Since more than 20 years, CEA Saclay developed and built high intensity ion sources for accelerators, mainly heated by the electronic cyclotronic resonnant mechanism (ECR). The experience of the CEA is well recognize worldwide, our group was chosen to built ion sources for different facilities: IFMIF/LIPAc (Japan), SPIRAL2 facility (France) and FAIR in Germany.

High performances, in particular the high reliability of our ions sources made them essential for futur high intensity neutron source for fusion reactor material research, or experiences in neutron diffraction or cancer cure with the boron neutron capture therapy (BNCT).

The aim of this thesis is to provide us to a better understanding of the physical phenomena inside the ion sources, as the microwave-plasma interaction/coupling, or the plasma confinement. The primary goal is to optimize beam quality for ions sources, in term of stability in time, in homogeneity and purity but also to increase the extracted current far beyond actual performances. Compact ion sources with a better efficiency are also expected.

This ambitious program could be only validated with various experimental measurements at Saclay on a plasma reactor or on an extracted intense light ion beam with dedicated diagnostics.

Mastering high intensity beam production is the key of the future. Those innovative ion sources will play a large part in maintaining CEA leadership in the field of light ion sources and also in particles accelerators.

Very high energy astronomy observes the sky above 50 GeV. It is a relatively recent part of astronomy (under 30 years old). After the success of the H.E.S.S. in the 2000s, an international observatory, the Cherenkov Telescope Array (CTA), should come into operation by 2024. This observatory, whose construction began in 2018, will include two sites equipped with about fifty telescopes. The IRFU is involved, in partnership with the CNRS and Spanish and German partners in the construction of NectarCAM, a camera intended to equip CTA's "medium-sized" telescopes (MST). A prototype of NectarCAM is being installed at the IRFU. After extensive tests to check that NectarCAM is capable of achieving the required performance, astronomical observations are planned at one of CTA's candidate sites. These observations will fully validate the operation of the camera. The thesis has two independent parts: on the one hand the tests in darkroom at the IRFU, then the preparation and realisation of the astronomical observations with the prototype of NectarCAM on the site of CTA.

In parallel, it is planned to participate in the analysis of HESS collaboration data on astroparticle subjects (search for primordial black holes, constraints on Lorentz Invariance using distant AGNs).

The goal of this thesis is to explore the potential of gravitational waves (GWs) at cosmological distance as standard sirens to measure the expansion history of the Universe. Since most GWs from merging black holes are not expected to have an electro-magnetic counterpart, we need to estimate the redshift of the GWs host galaxy statistically. For this, we propose to use galaxy clustering from wide and deep photometric galaxy surveys. The same data will be used to reduce the weak-lensing magnification contamination of the GW luminosity distance.



To analyse the GW Hubble diagram, we aim to understand and model the uncertainty in the luminosity distance (signal generation and propagation), the redshift uncertainty (using photometric and clustering redshifts, and machine learning), and parameter inference, for which we will use forward-modelling and likelihood-free methods to account for the non-Gaussianity of the data.

The central region of the Milky Way is a very complex region at very-high-energy (VHE, E>100 GeV) gamma rays. Among the VHE gamma-ray sources are the supermassive black hole Sagittarius A* lying at the the centre of the Galaxy, supernova remnants and pulsar wind nebulae. The detected diffuse emission at TeV energies revealed the detection of the first Galactic Pevatron - a cosmic-ray accelerator up to PeV energies. At the ten-to-hundred GeV energy range, the Galactic Center region harbors the base of the Fermi bubbles - giant bipolar structures extending on ten-degree spatial scale, possibly related to past activity of Sagittarius A*. Beyond the rich VHE astrophysics, the GC region is expected to be the brightest source of particle dark matter annihilations in VHE gamma rays. The H.E.S.S. observatory located in Namibia is composed of five imaging atmospheric Cherenkov telescopes. It is designed to detect gamma-rays in the ten GeV up to several ten TeV energy range. The observation of the Galactic Center region is one of a long-term key science observational program carried out by H.E.S.S. The four-telescope observations performed by H.E.S.S. led to the detection of the first Galactic Pevatron and provide the strongest constraints so far on the annihilation cross section of dark matter particles in the TeV mass range. The PhD work will be focused on the data analysis and interpretation of the H.E.S.S. observations of the inner Galaxy survey program with the full H.E.S.S. array. In the first part, the PhD student is expected to characterize the spatial and spectral properties of the Galactic Center TeV diffuse emission. Second, she/he will develop a novel analysis method to search for new diffuse emissions connected to the Galactic Center outflows, using a multi-component template-fitting technique. The third part of the work will be dedicated to the search for dark matter in the Galactic Center region and in the complementary dwarf galaxy satellites of the Milky Way. The PhD student will be involved in the data taking with the H.E.S.S. telescopes towards these objects and will participate to the detection prospects of dark matter with the next ground-based gamma-ray observatory CTA.

