1. MPGD 2013 Conference,Zaragoza July 1-4, 2012
Direct charge digital readout of dual phase Time Projection Chambers with GridPix
M. Alfonsi, N. van Bakel, A. P. Colijn, M. P. Decowski, H. van der Graaf, R. Schön, A. Tiseni, C. Tunnell
MPGD 2013 Conference,Zaragoza July 1-4, 2012

2. The GridPix detector Micro-Pattern Gaseous Detector with pixel readout
Aluminum mesh supported by pillars (50 µm gap)
Wafer post-processing (MEMS)
Timepix readout (256x256 pixels, 55 µm pitch)
4-8 µm resistive layer (spark protection)
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

3. The GridPix detector Micro-Pattern Gaseous Detector with pixel readout
Aluminum mesh supported by pillars (50 µm gap)
Wafer post-processing (MEMS)
Timepix readout (256x256 pixels, 55 µm pitch)
4-8 µm resistive layer (spark protection)
Single electron detection efficiency > 98%
< 20 µm spatial resolution
Time coordinate (µTPC)
Low noise (no dark counts)
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

4. Dual phase noble gas TPC
Prompt light (S1) is collected by photodetectors arrays, electrons drift to liquid surface
Charge is converted to light in the gas phase by proportional scintillation (S2)
Time Projection Chamber: Z from S2 – S1 time delay
S1/S2 ratio: large discrimination power between electronic and nuclear recoils
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

5. Direct charge readout
Within the DARWIN Consortium [arXiv: ], we investigate GridPix as direct charge readout
High spatial resolution
digital readout approach (high energy resolution at few e-)
Low noise (no dark counts)
Small device, mainly silicon, manufacturing processes:
Radiopurity
Low outgassing
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

6. Digital readout approach
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

7. Electroluminescence gain
Energy deposits from nuclear recoils up to 40 keV (e.g. Dark Matter searches)
~ few to 200 ionization electrons (depending on setup) make the S2
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

8. Electroluminescence gain
Energy deposits from nuclear recoils up to 40 keV (e.g. Dark Matter searches)
~ few to 200 ionization electrons (depending on setup) make the S2
Fluctuations to S2 due to:
Electroluminescence gain (proportional)
Light Collection Efficiency & PMT quantum efficiency (5-20% typical)
Xenon
Gain 31.4 sigma 7.5
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

9. Electroluminescence gain
Energy deposits from nuclear recoils up to 40 keV (e.g. Dark Matter searches)
~ few to 200 ionization electrons (depending on setup) make the S2
Fluctuations to S2 due to:
Electroluminescence gain (proportional)
Light Collection Efficiency & PMT quantum efficiency (5-20% typical)
Xenon
Gain 31.4 sigma 7.5
Xenon
Gain 31.4 sigma 7.5
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

10. Digital readout with pixels
Counting the number of hit pixels
Diffusion in the liquid negligible w.r.t the gas phase
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

11. Digital readout with pixels
Counting the number of hit pixels
Caveat:
Every electron in a different hole
100% single electron detection efficiency
Diffusion in the liquid negligible w.r.t the gas phase
(1) depends on pixel pitch and diffusion along the drift distance in the vapor phase.
Toy MC for the case of xenon (diffusion coefficients from Garfield/Magboltz)
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

12. Pixel pitch & diffusion in xenon
Pressure bar absolute
10kV, 55µm pixel pitch, 1.0 cm path
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

13. Pixel pitch & diffusion in xenon
Pressure bar absolute
10kV, 55µm pixel pitch, 1.0 cm path
10kV, 55µm pixel pitch, 3.0 cm path
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

14. Pixel pitch & diffusion in xenon
Pressure bar absolute
10kV, 55µm pixel pitch, 1.0 cm path
10kV, 55µm pixel pitch, 3.0 cm path
2kV, 55µm pixel pitch, 1.0 cm path
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

