1. GEM Development in India, test beam analysis and plan for next test beam
Anand Kumar Dubey
for VECC group, Kolkata

2. CBM Muon detector requirements:
Main issues:
The first plane(s) has a high density of tracks
-- detector should be able to cope up with
high rate. ~ 10 MHz/cm2
good position resolution
Should be radiation resistant
Large area detector – modular arrangement
suitable options:
micropattern gas detectors such as GEMs,
Micromegas, and more recenlty THGEMs.

3. Multi GEM configurations
For MUCH R&D : we have assembled and tested
double and triple GEMs prototypes

4. Schematic of prototype GEM chamber assembly
Readout PCB
GEMS
CERN made GEM foils obtained from
Area: 10cm x 10cm
Drift gap: ~7mm
Induction gap: 1.5mm
Transfer gap: 1mm
Drift plane (inner side copper plated)
12 x cm 12 cm x 10 mm

5. Detector fabrication at VECC for Sep08 beam test
Readout plane
256 Pads
8 mm x 3.5 mm
Outer side of the readout PCB
10 ohm Resistors for protection

6. Detector Biasing Scheme
---- symmetric mode of biasing scheme,
(i.e. same voltage across each GEM)

7. 3 GEM Signal from a fast preamp
Rms 40 ns~ 40 ns

8. Test with Fe-55 before shipping to GSI
det01
Tests done using standard NIM electronics at VECC

9. Test with Fe55 + nXYTER using 3GEM
Pulse height from Pad#20
nXYTER ADC
ADC
Subtracted ADC
ADC
DeltaV (GEM)
ADC

10. Testing of GEM chambers @GSI
At the SIS 18 beam line using proton beams of 2.5 GeV/c
Aim being :
-- to test the response of the detector to charged particles.
-- efficiency, cluster size, gain uniformity, rate capability,
position resolution and dynamic range study.
-- testing with actual electronics for CBM : nXYTER
-- testing with the actual DAQ
-- Aug08-- first successful test with n-XYTER(with 64
channels bonded ) + GEM was performed.
MIP spectra for 2GEMs and 3 GEMs were obtained.
-- Aug-Sep 09, In 2009 a fuller version of nXYTER with all
the 128 channels bonded was available. this offered a better
configuration for efficiency estimation and also for cluster
size estimation.

11. Sr-90 tests with nXYTER+3GEM
HV 3150V
HV 3050V
HV 2950V

12. Beam Region fired (2008) BEAM SPOT
3-GEM
BEAM SPOT
Only alternate channels hit, efficiency estimate couldn’t be possible

13. Test beam Aug-Sep: 2009
Main Features:
--- more number of days as compared to last test beam
--- A new fully connected nXYTER board
--- An X--Y movement facility was provided exclusively for the GEM ch.
--- A better trigger arrangement for efficiency studies.
--- STS, RICH + Panda (parasitic run with Panda)
Summary of data taken:
2 ROCs connected to one half of each detector
small cell size in det1 and large cell size in det 2
one day data: Both large pad sizes
--- First Day – Problem with SY1527 calibration
--- Movement in both X and Y
(Beam spot moved and went away)
Aux signals:
2 days data where Aux from different detectors can
be correlated (can be used for position resolution)
One day data for good AUX (crucial for eff)
Trigger data:
One run for 10 minutes

14. Readout Board for Test beam Aug-Sep 09
Inside view
Outside view
Two triple GEM chambers were built :
det 01 – with two different pad sizes(shown above)
det same size pads but with larger induction gap

15. TEST SETUP – Beamtest 2009

16. Aug-Sep09 test Protons of 2.3 Gev/c the beam profile on
Respective planes

17. MIP distribution of hit cell
Correlation between GEM1 and GEM2
Position of spots (cell units) from 2 detectors
Shown (well-correlated)
MIP distribution of hit cell

18. ADC distribution of main cell and variation with HV
4 fold increase in ADC for a deltaV(GEM) increase by 50V

19. PAD multiplicity -- no effect of induction gap on the cluster size
(Same granularity but different induction gap)
Two back to back
detectors similar pad
multiplicity..
No effect of increased
induction gap?
(Last day’s data, det2
had low eff, went
bad after 3500V)
Depends on beam profile, needs correlating with beam tracker
-- no effect of induction gap on the cluster size

