Scientific direction Development of key enabling technologies
Transfer of knowledge to industry

PhD : selection by topics

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New generation of coded aperture collimators for imaging ionising radiations

Département Métrologie Instrumentation et Information (LIST)

Laboratoire Capteurs et Architectures Electroniques

01-10-2020

SL-DRT-20-1056

vincent.schoepff@cea.fr

Factory of the future incl. robotics and non destructive testing (.pdf)

The localization of radioactive hot spots is a major issue for the initial characterization of an installation to be decommissioned. International research teams, in order to detect, localize and quantify the emitted radiations of radiological materials, developed specific tools for a long time. Miniaturized gamma imaging systems, equipped with coded masks (multi-pinhole collimators arranged according to a specific mathematical pattern) and pixelated semi-conductor detectors have been developed over the past twenty years, including by CEA List and CEA Irfu who are proposing the research project. Nevertheless, due to their nature, imaging high-energy radiations (from 10 keV to 2 MeV) still is challenging, and we propose to address those challenges in the frame of this subject. Aiming at developing a new generation of large field of view coded masks, the research program will lead to prototypes manufactured by sophisticated techniques of machining and/or by 3D metal printing processes, allowing the optimization of performances in the field of gamma and neutron imaging. Expected research paths will focus on two different encoding methods : non linear spatial encoding with 3D masks (hemispherical, conical or polyhedral) and temporal encoding (setting the mask in motion to allow temporal modulation of signals, a route generally considered risky in systems and rarely studied). The two encoding approaches will be studied independently and successively then coupled, in order to optimize performance.

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Development of uniform surface sources by functionalization for decommissioning & dismantling

Département Métrologie Instrumentation et Information (LIST)

Laboratoire de Métrologie de l'Activité

01-10-2020

SL-DRT-20-1058

valerie.lourenco@cea.fr

The decommissioning of nuclear installations and the management of the radioactive waste produced during this stage are major concerns for the future, especially with the ageing of the European nuclear plants. Improving the qualification of contamination assessment systems would make it possible to analyse more precisely and ideally identify more quickly the the appropriate waste management channel to help control the resulting costs. The thesis topic focuses on widespread cases where the activity is present on/in surfaces, flat or curved, as well as in pipes. The objective of the thesis is to realize uniform, traceable, flat or cylindrical surface sources, even deformable, with limited radiation attenuation (case of pure beta or alpha emitters). The added value associated with the traceability of these sources lies in the control of the deposited activity level, whatever the radionuclide considered. The approach adopted is the functionalization of a substrate to immobilise and distribute the radionuclides uniformly without excessive attenuation of the radiation emitted, while ensuring that the surface remains non-contaminating. The formation of strong chemical bonds with the surface will guarantee the stability of the layer formed and the chemical affinity with the grafted complexing molecules aims to permanently immobilise the activity. The choice of the functionalization method depends on the substrate on which the bonding takes place (metallic, polymeric, conductive or non-conductive, flexible or rigid). The other end of these molecules can be functionalized to make them specific to the target radionuclides. The tests of surface sources will be carried out first with Am-241, both alpha and low energy gamma emitter and pure beta or not emitters of interest for the elaboration of typical waste spectra. The problem of large surfaces and especially the criterion of source uniformity (variability of surface activity < 10 %, including uncertainties), constrain the method to be used for the functionalization of the surface. The evaluation of the uniformity of the activity distribution over the source surface will be carried out by autoradiography (imaging technique whose signal is proportional to the activity).

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Improvement and understanding of the performance of silicon cell-based solar generators in harsh environments

Département des Technologies Solaires (LITEN)

Laboratoire Photovoltaïque à Concentration

01-09-2020

SL-DRT-20-1061

philippe.voarino@cea.fr

Solar energy for energy transition (.pdf)

The thesis will be carried out at the interface of several laboratories of the Department of Solar Technologies (DTS) of the CEA located in Le Bourget du Lac on the campus of the National Institute for Solar Energy (INES). The objective of this thesis is to improve the resistance to environmental conditions (radiation, e/H+, UV, thermal cycling) of space solar generators based on silicon solar cells, and to better understand the degradation mechanisms of cells/materials associated. By finely controlling the manufacturing of cells (doping, impurity, architecture, etc.) and modules (materials, thickness, architecture, optical trapping, etc.), it is possible to improve the performance of silicon modules at the end of their lifetime while maintaining a competitive price (?/W), 1 to 3 orders of magnitude lower than space III-V modules.

