high precision measurements of track-segments of ionising particles with gridpix detectors · high...

Concept Characteristics Conclusion and Outlook Ongoing Studies

High Precision Measurements ofTrack-segments of Ionising Particles

with GridPix Detectors

Wilco Koppert

Nikhef, AmsterdamDetector R&D

January 18, 2012

Wilco Koppert (Nikhef) High Precision Measurements of Track-segments of Ionising Particles with GridPix Detectors 1 / 14


Concept: TPC

Gaseous Time Projection Chambers:

• Charged particles ionise the gas• Electrons drift to electrode (X,Y)• Drift time × drift velocity gives (Z)• Fit through all (X,Y,Z)

reconstructs track segment• Usually: huge (meters)



Concept: TPC

Gaseous Time Projection Chambers:

• Charged particles ionise the gas• Electrons drift to electrode (X,Y)• Drift time × drift velocity gives (Z)• Fit through all (X,Y,Z)

reconstructs track segment• Usually: huge (meters)

in the past!• GridPix detectors can be 1000

times smaller!



Concept: GridPix TPC

• Driftgap is meters-millimeters• TimePix chip, 256×256 pixels• 55 µm pitch• pixel: 10 ns time resolution

• The crucial part: the grid• Electrons drift through the grid• In between the grid and the chip

the field is large (100 kV/cm)• Multiplication takes place, signal

is measured by pixel

measures individual electrons!Wilco Koppert (Nikhef) High Precision Measurements of Track-segments of Ionising Particles with GridPix Detectors 3 / 14


GridPix

• Right: SEM picture from thechip with a grid

some example measurements:

• Sr-90 decay in B field (right),π-cathode interaction (left)



My Work: GridPix Performance Studies

• Analysis: resolution, efficiency• Tested :3 GridPixes (1 mm

gas layer) in the SPSaccelerator at CERN, tilted45◦

• Analysis is ongoing; someresults are shown in the nextslides



Track Position Resolution

Track Position Resolution is function of:

• ionisation number ∼ 5 mm−1 } gas property• electron diffusion ∼2×10−2 mm√mm

• clock cycle × drift velocity ∼0.01 mm• timewalk × drift velocity ∼0.13 mm• pixel pitch ∼ 5.5 × 10−2 mm } chip property

diffusion and drift velocity; function of the Electric field.timewalk; function of the charge on pixel

Resolutions can be adjusted by:-chip specs (see next talk, F. Zappon)-gas choice: CO2/DME (50:50)




Position Resolution for aGridPix (1 mm gas layer)




Position Resolution for aGridPix (1 mm gas layer)

Simulated resolutionagrees withmeasurements



Track Efficiency

• The number of ionisations is poisson distributed• The probability of 0 electrons is the inefficiency• From below the detection efficiency is estimated>98%



Conclusion and Outlook

Conclusion:• The position resolution agrees with simulations• The efficiency is as expected from simulations

Outlook:• The DAQ readout frequency is improved by factor 30• New beam tests are planned for this spring• A laser setup is being finished to investigate gas

properties• A step to mass production is taken (8” wafers)

because of high demands



Ongoing Studies

• GridPix is being investigated forusage in dual phase dark matterexperiments (right); see posterP07.13 (Rolf Schon)

• GridPix in proton therapy(bottom); data taken @ KVIGroningen, analysis ongoing.



Acknowledgements

• Nikhef: M. Fransen, H. van der Graaf, F. Hartjes, N.Hessey, J. Visser, P. Tsopelas, B. Huisman, R.Schon

• Bonn University: Y. Bilevych• KVI Groningen



Backup Slides (discharges)



Backup Slides (timewalk)



Backup Slides (gas)


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