2nd Allpix Squared User Workshop

17 Aug 2021, 13:00 → 19 Aug 2021, 18:00 Europe/Zurich

poster_2nd_allpix_squared_ws

Tuesday 17 August

14:00 → 15:00 Welcome & Allpix Squared Overview

Convener: Adriana Simancas (Deutsches Elektronen-Synchrotron (DE))

14:00 Welcome from the Workshop Organisers

The workshop organisers would like to welcome the participants to the 2nd Allpix$^2$ User Workshop. We would like to provide you with all necessary information to make this workshop a productive one.

Speakers: Adriana Simancas (Deutsches Elektronen-Synchrotron (DE)), Paul Schütze (Deutsches Elektronen-Synchrotron (DE)), Anastasiia Velyka (DESY), Katharina Dort (CERN, Justus-Liebig-Universitaet Giessen (DE)), Simon Spannagel (Deutsches Elektronen-Synchrotron (DE))

Welcome_APSQ_WS.pdf

14:20 Applications of the Medipix and Timepix ASICs

Hybrid pixel detectors have been the mainstay of vertex detection at the LHC because of their ability to provide clean images of particle events at extremely high rates. The Medipix and Timepix ASICs have demonstrated that the same technology can be applied to multiple other applications. These applications extend from the detection of background radiation in the classroom, to dosimetry in space, to the authentication of priceless art and to spectroscopic medical X-ray imaging and Single Photon Emission Computed Tomography. It was the combined efforts of a large community from different backgrounds which enabled the development of these very flexible ASICs leading to a myriad of new applications. This talk will try to demonstrate how from its origins in detector R and D for the LHC, hybrid pixel detector technology has reached and impacted on many other fields of science.

Speaker: Michael Campbell (CERN)

MC_Allpix2.pdf

MC_Allpix2.pptx

MC_Allpix2.pptx

15:00 → 15:30 Coffee break

15:30 → 17:10 Welcome & Allpix Squared Overview

Convener: Katharina Dort (CERN, Justus-Liebig-Universitaet Giessen (DE))

15:30 Allpix Squared 2.0 - An Overview

Allpix Squared has seen more than four years of continuous development and has been employed in a wide range of scenarios. Recently, the first major release since the initial stable version, 2.0, has been released. This version contains more than 1500 commits over the last feature release 1.6 and brings major improvements in many areas. Among them is a major rework of the framework core, introducing an efficient multithreading functionality including full reproducibility, as well as a large number of new features and physics simulation models.

This contribution provides a brief introduction to the framework and gives a overview of the new features.

Speaker: Simon Spannagel (Deutsches Elektronen-Synchrotron (DE))

2021-08-17-APSQWS-APSQ2.0.pdf

15:50 CSADigitizer: A Krummenacher Digitizer Module for Allpix Squared

This contribution presents the module CSADigitizer, a digitization module which translates the collected charges into a digitized signal, emulating a charge sensitive amplifier with Krummenacher feedback.

Speaker: Annika Vauth (Universität Hamburg)

2021-08-17_ap2_csa.pdf

16:10 The Multithreading Model in Allpix Squared

With the growing need for simulations of higher complexities, performance is critical to achieving acceptable simulation throughput. The large degree of independence of single events in high energy physics make them highly suited for parallel execution. For the release of Allpix Squared V2 the implementation of multithreading in the framework was completely rewritten from scratch to make use of the independence of Monte Carlo simulations.

This talk presents an introduction to the technical foundations of the multithreading model in Allpix Squared and how it handles abstraction from module developers. Various challenges are outlined that had to be overcome to bring strongly improved simulation performance without giving up on ease-of-use, one of the primary design goals of the framework. Finally, some real-world results are presented to show the possible gain in improvement compared to the previous version

Speaker: Koen Wolters (Eindhoven Technical University (NL))

multithreading_model_allpix_squared_wolters.pdf

16:30 Allpix Squared in Education & Outreach

Allpix Squared has become a powerful tool for studying and understanding complex silicon detectors. At the same time, the simple set up of simulation flows, the possibilities of visualising among others the charge carrier motion, the wide application range and the good availability of the software via e.g. CVMFS and local installations make the framework a valuable tool also for educational and outreach activities.

