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High Energy Physics

Faculty: Simone Buso, Giorgio Spiazzi

Introduction

High energy physics experiments require nowadays massive real time signal processing. The search for physically significant particle generation/disintegration events calls for the capability of detecting particle trajectories on the fly, followed by the application of pre-defined selection criteria and by the storage to memory of all data related only to potentially interesting events. This filter mechanism prevents the need for huge amounts of storage capability, but imposes very strict performace specifications to sensors and supervising electronic systems. It is interesting to note that the event generation rate can be as high as several tens of MHz, which defines the frequency of operation of all sensing and signal processing electronics. The specifications are so demanding that all such electronic circuitry has to be located inside the sensor array used to track particle trajectories and measure their energy. In this scenario, power electronics plays a key role. As the physical size of the experimental hardware increases, the number of sensors and required electronic controllers increases so much that it becomes unpractical to supply power from outside, through cables. Point of load (POL) converters are considered as an alternative. The term refers to those dc-dc converters that are physically located as close as possible to their electrical load. In the case discussed here, this means that power supply circuits are locate on the same boards where the signal processing and control electronics are located, i.e. inside the sensor array. The design of these converters is extremely challenging, basically because of size constraints and highly hostile environmental conditions (radiation, temperature, magnetic field).

LHC power supply layout

Research goals

The Power Electronics Group is active in this line of research, with particular reference to the Large Hadron Collider (LHC) experiment of the European Center for Nuclear Research, CERN. The group cooperates with CERN researchers in the identification and design of converter topologies to be employed as POL converters in the Super LHC experiment, representing the next generation of the one currently running. The planned increase in the sensitivity of the instrumentation calls for a thorough re-design of the power distribution network’s architecture, since the capability of the distribution system currently in use is incompatible with the larger overall power consumption that will characterize the future Super LHC. One of the considered alternatives involves the development of a distributed power supply network, in which integrated, monolithic POL converters are to be deployed at the very heart of the experimental set-up. There, every electronic device has to face a highly hostile environment due to the high flux of radiation particles - which poses a severe tolerance issue for the integration technology - and to the strong background magnetic field, that can reach 4 tesla. This scenario excludes the adoption of magnetic materials in the inductor cores; only inductor-less solutions - e.g. switched capacitor converters -  or high-frequency switching converters operating at several MHz and employing air core inductors, can be of interest. Additional specifications refer to the switching components: no commercially available devices can be adopted, because of the required tolerance to radiation induced damage; custom switching devices need to be developed, based on selected commercial CMOS processes. The maximum voltage rating is expected to be as low as 20 V.

Research areas

The areas covered by the research are both system level and circuit level, comprising:

  • Investigation of high frequency POL converter topologies and related control techniques
  • Characterization of switching devices
  • Design and characterization of air core magnetic components

150 nH air core toroid designed for CERN
LHC power supply applications

 

(Left) Developed prototype for LHC power supply applications and (right) its experimental efficiency

Publications

  • P. Tenti, G. Spiazzi, S. Buso, M. Riva, P. Maranesi, F. Belloni, P. Cova, R. Menozzi, N. Delmonte, M. Bernardoni, F. Iannuzzo, G. Busatto, A. Porzio, F. Velardi, A. Lanza, M. Citterio, C. Meroni, “Power supply distribution system for calorimeters at the LHC beyond the nominal luminosity”, 2011, IOP Publishing Ltd and SISSA, DOI:10.1088/1748-0221/6/06/P06005.
  • S. Orlandi, B. Allongue, G. Blanchot, S. Buso, F. Faccio, C. Fuentes Rojas, M. Kayal, S. Michelis, G. Spiazzi, "Optimization of shielded PCB air-core toroids for high efficiency dc-dc converters", IEEE Transactions on Power Electronics, 2010.
  • S. Michelis, B. Allongue, G. Blanchot, S. Buso, F. Faccio, C. Fuentes, A. Marchioro, S. Orlandi, S. Saggini, G. Spiazzi, M. Kayal, "An 8W-2MHz buck converter with adaptive dead time tolerant to radiation and high magnetic field", European Solid State Circuit Conference, ESSCIRC, Seville, Spain, September 13-17, 2010, pp. 438-441.
  • C. Fuentes, B. Allongue, S. Buso, G. Blanchot, F.  Faccio, S. Michelis, S. Orlandi, G. Spiazzi, “Power Distribution with Custom DC-DC Converters for SLHC Trackers”, 2009 IEEE Nuclear Science Symposium Conference Record (NSS/MIC), Orlando, Florida, USA, October 25-31, 2009, pp. 1300-1305.
  • P. Tenti, G. Spiazzi, S. Buso, M. Riva, P. Maranesi, F. Belloni, P. Cova, R. Menozzi, N. Delmonte, M. Bernardoni, F. Iannuzzo, G. Busatto, A. Porzio, F. Velardi, A. Lanza, M. Citterio and C. Meroni, "Power supply distribution system for calorimeters at the LHC beyond the nominal luminosity," Journal of Instrumentation (JINST), 2011, ISSN: 1748-0221, doi: 10.1088/1748-0221/6/06/P06005.
  • M. Alderighi, M. Citterio, M. Riva, S. Latorre, A. Costabeber, A. Paccagnella, F. Sichirollo, G. Spiazzi, M. Stellini, P. Tenti, P. Cova, N. Delmonte, A. Lanza, M. Bernardoni, R. Menozzi, S. Baccaro, F. Iannuzzo, A. Sanseverino, G. Busatto, V. De Luca and F. Velardi, "Power converters for future LHC experiments," Journal of Instrumentation (JINST), 2012, doi: 10.1088/1748-0221/7/03/C03012. Topical Workshop on Electronics for Particle Phisics, 26-30 September 2011, Vienna, Austria.
  • S. Baccaro, G. Busatto, M. Citterio, P. Cova, N. Delmonte, F. Iannuzzo, A. Lanza, M. Riva, A. Sanseverino, G. Spiazzi, "Reliability oriented design of power supplies for high energy physics applications," Microelectronics Reliability, SPECIAL ISSUE 23rd EUROPEAN SYMPOSIUM ON THE RELIABILITY OF ELECTRON DEVICES, FAILURE PHYSICS AND ANALYSIS (ESREF), Volume 52, Issues 9–10, September–October 2012, Pages 2465–2470. (doi: 10.1016/j.microrel.2012.06.088)