Riccardo Farinelli Physics Department University of Ferrara –...

Test beam resultsRiccardo Farinelli

Physics Department University of Ferrara – INFN Ferrara

R.Farinelli 2 Collaboration Meeting, 13-14 March 2017 - Beijing

Outline

●Brief summary on:

– GEM technology– Charge centroid and µTPC algorithm:

➢ Reconstruction method w/o magnetic field ➢ Results w/ angled tracks➢ Results w/ magnetic field

● Cylindrical GEM test beam and preliminary results

● Radioactive source studies


The Gas Electron Multiplier technology

Efield ~ 105 V/cm

● GEM detector amplified in 50µm holes produce by etching procedure. Here the Efield is ~105 V/cm

● A gain of ~ 103104 is achivable using several GEM. At this value the disharge rate is below 105

● Outside the holes an Efield is ~103 V/cm collect the electrons and to drift them to the readout plane made by segmented strips

● The signal shape depends by the gas mixture, the geometries and the involved fields.

50 µm

} ΔV = 200400 V

}

Gain ~ exp (ΔV)


Triple-GEM test beam characterization

● The tripleGEM characterized have 3 or 5 mm gap in the drift region and 2 mm in the others.

● The pitch size of the strip is 650 µm and a 2D readout

● A muon or pion beam @ H4CERN have been used● The dipole magnet Goliath can reaches 1.5 T in

both polarities● The gas mixtures used are Argon based:

Argon:CO2 (70:30) and Argon:iC4H10 (90:10)


● The avalanche dimension depends on the gas diffusion that is affected by the electric field and the gas mixture

● A weighted average position is measured from the fired strip and its performance goes beyond the digital readout that is constrained to the strip pitch

● The best performance of the charge centroid are achieved when the number of the fired strips is higher than 2

The charge centroid method

cathode

G1

G2

G3

anode

gap

qi

anode strip *

* Data with Ar:CO

2 (70:30)

gas mixture


µTPC method

• The time information can be used to improve the spatial resolution in magnetic field and in case of nonperpendicular tracks.

• Known the drift velocity from Garfield simulation, it is possible to assign to each fired strip a bidimensional point. These points are used to reconstruct the track in the conversion region

• A linear fit is used to reconstruct the path and to measure the particle position

cathode

G1

G2

G3

anode

z = ax + b

gap


CC & µTPC: angled tracks

cathode

G1

G2

G3

anode

cathode

G1

G2

G3

anode

cathode

G1

G2

G3

anode

• As the incident angle departs from the perpendicular one, the cluster size increase:

➔ this improve the µTPC performance but it degrades the CC because the 3 GEMs amplify the electrons and the diffusion increase the avalanche with a shape that it is not Gaussian.

*

* Data with Ar:iC

4H

10 (90:10)

gas mixture


● The magnetic field affects the electronic avalanche:

– the Lorentz force drifts the electrons,

– the magnetic field enlarges the charge distribution at the anode and the multiplicity largely increases,

➔ the charge distribution of the charge is no longer Gaussian and the charge centroid performance degrades

➔ µTPC reaches its best performance when the multiplicity is sufficient large

cathode

G1

G2

G3

anode

gap

qi

anode strip

CC & µTPC: magnetic field

LorentzAngle


What if we combine B and angle tracks?

Anode

G1G2G3

Cathode

B = 1 TB = 1 T B = 1 T


Scan angle w. B and Ar:iC4H10

● µTPC has to take into account the Lorentz angle to reconstruct the tracks with the magnetic field. That angle is calculated with simulations.

● The Lorentz angle with Ar:iC4H10 @ 1,5kV/cm drift field is ~ 26°. In this region CC is more efficient. In the other regions µTPC is flat around a resolution of ~130µm

● A combination of the two method should keep the resolution stable in the full range of incident angle


● This is the first implementation of the µTPC algorithm for GEMs in high magnetic field

● The Lorentz angle with ArCO2 @ 1,5kV/cm drift field is ~ 20°. In this region CC is more efficient. In the other regions µTPC is flat around a resolution of ~150µm up to high defocussing angle

● A combination of the two method should keep the resolution stable

Scan angle w. B and Ar:CO2


Which gas mixture can provide the best performance?


Gas mixture selection

● Ar:iC4H10 (90:10)– higher number of primary electron

generated per m.i.p. (~ 55.12 e in 5 mm gap)

– GEMs reach nominal gain (~10k) at ~ 270V/GEM and this leads to an higher electrical stability of the detector

● Ar:CO2 (70:30)– lower number of primary

electron generated per m.i.p.(~ 38.4 e in 5 mm gap)

– GEMs reach nominal gain (~10k) at ~ 360V/GEM and this leads to a lower electrical stability of the detector w.r.t. Ar:iC4H10

F.Sauli(1977)-- Principles of Operation of Multiwire Proportional and Drift ChambersA.Sharma – Properties of some gas mixture used in tracking detectors

* *

*

Optimization of the algorithm by varying the used drift field


What are the performances of a CGEM detector?


