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Development of a new generation of micropattern gaseous detectors for high energy physics, astrophysics and medical applications. A.Di Mauro, 1 P. Fonte 2 , P. Martinengo 1 , E.,Nappi 3 , R. Oliveira 1 , V. Peskov 1 , P. Pietropaolo 4 , P. Picchi 5 1 CERN, Geneva, Switzerland

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Development of a new generation of micropattern gaseous detectors for high energy physics, astrophysics and medical applications

A.Di Mauro,1 P. Fonte2, P. Martinengo1, E.,Nappi3, R. Oliveira1, V. Peskov1, P. Pietropaolo4, P. Picchi5

1CERN, Geneva, Switzerland

2 LIP/ISEK Coimbra, Portugal

3INFN Bari, Italy

4INFN Padova, Italy

5INFN Frascati, Italy

In the last two decades very detectors for high energy physics, astrophysics and medical applicationsfast developments happened in the filed of gaseous detectors of photons and particles. Traditional gases detectors: wire–type and parallel plate-type (RPCs) -which are widely used in high energy and astrophysics experiments have now serious competitors: Micropattern Gaseous Detectors(MPGDs)

Due to the importance of these developments an RD 51collaboration

was formed a CERN

The aim of this collaboration is to coordinate affords from

various groups working on MPGDs

There are four main designs of micropattern gaseous detectors:

1) Strip type

Example: Microstrip gas counters (MSGCs)

A. Oed, NIM A263, 1988, 351

Glass substrate

3) Parallel-plate type

Example: Micromesh gas

chamber (MICROMEGAS)

Y. Giomataris et al.,

NIM A376, 1996, 29

2) Microdot


S.Biagi et al., NIMA392, 1997, 131

4) Hole type


CAT/WELL, Gas Electron multiplier (GEM)

A.Del Guerra et al., NIM A257, 1987,609

M. Lemonnier et al., Patent FR 2727525 , 1994

F. Sauli, NIM,A386,1997,531




The main advantage detectors: of MPGDs is that they are manufactured by means of microelectronics technology, which offers high granularity and consequently an excellent position resolution.

Due to their advantages the MPGDs cangue more and more applications.

In high energy physics they were already successfully used in:


Their use in CMS, ATLAS ALICE and in some other experiments under consideration

However, the fine structure of their electrodes and the small gap between them make MPGDs electrically “weak.” In fact, their maximum achievable gain is usually not very high, compared to traditional detectors, and without special precautions they can be easily destroyed by sparks, which may occur during their operation

(which is not the caseof traditional detectors: wire and parallel-plate type)

See for example g charles et al nim a648 2011 174

See, for example G. Charles et al., NIM A648, 2011, 174 small gap between them make MPGDs electrically “weak.” In fact, their maximum achievable gain is usually not very high, compared to traditional detectors, and without special precautions they can be

.. and sparks, unfortunately, in experiments are practically unavoidable

There are several methods of protecting micropattern detectors and FEE from destruction: segmentation of electrodes on smaller parts, protective diodes…These methods were successfully implemented in the case of GEM and in some MICROMEGAS designs

Alternative approach, which becomes more and more frequent inside the RD51collaboration, is the use

resistive electrodes.

The first micropattern detector with resistive electrodes was GEM, and later this approach was also applied to otherdetectors: MICROMEGAS and CAT (all had unsegmented electrodes)

Res. mesh

R.Oliveira etal., IEEE Nucl. Sci

57,2010, 3744


R.Oliveira etal., IEEE Nucl. Sci

57,2010, 3744

  • Res. GEM

  • Oliveir at al., NIM A576, 2007, 362

  • Res. CAT

  • Di Mauro et al., IEEE Nucl. Sci Conf Rec,

  • 6, 2006,3852

They were hybrids layout between gem and rpc

They were hybrids layout between GEM and RPC was GEM, and later this approach was also applied to other




The principle of operation of RPC: discharge energy is quenched because of the resistivity of electrodes

This study triggered a sequence of similar developments, which are nowadays pursued not only by our group, but by several other groups in the frame work of CERN RD51 collaboration

See recent reports at the 2nd Intern. Conf. on Micro Pattern Gaseous Detectors,

August 2011, Kobe, Japan (to be published in JINST)


A couple of examples of main developments will be given below:

See for example: which are nowadays pursued not only by our group, but by several other groups a photo of RETGEMfrom: R. Akimoto et al,presentation at 1st MPGDs conference in Crete,2009or

