Putting Foils on the DUNE CPA

2

Introduction

● We are setting up a small working group to develop the method of installing WLS-coated reflector foils on the CPA.

● There is some R&D, tests and engineering work that needs to be done.

● This talk is a summary of things that were discussed or are happening.– Matching WLS with ARAPUCA coating

– Considerations about putting foils on DUNE CPA.

● Get in touch with me, if you'd like to get involved help out (andrzej.szelc@manchester.ac.uk )

3

Matching WLS between foils and ARAPUCA

ARAPUCA coating→

Foil Coating

pT TPB PEN Other

pTerphenyl

TPB Starting Point

PEN

Other

4

General comments

● ARAPUCA covered with same WLS as ARAPUCA – potentially best light collection efficiency (provided transparency of WLS on ARAPUCA is high – preparing measurements of TPB, PEN, pT on glass).

● ARAPUCA covered with a WLS “lower” than the foils – potentially good collection as well, although might have a 50% backwards effect.

● ARAPUCA covered with a WLS “higher” than the foils – lower light collections (ARAPUCA blind to reflected light) – need to add a lower filter version of ARAPUCA's (potentially no WLS on outside).

5

Tentative Light Yield Plots

Daniel Cookman, Manchester

Assuming 2.5%ARAPUCA efficiency.

Leaving some ARAPUCA's

uncoated on purpose to get uniform collection

(not best case scenario)

6

Tentative Light Yield Plots 2

Assuming 2.5%ARAPUCA efficiency.

Leaving some ARAPUCA's

uncoated on purpose to get uniform collection

(not best case scenario)

Daniel Cookman, Manchester

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● Current baseline design. Then:– Foils covered with pT:

● According to measurements, foils won't work at pT wavelenghts.

● Also, no experience with foils covered with pT.

– Foils covered with TPB● ARAPUCA's blind to reflected light (exclusive case).● Known technology.

– Foils covered with PEN● ARAPUCA's blind to reflected light (exclusive)● Need to figure out coupling to foils, and behaviour in

cold. ● Need to measure performance on foils (in progress)● Potentially could make foil preparation much easier.

– Foils covered with “other”. Bis-MSB?● Would need aging/behaviour in cold studies. Bis-

MSB less efficient than TPB for VUV.

ARAPUCA covered with pT

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ARAPUCA covered with TPB● Need a different WLS on the inside (ELJEN green?)

– Foils with pT, see previous slide. Also 50% backwards efficiency, probably not very useful.

– Foils with TPB● ARAPUCA's sensitive to reflected light (inclusive case, possibly with a small correction –

measurement being set up).● Known technology.

– Foils with PEN● ARAPUCA's sensitive to reflected light (inclusive case, possibly with a small correction –

measurement being set up).● Need to figure out coupling to foils, and behaviour in cold. ● Need to measure performance on foils (in progress)● Potentially could make foil preparation much easier.

– Foils with Other?● Would need aging/behaviour in cold studies. Bis-MSB less efficient than TPB for VUV.

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ARAPUCA covered with PEN● Similar wavelengths to

TPB. Would need R&D to develop coupling method. Not sure this is useful given the area of ARAPUCA's (evaporation is viable).

● Foils cases similar as per TPB.

Kuzniak & Broerman arXiv:1806.04020

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ARAPUCA covered with other(bis-MSB?)

● Bis-MSB efficiency measured by Ettore et al. Looks comparable to TPB at visible, but worse at VUV. Not as useful.

● Foil considerations then similar to TPB and PEN.

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Foil and ARAPUCA WLS matching

ARAPUCA coating→

Foil Coating

pT TPB PEN Other

pT

X X X X TPB Current:

LY excl.LY. Incl.– need WLS R&D on inside of AR.

X XPEN LY excl.

