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(from http://alice-its.web.cern.ch/Alice-ITS/ITS-Services/Serv_000-0.htm )

An overview of the mechanical support of the ITS, FMD, V0, T0 and alignment services on the RB26 side (absorber) is shown in this picture. More details on such mechanical support can be found here .

The patch panels (PP) shown in these pictures are the nearest to the interaction point (IP). They are located at Z= -1020 mm from the IP, that is at 280 mm from the border of the ITS cone. This Z-position avoids clashes during the dismounting of the temporary support used to install the third cone (carrying the FMD-Si1) and the SPD before they are fixed to the ITS cone . The clearance between the PP and the active thermal screen of the TPC cone is fixed to 30 mm; the one between the service channels and the same thermal screen at the TPC end-plate is fixed to 28 mm. At present, the maximum length of all the PP along Z is 350 mm. Clearances and Z-position have been approved by the TB on Jan.27, 2003.

(from http://alice-its.web.cern.ch/Alice-ITS/ITS-Services/Serv_000-0.htm )

On the RB26 side, the inner radius of the small air ducts (455 mm) is fixed by the front-absorber and by the thickness of the grid supporting both the patch panels and the service channels. At present, the overall thickness of the small air ducts has been fixed to 15 mm. The maximum outer radius of the PP (580 mm) is determined by the clearance to the TPC thermal screen. The left and right angular gaps of 34° are reserved for the ITS rails. The top and bottom angular gaps (of 11°) are kept for reasons of symmetry with the RB24 side, where, during the TPC sliding, they allow for the passage of the tooling used to fix the ITS to the TPC. (see also here). The four large air ducts on the top and the bottom are presently foreseen to allow for air circulation in the gap between the ITS and the central part of the TPC.

(from http://alice-its.web.cern.ch/Alice-ITS/ITS-Services/Serv_000-0.htm )

On the RB26 side, at the TPC end-plate, the small air ducts still keep their thickness of 15 mm and the service channels for cables and cooling pipes have an overall thickness of 35 mm. At present, the structure of each cable channel + air duct for SPD, SDD, SSD and FMD is as shown here; no air duct is foreseen for T0-V0 and for the alignment monitoring (see here). More details on the patch panels for the different sub-detectors can be found at the following pages: SPD .

With respect to the RB26 side, at RB24 the services for ITS, FMD and alignment monitoring have to obey somehow opposite constraints: here the most critical constraint is on the maximum outer radius of the patch panels and of the services. This is because, during the installation procedure, the services and their support structure have to slide through the TPC to reach the ITS. After the services have been connected to the ITS and the FMD, the TPC slides over the service support and the ITS up to the nominal position.

When the TPC is brought to the nominal position, the conical section of the service-support chariot is inserted, bolted to the cylindrical section of the chariot and linked to the TPC service support wheels. Then, thanks to the hinges they have at their bend point, the service channels are opened to minimize the interferences with the PMD acceptance cone. In the present preliminary design the undisturbed PMD acceptance corresponds to 11.6°. This picture shows that the thickness of the PP can be significantly extended at smaller radii without interferences with the PMD acceptance cone. Also the length of the PP along Z (tentatively 355 mm, against the 350 mm on the RB26 side) is not particularly constrained.

The main constraint is related to the inner radius of the ITS-TPC interface rings carrying the devices, pointed by the red arrows, to which the ITS is effectively appended (top) and fixed (bottom). The value of such inner radius (560 mm) is partly determined by the need of adjusting the x-y position of the rings onto the TPC. This is to compensate for the small deformation of the TPC inner vessel under the ITS weight, and, therefore, to have TPC and ITS coaxial at the end of the installation. The clearance of the service chariot and of the patch panels with respect to the mentioned rings is fixed to a safe value of 20 mm (smaller than the clearances on the RB26 side). Therefore the maximum outer radius of any PP at RB24 has to be 540 mm.

Another major constraint is related to the opening of the service channels (once the TPC is at the nominal position) and to the support of the beam pipe. Due to a clash with the supports "C4" of the ITS rails, it is not possible to have 12 service channels per quadrant as for the RB26 side. The beam pipe has to be supported by four wires fixed to the TPC end-plate. Since they have to cross the service-channel shell, the service channels cannot be adjacent like at RB26. The upper part of this picture shows a preliminary placement of the channels and indicates that room is left for only 10 of them having the same size as those used at RB26. Taking into account that at RB24 there is no need for the V0 and T0 detectors (supported by the mini-spaceframe), 10 channels will be sufficient if the four light paths for the alignment monitoring can find place between the support chariot and the TPC (being verified). However, the different placement of the channels seems to impose a different routing of the services with respect to the RB26 side.

Here the envelopes of objects affecting the service routing at RB26 are reported. Referred drawings can be downloaded from: DRAWING 1, DRAWING 2, DRAWING 3, DRAWING 4. DRAWING 5, DRAWING 6. Drawing 1 and 2 show the envelope of the SPD cone for the RB26 side. It is assumed that a cone having the same outer dimensions will be used at RB24 for fixing the optical patch panel and supporting the SPD services when they are "opened" to their final position (in the space between this cone and the ITS cone). Drawing 3 shows the envelope of the SSD (and SSD) cones. Drawing 4 and 5 show the "third cone" at RB26. Its outer radius is such that the services of SPD, SDD, SSD and FMD can feed through between the 3rd cone and the ITS cone and reach the PP. Therefore the same (or smaller) outer radius has to be used at RB24 for the support of the beam pipe and of the FMD-Si2. Drawing 6, taken from Si-FMD preTDR v2.1, shows the positions of FMD-Si2 and of the second support point of the beam-pipe (detail A). It has been noticed that such position of the beam-pipe support cannot be used because: a) the stress applied to the wires of the beam-pipe support (10-40 kg per wire) is incompatible with the designed stiffness of the SDD and SSD cones; b) the tooling to stress the wires are hardly accessible because of the SDD services in that region; c) the same tooling risk to be in the acceptance cone of the FMD-Si2. Therefore, it was concluded that a dedicated structure for supporting the beam-pipe is needed at RB24 too.

Questo e' solo uno schizzo per mostrare i problemi che (mi sembra) stiamo avendo con gli FMD. In celeste ho disegnato il cono SSD, in rosso quello SPD, in verde il terzo-cono-lato-RB26. I rettangoli "honeycomb" sono scalati dalla figura 3.1 del TDR preliminare degli FMD e credo rappresentino le loro schede di elettronica. Ho cercato di ricavare le quote dai disegni di Beppe, Luciano e Adriano (spero senza grossi errori), nonche' da quelli sul sito FMD . E' del tutto evidente che serve un disegno serio almeno delle parti esistenti, inclusa la mensola dei connettori di Adriano (che forse e' addirittura in conflitto gia' con i rivelatori FMD) e la cosa mi sembra molto urgente guardano i possibili conflitti e pensando che gli amici di FMD saranno andati avanti a definire la loro schedina di elettronica. Urge definire gli spazi di cui abbiam bisogno come ITS prima che FMD vada troppo avanti.

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