In 2016, the announcement of the first direct detection of gravitational waves opened an era in which the universe will be probed in a new way. At the same time, the complete success of the LISA Pathfinder mission validated some of the technologies selected for the LISA (Laser Interferometer Space Antenna) project. This space observatory would consist of three satellites 2.5 million kilometres away and would allow the direct detection of gravitational waves undetectable by terrestrial interferometers. Its launch is planned by ESA for 2034.



Unlike ground-based observatories, which are sensitive to rare gravitational wave signals and subject to dominant measurement noise, a space interferometer will be continuously receiving a large number of distinct signals theoretically characterized at varying degrees of accuracy. Current estimates of source quantities and types include 60 million continuously emitting galactic binary systems, 10 to 100 annual signals from supermassive black holes, and 10 to 1000 annual signals from binary systems with very high mass ratios.



One of LISA's scientific objectives is to study the formation and evolution of galactic binary systems: white dwarfs, but also neutron stars or black holes of stellar origin. Several so-called "verification" binary systems are already identified as gravitational wave sources detectable by LISA, and this number is expected to increase significantly as a result of measurements collected by the Gaia satellite and the LSST telescope.



LISA should allow the characterization of about 25,000 galactic binary systems. The many other systems that escape individual detection will form a stochastic background, or confusing noise. In addition, as in any experiment, the actual data will be subjected to a number of noises and artifacts to be taken into account to optimize the scientific potential of the mission.



The main thread of the proposed work is a demonstration of the scientific and technical capacity to process real data in a reliable and robust way. Galactic binary systems are an excellent testing ground. This type of signal is measurable on LISA, and its form for an individual system is well known from a theoretical point of view. Nevertheless, extracting information of astrophysical interest from these signals requires solving different signal processing problems such as :

1. The separation of several individual sources, appearing as a spectrum of lines, from a stochastic background.

1. Taking into account unexpected deviations (glitches) in the analysis of data based on LISA Pathfinder's feedback.

2. Analysis based on incomplete data, due to periods of interruption in data acquisition (maintenance, subsystem instabilities, etc.).

3. The development of robust analysis methods against non-Gaussian, non-stationary or correlated noise.



It is expected that these various elements will have a significant impact on the estimation of gravitational wave signals. In this context, this thesis work will consist first of all in the study of their impact on the analysis, then in the development of new methods inspired by similar problems in image processing applied to astrophysics. These methods are based on the parsimonious modeling of signals. This allows the differences in shape or morphology between these signals and noise to be exploited to solve inverse problems. The candidate will adapt the algorithms that take advantage of this morphological diversity, implement them and analyze their contribution on realistic simulated data associated with LISA, and if possible on real data from ground interferometers.



However, this set of activities may evolve according to theoretical advances on the one hand, and the publication of new measures on the other. All these activities can lead to constraints in the design of the mission, tools or data processing methods. This subject has a dominant emphasis on signal processing and careful programming, but its multidisciplinary aspect makes it possible to explore many fields depending on scientific opportunities and the time frame of a thesis.

Galaxy evolution and star formation are controlled by physical and chemical processes directly related to the interstellar medium (ISM). The ISM is a fundamental component of galaxies, subjected to multiple heating mechanisms (ionization by UV, X-ray photons or cosmic rays, photoelectric effect on dust grains, shock waves...) and at the origin of new stellar generations in cold dense clouds. The main thermal mechanisms in the ISM of our Galaxy are known and relatively well constrained, but they remain largely unexplored in galaxies with low metallicity (quantity of heavy elements released by massive stars). Such metal-poor galaxies that have little evolved since their formation exist in the Local Universe, providing us with a useful comparison with primordial environments.



The following questions lie at the heart of this project, (1) is molecular gas really necessary for star formation? (2) how is molecular gas distributed in primitive galaxies and how can it be detected with ALMA and JWST? (3) what is the influence of compact objects on the ISM and on star formation?