Some R&D needed for PEN

LY Incl.- need WLS R&D on inside of AR.(similar for PEN)

X XOther

X X X X

Dielectric breakdown studies• foils on cathode will need to tolerate some

charge build-up or voltage variation

- eg 0.5 cm perforations lead to 300 V variation on foil surface (from simulations)

• Checked HV breakdown strength across film/foil samples submerged in LN- samples sandwiched between 6 cm diameter

electrodes

- stepped up voltage until breakdown occurred

18/09/1812

ν ,νµ,ντνµ ν

WLS Foils (CPA)

Photon Detection Systems (APA)

LAr TPCv

∼

0

1

2

3

4

5

6

SNnu

0 200 400 600 800 1000 1200Z Position [cm]

800

600

400

200

0

200

400

600

800

Y Po

sitio

n [c

m]

energy: 25.8 MeV X Position: 119 cm

N opt hits: 32 N wire hits: 13

Only hits from Super Nova neutrinos

SNnu

≥

+HV

Clark Griffith, Sussex

CPA with Reflector Foil Concept• The goal is to preserve the current CPA construction as much as

possible, and to provide the option of implementing the reflector foils post CPA production.

• The preferred solution is to maintain the current CPA design, and include a set of attachment holes on each CPA resistive panel to allow the installation of reflector foils in smaller tiles on both sides of the CPA surfaces at ITF or in the UG cleanroom.

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From Bo Yu, and Francesco Pietropaolo

Reflector module option 1:• Construction: Laminate the 3M reflector foil on a thin FR4

backing sheet, evaporate TPB on the reflector surface, mount the reinforced reflector foil on the CPA panel.

• Pros: simple construction, no CTE mismatch• Cons: high likelihood of surface charging on the reflector foil and

results in sporadic breakdowns through the reflector sheet

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Potential distribution on a 8cm square fully charged reflector foil. The maximum voltage at the center of the foil is 1.6kV.

Potential contours and drift lines on a vertical cut plane

diagonal of the foil.

From Bo Yu, and Francesco Pietropaolo

Reflector module option 2:• Construction: Evaporate TPB on the 3M reflector foil, Enclose the

reflector foil on the CPA surface with a metal wire mesh frame. The wire mesh will bleed the charge to the resistive CPA channel.

• Pros: Solves the charge up problem; relatively simple construction

• Cons: Reduces the effectiveness of the current resistive CPA design due to the large conductive areas• Remedy: use insulating frame to hold the wire mesh, use 2 (redundant) closely

spaced electrical contacts to the CPA surface.

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From Bo Yu, and Francesco Pietropaolo

Reflector module option 3:• Construction: Laminate the 3M reflector foil on a thin FR4

backing sheet, perforate the lamination with an array of holes to expose the resistive surface on the cathode, evaporate TPB on the reflector surface, mount the reinforced reflector foil on the CPA panel.

• Pros: reduces the magnitude of surface charging to avoid breakdown and drift field distortion

• Cons: more complex construction; reduced reflector coverage

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Potential distribution on a 1cm square cell with 5mm hole. The maximum voltage at the corners of the cell is 290V.

Potential distribution on a 1cm hex cell with 5mm

hole. The maximum voltage at the corners of

the cell is 220V.

From Bo Yu, and Francesco Pietropaolo

Reflector module option 4:• Assumption: Availability of a transparent and resistive plastic

sheet (~1mm thick), either surface or bulk conductive. The resistivity should be no less than that of the CPA panel.

• Construction: Evaporate TPB on the resistive side of the transparent plastic sheet (if surface conductive only), encase the 3M reflector foil on the CPA panel by the resistive plastic sheet.

• Pros: no charging, no degradation of the CPA resistive property• Cons: the transparent resistive material has not been identified;

CTE mismatch

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From Bo Yu, and Francesco Pietropaolo

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Tests/R&D/needed

● Ting has found acrylic that is resistive. We now have a copy and will test how evaporation works on it and how it performs (option 4).

● Will be measuring transmittance at visible light of TPB covered glass, 450 nm filter, and reflectance of pT covered foils.

● Plan to test performance of foils on CPA in CERN test stand – talking to Francesco to establish time, likely to be late November time frame.

● Next steps – looking into DAB tests, and protoDUNE run II tests. ● In parallel, simulations ongoing to repeat performance studies being

done without foils. ● Engineering: design of a 4Pi evaporator. Could use crucible design

from DEAP, need to design a structure that holds plates in 4Pi, and a walk in cryostat to hold it.

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Conclusions

● Gearing up to define the method to install WLS-covered reflector foils on the CPA.

● Help is needed, please get in touch with me if you would like to contribute.