IBF studies of triple and quadruple GEM for the ALICE TPC upgrade
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Transcript of IBF studies of triple and quadruple GEM for the ALICE TPC upgrade
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IBF studies of triple and quadruple GEM for the ALICE
TPC upgrade
V. Peskov
Behalf of the ALICE TPC upgrade team
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I. Motivation
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Current ALICE TPC
IBF suppression 10-4, Gate opening time 100μs
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Challenge:
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The idea of theGEM-based TPC(it is not ALICE TPC!)
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Space Charge Effects
= 5 = 10
Current goal: IBF~1%, at a gain of 2000, ε ~10
Resulting field distortion can be corrected
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II. Earlier measurements of IBF by different groups
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2 4%@0.4kVcm
Modified by us Breskin review/table on IBF measuremenst
At what current measuremenst were done!?
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At effective gains of 104
Killengebrg et al
Two examples of exper. data:
Bachman, NIM A438 (1999) 376Gain 105
ALICE TPC9
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III. Earlier measurements of IBF by our TPC upgrade
groups
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TUM
TPC upgrade experimental sub-groups, involved in IBF studies, and their interactions
FrankfurtCERN
Tokyo Yale
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New important results!
Two important observations was made by a CERN and TUM teams:
1) IBF depends on Rate
2) IBF depends on gas gain
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Note:the difference in absolute values of IBF is due
to the different voltage settings used in our earlier measurements:
TUM used “Aachen/DESY” setting (shown earlier)CERN –used a setting close to the “Bachman et al” (also shown
earlier)
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Simple back on the envelope calculations indicate that IBF drop with rate is due to the
space charge effect
Detailed simulations made by Tokyo group fully confirmed the
role of the space charge in the IBF suppression at high rates
E=mc2
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Example: effect of gain in the case of triple GEM (low rate)
IBF
(%)
Gain
TUM setting
CERN setting
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The observed effects forced us to critically evaluate earlier works and triggers scrupulous
studies
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IV. Latest measurementsperformed by ALICE TPC
upgrade sub-groups
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IV.1.Triple GEM
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IV.1.1 TUM results
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TUM setup
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IBF close to 3 % was achieved with triple GEMin Ar- and Ne-based mixtures23
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IV.1.2. CERN results
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IV.1.2a. Triple GEM
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GEM-2,standard
GEM-3, standard
Vdr
Vt2Vb2
Gas chamber
Experimental setup:
2mmVt3Vb33mm
GEM-1, standard2mm
Vt1
Vb1
Gas :Ar+30%CO2
X-ray gun
80 mm
Conditions/restrictions: 40kV/10mA, to minimize the space charge effect,Gain ~ 2000, Vdr=400V/cm, current on readout plate 20-50nA
Transfer 1
Transfer 2
Induction
Drift
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LabView
• Use programmable CAEN N1471A HV PS for GEMs
• Use N471 HV PS for manual setting of drift voltage and current measurement (the fun part)
• Measure pad-plane current with Ohm-meter (1 M)
• GSI GEMs 2-2-3 mm
13.04.2012GEM lab Measurements - TPC
Upgrade
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Results of CERN measurements with triple GEM at CERN
ΔGEM1=250 VΔGEM2= 380 VΔGEM3 =400 VEtr1=4.5 kV/cmEtr2=variableEind= variable
Although our detector is different (much larger drift region ) TUM results were wellreproduced: I BF close to 3% was achieved , however ε~60-too much
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4.543. 53 Eind
0.1
0.2
0.3
0.4
E2
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A new approach: use one large pitch GEM
As follows from earlier measurements
of Sauli and Ropelewski and as well as
from the recent simulations, misalignment is
a very important factor in achieving low IBF
After several discussions with Leszek we decided to use one large pitch GEM to create strong misalignment
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IV.1.2b. Triple GEMwith one large pitch GEM
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GEM-2,standard
GEM-3, standard
Vdr
Vt2Vb2
Gas chamber
Experimental setup
2mmVt3Vb33mm
GEM-1, 280 μm pitch2mm
Vt1
Vb1
Gas :Ar+30%CO2
X-ray gun
80 mm
Conditions/restrictions: 40kV/10mA, to minimize the space charge effect,Gain ~2000Vdr=400V/cm, current on readout plate 20-50nA
Transfer 1
Transfer 2
Induction
Drift
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Gain scan at Vdr=400V/cm
Gain is another parameter to reduce IBFhowever, the price is an increase of ε
e32
IBF(%)
Gain
So the improvement due to the large pitch GEM was an a factor of 1,65
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GEM-2, 280 μm pitch
GEM-3, standard
Vdr
Vt2Vb2
Gas chamber
We also tested the arrangement when the large pitch was in the middle
2mmVt3Vb33mm
GEM-1, 280 standard2mm
Vt1
Vb1
X-ray gun
80 mm
Results were similar…
Transfer 1
Transfer 2
Induction
Drift
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IV.1.2c. Quadruple GEMwith one large pitch GEM
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GEM-3, 280 μm pitch
GEM-4, standard
Vdr
Vt2Vb2
Gas chamber
Experimental setup and a resistive divider
2mmVt3Vb3
3mm
GEM-2, standard2mm
Vt1Vb1
Gas :Ne+10%CO2 +5%N2
X-ray gun 80 mm
Conditions/restrictions: 40kV/10mA ,to minimize the space charge effect,Gain ~2000, Vdr=400V/cm ;current on readot t plate 20-50nA
Transfer 2
Transfer 3
Induction
Drift
120MΩVariable
Total90MΩ
1mm
GEM-1, standard
Vmax=8kV
Transfer1
…etc
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Gain
IBF
(%)
Measurements without a vertical beam in the center(data obtained after N2 replacement, when both gain and IBF for unknown reason increased.