Over the past years, Allpix Squared has thus been used for university lab courses and research schools, with the goal of understanding the signal generation in silicon detectors as well as the possibilities to improve performance parameters such as the sensor resolution. In addition, the software has been used for the replication of complex test beam based experiments, e.g. within the context of the Beamline for Schools competition for high school students.

In this presentation, a few examples for the application of Allpix Squared in the fields of education and outreach are highlighted.

Speaker: Paul Schütze (Deutsches Elektronen-Synchrotron (DE))

2021-08-17_APSQ-WS-PS.pdf

16:50 Pyxel: the collaborative detection simulation framework

Pyxel is a novel python tool for end-to-end detection chain simulation i.e. from detector optical effects to readout electronics effects. It is an easy-to-use framework to host and pipeline any detector effect model. It is suited for simulating both Charge-Coupled Devices, CMOS Image Sensors and Mercury Cadmium Telluride hybridized arrays. It is conceived as a collaborative tool to promote reusability, knowledge transfer, and reliability in the instrumentation community. We will provide a demonstration of Pyxel’s basic principles, describe newly added capabilities and the main models already implemented, and give examples of more advanced applications.

Speaker: Matej Arko (ESA)

Pyxel_presentation_allpix_squared.pdf

Wednesday 18 August

13:00 → 15:00 User Applications & Studies

Convener: Adriana Simancas (Deutsches Elektronen-Synchrotron (DE))

13:00 Allpix2 simulations of the ELAD sensors.

The enhanced lateral drift (ELAD) sensor concept seeks to improve the position resolution by increasing the lateral size of the charge distribution already during the drift in the sensor material. The ELAD sensor design has been optimised using SYNOPSYS TCAD tool. The geometry of the buried implants, their doping concentration and the position inside the sensor were optimised for different sensor thicknesses and different types of substrate.
To estimate the position resolution of an ELAD sensor, the Monte Carlo simulations using the Allpix2 software have been performed applying the realistic electric field profiles from the TCAD simulations. In the Allpix2 simulations, 2D and 3D electric fields have been used. Results of the geometry optimisation are shown realising an optimal charge sharing and hence position resolution.

Speaker: Anastasiia Velyka (Deutsches Elektronen-Synchrotron (DE))

AP2_2021.pdf

13:20 Performance of Allpix Squared with regard to the usage in proton therapy

Proton therapy is, due to its higher precision of energy deposition, an effective
alternative to conventional x-ray therapy. Occurring uncertainties due to the use
of x-ray computed tomography in treatment planning can be reduced through
the use of proton computed tomography. To accurately predict the range of the
protons in tissue, it is necessary to reconstruct the tracks of the protons through
the body with the help of detectors.
A new track reconstruction software, Corryvreckan, was published in 2017 with
the intention of equally good track reconstruction capability with respect to
EUTelescope while reducing external dependencies. It bears great similarity
in its modular structure with the simulation software Allpix$^2$, creating good
compatibility between the two frameworks. The different implemented modules
in Corryvreckan ensure its usability for track reconstruction and analysis in
complex environments.
Applications of track reconstruction with pixel sensors are investigated at TU
Dortmund with regard to proton computed tomography.
The use of Allpix$^2$ in the context of proton computed tomography is presented
in this talk, for its utility of creating valid simulations, which can be further
processed with Corryvreckan.

