by Stefan Rossegger & Panos Charitos. Published: 13 October 2012

Stefan Rossegger - a CERN
fellow and creator of 3D models

Stefan Rossegger has been working with ALICE for the last 5 years. Originally he pursued his PhD thesis in ALICE working particularly on the calibration of the Time Projection Chamber (TPC). He has recently been awarded the ALICE Thesis award for his work on the TPC. Following that, he got a fellowship at CERN. Within the first year of his fellowship, Stefan implemented the calculation & calibration techniques of various field distortions within the AliRoot framework in order to improve the space point resolution within the TPC drift chambers.

Following this project, he decided to change topic. Therefore he moved on to work with the Inner Tracking System (ITS) upgrade project. “Since about 1.7 years, I am studying different options for the upgrade while being involved in the preparation of the Conceptual Design Report”.

When Stefan is not studying the performance of ALICE detectors he spends a bit of time in constructing 3D models. He explains to us that this is just a hobby for him as he tries to understand new things and techniques available on the open source market. He was always fascinated with geometry from a mathematical and artistic point of view.

"So 3D printing (or rapid prototyping in general) really simplifies things in this respect. My ideas are not restricted to ALICE, for example, I also designed a car-mount for my android phone in order to make better use of the built-in navigation."

The time needed for the creation of a 3D model always depends on its complexity and the availability of a drawing that would help in designing the object. For example “if a drawing exists, a simple detector model would take about a weekend”. On the other hand “tracks are obviously more tricky”. When Stefan and Magnus Mager worked on an import script into Blender which loads ESD files or even Kinematics – in order to produce a 3D animation movie of collisions – one of the ideas was to make a real time online event display for the public. In the end, the outcome was a small animation of a collision which also showed some parts of the ITS upgrade project. This small project was superseded by a much more professional work done by Kajsa Christiansson (see link).

After that, Stefan spent a few more weekends to create a python script in order to build a printable 3d model out of those imported tracks. “Printable means, no overlaps are allowed, minimal wall (and line) thickness had to be considered, some support had to be included since the parts cannot float freely etc.”

Printable 3D model of the ALICE TPC (including reconstructed tracks from the first PbPb collisions) and the current ALICE ITS by Dr. Stefan Rossegger

Stefan was familiar with 3D CAD programs since he attended a mechanical engineering school from the age of 14 to 19 before moving on to study physics. Although he adds that “Nevertheless, this foreknowledge became obsolete after blender, sketch-up and Co became available because now everybody can do those things with license free programs.

"It does not take a lot of time as long as you are willing to spend a few hours of learning and show some enthusiasm. So if you feel enthusiasm you can always try and see what you get up"

It might take some time in the beginning but once you familiarize yourselves with the software you can come up with amazing 3D models. Stefan recalls that “with blender (the program he used for the models) I started half a year ago. I spend a few days per month on some little ideas I had, one being the 3D "sculpture" of one of the first PbPb events recorded in the ALICE TPC". The outcome is shown below.

3D view of a "printable ALICE collision model" (collision details below):
Pb+Pb @ sqrt(s)=2.76TeV
Date/time: 08-11-2010 / 11:30
LHC fill: 1482; ALICE Run: 137124; Event #: 620;
Detector model: ALICE TPC - M 1:100

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