Radiation mitigation for SRAM-Based FPGAs in the CBM experiment

  • Detectors of modern high-energy physics experiments generate huge data rates during operation. The efficient read-out of this data from the front-end electronics is a sophisticated task, the main challenges, however, may vary from experiment to experiment. The Compressed Baryonic Matter (CBM) experiment that is currently under construction at the Facility for Antiproton and Ion Research (FAIR) in Darmstadt/Germany foresees a novel approach for data acquisition. Unlike previous comparable experiments that organize data read-out based on global, hierarchical trigger decisions, CBM is based on free-running and self-triggered front-end electronics. Data is pushed to the next stage of the read-out chain rather than pulled from the buffers of the previous stage. This new paradigm requires a completely new development of read-out electronics. As one part of this thesis, a firmware for a read-out controller to interface such a free-running and self-triggered front-end ASIC, the GET4 chip, was implemented. The firmware in question was developed to run on a Field Programmable Gate Array (FPGA). An FPGA is an integrated circuit whose behavior can be reconfigured "in the field" which offers a lot of flexibility, bugs can be fixed and also completely new features can be added, even after the hardware has already been installed. Due to these general advantages, the usage of FPGAs is desired for the final experiment. However, there is also a drawback to the usage of FPGAs. The only affordable FPGAs today are based on either SRAM or Flash technology and both cannot easily be operated in a radiation environment. SRAM-based devices suffer severely from Single Event Upsets (SEUs) and Flash-based FPGAs deteriorate too fast from Total Ionizing Dose (TID) effects. Several radiation mitigation techniques exist for SRAM-based FPGAs, but careful evaluation for each use case is required. For CBM it is not clear if the higher resource consumption of added redundancy, that more or less directly translates in to additional cost, outweighs the advantaged of using FPGAs. In addition, it is even not clear if radiation mitigation techniques (e.g. scrubbing) that were already successfully put into operation in space applications also work as efficiently at the much higher particle rates expected at CBM. In this thesis, existing radiation mitigation techniques have been analyzed and eligible techniques have been implemented for the above-mentioned read-out controller. To minimize additional costs, redundancy was only implemented for selected parts of the design. Finally, the radiation mitigated read-out controller was tested by mounting the device directly into a particle beam at Forschungszentrum Jülich. The tests show that the radiation mitigation effect of the implemented techniques remains sound, even at a very high particle flux and with only part of the design protected by costly redundancy. The promising results of the in-beam tests suggest to use FPGAs in the read-out chain of the CBM-ToF detector.

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Author:Sebastian Andreas Manz
Place of publication:Frankfurt am Main
Referee:Udo KebschullGND, Lars HedrichGND
Advisor:Udo Kebschull
Document Type:Doctoral Thesis
Date of Publication (online):2015/11/12
Year of first Publication:2015
Publishing Institution:Universitätsbibliothek Johann Christian Senckenberg
Granting Institution:Johann Wolfgang Goethe-Universität
Date of final exam:2015/09/24
Release Date:2015/11/12
Page Number:180
Institutes:Informatik und Mathematik / Informatik
Dewey Decimal Classification:0 Informatik, Informationswissenschaft, allgemeine Werke / 00 Informatik, Wissen, Systeme / 004 Datenverarbeitung; Informatik
Licence (German):License LogoDeutsches Urheberrecht