Recently, we have shown that ultraluminous X-ray sources ("off-nucleus", i.e., spread throughout the galaxy) can dominate the ISM heating at large spatial scales in primitive galaxies, bringing important constraints on the reservoir of molecular gas (which should be linked to the star formation process). We now need to extend and generalize these results in order to build diagnostics that will serve to provide fundamental references for future observations with ALMA, JWST, or ATHENA and for numerical simulations of the early Universe. A parallel objective will be to solve the inverse problem, i.e., to infer the properties of the compact objects from their signatures in the ISM and determine the nature of these sources (intermediary-mass black holes, neutron stars...) and their role in galaxy evolution.

The CTA observatory is a next-generation ground-based instrument for exploring the sky in gamma rays at very high energies, with a sensitivity ten times better than the existing and an amazing new capacity for the search of transient source counterparts.

The objective of the PhD is the study of the influence of the extragalactic background light on the detectability of the gamma ray bursts in CTA, and to optimise the real-time search strategy for gamma ray bursts and gravitational wave counterparts.

The research will contribute to the development of the data pipeline and the data analysis tools using the first observatory data.

Because of the lack of emission, large quantities of gas escape from the inventory of the interstellar medium [1]. This dark gas is concentrated at the interface between the atomic and molecular phases of clouds. It plays a decisive role in the interstellar cycle and it informs us on the capacity of the large gas reservoirs of galaxies to produce molecular clouds to form stars. Yet, we know hardly anything about the composition, state, and abundance of the dark gas, or how these properties vary across a galaxy. Finding direct means of observation and characterising this interstellar phase are therefore two major objectives for understanding galactic ecosystems.

The dark gas is indirectly revealed by coupling observations of the dust that it contains and of the cosmic rays that diffuse in it and radiate in gamma rays. The proposed goal for the thesis is to exploit the Fermi gamma-ray data and the data from multiple interstellar surveys (Planck, WMAP, Gaia, new radio and mm surveys) to study the largest dark-gas complex in the solar neighbourhood. The analyses will allow to quantify the content of visible and dark gas in the clouds, to follow the penetration of cosmic rays in the dense phases, and to characterise the evolution of the dust properties across the gas phases. This last point is essential to pave the way for reliable Galactic and extragalactic studies of the dark gas exploiting only dust radiation.

The study will face the challenge of separating the interstellar gamma-ray emission from that of the Fermi Bubbles (large jets of high-energy particles expelled from the central regions of the Galaxy) by developing a multispectral component separation method.

The student will also be able to participate in the CNES co-PILOT sub-millimetre balloon project that is planned for 2020 to look for C+ recombination signatures in the local dark gas.

The work will be carried out within the Fermi International Collaboration and will benefit from numerous exchanges with interstellar experts in France (at ENS and IRAM), the United States (Alma, Stanford), Australia (SKA-GASKAP), and China (FAST). The student will participate at the beginning of the thesis in the month-long international workshop to be held on dark gas at the Pascal Institute of Paris-Saclay University.

[1] Grenier et al., 2005, Science 307, 1292

The supernova explosion of massive stars is a spectacular phenomenon which can be observed up to cosmological distances. Its elusive mechanism challenges our understanding of the interplay of gravitation, fluid mechanics up to nuclear densities and neutrino interactions.

Supernovae are crucial to enrich the chemical composition of galaxies and give birth to compact objects such as neutron stars and black holes. Understanding the supernova mechanism would establish a connection between the stellar structure resulting from stellar evolution and the properties of compact objects such as their mass, spin and velocity. The prospect of detecting neutrinos and gravitational waves emitted during the explosion opens up the possibility of a direct signature from the explosion dynamics, provided one knows how to interpret this signal. This PhD project proposes to characterize this multi-messenger signature as well as the properties of the newly born compact object, using our understanding of the hydrodynamical instabilities developing during the collapse. The student will explore the diversity of the explosion scenarios using numerical simulations with the code RAMSES, and characterize the eigenfrequencies using perturbative calculations. He will also determine the properties of the explosion mechanism and the information

about the progenitor structure which can be extracted from the multi-messenger signal from a galactic supernova.

We seek to study stellar magnetism and how rotation and metallicity impact their level of activity, rotation state and wind of particles.

The knowledge of the Earth's natural radiative natural environment (NRE) and its dynamics is an important issue for controlling the risks of malfunctioning of advanced technologies, dosimetric risks (biological effects), and in assessing the impact of albedo neutrons escaping from the upper atmosphere to the radiation belts. The latter contribute on the one hand to the population of the proton radiation belt (Salammbô models) and on the other hand induce instrumental background noise on all equipment operated in low or high altitude orbit, including in particular instruments dedicated to astronomy or to the study of the globe. For their part, cosmic rays (essentially composed of protons and helium nuclei) interact with atoms in the upper atmosphere either by losing part of their energy through ionization or for the most energetic particles, by causing nuclear reactions. These secondary reactions in turn cause cascade reactions and up to ground level, the result being the generation of secondary particles of the neutron, proton, electron or muon type, whose spectra will vary according to altitude, longitude, latitude, atmospheric conditions and solar activity.



