50 mm
140 mm
Micromegas:
Maxim Titov, CEA Saclay, France
OUTLINE:
• Pestov Counters
Thick GEM +
(THGEM)
GEM +
CMOS ASIC
• Resistive Plate Chambers
• Micro-Pattern Gas Detectors
(GEM, Micromegas, Thick GEM)
• RD51 Electronics (Scalable Readout Systems)
«The Factors that Limit Time Resolution in Photodetectors»,
Timing Workshop, University of Chicago, April 28, 2011
Yu. Pestov, NIM 196(1982)45
GOOD TIME RESOLUTION ---> THIN GAP
GOOD EFFICIENCY---> THICK GAS LAYER
THIN GAP (100 µm) AND HIGH
PRESSURES (~10 bar)
HIGH RESISTIVITY ELECTRODE
(PESTOV GLASS, 109 Ω cm
PHYSICAL ORIGIN OF TAILS IN THE
TIME RESPONSE OF SPARK COUNTERS:
Yu Pestov et al. NIMA265 (1988) 198
Yu. Pestov et al., NIMA456 (2000) 11
Mangiarotti and A. Gobbi, NIMA. A482(2002)192
HIGH-PRESSURE GAS VESSEL
METAL CATHODE
SEMI-CONDUCTING GLASS ANODE
SIGNAL PICK-UP STRIPS
Time resolution is proportional to discharge delay time (fluctuation of delay time is the
sum of the fluctuation of the avalanche development and the occurrence of the streamer)
READOUT STRIPS X
HV
INSULATOR
GRAPHITE COATING
HIGH RESISTIVITY ELECTRODE (BAKELITE)
GAS GAP
GND
R. Santonico, NIMA 187(1981)37
P. Fonte, NIMA449 (2000) 295 ;
P.Fonte, A.Smirnitski, C Williams, NIMA443(2000)201
I.Crotty et al, NIM A337(1994)370
READOUT STRIPS Y
Time resolution of a RPC can be parameterized as:
Δτ = λ/v
λ is the mean free path of electrons in avalanche, v is drift velocity of electrons
LOW λ and HIGH v can be obtained with dense/fast gas mixtures:
C2H2F4 – iC4H10 – SF6
Typical values: λ ~ 10μm, v ~ 100 μm/ns → Δτ ~ 100ps
Only avalanches within a few hundred mm from cathode generate signals
Raether limit: G = ed/λ < 108 → for λ ~ 10μm
dgap ~ 200μm
To avoid discharges the gap must be reduced → MICROGAP
• INCREASING THE GAP PROVIDES BETTER EFFICIENCY PLATEAUX
• For gas gaps of 0.3 mm or larger, the timing jitter in parallel-plate detectors
varies almost linearly with the width of the gaps
HV
GND
DOUBLE GAP
FWHM=1.7 ns
SINGLE GAP
FWHM 2.3 ns
M. Abbrescia et al, NIM A431(1999)413
(caveat - table last updated in 2003)
Add boundaries that stop avalanche development. These boundaries must be
invisible to the fast induced signal – induced signal on external pickup
C. Williams, RD51 Mini-Week, July 20, 2010
Would like large fast signal and small total charge (high rate capability)
(After time correction using pulse-height)
HV
FLOATING
GND
E. Cerron Zeballos et al, NIMA 374(1996)132
A. Akindinov et al, NIMA 456(2000)16
C. Williams, RD51 Mini-Week, July 20, 2010
Trigger RPC: R. Cardarelli, R. Santonico
 ATLAS, CMS (~ 2000 – 4000 m2)
 timing resolution ~ 1-5 ns (MIPs)
X readout strips
r ~ 1010 Wcm
E ~ 50 kV
2 mm Bakelite
2 mm gas gap
2 mm Bakelite
Y readout strips
Timing and Multi-Gap RPC  ALICE TOF
P. Fonte, V. Peskov, C. Williams (~50 ps)
Pickup electrodes
0.4 mm glass
plates
0.3 mm gas
gaps
Pickup electrodes
E ~ 100 kV
`Renaissance of particle identification’
using Multi-Gap RPC in ALICE:
B
10 ps devices could be
feasible – one of the
biggest problem could
be the electronics :
the TDC
C. Williams, RD51 Mini-Week,
July 20, 2010
• Micromegas
0.18 mm CMOS VLSI
• GEM
• Thick-GEM, Hole-Type Detectors and RETGEM
• MPDG with CMOS pixel ASICs
CMOS high density
readout electronics
• Ingrid Technology
Ions
40 %
60 %
Electrons
Micromegas
GEM
THGEM
MHSP
Ingrid
Thin metal-coated polymer foil chemically pierced by a high density of holes
A difference of potentials of ~ 500V is
I+
applied between the two GEM electrodes.