Cylindrical GEM test beam


Motivation

The aim of this TB is to measure the performance of the CGEM and to compare it with the results obtained with the planar GEM


Setup

● A CGEM and 4 planar GEMs have been used

● The CGEM geometry is 3/2/2/2 mm between the gaps

● We instrumented only a portion of the detector

● The CGEM and the GEM have the same reference system

● The CGEM has a 42° angle rotation to test the performance of the CGEM with 1T magnetic field along the longitudinal strip 42°


HV issue

● During the test beam there was a HV sector that could not reach the standard HV.

● We had to operate the data taking using a lower HV setting:– STD setting are these field: 1.25/3/3/5 kV/cm

➔ The results shown up to now use this configuration

– TB setting are these field: 1.25/2/2/4 kV/cm ➔ The transfer and induction fields are lower and this affect the charge collection and the performance of the CGEM

● During the data taking and the subsequent test the CGEM has been stressed, i.e. intense discharge (up to 30 µA), intense rate (up to 106 Hz/cm2), high gain (close to 105), ... ● The detector shows a very high stability and robustness. The only damage is the loss of a 1 of the 240 HV microsectors and this one was due to a human error during the power supply of the detector


Dependency of the charge collection from the fields in the literature

● Data measurements and simulations in literature show a strong dependency of the charge collection from the HV fields

➔ We have to fix the HV issue to increase the charge collection

0-7803-7324-3/02/$17.00 © 2002 IEEES. Bachmann et al. / Nuclear Instr. A - 438 (1999) 376}408*

*

*


The differences between STD and TB field setting

● Using a radioactive source of Sr90 we measured the charge collected by a planar tripleGEM for different setting:– low field vs high field setting

➔ Increasing the fields to the nominal values we increase the charge collection of about a factor ~1.5

– 3mm vs 5mm drift gap➔ Comparing the charge collection at the same fields the 5mm gains

a factor ~3 w.r.t. the 3 mm.


● Using a radioactive source of Sr90 we measured the charge collected by a planar tripleGEM for different setting:– low field vs high field setting

➔ Increasing the fields to the nominal values we increase the charge collection of about a factor ~1.5

– 3mm vs 5mm drift gap➔ Comparing the charge collection at the same fields the 5mm gains

a factor ~3 w.r.t. the 3 mm.

Courtesy of Lia Lavezzi*

*

The differences between STD and TB field setting


After several work on the CGEM to fix the HV issue ...


...we reached the STD setting

We repeated the radioactive measurement with the CGEM detector and we observed that the charge collected (blue line) is comparable with the 3 mm planar GEM (green line)

Courtesy of Lia Lavezzi*

*


CGEM preliminary results w/o B

● The collected charge increase as expected w/ the HV

● Also the cluster size increase with the HV

● An efficiency of 97.3% has been reached @ 395V on each GEMs

➔ The CGEM does not reach the efficiency plateau due to the uneffective HV settings that do not properly extract the electrons from the GEM holes

Cluster size

Charge

Efficiency


Comparison between CGEM and planar triple-GEM

● Comparing the results obtained for a planar tripleGEM and CGEM with 3 mm drift gap, we found same behavior

● The main difference between the two set of measurements is due to the electric field used that affect the CGEM performance by shifting its working point of several tens of Volts


Charge centroid spatial resolution

A spectacular spatial resolution has been achieved in these configuration !!

Remarks: no magnetic field is present and the results is measured with orthogonal tracks


Are these performance enough to match

the planar triple-GEM results?


CGEM Layer-2 remake and test

● A 5 mm drift gap allows to improve the efficiency above 98% in with a lower HV setting. This give the chance to vary the electric setting in a certain range, if needed

● Moreover a larger drift gap increases the cluster size of the signal and this is an important requirement of the µTPC performance that return its best value when the size is above 3.5

● The CGEM layer2 is going to be rebuilt● Two test beam are planned for the following period:

– Mainz TB: high rate TB to measure the µTPC performance with a particle rate above 104 Hz/cm

– CERN TB: muon and pion tracks to test the CGEM layer1 with a 5mm inside a magnetic field (1 T)


Conclusion

● A CGEM detector has been studied with a test beam in suboptimal setting. We could find an efficiency of 97.3% and 100µm w/o magnetic field by increasing the gain to very high values

● The results in the suboptimal condition can reach the ones in STD setting if we can collect the same charge

● A study with a radioactive source shows that if we run the CGEM in optimal condition we can reach the same performance of a planar tripleGEM

● In order to have an higher charge collection with a lower gain we decide to remake the CGEM layer2 with 5mm conversion gap. This will allow to increase the efficiency above 98% with lower HV, moreover it improves the µTPC performance and allow to reach the required performance on the entire detector area

Riccardo Farinelli Physics Department University of Ferrara –...

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