Spark protected RETGEMs and Res. CAT:

Several groups (mostly

Japanese) are now successfully

developing various designs of


Res. CAT developed by Breskin group

L. Arazi et al., JINST 7 C05011, 2012

Today we would like to present which are nowadays pursued not only by our group, but by several other groups

a new approach:

resistive electrodes segmented on strips

with a network of metallic readout strips

located under the resistive grid

Advantages: 1. More suitable for large-area detectors2. Better fit requirements for position measurements 3.Flexible in design implementation4. In some designs offer better rate characteristics


Tested configurations:

1) Resistive strips without intermediate layer between the strips and the metal readout strip

(see for example V. Peskov et al., NIM, A610 2009 169)

2) Res. electrode strips with a thin FR-4 glue intermediate layer

(R. Oliveura et al., NIM,A576,2007,362)

3) Resistive strips with a thick FR-intermediate layer

(T. Alexopoulos et al NIM A 640, 2011, 110)



As was shown in the previous slide, first we applied this new technology to resistive GEMs (~2009).In the last couple of years (2010-2012) we extended this approach to all other main micropattern designs.Below are examples of only three of such detectors.We choose them because they are oriented towards applications in which some members of our team are currently involved:1.RICH,2.Dual-phase noble liquid TPCs, 3. X/gamma ray imaging deices

1 resistive microstrip detector

1. Resistive microstrip detector new technology to resistive GEMs (

PCB with 5 new technology to resistive GEMs (μm thick Cu layer on the

top and two layers of readout strips

(oriented perpendicularly) on the








Milled grooved 100 μm deep and

0.6 μm wide, pitch 1mm.



Cathode res. strips


The grooves were then filled with

resistive paste (ELECTRA Polymers)


Anode strips

By a photolithographic technology

Cu 20 μm wide strips were created

between the grooves



Finally the entire detector was

glued on a supporting FR-4 plate

Cathode resistive new technology to resistive GEMs (


Connections to

X pick up strips

Anode strips

Connections to

Y pick up strips

Gas gains new technology to resistive GEMs (

Pos. resol. measurements

Rate characteristics


2 resistive microdot microhole detector

2. Resistive microdot-microhole detector new technology to resistive GEMs (

Manufacturing steps: new technology to resistive GEMs (

Multilayer PCB with Cu

layers on the top and

bottom and with the

inner layer with

readout strips






Upper Cu layer etching




The remaining grooves

were then filled with

resistive paste

(ELECTRA Polymers)






Removal of the Cu

Resistive cathode strips

Resistive anode dots

Filling with

Coverlay with

“dot” opening


Readout strips


Schematic drawing and a principle of new technology to resistive GEMs (

operation of res. microdot detector

(resembling MHC, see:

J. Maia et al., IEEE Trans. Nucl. Sci 49, 2002, 875)

Magnified photograph

Gas gain vs. the voltage of R-Microdot new technology to resistive GEMs ( measured in Ne and Ne+1.5%CH4 with alpha particles

(filled triangles and squares) and with 55Fe (empty triangles and squares).

Gain (triangles) dependence on voltage applied to

R-Microdotmeasured in Ar (blue symbols) and

Ar+1.6%CH4 (red symbols)and in Ar+9%CO2.

Filled triangles and squares –measurements

performed with alpha particles, open symbols - 55Fe.

In all gases tested the maximum gains achieved with the R-Microdot detectors

were 3-10 time higher than with R-MSGCs

Interesting feature: at high gains operates in self-quenched streamer mode

3 resistive microgap microstrip detector

3. Resistive microgap-microstrip detector new technology to resistive GEMs (

M-M- RPC manufacturing steps: new technology to resistive GEMs (

Multilayer PCB with a Cu

layer on the top and

one layer of readout strips

on the bottom, 0.5 pitch





Upper Cu layer etching


The grooves were then

filled with resistive paste

(ELECTRA Polymers)


0.5 mm



Removal of the Cu

Resistive strips

If necessary, filling with

Coverlay (an option)



Readout strips

Top view: new technology to resistive GEMs (




Surface resistivity

100kΩ/□(can be

adjusted to exper.