The primary electrons released by the
ionizing particle, drift towards the holes
e-
where the high electric field triggers the
Induction gap
electron multiplication process.
eS1 S2 S3 S4
Electrons are collected on patterned readout board.
A fast signal can be detected on the lower
GEM electrode for triggering or energy discrimination.
All readout electrodes are at ground potential.
F. Sauli, Nucl. Instrum. Methods A386(1997)531
F. Sauli, http://www.cern.ch/GDD
F. Sauli, NIM A386(1997) 531;
F. Sauli, http://www.cern.ch/GDD
Full decoupling of amplification stage (GEM)
and readout stage (PCB, anode)
Cartesian
Compass, LHCb
Small angle
Amplification and readout structures can be optimized independently !
33 cm
Hexaboard, pads
MICE
Compass
Totem
NA49-future
Mixed
Totem
Time-resolution is determined by the fluctuations in the photoelectron transit time
from their emission point at the PC and, after multiplication, to the anode.
 depends on the detector geometry, the electric field conditions and properties
of the gas composition, namely on the electron diffusion and drift velocity.
Induction gap ~ 1mm
Single Photon Time Resolution:
low diffusion &
CF4
high electron drift
770 torr
velocity in CF4
Single Photon Position Accuracy:
200 µm
Intrinsic accuracy
s (RMS) ~ 55 µm
FWHM ~160 µm
Beam ~ 100 µm
T. Meinschad et al, NIM A535 (2004) 324;
D.Mormann et al., NIMA504 (2003) 93
Triple GEM for CMS Upgrade:
Triple GEM for LHC-b Detector :
Time Resolution ~ 5 ns
Time resolution for different
gas mixtures and gap configurations:
• Ar(45):CO2 (15):CF4 (40) [gaps 3/1/2/1]
• Ar(70):CO2(30) [gaps 3/2/2/2]
G. Bencivenni,
IEEE
A. Bressan et
al, TNS 49(6), 3242 (2002)
Nucl. Instr. and Meth. A425 (1999) 262
A. Sharma, private communications
Simple & Robust  Manufactured by standard PCB techniques
of precise drilling in G-10 (and other materials) and Cu etching
STANDARD GEM
103 GAIN IN SINGLE GEM
THGEM
105 gain in single-THGEM
Other groups developed
similar hole-multipliers:
- Optimized GEM:
L. Periale et al.,
NIM A478 (2002) 377.
1 mm
0.1 mm rim - LEM: P. Jeanneret,
to prevent - PhD thesis, 2001.
discharges
C. Shalem et al, NIMA558 (2006) 475;
Double THGEM or THGEM/Micromegas
1,0E+07
1,0E+06
1,0E+05
106
1,0E+04
Gain
• Effective single-electron detection
(high gas gain ~105 (>106) @
single (double) THGEM)
• Few-ns RMS time resolution
• Sub-mm position resolution
• MHz/mm2 rate capability
• Cryogenic operation: OK
• Gas: molecular and noble gases
• Pressure: 1mbar - few bar
1,0E+03
1,0E+02
1,0E+01
MM = 330 NeCF4 10%
MM = 290 NeCF4 5%
DTHGEM NeCF4 10%
DTHGEM NeCF4 5%
1,0E+00
1,0E-01
1,0E-02
0
200
C. Azevedo et al.; arXiv: 0909.3191
400
600
DV THGEM (V)
800
1000
Signal shape is determined by the electron drift velocity and
the width and field strength in the induction gap.
