Etude et modélisation du comportement du FPGA A54SX72A d’Actel en milieu radiatif et à températures contrôlées - Application a l’environnement du LHC

The Large Hadrons Collider (LHC) at CERN (Geneva) will provide proton-proton collisions at center of mass energy of 14 TeV. The beam bending and trajectory in the 27 km ring is maintained by superconducting dipole magnets. The dipole coils are made of Nb-Ti filaments cooled at a temperature below 1.9 K and provide a nominal field of 8.65 T. The monitoring of the cryogenic system, such as the measurement of the temperature and the pressure, is provided by a set of resistive cryogenic sensors placed inside the magnets. However, some of these sensors should be fed with currents not exceeding 1A. Therefore the output voltages are very small and the readout electronics should be placed very close to the sensors. The readout electronic cards are placed under the dipole magnets. The main digital component, embedded in the cards, is an FPGA chip. It is an integrated circuit (IC) of type FPGA A54SX72A from Actel (CMOS technology) whose purpose is signal filtering and analysis. Depending of the location along the 27 km accelerator ring, the readout cards will be exposed to different amount of radiation. Furthermore, depending of the environment (i.e. other hardware devices in the surroundings), the cards will be at different functioning temperatures. Results of the irradiation tests that can be found in the literature do not take into account the temperature effect to describe the IC behavior. The main goal of my thesis is to model the behavior of the IC taking into account simultaneously both the temperature and the amount of irradiation. These two parameters are monitored with accurate continuous measurements. The behavior is characterized by the electrical current consumption of the IC and the rate of TTL logic errors. The model is empirical and it is built such as to reproduce the measurements and their correlations. The first set of measurements is performed with X-ray radiations. It allows the study of dose effects in the silicon dioxide. The second test campaign, performed with a proton beam, allows the study of the IC single events cross sections as a function of the dose and the temperature. The results of theses studies allows to build a model able to predict the behavior of any given readout card in the LHC tunnel. This allows designing a maintenance plan of the readout system and will minimize the number of unexpected failures, sometimes in critical conditions. The model is characterized by an equation which describes the functioning time of the IC versus the temperature and the dose rate for X-ray irradiations, i.e. only for the dose effect. The equation is , with the functioning time in hours, the IC temperature in °C and the dose rate in rad(SiO2)/s. The equivalence with protons has been determined by measurements at the Paul Scherer Institute in Switzerland, with a proton beam at energy of 63 MeV. The protons appear to be 8 times harder than X-rays for the equivalent dose rate. An extrapolation of this model, with the factor 8, to the dose rates in the tunnel of the LHC predicts an order of 5 years before functional failures in the worst conditions predicted by particle simulation environments.