Mechanical design of the Pre-Production Detector Unit Model of KM3NeT Mario MUSUMECI and Riccardo PAPALEO KM3NeT PP DU subgroup coordinators

Mario MUSUMECI and Riccardo PAPALEO on behalf of DU subgroup mechanical specifications of the preproduction model - mooring line, anchored to the sea bed and tensioned by means of a top buoy, made by a vertical sequence of storey, able to host the scientific instrumentation necessary to perform the deep sea water neutrino detection and tracking -storey design compliant (shadowing, lightweight,...) with the Digital Optical Modules, hosting one DOM on each end - DOM’s horizontal spacing (storey’s length), 6 m - 20 storey, vertically spaced of 40 meters and twisted of 90°, around the vertical axis, one respect to the other, first from the seabed -DU deployable in a compact (stake) configuration, unfurl able once arrived on the sea bed 6m 40m

Mario MUSUMECI and Riccardo PAPALEO on behalf of DU subgroup to design an effective bracket to support the Digital Optical Module, due to its large active area, is a non trivial job. the system has, at the same time: to respect the specifications in terms of maximum shadowing (less than 2%), to follow the glass sphere’s squeezing due to the environmental pressure, to stand to the stresses due to the use in sea water DOM’s brackets preliminary design current design see E. Berbee Talk

Mario MUSUMECI and Riccardo PAPALEO on behalf of DU subgroup once decided to design an unfurl able mooring line, to find out a way to store the ropes in a safe and efficient manner is fundamental for the reliability of the system both during the unfurling and the entire lifespan of the Detection Unit at the same time, also the backbone has to be stored and maintained in position during the DU’s life ropes management system at the moment, the concept under testing is: to wind the 4 ropes of each storey around reels (2 on each storey’s side) and to arrange the 2 curled backbones around 2 of them

Mario MUSUMECI and Riccardo PAPALEO on behalf of DU subgroup the storey the storey design fits with the following specifications: maintain the DOMs at the assigned horizontal spacing host the ropes management system and the backbone keep the ropes system in the correct configuration minimize the drag stand to the stresses imposed by the surrounding environment and by the deployment minimize the shadowing on the DOMs (less than 2%) the storey are made by slender tubes (40mm OD) welded to made a lattice girder a sea water resistant aluminium alloy (5000 series, peralluman) is the material chose for the tubes 6m two further simplified and non instrumented beams, called “separator”, will be installed between the anchor and the first storey to guarantee to the DU stiffness against torsion around the vertical axis 6m the tapered shape of the beam aims to: minimize the shadowing on the PMTs maximize the strength of the girder maintain the centre of buoyancy above the centre of gravity the red bricks, made of syntactic foam, arranged in the middle of the storey are used to distribute the buoyancy over the DU, in according with the KM3NeT TDR, in order to avoid that a top buoy’s failure could have destructive effects.

Mario MUSUMECI and Riccardo PAPALEO on behalf of DU subgroup the storey Storeys at CPPM

Mario MUSUMECI and Riccardo PAPALEO on behalf of DU subgroup the anchor design fits with the following specifications: maintain the storeys in the packaging configuration during the assembly and deployment phase host the tool necessary to unfurl the DU after the connection with the secondary JB permit the safe unfurling of the storey (protection of the DOM) host the top buoys maintain the DU in stable position on the seabed after the unfurling phase First prototype built at CPPM the anchor

Mario MUSUMECI and Riccardo PAPALEO on behalf of DU subgroup fence the anchor

Mario MUSUMECI and Riccardo PAPALEO on behalf of DU subgroup status of the project, Feb by the middle of September the first so called “assembly meeting” has been organized. The meeting aimed to verify the interfaces between the single sub components, by using some real scale prototype. a mock-up of the anchor has been used to assembly to storeys, the ropes management system, the backbone and the DOM’s brackets. 2.all the components for the PPM-DU prototype (anchor + 5 storeys + 2 separators + 1 base + 2 dummy Dom + DOM support system and rope management system + buoy) are ready. The FAT of the buoy will be performed this week. 3.by the first weeks of march the second assembly meeting will be held at CPPM. first assembly meeting images

Mario MUSUMECI and Riccardo PAPALEO on behalf of DU subgroup sea qualification test the sea qualification test of the mechanical structure (with the oil filled backbone) will be performed thought different steps. the program of work is to qualify each sub item (the most critical) in a dedicated deployment test. in such way the complexity of the system under testing will be eased, in order to simplify the fault finding process. the qualification test will be focused on: - anchor’s - DU bottom item’s (anchor + base + separators) -unfurling trough 2 columns (4 storeys, 1 full column, + 1 storey in the second column) at the end of these three phases, if the concept idea shall be qualified, the group will setup a full mechanical tests with a complete DU made by - anchor - base + 2 separators - 20 storeys fully equipped with dummy DOMs, dummy backbones and storey buoyancy - top buoy See S. Henry Talk

Mario MUSUMECI and Riccardo PAPALEO on behalf of DU subgroup Conclusions The mechanical project of the Tower has been completed The manufacturing of the components for the PPM-DU prototype has been completed (some items have been built for the full DU, i.e. the buoy) within the middle of march will be completed the assembly of the PPM-DU prototype between March and April the DU group should be able to perform the first see qualification test of the PPM-DU prototype (See S. Henry Talk) Soon after the sea qualification test, a review meeting will be organized within a couple of weeks the program for the full qualification test of the mechanical items to be performed in the next months will be completed