Experiment Proposal - opera - Infn

order to suck air out, one side is not complete sealed. The packed brick is then pushed into a vacuum
vessel equipped by a heat sealer. After a vacuum tightness check, packed bricks are ready for installation
in the detector. Each brick is marked for further book-keeping.
Figure 36: Schematic layout of a brick assembly system. From left to right, ECC brick stacking,
temporary strapping, origami packing and vacuum packing machines.
4.3 Target walls
The ECC bricks are assembled in vertical walls perpendicular to the beam direction. Bricks are placed
with the 12.7 cm long side of the film along the horizontal direction. The mechanical accuracy in the
positioning must be of the order of 1 − 2 mm (Fig. 83). Each target wall is approximately square
and houses 51 bricks horizontally by 64 bricks vertically. Including clearances the total size of the wall
amounts to about 6.7 × 6.7 m 2 . The total weight of the 3264 bricks to be supported in a wall is about
27 ton.
The wall support structure is shown in Fig. 37 and Fig. 38. The mechanical structure in which
bricks are accomodated is made of thin stainless steel vertical bands linked with light horizontal trays
where the bricks are placed. This choice allows a light mechanical design in order to limit as much as
possible neutrino interactions in the target area outside the bricks themselves and to permit a small
spatial separation between bricks in transverse and longitudinal directions. The brick support structure
is suspended from the general wall support and pulled from the bottom.
Apart from the requirement of a minimum amount of dead material the main constraint in the
mechanical design of the target walls is to ensure easy and quick removal of bricks. The wall structure
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