The objective of this thesis is to characterize secondary particles of atmospheric RNE from adapted nuclear transport codes (GEANT4, MCNPx, FLUKA or Corsika) based on a 3D model of the atmosphere. In addition, this 3D approach will allow to characterize the angular distribution of secondary particles and quantify the components escaping from the upper atmosphere to the radiation belts. The impact of cosmic radiation modulation as a function of the solar cycle on the population of atmospheric neutrons and albedo will be quantified. The model results will be validated with the neutron spectrum measurements performed by ONERA/DPHY at Concordia (Antarctica). In addition to its high neutron detection level (altitude 3223m, cut-off rigidity ~ 0GV), this measurement site is characterized by a scene that can be easily modelled thanks to its stable water conditions. Additional comparisons may be made from other spectrometers and/or instruments (neutron monitors). The model results will also be compared with instrumental background noise measurements from several space missions. In the long term, this model could be extended to study the impact of solar flares on their contributions to neutron generation in the Earth's atmosphere and its albedo component (SPAND). Another perspective will be to apply this cosmic shower modeling to the case of Jupiter, whose atmospheric and magnetic conditions are very different from the terrestrial case.



The bibliographic work will cover the fields of cosmic rays, atmospheric modelling and radiation-matter interactions (cosmic showers). An important task will be to orient the choice of a nuclear transport tool (GEANT4, MCNPx, FLUKA or Corsika) according to the problem and the relevance of the physical models. The thesis work will be divided into several steps:



1) Development of a 3D model of the atmosphere (latitude, longitude and altitude) based on the state of the art.



2) Characterization of secondary particles of atmospheric RNE from adapted nuclear transport codes based on the 3D model of the atmosphere (angular properties of secondary particles integrating the component escaping from the upper atmosphere to the radiation belts). [1]



3) Validation of 3D modelling with neutron spectrum measurements performed by ONERA/DPhIEE at Concordia (Antarctica). Additional comparisons may be made from other spectrometers and/or instruments (neutron monitors). [2]



4) Valuation of this new physical description in the "Salammbô 3D" and "MUSCA SEP3" themes. [3]



5) Assessment of expected background noise in low orbit for different space missions and comparison with flight data (ESA/Integral for gamma albedo, JAXA/Hitomi for neutron albedo); application to space missions in preparation (CAS/Einstein Probe, ESA/Theseus).



References

[1] Natacha Combier, Arnaud Claret, Philippe Laurent, Vincent Maget, Daniel Boscher, Alfredo Ferrari, and Markus Brugger, "Improvements of FLUKA Calculation of the Neutron Albedo", IEEE Transaction on Nuclear Science, VoL. 64, NO. 1, January 2017.

[2] G. Hubert and A. Cheminet, "Radiation effects investigations based on atmospheric radiation model (ATMORAD) considering GEANT4 simulations of extensive air showers and solar modulation potential", Radiation Research, Vol. 184, No. 1, pp. 83-94, July 2015.

[3] G. Hubert, S. Duzellier, C. Inguimbert, C. Boatella-Polo, F. Bezerra, and R. Ecoffet, "Operational SER calculations on the SAC-C orbit using the Multi SCAles Single Event Phenomena Predictive Platform (MUSCA SEP3)", IEEE Trans. Nucl. Sci., Vol. 56, No.6, pp. 3032-3042, Dec. 2009.

it is desirable that the candidate carries out his or her M2 internship at ONERA Toulouse prior to the thesis which will take place partly at ONERA Toulouse and partly at CEA Saclay.

The aim of this thesis is to improve the characterization of pressure modes and (if possible) high-frequency gravity modes of solar-type stars of spectral class F and the Sun. Gravity modes are modes of oscillation excited by the surface turbulence of low-mass stars such as the Sun. They evolve in the radiative zones and they become evanescent in the outer convective layer of these stars. In the case of the Sun, these modes, which are supposed to have a periodicity of a few hours, have not yet been measured on the surface of our star: it has only been possible to study them by indirect methods (Garcia et al. 2007, Fossat et al., 2017).



To visualize these modes, two steps are crucial:



1) To develop new analyses methods and / or instrumental set ups to reduce convective noise.



2) Study in detail the stars where the outer convective layer is thinner than in the sun (30% in radius).

