sergey belogurov, itep, moscow sts cad model. gsi, 19.04.07 sts mechanics: conceptual cad model...

Sergey Belogurov, ITEP, Moscow STS CAD model. GSI, 19.04.07

STS mechanics: Conceptual CAD model development Sergey Belogurov ITEP, Moscow

Engineer: Sergey Iovenko Baumann TU students: Alexander Semennikov, Sergey Glushkov


Outline

• Starting point – ALICE SSD mechanics• Effect of CBM peculiarities• Narrow or wide cabling• Integration of the Stations (sensors, modules, stations)

• Particular case – central hole of arbitrary size• Dead gaps in the long sensors• Few words about stereo-strips readout• Mechanical simulations• Conclusions


Starting point – ALICE SSD

Principal distinctions:- Barrel geometry ⇒ sag, extra rigidity- Cooling tubes (in our case air cooling is foreseen)- Equal sensors ⇒ translation symmetry ( CBM –

variable sensor size due to steep change of the track density vs. angle)

- More severe request for minimization of material

Ladder,top

ALICE SSD girder 0.25 g/cm (≈ Si in CBM)


How our design is affected by the CBM peculiarities The main goal of the conceptual design is to reduce amount of material inside the acceptance and to understand integration of the STS stations. 1 – We put a rigid frame outside the acceptance and thin support taut for rigidity inside (like a drum or a tennis racket). The support may be either planar or slightly developed in the 3-d dimension.2 - Cooling tubes are just removed3 - Different length of sensors require variable tilting angle for overlapping4 - attempts to minimize material in a single sensor supporting elements should be undertaken

1

• \



1

3

The gap, not angle is kept constant



1

3

4


Narrow or wide cabling?

For the discussion of the supporting structure one should decide about width of cables. Narrow cables allow to make more elegant construction.


Integration of the STS stations

In the case of CBM There is strong nonuniformity in track density, usage of only one type of the sensors is not possible. Nevertheless we foresee a kind of unification with a concept of basic module for each station.

Basic module for station 6 and station 6 (z=0.5 m)

4 cm

Overlap between modules


Integration of the STS stations

7 (z=0.6 m) 8 (z=0.75 m)9 (z=1.0 m)


Case of the station 8 – arbitrary central hole

Initially special size of central sensors was considered for st. 8. Here we explore another possibility

90 degree sectors of the station are shifted with respect to each other. It allows to have hole of an arbitrary size

Specially designed planar supporting structure may be used for realization of this positioning in a case of narrow cables.




The modules are mounted alternately from the front and the rear sides and overlapped in the following manner




Solution for narrow cables

Note that the leg of a bench-like part is rather short



For the wide cabling construction becomes more complicated with 2 separate layers


Dead gaps in the long sensors

A problem of the current layout: we overlap the sensors but do not care of the gaps between wafers!

Thinking about this problem we had a couple of simple (may be useless) considerations that I would like to communicate now.




1. It would be nice if double metal layers allow something like this (contact pads are away from the edge)




1. It would be nice if double metal layers allow something like this (contact pads are away from the edge)

2. Some dead gaps are probably unavoidable. In this situation one can try to improve the total efficiency by matching dead regions from different stations with each other. It would be interesting (if feasible) to extend this approach to full CBM.


About readout of stereostrips

N+N channels, S1= S0/8

θ~15°(tgθ=1/4)

N+N/2 channels, S1= S0/4

N+N/4 channels, S1= S0/2

N+N/8 channels, S1= S0

3. Double metal connection of the strips inside a sensor may help to control occupancy.Let S1 be an area around a hit, where any other hit

would introduce ambiguity in position measurement

Let sensor size be 2x4 cm2


Mechanical simulationsGenerally mechanical simulations may be used for analysis of the following issues• - Static distribution of stress and deformation under a specified load. • - Eigen frequencies of a mechanical systems• - Dynamic behavior in the vibrating environment.• - Stabilty loss (jumping to another metastable configuration under certain load).• - Thermal effects

Currently we are dealing with the first two questions.

Carbon fiber composites have a wide range of parameters (factor ~3 for E and Besides, it is an anisotropic material. For plausible simulations we need precise data about material to be used.

As a first approximation we took: Tensile modulus (E) 343 GPa

Tensile strength ( 4.7 GPa Poisson ratio 0.25 Density 1.75 g/cm3


Mechanical simulations (examples)

ALICE like girder has about 105 SF under

weight of the sensors

Various loads were applied to the ladder type module, leg cross section 0.3 mm x 1.1 mm Si wafers are well defended from stress in this configuration. One can carefully handle a module without breaking.

0.1 Nm


Mechanical simulations (examples)

Local bending of a combined sensor on the ladder


Conclusions

The model reported here is just one of many iterations.

It is much easier to make a new model than a real device.

However, it seems to be useful to check as early as possible how the detector would look like and what problems would be encountered.

We are strongly interested in communications with carbon structures manufacturers and experts, because realistic optimization work should let us to minimize amount of constructive material in CBM

sergey belogurov, itep, moscow sts cad model. gsi, 19.04.07 sts mechanics: conceptual cad model...

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