20. Time difference between trigger(aux) and GEM ROC
Procedure:
Select fired GEM cells in nsec after last Aux.
All Aux channels: eff:10%
Aux-Channel=2 (4 fold) eff = 71%
Offset + Drift time(~150 ns)
-- why this large spread ??
---- copied from Sauli’s slides

21. Efficiency of detector 1 (large pad size)
Using AUX trigger
Time window:
nsec

22. Efficiency of detector 1 (large pad size)
Using STS hits
as reference
-- slides from Bipasha Bhowmick
(Calcultta University, India)

23. Efficiency Eff_66 HV= 3650 HV= 3750
Looks like the detector takes some time to become stable,
-- for HV scan, maybe 2 hours is perhaps short.
-- slides from Bipasha Bhowmick (Calcultta University, India)

24. Position resolution (Run #63)
-- slides from Bipasha Bhowmick (Calcultta University, India)

25. Cosmic Ray test setup at VECC
1. Detector+Ortec_142IH +572A+SCA+CFD
Detector+Ortec_142IH+TFA+CFD
3. Using MANAS coupled to PCI CFD card
4. Cosmic + Aux and nXYTER

26. Cosmic Setup and test with MANAS
TOP PMT(1)
LOWER PMT(2) IN
2FOLD OUT IN
Ch1
OUT
Ch1
GEM(4) IN
3FOLD OUT
Middle
PMT(3) IN
Ch2
OUT
Ch2 IN
4FOLD OUT
Ch3 IN
Ch3
Ch4
Ch4
Quad CFD
Quad COINC
P.AMP
MANAS
3FOLD IN
TFA
1.2 micro sec
Delay
Dual
Timer
Quad
Counter
NIM – TTL
Converter
Translator
Board
DAQ
(PCI CFD Card)
Patch Bus cable
Trigger
to DAQ
HV is from CAEN N470

27. Results with MANAS GEM signal connected to Channel 56 of FEE (MANAS)
Pedestal
64 channels for 4 MANAS
No of triggers( from 3 FOLD) = 187
Entries =158 => 85%
After pedestal subtraction -ADC of Channel 56

28. Thick GEM (THGEM) fabrication and testing
first attempt in India
THGEM – a thicker variant of GEMs(>0.4mm)
with 0.3 mm holes and annular etching
region of 0.1 mm
Main advantages:
-- Can be made from normal PCB’s using
simple mechanical drilling technique.
It “can” be damn cheap relative to GEMs !
-- is free from the complex operation of
framing and stretching unlike thin GEMs
-- easy to handle and hence more robust
Constraints: position resolution ~ 500 microns
10 cm x 10 cm
Obstacles: Accuracy in drilling holes
and etching of the annular region
0.5mm thick double-sided copper clad FR4 material.
hole size is 0.3mm and the pitch is 1.2mm.
made locally.

29. THGEM

30. A closer view of THGEM holes “eccentricity” problems
0.1 mm
0.5 mm
1.2 mm
“eccentricity” problems
The position of the rim is not concentric with the G10 holes
and the gap is too little at some places. Lost few
boards during tests
Fresh Boards ordered – tests going on

31. Fe55 Signal from Double THGEM
Not all THGEM boards could give a reasonable energy resolution.
--- this could be because of the eccentricity problems.
--- we are trying to think of different ways to improve on this.

32. Preparation for the next beam test
-- Two 3 GEM chambers with following granularity:
-- 3 mm x 3 mm 512 pads
-- 4 mm x 4 mm 512 pads
-- Get the efficiency problem fully understood using
cosmic trigger in lab
-- detector design:
The top cover would be sealed via an O-ring instead
of the present two component RTV.

33. Chamber PCBS for Test beam 2010
Bottom copper
Connector with
resistors
Top copper
GND Plane
Connectors for FEBs
Inner 1
Inner 2
Top copper
Pad area-
67*73 Sq mm For 3mm.
For 4mm - 88*97 sq mm
Main Features :
Both 3 and 4mm square pad sizes
Not Staggered (‘09 test beam module)
Symmetric Square Pads
Multi Layers ( 4) with GND Planes
Signal Tracks are distributed in 3 planes
Reduce the capacitance
Track to Track spacing increases
Reduce Cross talk
Blind Vias for gas integrity
Gnd Tracks between Signal Tracks

