Background simulation in Geant-4

Progress Report

G.Calderini, M.Bondioli

T.Fieguth (Turtle), C.Carr (MD)

At the time of the last presentation:

We had succeeded to have a G4 code reading a Turtle file as input

A few inconsistencies/bugs had been fixed and the code had been cross-checked.

We were ready to start extending the geometryof the beamline

Progress since last presentation

A) New elements

Radiation detectors:Jerry’s IP CsI/QuartzSVT PIN-diodesSVT diamonds

Beamline:

Q2 chambers

B) New tools

CAD support:

Solid Edge files for beam-line elements

CAD interface tools:

Tools to extract information automaticallyfrom CAD file and to translate to simulation

C) Implementation in GeantStrategy choice: use of Boundary Representation(BREPS) solids instead of Constructive SolidGeometry (CSG).

A) New elementsIn view of validation we started to implement radiationsensors in the simulation.

Example: CsI sensors

Lead box

Crystal

CsI / quartz IP sensors implemented

Diamond sensors / SVTRAD PIN diodes

Diamond sensor envelope

More complex structures, like the Q2s chambers,require a different approach

We reverted to CAD electronic files

The paper drawings were completely inadequate to provide enough information, given the complexity of the design.

B) New tools

CAD applications allow a much deeper insight in the structure of objects, by manipulation, zooming, change of viewpoints, direct measurement of length and distances

Even in this way, though, the retrieval of information is long and painful,even in the unavoidable case of simplifying the objects as much as possible

To this extent, Mario wrote an application which connects to Solid Edge (TM) , exploits OLE exported methods to browse the list of geometrical objects and their properties.

This allows to select a given part and to dump the information relative to that part with a formatthat we can choose at our convenience

Object browser

The procedure is actually more flexible than using formats like STEP, since:

It’s possible to select only one or few parts(oronly features, like edges or corners). More controlon objects against inconsistencies

It’s possible to simplify the structure inside SolidEdge and then save the simplified information

The output can be filtered, for instance to selectonly key points or primary objects (to further simplify the structure)

The output can be saved in a custom format(in the format of Geant-4 C++ description)

C) Implementation in Geant-4

The lack of Geant classes suitable to deal with irregular geometrical shapes (very common along the beamline!) prevented us from using the Constructive Solid Geometry approach.

We preferred an approach based on description by surfaces, which is available in Geant-4.The interface application to SE makes this processeasier, faster and more robust.

Compromise between accuracy in the description, time for implementation and lightness during execution

The time invested in the development of new tools will pay back in the future allowing:

The strategy was tuned using a complex partas are the Q2s, for which the parameterization is almost finished.

faster insertion of next elements easier implementation of changes in the accelerator design