MIT Light Guides Jarrett Moon CSU DUNE Workshop 5/17/16
Overview Light Detection Goals Building Our Light Guides Attenuation Measurements Argon/Air Behavior Modeling Future Improvements & Construction Costs and Final Analysis Conclusions 2
Light Detection Goals (1) Efficient space usage – Want to use minimal space, need a low profile system (2) Collect lots of light – However we design our system, we need to ensure that lots of light is collected and subsequently transmitted to photodetectors How about SiPMs and flat panel light guides? Definitely space efficient, but can we collect lots of light? 3
Checklist... Breaking down some attributes we want from our system Space Efficient Collects lots of light Robust Design Economical Ease of Building 4
Checklist... Breaking down some attributes we want from our system Space Efficient Collects lots of light Robust Design Economical Ease of Building 5
Overview Light Detection Goals Building Our Light Guides Attenuation Measurements Argon/Air Behavior Modeling Future Improvements & Construction Costs and Final Analysis Conclusions 6
Building Our Light Guides ● Two well known major problems – Bars needed for (proto)DUNE will be long, we may lose lots of light to attenuation – Standard photodetectors can't see the 128 nm light from LAr 7
Wavelength Shifting With TPB ● Tetraphenyl Butadiene (TPB) is a well known and studied solution to the 128 nm insensitivity problem ● Use TPB to shift the VUV light to visible – Absorbs VUV and isotropically re-emits at 425 nm A TPB coated guide illuminated by a UV flashlight 8
Light Guide Construction ● Bars made of diamond polished UTRAN UVT acrylic ● The bars are annealed to prevent crazing ● The wavelength shifting coating is applied – TPB (shifter) – Toluene (solvent) – Ethanol (surfactant) – Dissolved acrylic (equal n) An acrylic bar being hand dipped in TPB solution 9
Light Guide Construction ● Latest and greatest series of bars (MIT 'wunderbars') are produced using the following recipe – 0.1 g TPB – 0.1 g Dissolved acrylic – 50 mL Toluene – 12 mL Ethanol ● Bars are dipped in this solution for 10 minutes then allowed to dry See our latest paper for a full description of the technique! http://arxiv.org/pdf/1604.03103v1.pdf 10
Light Guide Construction ● The latest bars have also been partly produced using a mechanized dipping system as opposed to hand dipping – Necessary for control over humidity – Allows for consistent dipping procedure 11
Overview Light Detection Goals Building Our Light Guides Attenuation Measurements Argon/Air Behavior Modeling Future Improvements & Construction Costs and Final Analysis Conclusions 12
Measurement in Air ● Measurements in LAr are costly and slow ● Use air data as input to model performance in LAr ● Use a position adjustable UV LED in a dark box to extract attenuation performance Example readout distribution Dark box setup with PMT, bar, and stepper 13
Results of Air Measurement ● Measurements in air show multi-meter attenuation lengths! ● Performance is tightly distributed 14
LAr vs Air Results ● Measurements in air are a great guide, but ultimately we really need a benchmark for LAr performance ● LAr measurements just too slow and expensive to do them for every bar ● Can we link the behavior in LAr to that in air in a rigorous fashion? 15
Overview Light Detection Goals Building Our Light Guides Attenuation Measurements Argon/Air Behavior Modeling Future Improvements & Construction Costs and Final Analysis Conclusions 16
Modeling LAr/Air Connection ● Try a 3 parameter ray tracing model – Internal reflection depends only on n air and n Ar – Photon loss per reflection – Coating thickness gradient ● Simultaneously fit forward and backward bar runs in air to extract these parameters 17
Model Results The model agrees well with our data, yielding a good prediction of the ● LAr curve based on air data – It correctly predicts the attenuation in LAr using only air data and n Ar – Essentially, can characterize LAr performance via air measurements An example of air measurements, predicted LAr attenuation curve, and overlaid LAr measured performance. 18
Model Predictions How do we anticipate our latest bars performing in LAr based on our air ● data? 19
Overview Light Collection in Liquid Argon Building Our Light Guides Attenuation Measurements Argon/Air Behavior Modeling Future Improvements & Construction Costs and Final Analysis Conclusions 20
Better Acrylic ● We noted that for our latest 'wunderbars' that the results were consistent with the bulk attenuation of pure acrylic ● Leads us to think we may not have actually seen the full potential of our current coating! ● Research currently underway has identified acrylics with attenuations ~2X better, tests on these will be carried out later this year – These acrylics have bulk attenuation > 4m – Every reason to expect substantial improvement with better acrylic! 21
Full Scale Construction Preparations to ramp up for full scale construction are underway! Main problem is sufficient clearance to dip/dry long bars Also need good climate control, ventilation, clean working conditions Suitable locations for performing bar coating and testing have already been identified at FNAL 22
Full Scale Construction Need to make modifications to dipping / testing equipment to facilitate large scale production Upgraded testing unit to run air measurements Upgraded mechanical dipping unit to perform on multiple bars simultaneously multiple dry air dips simultaneously 23
Construction Schedule Additional reinforcements arrive this fall as Len Bugel and new postdoc Adrien Hourlier join us at FNAL 24
Overview Light Collection in Liquid Argon Building Our Light Guides Attenuation Measurements Argon/Air Behavior Modeling Future Improvements & Construction Costs and Final Analysis Conclusions 25
Checklist... ● We have >2m attenuation length with more improvement possible! As a major bonus, quality control can be done in air ● Minimal number of parts, all of which are known to be stable under cryogenic conditions Space Efficient Collects lots of light Robust Design Economical Ease of Building Easy Quality Control 26
Easy to build? ● The construction and testing process is straightforward,well documented, and uses easily obtained parts ● With minimal training, the process is amenable to being performed by any interested university Space Efficient Collects lots of light Robust Design Economical Ease of Building Easy Quality Control 27
What Does it Cost? Item Cost for 2.2m x 4” bar UVT Acrylic, polished ~ $185 Coating ~ $68 Labor How hungry are the students? ● The bars and coating themselves are relatively cheap ~$253 each ● The labor involved can easily be done by students (i.e. both educational and cheap) 28
Checklist... ● So we can afford it too! Yay!!! Space Efficient Collects lots of light Robust Design Economical Ease of Building Easy Quality Control 29
Conclusions ● The attenuation length of the MIT 'wunderbars' is >2m, more than sufficient to be an effective light collection system ● It has a well established production and quality control protocol with several associated papers ● It is both spatially and economically efficient ● Production can be done at universities, resulting in greater collaboration and educational opportunities as well as low overhead 30
Acknowledgments Special thanks to the whole light guide team! Janet Conrad Len Bugel Gabriel Collin Ben Jones Zander Moss Kanika Sachdev Matthew Toups Stefano Vergani Taritree Wongjirad 31
Thank You! Questions? 32
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