1. WPs assigned to the Accelerator Sector Groups for the neutrino platform TE-VSC involvement in: Tetra-Phenyl-Butadiene (TPB) coating of photomultipliers for the WA104 ICARUS experiment Paolo Chiggiato

2. This memorandum describes in detail the TE-VSC contribution. It is stored in EDMS 1531005.

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4. Why TPB coating onto photomultipliers? Energetic particles interacting with LAr produce scintillation ligth. The scintillation emission spectrum is in the VUV range with a peak at 128 nm. Such photons are perfectly transmitted in LAr, but will not be transmitted through glass. A fluorescent material is used to absorb VUV photons and emit photons in the visible range. For this purpose, TPB (tetraphenyl butadiene) is commonly coated onto the glass of the PMT. It is an organic material emitting in the blue range with a peak at 430 nm.

5. TPB deposition for WArP, irradiated with UV light.

6. Courtesy of B. Jones, MIT The transmittance of glass and the photocathode quantum efficiency are sufficiently high in the wavelength of TPB emission. wl shift Ar scintillation

7. Sharing of work and responsibility ICARUS Collaboration Logistic before and after coating. Cleaning of PMT surfaces. Availability of the coating equipment except the vacuum pumps and their control. Participation in the installation. Supervision of the series production. Functional tests. Dismounting and relocation of the equipment by end of June 2016. CERN TE-VSC (September 2015-June 2016) Availability of the vacuum pumps and their control. Technical support during installation. Technical guidance including quality tests of the coating during the commissioning. Technical assistance and quality assessment of the coating during the series production. Availability of the appropriate space in B. 169.

8. Present status The dedicated room has been cleaned (August-September 2015). Minor change of the compressed air circuit. Modification of lighting. Disassembly of the equipment for a complete cleaning in B. 867. First coating is expected on the last week of September. A status report will be prepared after the commissioning phase. Evaporation unit Storage 10.6 5.2 desk B. 169

9. Evaporator before disassembly for surface cleaning

11. Excellent and friendly collaboration between the two groups. No doubt we will provide the project with state-of-the-art TPB coatings in due time.