Quality control for large volume production gem detectors
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Quality control for large volume production GEM detectors. Christopher Armaingaud On behalf of the collaboration GEMs for CMS. Gain calculation. ). Counting the number of events with amplifier- Discriminator - counter Measuring the current with a picoampermeter.

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Quality control for large volume production GEM detectors

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Quality control for large volume production GEM detectors

Christopher Armaingaud

On behalf of the collaboration GEMs for CMS

Gain calculation


  • Counting the number of eventswith amplifier-Discriminator-counter

  • Measuring the currentwith a picoampermeter

Argon/CO2 (70/30)

NS2 chamberII

Computing the gain for every24sectors


About 2 weeksneeded to measure one single chamber.

Many manipulation needed.

External conditions change during the measure.

Gain Uniformityusing SRS system

Signal on the readout

Signal on the GEM used as a trigger

  • Difficulty of the measurement :

  • The noise of the signal on the GEM is high because of the size of the GEM.

  • APV needsverylow input charge, we have to run the detector withlow gain.

Reducing the noise with a large copper plate grounded and a filter to cutlowfrequencysignals

Pedestalrun to determine the level of the noise and offset for each APV

Raw data fromeach APV.

Charge collected

Time frames

« rawdata »

Weproduce a root file thanks to AMORE software


And weget the clusters informations

Withthesethreeobjects and a root macro wecan have everything

X dimension

ADC counts

Eta sector (Y dimension)

X dimension

Eta Sector 4

15 slices ->1 slice ~ 3cm

  • For eacheventwecompute the charge per cluster, and wereconstruct the spectrum of the X-Ray source

Eta Sector 4

  • Wefollow the peak position of the spectrumalong the chamber

Peak Position (ADC counts)

X Position (mm)

Eta Sector 5

Peak Position (ADC counts)

X Position (mm)

Eta Sector 6

Peak Position (ADC counts)

X Position (mm)

Eta Sector 7

Peak Position (ADC counts)

X Position (mm)

Eta Sector 8

Peak Position (ADC counts)

X Position (mm)

Uniformity Plot

PeakPosition Variation (%)

Top view

PeakPosition Variation (%)


Eta Sector

Time estimation with APV

  • Install the chamberat the end of the day and leaveflushingwithgas all night

  • 2h data taking

  • ½ day data analysis

  • 2 days are enough to install and test one chamber

  • This reducesenormously the QC/repair and validation of production chambers


    Compare twoweeks to twodays !!

GEM foil quality control

Paschen’slaw, experienced in nitrogen(http://www3.nd.edu/~dgo/teaching/AME60637/reading/1974_E_Dakin_Luxa_Oppermann_paschen_curves.pdf)

Breakdown voltage (V)

For a GEM foil, underatmospheric pressure 1,013Bar

60µm thickness, in nitrogen

P.d = 6.10-2 bar.mm

Vbreakdown= 600V (±50V)

Product pressure x distance (bar.mm)

GEM foil preparation

Atthis point wecan test the leakagecurrentbetween the sectors.

Soldering the protective resistors

Carefullleakagemeasurement of the foil


Under Nitrogen, atmospheric pressure.

From 0V to 500V weshould not seesparks.

And weshouldmeasure a smallleakagecurrent.


Set up already in place at RD51

Made by Eraldo.

Box withnitrogenflushing





Labview control and recording

HV Power supply

Current monitoring


Setting HV and measuring the leakagecurrentwith 50pA resolutionwith the samedevice.


From 0 to 500V by steps of 50V, waiting 120s ateach value.

If thereis a high currentrecorded, one step back in the voltage, if there are more than 3 steps back switch off.

On this 10x10 wesawsome high leakagecurrent, but thenitstabilized.

Volts applied on the GEM

Time (s)


Time (s)

Future plans

  • About the gain uniformity: severalotherrunsforeseenwhen the 6 large scale prototypes willbeready.

  • A cosmic stand needs to bedesigned to validate the final electronic and check chambersefficiency.


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