Optical Readout Technology for Large Volume Liquid Argon Detectors
Nicola McConkey
University of Warwick
IPRD 2010, Siena, Italy
7 ‐ 10th June 2010
Liquid Argon TPCs
• Liquid Argon has been shown (ICARUS) to be a suitable medium for TPCs
– Calorimetry
– Fine Grain tracking
(A. Rubbia NuFact’05)
• Scaling up to large volume (100kton) necessary for application to next generation ν detectors
• Design of readout planes must keep electronics cost reasonable
The Concept
Liquid Argon Time Projection Chamber (TPC) with Thick Gas Electron Multiplier (THGEM) and optical readout using Silicon Photomultipliers (SiPM)
THGEMs
• Copper‐clad PCB with holes, with high voltage applied across dielectric.
• Excitation of Ar in the strong dipole electric fields in the holes leads to electroluminescence.
Light readout concept for Tracking
SiPM
THGEM
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• Arranging sensors in a sparse array The electroluminescence from above the THGEM allows fewer the THGEM holes can be imaged readout channels than holes, with by an optical readout device
no reduction in resolution.
Silicon Photomultipliers (SiPM) • Row and column readout gives 2N from SENSL have been shown to 0
readout channels rather than N2
work appropriately at ‐196 C (PK Lightfoot et al, 2008 JINST 3 P10001)
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Strong signal output
Features of this system
• Cost Effective:
– Modest number of readout channels
– Argon, PCBs for THGEMs cheap
• Strong signal:
– SiPM sensitivity varies with overvoltage used
– High gain of SiPM (of the order of 106)
• Stable detector:
– Homogeneous detector ‐ Liquid Argon only
– Short term temperature and purity stability
Proof of Principle
(PK Lightfoot et al, 2009 JINST 4 P04002)
• As the Drift field is turned down, the amount of scintillation light decreases:
• This suggests there was light produced in the THGEM by the drifted electrons from the Fe55 source
Proof of principle
Drift Field
2.5kV/cm
Secondary scintillation light pulse
produced by Fe55 source in LAr system
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The Energy spectrum of the SiPM was calibrated using the dominant peaks in the Fe55 spectrum.
There are clear differences visible between results with and without Drift field.
Secondary scintillation light spectrum from Fe55 in LAr
system, drift field 2.5kV/cm, (above) 0kV/cm (below)
No Drift
Field
(PK Lightfoot et al, 2009 JINST 4 P04002)
The Warwick Setup
• The basic experimental setup:
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Low energy γ source
THGEM
SiPM optical readout
Charge readout from THGEM upper plate
• The system includes:
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3 PT100 temperature sensors
2 Level metering devices
Pressure Sensor
Purity Monitor: • 2 ionisation chambers + drift chamber
• Detects cosmic ray muons
The Warwick Setup
Argon enters the system as gas, and is cooled and condensed by the liquid nitrogen in the surrounding bath and outer jacket.
Initial experiment plan
Confirm proof of principle:
– Investigating energy resolution:
• Using manufactured THGEMs, more uniform surface than one used in previous experiment
• Larger SiPM gives better statistics
– Multiple holes
• In the previous setup the SiPM was shielded to pick up only the light from one hole
• The SiPM will be exposed to the full 900mm2 area of THGEM
Improving THGEM models
• Measure frequencies of secondary scintillation light emitted
– Models suggests the majority of scintillation light is in the UV range
• Wavelength shifter used in the previous experimental setup
• Further work suggests photons in the near infra‐red range (A. Buzulutskov et al., arXiv: 1003.1597) • The current setup uses no wavelength shifter
– Further work will include SiPMs with varying optical filters to further categorise which wavelengths are produced
Tracking
• Application of the readout technology
• Small array of SiPMs
– Testing resolution of tracking
– Cold electronics for x, y plane
• Track cosmic ray muons
• Demonstrate readout technology is fit for purpose:
– Measuring first tracks using THGEM with optical readout in a LAr TPC
Future development
• With development, THGEM with optical readout could be used as part of a large volume (100kton) LAr TPC
• Modular setup gives a reasonably short drift distance, relaxes purity requirements
• This readout technology has the potential to provide a feasible alternative to the wire readout for LAr TPCs of the future