direct charge digital readout of dual phase time projection chambers with gridpix

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

The GridPix detector

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

• 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)

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)

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

Direct charge readout

• Within the DARWIN Consortium [arXiv:1012.4767], we investigate GridPix as direct charge readout

• High spatial resolutiondigital readout

approach(high energy resolution at few e-)

• Low noise (no dark counts)

• Small device, mainly silicon, manufacturing processes:RadiopurityLow outgassing


Digital readout approach


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:1.Electroluminescence gain (proportional)2.Light Collection Efficiency & PMT quantum

efficiency (5-20% typical)


XenonGain 31.4sigma 7.5




• Fluctuations to S2 due to:1.Electroluminescence gain (proportional)2.Light Collection Efficiency & PMT quantum

efficiency (5-20% typical)




Digital readout with pixels

• Counting the number of hit pixels


Digital readout with pixels

• Counting the number of hit pixels

• Caveat:1. Every electron in a

different hole2. 100% single electron

detection efficiency


• (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)

Pixel pitch & diffusion in xenon

Pressure 1.0757 bar absolute• 10kV, 55µm pixel pitch,

1.0 cm path




1.0 cm path• 10kV, 55µm pixel pitch,

3.0 cm path





3.0 cm path

• 2kV, 55µm pixel pitch, 1.0 cm path





3.0 cm path

• 2kV, 55µm pixel pitch, 1.0 cm path

• 2kV, 55µm pixel pitch, 1.0 cm path,95% efficiency


Application to large areadual phase TPC ?


Large Area dual phase TPC?


Large Area dual phase TPC?

• Maybe!• Recent production on

8” wafers prospects industrialization and large volume at reduced cost.


A small-sizehigh-impact application


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) 025808

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


Adapted from Manzur et al., Phys.Rev.C81 (2010) 025808

From G. Plante et al., arXiv:1104.2587

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

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

Xe TPC @ Nikhef


Measurements

with GridPix


Cryogenic robustness


New geometries under test

New geometries for the dykes (the “perimeter support” for the mesh).

Pillars with additional extended structures.(NIM A718 (2013) 446-449)

Dummy wafers (full anode instead of Timepix) under test.


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

Pure noble gasses

• Stable operation with a reasonable charge amplification only with non ultra-pure gas (e.g. industrial standard argon 99.997%).


• With argon 99.9999% or xenon 99.999% we observe a sharp transition between a too small gas amplification region and the discharge regime

Future plans


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


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


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


Thanks for your attention!


Spare slides


M. Alfonsi 36

CERN 2011

MPGD 2013, Zaragoza July 2nd, 2013

In collaboration with the ETH Zurich:- gaseous warm / cold argon TPC.- dual phase argon TPC.

IEEE NSS-MIC Conf. Rec. 2011, 92-98

M. Alfonsi 37

CERN 2011: cold argon gas

The amplification of the GridPix can be verified with the light detected by PMT.


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M. Alfonsi 38

CERN 2011: cold argon gas


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direct charge digital readout of dual phase time projection chambers with gridpix

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