15. Pixel pitch & diffusion in xenon
Pressure bar absolute
10kV, 55µm pixel pitch, 1.0 cm path
10kV, 55µm pixel pitch, 3.0 cm path
2kV, 55µm pixel pitch, 1.0 cm path
2kV, 55µm pixel pitch, 1.0 cm path, 95% efficiency
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

16. Application to large area dual phase TPC ?
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

17. Large Area dual phase TPC?
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

18. Large Area dual phase TPC?
Maybe!
Recent production on 8” wafers prospects industrialization and large volume at reduced cost.
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

19. A small-size high-impact application
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

20. Light & charge yield in xenon
The response of the medium, i.e. the scintillation light (Ly) and the ionisation charge (Qy) yield, must be measured for electronic and nuclear recoils
Scheme from Manzur et al., Phys.Rev.C81 (2010)
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

21. Light & charge yield in xenon
The response of the medium, i.e. the scintillation light (Ly) and the ionisation charge (Qy) yield, must be measured for electronic and nuclear recoils
From G. Plante et al., arXiv:
Adapted from Manzur et al., Phys.Rev.C81 (2010)
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

22. Ly & Qy measurements Dedicated measurements:
neutron elastic scattering for nuclear recoils
Compton scattering for electronic recoils
small size noble liquid target θ
Neutron / Gamma generator
detector
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

23. Ly & Qy measurements Dedicated measurements:
neutron elastic scattering for nuclear recoils
Compton scattering for electronic recoils
small size noble liquid target
Systematic uncertainty from the unknown position within target or double scatters.
GridPix adds high resolution position reconstruction and digital charge readout! θ
Neutron / Gamma generator
detector
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

24. Xe Nikhef
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

25. Measurements with GridPix
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

26. Cryogenic robustness
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

27. New geometries under test
New geometries for the dykes (the “perimeter support” for the mesh).
Pillars with additional extended structures.
(NIM A718 (2013) )
Dummy wafers (full anode instead of Timepix) under test.
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

28. Pure nobles gasses
Measurements at CERN in 2011 in a gaseous and dual phase argon TPC
Measurements at Nikhef in a gaseous argon or xenon TPC
CERN 2011
Nikhef
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

29. Pure noble gasses
Stable operation with a reasonable charge amplification only with non ultra-pure gas (e.g. industrial standard argon %).
With argon % or xenon % we observe a sharp transition between a too small gas amplification region and the discharge regime
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

30. Future plans
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

31. Towards full ceramics Full ceramics devices under study:
SiO2 as insulator
Si-rich Si3N4 as the resistive material
Matching thermal expansion properties
Low Outgassing and high radiopurity
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

32. Towards full ceramics Full ceramics devices under study:
SiO2 as insulator
SiRN is the resistive material
Matching thermal expansion properties
Low Outgassing and high radiopurity
A resistive grid can limit the charge available for a spark to only one cell.
An embedded conductive network can distribute voltage uniformly
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

33. In the meanwhile… A more sensitive pixel electronics would be helpful
Recent literature keeps emphasizing that closed structure and confined amplification region are the key of success
Producing and testing GridPix with any GEM-like or other specific amplification structure can be time / money consuming
“Test the water” placing the amplification structure very close to a bare TimePix
Investigate some specific quencher that does not spoil the scintillation signal
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

34. Thanks for your attention!
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

35. Spare slides
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

36. CERN 2011 In collaboration with the ETH Zurich:
gaseous warm / cold argon TPC.
dual phase argon TPC.
IEEE NSS-MIC Conf. Rec. 2011, 92-98
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

37. CERN 2011: cold argon gas
The amplification of the GridPix can be verified with the light detected by PMT.
Average waveform (A.U.)
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

38. CERN 2011: cold argon gas Average waveform (A.U.)
MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi

39. MPGD 2013, Zaragoza July 2nd, 2013
M. Alfonsi