Speaker: Christopher Krause (Technische Universitaet Dortmund (DE))

Christopher_K_Presentation.pdf

13:40 Detection efficiency simulations of the ATLAS-TPX detector

The ATLAS-TPX detector is a telescope made of two Timepix ASICs with silicon sensors facing each other. A network of 16 such detectors was installed in ATLAS during Run 2 (2015-2018) for characterizing the radiation environment. In order to measure charged particle fluences several effects had to be assessed, such as the performance of tracking algorithms, the impact of delta-rays or the background caused by gamma particles. For this purpose, a detection efficiency study has been performed using the Allpix2 framework.

Speaker: Dr Thomas Billoud (Czech Technical University in Prague (CZ))

Billoud.pdf

14:00 Sensor-level simulation of MAPS ECal test-beam data

A prototype of a digital pixel electromagnetic calorimeter, EPICAL-2, has been designed and constructed. It consists of alternating W absorber and Si sensor layers, with a total thickness of ~20 radiation lengths and an area of 30 mm x 30 mm. The design is the next step in pixel calorimetry, following up on a previous prototype using MIMOSA sensors [1]. The new EPICAL-2 detector employs the ALPIDE sensors developed for the ALICE ITS upgrade. This R&D is performed in the context of the proposed Forward Calorimeter upgrade for ALICE.
We have used the Allpix2 framework [2] to perform simulations of the detector response and the shower evolution in EPICAL-2. The detector geometry was implemented and simulation parameters were tuned to reproduce electron test beam results. The general performance of EPICAL-2 for electromagnetic showers was investigated as well as more detailed microscopic features of the shower development.

[1] JINST13 (2018) P01014
[2] Nucl. Instr. Meth. A901 (2018) 164–172

Speaker: Tim Sebastian Rogoschinski (Goethe University Frankfurt (DE))

210818_APSQ_TimR.pdf

14:40 Transient simulations of monolithic small collection diode CMOS sensors in Allpix Squared

Monolithic CMOS silicon sensors with a small collection diode are characterised by a low input capacitance that allows for a reduction of power consumption, a lower detection threshold and an increase in signal/noise ratio. However, the small collection diode design gives rise to non-uniform field configurations that are challenging to simulate and model, requiring an advanced simulation approach using a combination of Allpix Squared and 3D TCAD. In this contribution, the combined simulation is presented for the CLIC Tracker Detector (CLICTD), a monolithic pixelated silicon sensor fabricated in a modified 180 nm CMOS imaging process. The simulations are compared to test-beam data for devices with different sensor designs, different sensor thicknesses and different starting materials. Most notably, results for high-resistivity Czochralski wafers are shown, that enable a combination of the small collection diode design with a large depleted volume.

Speaker: Katharina Dort (CERN, Justus-Liebig-Universitaet Giessen (DE))

20210817_apsqUserWorkshop_smallCollElectrodeCMOS_kdort.pdf

15:00 → 15:30 Coffee break

15:30 → 17:00 User Applications & Studies

Convener: Anastasiia Velyka (Deutsches Elektronen-Synchrotron (DE))

15:30 Simulation of charge carrier transport in a dual-sided microstructured semiconductor neutron detector (DSMSND)

The dual-sided microstructured semiconductor neutron detectors (DSMSND) provide a much higher neutron detection efficiency as compared to a coated planar semiconductor device. This is achieved by alternatively staggering 6LiF-filled trenches between the top and bottom surface of a microstructured silicon diode. This design restricts neutron streaming paths and generates a more complex electric-field distribution and depletion characteristics in the diode, thus creating an indirect path for signal charge-carrier transport between device electrodes. Simulation of signal formation in these devices is performed in multiple steps. COMSOL Multiphysics software is used for simulating semiconductor physics and to obtain important quantities including depletion characteristics, electric field solution, and the weighting potential solution. Geant4 is deployed for radiation transport, interaction modeling, and optimization of the sensor geometry. Finally, Allpix2 is used for mobile charge carrier transport and total charge collection. The results of this simulation work provided an estimate of charge cluster shape and intensity for a pixel array configuration corresponding to the Timepix3 read-out system. The simulated neutron detection efficiency was 57.6%.