Before IBF was 25% lower-changes in gas mixture?)
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Scans with vertical X-ray beam
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Gain 2310Distance (cm)
Distance (cm)
An
od
e c
urr
en
t (n
A)
IBF
(%)
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Scan in a perpendicular direction
ΔV1=210VΔV2=250VΔV3=285VΔV4=340VEtr1=4.3kV/cmEtr2=4.3kV/cmEtr3=0.12kV/cmEind=4.7kv/cm
IBF(%)
Distance (cm)
Due to the nonuniformity IBF measured with a parallel beam were always 30-50% better39
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Preliminary energy resolution measurement
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GEM-3, 280 μm pitch
GEM-4, standard
Vdr
Gas chamber
Experimental setup and a resistive divider
2mm
3mm
GEM-2, standard2mm
Gas :Ar+30%CO2
X-ray gun 80 mm
Transfer 2
Transfer 3
Induction
Drift
120MΩVariable
Total90MΩ
1mm
GEM-1, standard
Vmax=8kV
Transfer1
55Fe
Ortec142pc
Cu
The only transparent place
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ΔV1=325ΔV2=340VΔV3=380VΔV4=420VEtr1=4.5kV/cmEtr2=3.5 kV/cmEtr3=0.3kV/cmEind=4.5kV/cm
ΔV1=365ΔV2=365VΔV3=365VΔV4=365VEtr1=4.5kV/cmEtr2=3.5 kV/cmEtr3=0.3kV/cmEind=4.5kV/cm
41%FWHM
37% FWHM
Rodrigo treatment
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IV.1.2d. Quadruple GEMwith two large pitch GEMs
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GEM-3, 280 μm pitch
GEM-4, standard
Vdr
Vt2Vb2
Gas chamber
2mm Vt3Vb3
3mm
GEM-2, standard2mm
Vt1Vb1
X-ray gun
80 mm
Transfer 2
Transfer 3
Induction
Drift
120MΩVariable
Total90MΩ
<1mm
GEM-1, 280 μm pitch
Vmax=8kV
Transfer1
PicoammeterCurrent:45-185nA
Cu
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Example of a scan (for the first time with the vertical beam we observed IBF around 0.8%)
ΔV1=210VΔV2=250VΔV3=285VΔV4=340VEtr1=4.3kV/cmEtr2=4.3kV/cmEtr3=0.1-0.3kV/cmEind=4.7kv/cm
Etr3
Etr3
Ga
in
IBF
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V. Important works performed in parallel by TUM and
Frankfurt groups
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V.1.TUM results with quadruple GEM (all ordinary)
IBF of ~1% was reached 47
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One of TUM scans with usual quadruple GEM
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Cross –check: similar scans in the case of our/CERN quadruple GEM containing two
large pitch GEMs
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ΔV1=225V ΔV2=250V ΔV3=variableΔV4=variableEtr1=0.1-4 kV/cm Etr2=0.1kV/cm Etr3=4kV/cm Eind=4kV/cm
Our results at similar conditions
Etr1(kV/cm)
Etr1(kV/cm)
Ga
in
IBF
(%)
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Epsilon
Etr1(kV/cm)
ε
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V.2.Frankfurt results with quadruple GEM with two large
pitch GEM
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CERN, TUM and Frankfurt results have a tendency to
merge!
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Conclusions:
•We are approaching IBF ~0.5 and ε ~ 10 which is even better than our goal
• This can be achieved by various voltage settings which gives us flexibility in optimization
• We are focused now on finding optimum operational points offering at the same time low IBF (ε), sufficient energy resolution, stability with time and low sparking probability
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Acknowledgement
This work will be impossible without support from the RD51 collaboration.
Special tanks to Leszek and Eraldo for daily help and discussions,
and to Miranda and Rui –for efficient technical support
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