)
Expon. (g=4000)
Expon. (g=8000)
single-electron avalanche distribution
0
0.0005
0.001
0.0015
0.002
0 1000 2000 3000 4000
electrons in avalanche
Pro
b(n
)
G=500
G=1000
G=2000
G=4000
G=8000
Expon. (G=500)
Expon. (G=1000)
Expon. (G=2000)
Expon. (G=4000)
Expon. (G=8000)
Prob(n) = 1/G . e-n/G