Speaker: Sanchit Sharma (Kansas State University)

Sanchit_AllPixWorkshop.pdf

Sanchit_AllPixWorkshop.pptx

15:50 Studies of anti-proton annihilation at rest with nuclei using Timepix3

Production of antihydrogen and its detection through annihilation are the basis of most of the precision experiments at the Antiproton Decelerator at CERN, which makes the antiproton-nucleus annihilation at rest one of the key processes. Monte Carlo simulations are mostly performed with the physics models included in Geant4, such as CHIPS and Fritiof (FTF), and recently also with FLUKA. However, they were developed either for hadronic interaction at high energy or for medical physics applications, where they have to be consistently accurate over MeV to TeV energy range. Their use at low energies was enabled by theoretical extrapolations, in spite of the fact that the low-energy annihilation mechanism is neither well understood nor accurately described. The near absence of low energy antiproton-nuclei annihilation data also remains the greatest obstacle for validation of the models.
We present here a systematic study of antiproton annihilation in carbon, molybdenum and gold, performed at the ASACUSA experiment at CERN, which involved the use of the quad array of Timepix3 detectors for detection and identification of the outcoming charged pions, protons, alphas and heavy fragments. This work consists on comparison between data and Monte Carlo simulations, which were digitized using the $Allpix^2$ simulation framework. Special features added to the framework to characterize better the clusters produced by the heavy charged particles will also be discussed.

Speaker: Giovanni Costantini (Università di Brescia)

allpix_workshop.pdf

16:10 Simulating hexagonal pixel cells in Allpix Squared

Silicon sensors featuring a hexagonal pixel pattern benefit from an accelerated charge collection in the pixel corners and reduced charge sharing due to fewer neighbouring pixel cells, which has the potential to improve time resolution and efficiency. The detector models commonly used in Allpix Squared assume rectangular pixel cells and cannot be used for devices with a hexagonal grid. To investigate the hexagonal pixel arrangement with Monte Carlo simulation, the HexagonalPixelDetectorModel is implemented, a new detector model class that is specifically designed for hexagonal pixel cells. In this contribution, the new detector model is introduced and the design concepts are outlined.

Speaker: Ryuji Moriya

Simulating_Hex_Pixels.pdf

17:00 → 18:00 Social Activity: Virtual DESY Tour

Thursday 19 August

13:00 → 15:00 New Features / Under Development

Convener: Paul Schütze (Deutsches Elektronen-Synchrotron (DE))

13:00 Simulation tools for radiation detectors before and after irradiation

Overview of simulations tools and techniques for irradiated silicon detectors

Speaker: Joern Schwandt (Hamburg University (DE))

Allpix2_js_20210819.pdf

13:20 Modeling of charge trapping after radiation damage in Allpix Squared

Radiation damage in silicon causes changes in the full depletion voltage, leakage current, and causes trapping of electric charge. This results in a decreased performance in silicon detectors as a result of decreased charge collection efficiency. At the large hadron collider, unprecedented levels of radiation will be seen by the next pixel detectors to be installed in the four large LHC experiments. To model signal in such pixel detectors after radiation damage using Allpix Squared, trapping is implemented on the level of charge propagation in Allpix Squared. The method and an usage are presented, as well as some first results.

Speaker: Jory Sonneveld (Nikhef National institute for subatomic physics (NL))

20210819_trapping_in_allpix2.pdf

13:40 Digitizer plug-in for Krummenacher CSA

Spectral fidelity, sub-pixel resolution and accurate timing are of particular importance for spectroscopic X-ray imaging as well as single particle track reconstruction. The maximum achievable detector performance strongly depends on the signal formation in the sensor, the transfer function of the charge sensitive preamplifier and the applied energy threshold.
For Timepix-like hybrid pixel detectors providing Time-over-Threshold and Time-of-Arrival information an additional per-pixel calibration for deposited energy and timewalk is needed. This calibration represents a crucial component in the detection process.