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Modeling the energy consumption flexibility on several spatial and temporal scales

Département des Technologies Solaires (LITEN)

Laboratoire Systèmes Electriques Intelligents

01-10-2020

SL-DRT-20-1068

xavier.lepivert@cea.fr

Energy efficiency for smart buildings, electrical mobility and industrial processes (.pdf)

In a context of massive integration of non-dispatchable renewable production (wind and photovoltaic), the fullfilment of « production = consumption » will imply in the future to act more and more on the second term of this equality. Many questions arise about the real potential of consumption flexibility in a smartgrid, and this depending on the geographic level and also the time range of activation. The management of flexibilities as well as their valuation, will require various models, different depending on the markets (ancillary services, SPOT, intraday, balancing market) and the geographic level considered (house, building, district, city). The thesis will focus on developing: - Electrical consumption and flexibilities modelling - Learning algorithms / parameterization of these models. These will be oriented ?big data?. - Methodologies for getting one model from another To carry out this work, we will use existing simulation tools for the finest spatial scales as well as a consumption measurement database (« Linky » smart metering).

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Scalable and Precise Static Analysis of Memory for Low-Level Languages

Département Ingénierie Logiciels et Systèmes (LIST)

Laboratoire pour la Sûreté du Logiciel

01-10-2020

SL-DRT-20-1088

matthieu.lemerre@cea.fr

Cyber security : hardware and sofware (.pdf)

The goal of the thesis is to develop an automated static analysis (based on abstract interpretation) to verify absence of memory errors in compiled, low-level languages (C, C++, Assembly, Rust). This issue is very important for cybersecurity since most of the software-related security issues come from memory safety (buffer overflows, use-after-free, wrong type punning). The three issues when designing such an automated static analysis is to keep the verification effort low, to handle large and complex systems, and to be precise enough so that the analysis does not report a large amount of false alarms. We draw on the success of a new method using abstract domains parameterized by type invariants, which allowed in particular to fully automatically prove memory safety of an existing industrial microkernel from its machine code, using only 58 lines of annotations, and seek to extend this analysis to larger systems. In particular, the analyzer should be extended to improve scalability (using compositional analysis), to improve precision (using separation logic and SMT/formula-based abstract domains), and to further reduce the amount of annotations (using automatic inference of more precise type invariants).

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Development and characterization of advanced tunnel/recombination layers for 2T and 3T tandem integration

Département des Technologies Solaires (LITEN)

Laboratoire HETerojonction

01-10-2020

SL-DRT-20-1092

delfina.munoz@cea.fr

Emerging materials and processes for nanotechnologies and microelectronics (.pdf)

Today, single junction silicon technology dominates the photovoltaic market, with more than 90 % of market share. However, the power conversion efficiency of silicon solar cells, with a reported record at 26.7 %, has neared its theoretical limit (29 %). To reduce thermalization losses and push efficiency further, silicon cells have been coupled to higher band gap semi-conductors to form tandem cells. Coupling silicon to perovskites appears as a particularly promising solution since perovskites show high performance (25.2 % power conversion efficiency has been reached in a few years), band-gap and thickness tunability and processing versatility. Therefore, silicon/perovskite tandems have the potential to become a high-efficiency technology in the future of photovoltaics. Since 2015, several demonstrations have already been published, either in 2-terminal configuration (2T, both cells connected in series) or in 4-terminal architecture (4T, cells stacking), with record efficiencies above 29 % today. One of the main challenges is the junction between the two sub-cells, which must ensure electrical behavior of charge passage without loss by recombination or optics. Currently transparent conductive oxides are the most used, but they have significant parasitic absorption with associated losses. In this thesis, we aim to develop new materials for the interface layer of a tandem perovskite / heterojunction cell with adaptation of optical index by different techniques and with the two possible configurations, in tunnel junction or in recombination and then characterize electrically, optically and morphologically. In addition, the electrical and optical materials simulation will optimize the complete cell in the different configurations. Finally, stability and integration studies will be done on the most promising junctions.

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