Total resistivity of

the zone B 500MΩ


Resistivity of

zones A and C

500MΩ (adjustable)





Resistive strips

This plate is in fact a reproduction of the resistive MICROMEGAS anode board(see the following talks)

The idea is to assemble from these plates a parallel- plate detector (M-M-RPC), so that the cathode metallic mesh is not used

Artistic view of the M-M RPC MICROMEGAS anode board

PCB sheet

Inner signal strips


resistive strips

From these plates RPC were assembled with gaps ether 0.5 or 0.18mm

An option with pillars similar to micromegas

An option with pillars (similar to MICROMEGAS) MICROMEGAS anode board

Res. strips


A fundamental difference between classical rpc and m m rpc

A fundamental difference between “classical “ RPC and M-M- RPC








Film resistor



resistive strips

Inner signal strips

M-M-RPC offers high2D position resolutions (with orthogonal strip or various stereo

strip arrangements to avoid ambiguity) and have potential for good timing properties

Gain estimation in an rpc geometry

Gain estimation in an RPC geometry: M-M- RPC



Photoelectron tracks


Fe anode




CsI layer

(Due to the time constrains the CsI coating was done by a spray technique)

M m rpc with spacers in corners

M-M-RPC with spacers in corners M-M- RPC

The highest gains were obtained with resistive micropattern detectors

(combined current and pulsed measurements)

Typical rate response

1 rich

1. RICH involved

(recent results)

The involvedVHMPID should be able to identify, on a track-by- track basis, protons enabling to study the leading particles composition in jets (correlated with the π0 and /or γ energies deposited in the electromagnetic calorimeter).

There is a proposal (LoI) to upgrade ALICE RICH detector in order to extend the

particle identification for hadrons up to 30GeV/c. It is called VHMPID.


The suggested detector will consist of a gaseous radiator (for example, CF4 orC4F10 ) and a planar gaseous photodetector

The key element of the VHMPID

is a planar photodetector


For details see a talk at this conference: DI MAURO, Antonello (CERN)

R&D for the high momentum particle identification upgrade detector for ALICE at LHC

Our previous prototype (very successful!) (for example, CF


Triple res. GEM with metallic strips

P. Martinengo, V. Peskov, et al.,

NIM, 639,2011,126

V. Peskov et all.,

arXiv:1107.4314 (2011) 1-7

HMPID readout


Cherenkov ring

Cherenkov light was detected


(For more details see A.Di Mauro talk)

Pilot studies: (for example, CF

(while LoI was written and circulated)

Main advantages:

Two times less elements,

Less voltages,

Very high gain

(an important safety factor)


Aging (to be studied)

New prototype (recently tested)


coated with CsI








FWHM (%)


Tests with EF vapors (for example, CF

Ist day

2d day


Inject EF and sealed when the signal was close to maximum

QE enhancement (after correction) is about 50%; work is still going on)

2 a new double phase detector work in progress

2.A new double-phase detector (for example, CF(work in progress)

The concept of usual double phase noble liquid dark matter detectors

The concept of (for example, CFusual double phase noble liquid dark matter detectors

Two parallel meshes

where the secondary

scintillation light is produced

From the ratio of


lights one can

conclude about the

nature of the interaction

Primary scintillation light

Several groups are trying to develop designs with (for example, CFreduced number of PMs

(there was work from Novosibirsk group, we made sealed gaseous PMs, Breskin group is working on sealed gaseous PMs ..)

One large low

cost “PM”

Large amount of PMs in the

case of the large-volume detector

significantly increase its cost

In E. Aprile XENON: a 1-ton Liquid Xenon Experiment for Dark Matter

It was suggested to use CsI photocathode immersed inside the noble liquid

(Another option for the LXe TPC, which is currently under the study in our group, is to use LXe doped

with low ionization potential substances (TMPD and cetera).

This suggestion was based on our (for example, CF

early studies which we made together

with Aprile’s team

However, this concept was never materialized in any detector…To verify feasibility of this approach we made some preliminary tests

PM detector…


10 cm

CsI photocathode

Experimental setup

(ICARUS cryostat combined

with a purification system)

Ar gas

Ar gas, room temper., 1 atm

Alpha source


V. Peskov, P. Pietropaolo, P. Pchhi, H. Schindler

ICARUS group

Performance of dual phase XeTPC with CsI photocathode and

PMTs readout for the scintillation lightAprile, E.; Giboni, K.L.; Kamat, S.; Majewski, P.; Ni, K.; Singh, B.KetalDielectric Liquids, 2005. ICDL 2005. 2005 IEEE International Conference Publication Year: 2005 , 345 - 348

LAr+ gas phase

The possible way to suppress the feedback detector…

Photodetectors?? (if microdot gain is insufficient)



Multiplication region

Resistive cathodes



(with HV gating







CsI photocathode

In hybrid R-MSGC, the amplification region will be geometrically shielded from the CsI photocathode

(or from the doped LXe) and accordingly the feedback will be reduced

Measurements in Ar at room and cryogenic temperatures (preliminary)



Results obtained

with alphas and 55Fe

No feedback pulses were observed



Stability with time

3 micrpstrip microgap for imaging applications

3. Micrpstrip-microgap for imaging applications (preliminary)

(Work just started)

Scanners: (preliminary)

  • X-ray

  • (edge on)

Pos. resol.

