Mirco Christmann MAGIX Collaboration Meeting 2017 Construction and characterization of a GEM prototype detector for MAGIX Mirco Christmann MAGIX Collaboration Meeting 2017

Outline detector challenges construction of a GEM prototype detector data acquisition laboratory measurements measurements in the electron beam of MAMI summary and outlook short review of detector challenges for MAGIX and working principle of GEM detectors GEM detectors ideally suited for the MAGIX experiment proceed delivery  prototype detector introduce the system for data acquisition Iron source and cosmics beamtime end of June results relating to efficiencies

Detector challenges precise detector system active area: 1.20 x 0.30 m2 spatial resolution < 50 μm multiple points for track reconstruction high rate capability O(1 MHz) alternative to drift chambers Where we can not get the highest counting rates and the best spatial resolution at the same time A possibility to full-fill this detector challenges are micro structured gas detectors

GEM detectors they satisfy this criteria GEM foils have a low radiation length as well high electric fields in the holes e- avalanche high counting rates and spatial resolution reached routinely working principle pitch 140 micrometres Amplification foil double conical form thin structure

Construction of a GEM detector stretching and framing the foils condition at delivery active area: 10 x 10 cm2 electrical contacts leakage current < 10 nA @ 500 V no frame yet nitrogen  dry/ clean electrical contacts on both sides

Construction of a GEM detector stretching and framing the foils coefficient of thermal expansion is different cooled frame for stretching laboratory oven stretching thermal 0.07 mm per m and °C  three times larger Plexiglas about one hour at 50-60°

Construction of a GEM detector stretching and framing the foils glue a fibreglass frame on the foil cures in the laboratory oven cut into shape check leakage current again quickly 12 hours at 50-60°

Construction of a GEM detector stretching and framing the foils glue a fibreglass frame on the foil cures in the laboratory oven cut into shape check leakage current again ready for assembling do this for at least 3 gems and one cathode because we work with triple-gem-detectors

Construction of a GEM detector profile measurements of the foils evaluate the stretching procedure laser sensor plane table curvature much lower than for pre-framed ones how good our … is foil fixed on Al-block moved in a grid to measure the distance raw data + calibration matrix from measurement without foil distinguish between foil and rest  planar and quadratic fit Good tool for larger foils in the future

Construction of a GEM detector additional detector components needed 512-channel readout board 512 crossed copper stripes how to read out the data  topic of next chapter

Construction of a GEM detector additional detector components needed 512-channel readout board chamber (frame and cap) high voltage connection box

Construction of a GEM detector additional detector components needed 512-channel readout board chamber (frame and cap) high voltage connection box gas system prevent to have air in the chamber In this basic setup  system for data acquisition still missing

How to readout data? SRS (Scalable Readout System): data acquisition APV cards (128 channels each) Frontend chip Need an external trigger signal scalability

How to readout data? SRS (Scalable Readout System): data acquisition APV cards (128 channels each) scintillators for trigger signal Frontend cards of the SRS Max. current of PMTs 200 micrometres  relevant in later parts of this talk

How to readout data? SRS (Scalable Readout System): data acquisition APV cards (128 channels each) scintillators for trigger signal APV signals ① synchronisation peaks ② separation of timing frames ③ signal in a timing frame Take waveforms with a rate of 40 MHz Time frame adjusted to the signal length To make it more stable neighbouring channels

How to readout data? SRS (Scalable Readout System): data acquisition APV cards (128 channels each) scintillators for trigger signal APV signals 1-d hit position hit time Now we have all tools to start measurements and analyse the results.

Lab measurements basic tests with more simple setups energy resolution 55Fe-Spectra photo peak 5,89 keV escape peak 2,9 keV used only one strip  moved low energy iron 55 source over it  counted the pulses one measured the deposited charge of a hit with a QDC charge spectrum electron capture FWHM: 16%

Lab measurements basic tests with more simple setups energy resolution 55Fe-Spectra gain curve (vary UGEM) GEM voltages between 375 and 390 volts !!!Expected this behaviour!!! detailed study of the gain of each electronic part  real electron gain could be specified

