The official FLUKA site: Single module geometry implementation.

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The module geometry was designed trying to profit of the big degree of symmetry of the calorimeter structure. The first version of this geometry was realized in rectangular shape [Implementation to FLUKA package was done by: G. Battistoni, B. Di Micco, A. Ferrari, A. Passeri and V. Patera ] with the material description given in the previous section.
FLUKA allows to define a symmetric geometric structure as recursive isometric transformations of a base structure. The base structure (referred to as base cell in the following) has to be defined in its shape and material composition, while the transformed regions (referred to as replicas in the following) are defined as void boxes whose boundary surfaces can be overlapped to the boundaries of the base cell. At the tracking level each time a particle enters in a replica region a transformation is performed in the base cell. The particle is propagated in the base cell and transformed back to the replica when it reachs the boundary of the base cell. These transformations, forward and backward, have to be provided by the user in the lattic.f routine whose code is reported in source code area .
In the reference system shown in Fig. 3 (the blue axis denote the frame which was used for simulations with FLUKA, the red coordinate system presents the coordinate frame of the KLOE detector) the base cell has dimensions of 52 cm x 1.2 mm x 430 cm, it consists of a lead block filled with 385 scintillating fibers and glue cylinders (Fig. 4).

Figure 3: The coordinate systems used in simulations.

Figure 4: Details of the implementation of the calorimeter layers [3].

This cell is replicated 199 times to build a total number of 200 layers forming the calorimeter module (see left panel in Fig. 5).

Figure 5: Cross section of the EmC module with rectangular and trapezoid geometry.
Visualization by the FLAIR program [4] using as an input a geometry setup files of FLUKA.

Each plane is alternatively shifted of 0.675 mm in order to reproduce the real fiber configuration (Fig. 6).

Figure 6: The KLOE fibers schematic view.

In order to implement the whole barrel calorimeter into FLUKA we extended the rectangular module to the realistic trapezoid shape. This has been achieved by declaration of a new base cell consisting of a scintillating fiber and glue cylinder both inserted into a small block of lead. The length of the cell is equal to the length of the module (4.3 m) and its cross section corresponds to the square of 1.2 mm, where the fiber diameter is equal to 1 mm and width of the glue cylinder equals to 0.1 mm.
Then this new base cell was replicated about 4000 times to build two triangular sections on the left and right side of the module (see Fig. 7). A lattice transformation from the 4000 replica to the base cell provides the needed translation.

Figure 7: Structure of the single module with trapezoid shape.

A complete visualisation of the new trapezoid geometry [Visualization is based on the FLUKA sources and prepared using a FLAIR (FLUKA advanced visualization geometry tool [4])] is shown in Fig. 5, whereas the scatter-plot of single energy deposits from homogenously distribution photons hittting the module are shown in Fig. 8: a trapezoid structure which was built with realistic energy deposits from the scintillating fibers can be easily recognized.

Figure 8: Distribution of energy deposits in scintillating fibers
of a single unit of the electromagnetic calorimeter.

As a next step, it would be natural to replicate 23 times the defined geometry for one module and to build a full barrel. This task was unfortunately impossible to realise with the using by us version of FLUKA [FLUKA 2008.3 for GNU linux operating system] because this version doesn't permit to replicate the region which had been replicated before [5]. It is due to the fact that the lattice replication on the second and higher levels is not implemented yet. This is the reason why geometry was built in another, unfortunatelly much more complicated way.

Giuseppe Battistoni; INFN, Milano
Jaroslaw Zdebik; UJ, Cracow

Last updated: 26th of October, 2010

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