50μm in digital


rate 105Hz/strip

T. Francke et al.,

NIM A471, 2001, 85

T. Francke et al.,

NIM A508, 2003, 83



b) Gamma ray

30% efficiency for 400 keV

at shallow angle

Contacts with industry are established;

they already evaluate our prototypes

I. Dorion et al., IEEE Nucl, Sci., 34. 1987,442

Another goal was/is to combine (preliminary)

high pos. resolution with high time resolution.

First step in this direction was

already successfully done by Fonte et al

(see Proc. of Science, RPC 2012, 081).

Bidimentional position resolution 70μm

in with combination 80 ps timing

Besides the particle detections another application is

TOF- PET on which Fonte group is actively working

Above only three examples of applications in which members of our team are currently working were given

In reality much more work is going on

restive strip micropattern detectors.

A few more examples:

1) Res. TGEM with metallic strips for environmental and safety applications

(CERN-KTT project)

(this project is in a final stage, ready for commercialization)

Prototype of a flame detector

Sensitivity 100 higher any commercial


Prototype of Rn detector

Sensitivity is equal to commercial Rn detectors

Operating in on line mode, but ~50 times cheaper

2 a ochi et al resistive strips microdot detector

2) A.Ochi et al., Resistive strips microdot detector safety applications

Presented 10th RD51 collaboration meeting, October 2012

3) D. Attie et al.,

A piggyback resistive Micromegas

Presented at the RD51 meeting, December 2012

4) However, the most remarkable example is MICROMEGAS for safety applicationsATLAS upgrade

Resistive MICROMEGASis planned to be also used insome other applications, for example environmental (muon tomography of undergroundwater reservoir),

P. Salin, Presenation at the RD51 meeting,


…see also today presentations


Conclusions: safety applications

In progress

In a final stage

A new generation of micropattern gaseous detectors with resistive-strip electrodes combined with metallic 2D readout strips was developed. They offer excellent position resolution and are spark protected

2) We try to implement these detectors in several applications:


Noble liquid TPC,



3) A similar approach was in parallel developed by MAMMA collaboration and resistive strip MICROMEGAS will be employed in the ATLAS small wheel. More developments are in progress

4) Of course, these detectors have limited rate capabilities and this can be an issue in high rate environment, however some improvements in their rate characteristics still are possible

Back up slides

Back up slides safety applications

Optimization of the RPC electrodes resistivity for high rate applications

P. Fonte et al., NIM A413,1999,154

ATLAS R-MICROMEGAS characteristics applications



T. Alexopoulos et al., NIM A640, 2011,110

The concept of this detector is resembling the so called MHCP detector , however the important differences were that it was manufactured from a printed circuit plate 0.4 mm and had resistive cathode strips making it spark-protective.

Anode strips

Cathode strips


J.M. Maia et al., NIM A504,2003, 364

Rate response (MSGC): MHCP detector


The gas gain variations with counting rate.

Measurements were performed in Ne+10%CO2 at gas gain of 5103

(signal drop at counting rate >103Hz/mm2 is due to the PCB board surface

charging up, but not due to the voltage drop on resistive strips)

Preliminary MHCP detectorresults of measuremenst the induced signals on the strips:

Profiles of signals induced on pick up strips

(0.3mm wide collimator)

Results of measurements induced signals profile

from the readout strip oriented along

(green curve with crosses) and perpendicular to

the anode strips of R-MSGCs

(rhombuses, triangles and squares).

Rhombus- the collimator is aligned along the

strip #0. Triangles -the collimator was moved

on 200μm towards the strip#1.

Squares- the collimator was aligned between

the strip#0 and # 1. Measurements were

performed in Ar+10%CO2 at a gas gain of 5x103.

Correlation between the measured and actual

position of the collimator

More precisely the position

resolution will be determined

during the oncoming beam test



Gas gains MHCP detector

Pos. resol. measurements

Rate characteristics

The main detectors on which RD-51 is focused MHCP detector







All of them can be done resistive, hence spark protected