Lab measurements basic tests with more simple setups energy resolution 55Fe-Spectra gain curve (vary UGEM) homogeneity test cosmics less events at the edges geometry of the setup First lab measurement with SRS Cosmics suited perfect Coincidence setup of two scintillators Explained by exp. Setup: -area of the scintillators covers only active GEM area -distance between scintillators -cosmics: angle not vertical apart from that: results very homogenous from electronic side: all channels work

Lab measurements basic tests with more simple setups energy resolution 55Fe-Spectra gain curve (vary UGEM) homogeneity test cosmics less events at the edges geometry of the setup 16 by 16 channels taken together find out if there are regions where the gas amplification of the GEM‘s is not so good the validity of this measurement is not so high, because it included only about 30,000 events in the electron beam of MAMI we get a much higher rate

MAMI beam time @X1 28/29th of June 2016 behind HV-MAPS detector on xy-table, scintillators fixed up to 350 fA 855 MeV setup located beamtime was no dedicated beamtime for MAGIX High Voltage Monolithic Active Pixel Sensors upcoming beamoptimization Wehnelt voltage was varied But before we come to the results I will show you the tools for data filtering

Filtering the raw data filter out the noise pulse width at 20% of Qmax aim is to distinguish between signals, which belong to the ionisation… and noise signals need suitable filter criteria for the raw data therefore we have a look at the individual pulses again

Filtering the raw data filter out the noise pulse width at 20% of Qmax distribution of pulse widths [25 ns] done for all pulses … is created steps are 25ns minimum after first 2 bars, could be a good cut level (pedestal peak?)

Filtering the raw data (A) width 1x25 ns (C) width 10x25 ns confirmed if we have a closer look at typical waveforms for specific pulse widths (A) No waveform  single short pulses are spread statistical  in average: a slight shift to the baseline (C) Single pulses correlate with the trigger signal; light blue regions: two peaks in the average shape  probably belong to double hits waveforms can be explained by two hits in a short time frame and they could cause a different number of electrons to drift in the direction of the readout board (B) width 4x25 ns (D) width 14x25 ns

Filtering the raw data filter out the noise pulse width at 20% of Qmax distribution of pulse widths [25 ns] B+D: mainly double hits A: mainly noise second filter: charge (A) Part is mainly shock noise and should be filtered out charge filter: in some cases necessary, but in most cases done by the SRS via a Pedestal File and a Zero Suppression Factor Pedestal Run: charge sensibility of each channel ZSF defines minimum charge of each channel With this filter tools we can determine the efficiencies of the measurements taken at our beamtime

Results: High Rate Tests 6 series of measurement: 0.5 - 2.2 MHz limited by trigger system electron detection at 1 MHz with efficiency >99.9% at maximum rate: efficiency >99.5% requirement full-filled look at the remaining events  efficiency High rate capability order of 1 MHz

Results: XY-Scan 25 series of measurement: 11.4 kHz, raster pitch 2 cm 9 measurements in the middle: 99.85±0.04% efficiency lower efficiencies @ edges efficiency is plotted as a colour scale each square stands for one measurement expected, because some electrons of the beam already hit the GEM frames field distortions but why is efficiency so much lower on the left and also in the lower part?

Results: XY-Scan 25 series of measurement: 11.4 kHz, raster pitch 2 cm 9 measurements in the middle: 99.85±0.04% efficiency lower efficiencies @ edges alignment of detector shift in beamspot positions I had a look at the beam positions of each measurement detector was not aligned perfectly  should be improved in following beam times

Summary & Outlook stretching and framing procedure profile measurements uniform result readout data: 512 crossed copper stripes SRS filter data by pulse width high rate tests efficiency >99.9% @ 1 MHz XY-Scan 99.85±0.04% efficiency in the middle physical introduction proofed: stretching procedure is suited assembling of the detector first tests with iron source and cos. in lab @ 20% of the charge maximum able to calculate the efficiencies of some measurements @ MAMI and a reduced efficiency at the edges due to the GEM frames

Summary & Outlook go bigger go thinner 30 x 30 cm2 GEMs are ordered same procedure (stretching, framing, …) go thinner thinner GEMs are ordered (10x10 cm²) foil based readout (Master Thesis: Yasemin Schelhaas) may improve it a little bit reduce the material budget in particular the 5 um copper coating for the readout structure a foil based readout is also planned. And there Yasemin will continue with her talk.