• Smaller induction gap &
Single
photons
Electron drift time from THGEM
surface into holes (simulation)
R. Alon et al., arXiv: 0809.4382
R. Alon, MsD 2007, Weinzmann Institute
• Higher electric field
 Faster and narrower
signals
Time Resolution with MIPs:
Variations in rise-time, shape and amplitude
(in addition to statistics of primary ionization)
Micromesh Gaseous Chamber: a
micromesh supported by 50-100 mm
insulating pillars
Multiplication (up to 105 or more)
takes place between the anode and
the mesh and the charge is collected
on the anode (one stage)
Small gap: fast collection of ions
Y. Giomataris et al, NIM A376(1996)29
Single photon pulse height distribution (Polya)
CsI coated mesh
Excellent S/N performance:
Single Photon Time Resolution:
Physical time jitters for UV photons 
electron diffusion in the gas and noise.
Micromegas Time Resolution : s ~ 700 ps
J. Derre et al., NIM A449 (2000) 314
The time information for each channel
is extracted from the peak time of the
ADC spectra. The strip with the earliest
arrival time is taken as reference.
A time resolution of ~1 ns results in space points with a
resolution along the drift direction of ~50 μm
T. Alexopoulos et al,
NIM A617 (2010) 161
InGrid: integrate Micromegas & pixel chip
by Si-wafer post-processing technology
• Grid robustness & Gap/Hole accuracy
Deposit
50 µm SU(8)
UV Exposure
0.8 µm Al grid
Pattern Al
Development
of SU8
photoresist
“Ingrid” + Silicon Protection Layer:
Apply Si3N4 (high
resistivity layer 3-20 mm)
for discharge quench
& SPARK
PROTECTION
“InGrid” Detector:
SiProt Layer
before InGrid
production
M. Chefdeville et al, NIMA556(2006) 490
Observe electrons (~220) from an
X-ray (5.9 keV) conversion one by
one and count them
in micro-TPC (6 cm drift)
Provoke discharges by introducing
small amount of Thorium in the Ar
gas - Thorium decays to Radon 222
which emits 2 alphas of 6.3 & 6.8 MeV
 Study single electron response
 Round-shape images of discharges
1.5 cm
Fe55
source
P. Colas, RD51 Collab. Meet.,
Jun.16-17, 2009, WG2 Meeting
M. Fransen, RD51 Collab. Meet.,
Oct.13-15, 2008, WG2 Meeting
http://rd51-public.web.cern.ch/RD51-Public
Collaboration of ~75 institutes
worldwide, ~ 430 authors
“RD51 aims at facilitating the development of
advanced gas-avalanche detector technologies
and associated electronic-readout systems, for
applications in basic and applied research.”
