CERN: TRACS – Transient Current Simulator

In 2016, I was a Summer Student at CERN, the European Organization for Nuclear Research [1, 2], as the only student from Slovenia.
The emphasis was on working on an individual research project, supervised by a senior CERN scientist. Complementing the highly specialized research was a series of special invited lectures ranging from Particle Physics to Computing and Engineering [3]. Students also got a chance to attend hands-on workshops – I took part in the Cloud Chamber, ROOT, Silicon Sensors and Micro Pattern Gas Detectors workshops. All in all, it was an extremely valuable experience, being part of the world’s largest experiment, meeting fellow students from all over the world and also experiencing how big collaborations work efficiently towards a common goal of pushing forward the frontiers of human knowledge.

During my research stay at CERN, I was part of the EP-DD-DT: Solid State Detectors Lab, whose members specialize in R&D activities around semiconductor particle detectors and radiation damage [4]. The group is led by Dr. Michael Moll and is part of the CERN RD50 Collaboration [5]. I was supervised by Dr. Marcos Fernández (IFCA – Instituto de Física de Cantabria).
My project was further developing TRACS, a fast open-source simulator of transient currents in irradiated particle detectors, upgrading the functionality developed by previous Summer Students in C++ [6].
The basic calculation is based on the Schockley-Ramo theorem [7, 8], which states that the instantaneous induced current on a metal electrode due to the motion of a proximal charge particle is given by

(1)   \begin{equation*} i(t)=q\vec{v}(t)\vec{E}_w, \end{equation*}

where q is the charge of the particle, \vec{v} the velocity, and \vec{E}_w the so-called weighting field.
Radiation effects were implemented as a modification of the effective space charge and traps (radiation-induced defects in the material). The simulator is built on top of powerful open-source FEM libraries [9].

My main contribution was a severalfold improvement of speed (i.e., simulation time reduction) by parallelizing the code, enabling individual calculations to run concurrently on a larger number of physical processor cores.

The project report [10] can be found HERE.

I also presented my work at the CERN Poster Session [11].

The Poster is available HERE.

At the end of my summer studentship, a new CERN Fellow at SSD, Dr. Julio Calvo Pinto, took over the development of TRACS. Since then, the functionality has been greatly extended, including the initial idea behind TRACS: utilizing its speed and versatility to extend it into a fitting tool to match e-TCT measurements [11] by fine-tuning parameters. Using this procedure, we can extract parameters which cannot be measured in the lab, e.g. the effective space charge inside an irradiated particle detector.
A paper will soon be published in a peer-reviewed journal.



[1] CERN, the European Organization for Nuclear Research.

[2] CERN Summer Students.

[3] CERN Summer Lecture Programme 2016.

[4] CERN EP-DT-DD: Solid State Detectors group.

[5] CERN RD50 – Radiation hard semiconductor devices for very high luminosity colliders.

[6] Pablo de Castro, Álvaro Díez and Urban Senica. TRACS: TRAnsient Current Simulator., 2016

[7] Shockley, W. Currents To Conductors Induced By A Moving Point Charge. J. Appl. Phys. 9.10
(1938): 635.

[8] Simon Ramo. Currents Induced By Electron Motion. Proceedings of the IRE 27.9 (1939): 584-585.

[9] Fenics Project. Fenics Libraries.

[10] Urban Senica, Marcos Fernández. Optimization of a simulator of Transient Currents: parallelizing TRACS.

[11] Urban Senica, Marcos Fernández: Calculation of effective space charge of irradiated Si detectors: Comparing simulations with measurements.

[11] García, M. Fernández et al. Radiation Hardness Studies Of Neutron Irradiated CMOS Sensors
Fabricated In The Ams H18 High Voltage Process. J. Inst. 11.02 (2016): P02016-P02016.