The most commonly used energy calibration is based on the measurement of the single pixel hit spectra for a set of X-ray fluorescence lines. In order to replicate measured energy calibrations and, as a further step, improve the quality of the calibration, a realistic simulation of the full detector system is needed.

In this paper we present an implementation of the simulation of the charge sensitive preamplifier, taking into account the dependence of the effective feedback current on the signal amplitude, the bandwidth limited output noise, threshold and feedback current variations, ToA and ToT clock frequency and clock phase shifts, which can be parametrized via the configuration file.

As a first test the plug-in will be used to validate and improve the energy calibration procedure for Timepix3 detectors. First results of the comparison of simulated and measured energy calibrations are presented.

Speaker: Pinelopi Christodoulou (Czech Technical University in Prague (CZ))

Allpix^2 Workshop.pdf

14:00 Simulations of ATLAS ITk strip detectors in Allpix-Squared

The ATLAS Inner Tracker (ITk) is the future central tracking system designed for the high-luminosity upgrade of the ATLAS Experiment. It will consist of pixel detectors at small radius close to the beam pipe and large-area strip detectors surrounding them. The strip subsystem is split into a central region with rectangular sensors and two forward end-cap regions with sensors featuring radial strip geometry.

The Allpix-Squared framework has been used for simulation and performance studies of the rectangular ITk strip detectors, yielding results in good agreement with experimental data obtained from test beam measurements of strip detector prototypes at the DESY-II test beam facility. This contribution will summarize recent developments focused on extending the Allpix-Squared framework to enable simulation of end-cap strip detectors with radial geometry. Such simulations will provide further insight into ITk strip detector performance and extend the scope of the simulation studies to the entire ITk strip subsystem.

Speaker: Radek Privara (Palacky University (CZ))

Strip-detectors_AP2UW.pdf

14:20 Allpix Squared Simulations of Multi-element Germanium Detectors for Synchrotron Applications

One of the major limitations of the X-ray Absorption Spectroscopy (XAS) experiment at synchrotron facilities is the performance of the detectors. In order to be able to measure more challenging samples and to cope with the very high photon flux and input count rate of the current and future light sources, technological developments to enhance the performance of various
detectors are necessary. A new generation of monolithic multi-element detectors with hexagonal pixels have been proposed for XAS applications mainly to maximize the compactness and granularity of the traditional multi-element germanium detectors. In order to study detector performance, several configurations of the
new generation of multi-element germanium detectors have been simulated.
A simulation chain combining Allpix Squared simulation with 3D electrostatic field simulation performed with COMSOL Multiphysics® has been used. As Allpix Squared is dedicated to the simulation of silicon detectors, a special derived version of Allpix Squared has been developed and used to simulate germanium detectors as well as hexagonal pixel geometries. In this talk, several simulation examples to study the performance of simulated multi-element germanium detector will be shown. These simulations help to build a trusted simulation model to be used in studying variant hexagonal shaped germanium detector for future applications.

Speaker: Tasneem SALEEM (SOLEIL Synchrotron)

TSALEEM_AP2_Workshop_20210819.pdf

14:40 Collaborative Coding for Scientific Software

When collaborating with other scientists and engineers on a common framework, using the right tools and procedures are key to a successful result and a long-term maintainability of the software.

This contribution aims at providing an insight into the stance taken by the Allpix Squared developers on topics such as unified code formatting and coding conventions as well as the workflow of merge requests and code review and merge requests. Special attention is payed to the GitLab platform and its continuous integration feature used for ensuring integrity and functionality.

Speaker: Simon Spannagel (Deutsches Elektronen-Synchrotron (DE))

2021-08-19-APSQWS-Collaborative-Coding.pdf

15:00 → 15:30 Coffee break

15:30 → 17:00 Discussion & Open Questions

Conveners: Paul Schütze (Deutsches Elektronen-Synchrotron (DE)), Simon Spannagel (Deutsches Elektronen-Synchrotron (DE))