RD51 Collaboration Meetings:
1st - Amsterdam April 16-18, 2008 : http://indico.cern.ch/conferenceDisplay.py?confId=25069
2nd - Paris, October 13-15, 2008 : http://indico.cern.ch/conferenceDisplay.py?confId=35172
3rd - Crete (Greece), June 12-16, 2009 : http://candia.inp.demokritos.gr/mpgd2009/
4th – CERN, November 23-25, 2009 : http://indicobeta.cern.ch/conferenceDisplay.py?confId=72610
5th – Freiburg, Germany, May 24-27, 2010 : http://indico.cern.ch/conferenceDisplay.py?confId=89325
6th – Bari (Italy), October 7-10, 2010: http://indico.cern.ch/conferenceDisplay.py?ovw=True&confId=102799
7th –CERN, April 12-15, 2011: https://indico.cern.ch/conferenceDisplay.py?confId=132080
22
Freiburg , Germany, May 2010
Bari, Italy, October 2010
GEM
Consolidation around common projects: large area MPGD R&D, CERN/MPGD
Production Facility, electronics developments, software tools, beam tests
WG1: large area Micromegas, GEM; THGEM R&D; MM resistive anode readout (discharge
protection); design and detector assembly optimization; large area readout electrodes and
electronics interface
WG2: double phase operation, radiation tolerance, discharge protection, rate effects, singleelectron response, avalanche fluctuations, photo detection with THGEM and GridPix
WG3: applications beyond HEP, industrial applications (X-ray diffraction, homeland security)
WG4: development of the software tools; microtracking; neBEM field solver,
electroluminescence simulation tool, Penning transfers, GEM charging up; MM transparency
and signal, MM discharges
WG5: MPGD Scalable Readout System (SRS); Timepix multi-chip MPGD readout
WG6: CERN MPGD Production Facility; industrialisation; TT Network
WG7: RD51 test beam facility
23
Development of a portable multi-channel readout system:
• Scalable readout architecture: a few hundreds to several thousand channels
 Suited for small test systems up to very large systems (> 100 k ch.)
• Project specific part (ASIC) + common acquisition hardware and software
• Scalability from small to large system
• Common interface for replacing the chip frontend
• Integration of proven and commercial solutions for a minimum of development
• Default availability of a very robust and supported DAQ software package(DATE).
DATE
Root-based offline
Analysis
Contro
l
PC
Trigger,
clock and
control
Common
Clock
Data + Control
Control
SRU
40x
DTC point-to-point links
FEC
1000 BASE-SX up 500 m Multimode fiber (1 Gbit)
10 GBASE-SR up 300 m Multimode fiber ( 10 Gbit)
10 GBE
GBE
switch
network
(only for multi-SRU architectures)
....
SRU
....
40x
simultaneous data up 200Mbit/s per FEC.
...
FEC
FEC
FEC
FEC
chip
s
chip
s
chip
s
chip
s
Chip link interface
Application specific chip-carriers
HLT
GB-ethernet MM fiber or copper
ethernet
Specific
TTC
&
Trigger
Clock & timing
fibers / CAT6
Readout
Units
LHC machine:
GBE copper
Test systems:
DA
Q
Single mode fiber
Online/
Offline
…
DETECTOR
ADC frontend adapter
for APV and Beetle chips
ADC plugs into FEC to make a 6U
readout
unit for up to 2048 channels
18 ADC V1.0 produced in 2010
18 ADC V1.1 waiting for production
2011
FEC cards
Frontend hybrids
so far all based on APV25 chip
Version 1 proto: 5 working
Version 2 users: 11
Version 3 systems: 16 (CERN PCB + bonding
workshops), 320 (ELTOS + Hybrid SA ) = ongoing
Virtex-5 FPGA, Gb-Ethernet,
DDR buffer, NIM and LVDS
pulse I/O
High speed Interface
connectors to frontend
adapter cards
22 FECs V1.1 produced in
2010
16 FEC V1.3 ready for
production (all users booked)
Industrial partners survey for the production
For details please contact :
hans.muller@cern.ch
Detector Technology
• Pestov Counter
Typical time
resolution*
30-50 (ps)
(High pressure,
streamer discharge mode)
• Resitsive Plate
Chambers (RPC)
~ 1-5 ns (MIPs)
• MultiGap RPC
~ 50 ps (MIPs)
• Gas Electron Multiplier
~ 1-2 ns
- UV photons
~ 5-10 ns
- MIPs
• Micromesh Gaseous
Structures
- UV photons
- MIPs
~ 700 ps
~ 1-10 ns
* Numbers should be considered only as approximate