37. Connectivity Between FEB and ROC
TID: Total Ionizing Dose
at the outer edged of the
detector is around 10krad
Radiation dose
ROC boards may be affected by this radiation environment
Plan to put the ROC boards 3mt apart from the 0-axis
Detail dose calculation is needed at that point (seems to be falling fast)
The breakdown value of TID is also to be investigated for ROC components
Cable Type
Length of the cable to be known for error free communication
Shielded twisted pair flat type may be a good choice
Ref :
10 March 2010
Physics With FAIR: Indian Perspective, Susanta K Pal

38. Placement of ROC Boards
ROC stack
ROC stack
Tracking station plane
3mt (approx) 2m
10 March 2010
Physics With FAIR: Indian Perspective, Susanta K Pal

39. Physics With FAIR: Indian Perspective, Susanta K Pal
MUCH PCB design
Inner 1
Inner-2
Bottom Copper
Top copper
Blind vias from
inner layers( blue)
Blind vias (red )
to inner layer
2.6 mm
square pads
Modular Approach
Pads arranged in one block of 32*8=256.
Connected to 300 pin connector.
Tracks - shorter and not closer .
can be easily duplicated for bigger sizes.
40 such FEE Boards for One Slat of 1mt. Length..
Each block read by 1 FEB with 2/4 n-XYTERs ( 128/64 Channels)
FEBs can be mounted horizontal or vertical
10 March 2010
Physics With FAIR: Indian Perspective, Susanta K Pal

40. Physics With FAIR: Indian Perspective, Susanta K Pal
Conceptual sketch of Triple GEM chamber module
1 mt
Gas out HV
10cm
Gas in
To be decided
LV connector
Segmented LV power line/power plane on Detector PCB
each power line is feeding 5-FEBs
ground plane of LV line is in other layer of PCB
40 FEBs in one module in 1mt slat with about channels
10 March 2010
Physics With FAIR: Indian Perspective, Susanta K Pal

41. Chamber PCB Top side Inner 1 layer Bottom side GND Plane Inner 2 layer
4 sq mm pads. 32*32 Array(1024 pads).
PCB active area is 135mm *135 mm.
Read by 2 chip FEB(256 channels)
Basic block=32*8 array. Track lengths are short.
Top side
Inner 1 layer
Bottom side
GND Plane
Inner 2 layer Sa
SAMTEC-300 Pin connectors
2chipFEBs

42. Chamber PCB with 4 FEBs FEB 1 FEB 4 FEB 2 FEB 3 Bottom view of FEB
Top view with 4 sq mm pads
Bottom view –Connectors for FEBs

43. SUMMARY We are also trying to develop THGEM boards locally.
Double and Triple GEMs have been assembled at VECC.
Tests performed with radioactive sources as well with
proton beams.
We are also trying to develop THGEM boards locally.
Test with proton beams: Double GEM and triple GEMs
coupled to the first prototype of n-XYTER readout chip.
– preliminary response looked encouraging.
-- charged particle detection efficiency needs to be still higher.
investigations underway, using tests with cosmic rays.
cross talks issues to be resolved.
Next test beam: two chambers of 3x3 sq. mm 4x4 sq. mm chamber
would require 8 FEBs. May also skip resistor protection
Several layout s of the actual design of the Muon Chamber
are under discussion.

44. Thanks For Your
Attention

45. BACKUPS

46. The readout PCB beam only alternate channels connected to nXYTER.
This was because the first prototype of nxyter had this bonding problem.
beam

47. A 2-GEM ASSEMBLY at VECC – A FIRST ATTEMPT
10 cm x 10 cm GEM foil
Frame for GEM gluing
(0.5 mm in thickness)
stretching and gluing Jig
In the direction towards making a GEM based prototype, we started with assembling a double GEM

48. Slide from (Kondo GNANVO)
GEM & Micromegas : Gain
Gain stability
GEM
MWPC, MSGC & Micromegas
Slide from (Kondo GNANVO)

49. Readout plane-bottom Copper
ERNI Part no
4 No –68Pins
68 Pin connectors
for FEB 1nXGen
Resistors for
input Protection
68 Pin connectors
for FEB 1nXGen

50. Triple GEM: Test with Fe-55
3GEM: Gain vs. Vgem

51. Pad multiplicity/cluster size Position resolution
Questions remaining from last test beam
Absolute efficiency and HV dependence
Beam intensity dependence
Absolute gain estimate
Uniformity over small zone
New questions:
Pad multiplicity/cluster size
Position resolution
Required dynamic range before saturation
Induction gap (does it increase cluster size?)