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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 Characteristics Conclusion and Outlook Ongoing Studies
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)
Wilco Koppert (Nikhef) High Precision Measurements of Track-segments of Ionising Particles with GridPix Detectors 2 / 14
Concept Characteristics Conclusion and Outlook Ongoing Studies
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!
Wilco Koppert (Nikhef) High Precision Measurements of Track-segments of Ionising Particles with GridPix Detectors 2 / 14
Concept Characteristics Conclusion and Outlook Ongoing Studies
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
Concept Characteristics Conclusion and Outlook Ongoing Studies
GridPix
• Right: SEM picture from thechip with a grid
some example measurements:
• Sr-90 decay in B field (right),π-cathode interaction (left)
Wilco Koppert (Nikhef) High Precision Measurements of Track-segments of Ionising Particles with GridPix Detectors 4 / 14
Concept Characteristics Conclusion and Outlook Ongoing Studies
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
Wilco Koppert (Nikhef) High Precision Measurements of Track-segments of Ionising Particles with GridPix Detectors 5 / 14
Concept Characteristics Conclusion and Outlook Ongoing Studies
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)
Wilco Koppert (Nikhef) High Precision Measurements of Track-segments of Ionising Particles with GridPix Detectors 6 / 14
Concept Characteristics Conclusion and Outlook Ongoing Studies
Track Position Resolution
Position Resolution for aGridPix (1 mm gas layer)
Wilco Koppert (Nikhef) High Precision Measurements of Track-segments of Ionising Particles with GridPix Detectors 7 / 14
Concept Characteristics Conclusion and Outlook Ongoing Studies
Track Position Resolution
Position Resolution for aGridPix (1 mm gas layer)
Simulated resolutionagrees withmeasurements
Wilco Koppert (Nikhef) High Precision Measurements of Track-segments of Ionising Particles with GridPix Detectors 7 / 14
Concept Characteristics Conclusion and Outlook Ongoing Studies
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%
Wilco Koppert (Nikhef) High Precision Measurements of Track-segments of Ionising Particles with GridPix Detectors 8 / 14
Concept Characteristics Conclusion and Outlook Ongoing Studies
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
Wilco Koppert (Nikhef) High Precision Measurements of Track-segments of Ionising Particles with GridPix Detectors 9 / 14
Concept Characteristics Conclusion and Outlook Ongoing Studies
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.
Wilco Koppert (Nikhef) High Precision Measurements of Track-segments of Ionising Particles with GridPix Detectors 10 / 14
Concept Characteristics Conclusion and Outlook Ongoing Studies
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
Wilco Koppert (Nikhef) High Precision Measurements of Track-segments of Ionising Particles with GridPix Detectors 11 / 14
Concept Characteristics Conclusion and Outlook Ongoing Studies
Backup Slides (discharges)
Wilco Koppert (Nikhef) High Precision Measurements of Track-segments of Ionising Particles with GridPix Detectors 12 / 14
Concept Characteristics Conclusion and Outlook Ongoing Studies
Backup Slides (timewalk)
Wilco Koppert (Nikhef) High Precision Measurements of Track-segments of Ionising Particles with GridPix Detectors 13 / 14
Concept Characteristics Conclusion and Outlook Ongoing Studies
Backup Slides (gas)
Wilco Koppert (Nikhef) High Precision Measurements of Track-segments of Ionising Particles with GridPix Detectors 14 / 14
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