Astrophysical research requires the development of very high performance cameras embedded in space observatories. The observation of the universe in the X-ray range (X-ray spectro-imagery) needs detectors made of matrices of micro-calorimeters operating at very low temperature (50 mK). The absorption by the detector of an X-ray photon coming from the observed celestial object causes a micro-rise in the temperature of the detector. The measurement of this temperature rise, which makes possible to determine the energy of the photon, requires ultra-sensitive micro-thermometers, and a cryogenic electronics, with very low noise, capable of reading them.

Two technologies of thermometers have been used so far : high-impedance silicon-doped metal insulator sensors (MIS), and very low impedance transition edge sensors (TES). Each requires a very specific electronics, either based on HEMT transistors for adapting to high impedances, or based on SQUIDs for adapting to very low impedances. The high impedances have the advantage of an extremely reduced heat dissipation on the detection stage, which allows a large number of pixels, while the very low impedance TES, more sensitive than the MIS, make easier to obtain excellent spectral resolutions.

A few years ago, a new type of thermometer has been developed by the CNRS/CSNSM : this is high impedance TES, potentially allowing to combine the advantages of one and the other types of detectors. A first thesis was carried out in our laboratory (2016 - 2019), with the aim of evaluating this new path by implementing it for the first time, and by associating it with an innovative readout electronics architecture that performs an active electro-thermal feedback. This thesis has highlighted the extremely promising nature of the device, by obtaining very interesting first experimental measurements.

The objective of the new thesis, proposed here, is to continue this exploratory work by going one new major stage further : validate from this new technology the feasibility of a matrix of several thousand pixels. For this, the work will focus on two parallel axes : on the one hand carry out a complete work of improvement and optimization, in order to draw from the device its best performances, and on the other hand design and test the integrated electronic system (ASIC) essential for the realization of the future large matrices.

The main difficulty lies in the conditions of implementation of the system : the detector must be placed in a cryo-generator to be cooled to very low temperature (50 mK), and equipped with a cryogenic electronics, to be designed, operating at 4 K. This one will have to ensure not only the multiplexing and the amplification of the signal but also, despite this multiplexing, the maintenance of the active electro-thermal feedback of the detectors, and this while satisfying the extremely severe noise and thermal dissipation constraints required by space cryogenics.

Measurements of the statistical properties of the large-scale structure (LSS) of the Universe can provide information about the physics that generated the primordial density fluctuations. In particular, they offer the possibility to distinguish between different models of cosmic inflation by measuring primordial non-Gaussianity (PNG), the deviation from Gaussian random field initial conditions.



Our plan to study the PNG is to use a spectroscopic survey, DESI, starting its observations by the end of 2019. The LSS will be measured with two different tracers of the matter : Emission Line Galaxies (ELG), which are star-forming galaxies and quasars. These two tracers allow us to cover a large redshift range from 0.6 to 2.5.



DESI will perform a 3D survey of tens of millions of galaxies and quasars in 5 years over 14 000 squared degrees. The observations will take place at the 4-m Mayall telescope in Arizona.



During its first year of thesis, the student will participate to the commissioning of the new instrument and to the survey validation. In particular, he/she will be in charge of the validation of the ELG and quasar target selection. Then he/she will study the correlation function at large scale of these tracers in order to measure the PNG. With the first year of DESI, we should achieve an sensitivity better than all the previous measurements with LSS.

The Herschel submillimeter space observatory has revolutionized some areas of astrophysics, such as star formation, showing that stars are formed mainly in filaments of gas and dust. This rises a fundamental question on the role of the magnetic field within these structures that cannot be solved by the current astrophysical instruments. The B-BOP instrument, installed on the future SPICA international space observatory and proposed by CEA Saclay, will be able to detect a wide variety of far-infrared filaments, as well as their possible associated magnetic field (through the polarization of the light coming from these regions).

B-BOP will contain 3 focal planes of cryogenic silicon bolometers currently developed by CEA (LETI and Saclay). These are very innovative detectors, operating at 50 mK, with a very high sensitivity. Each pixel is intrinsically sensitive to the polarization of incident radiation.

For this thesis, the first step will be to model, and test the bolometers of Safari-Pol (measurement of sensitivity, time constant, cross-polarization, etc ...). This work will require the development of dedicated state-of-the-art instrumentation (very low flux optical sources, ultra low temperature cryostat). The results obtained will then be discussed in the more general framework of the instrument's preparation, in particular concerning its calibration, the estimation of its performance in space, as well as the optimization of future observation modes.

The matter distribution on cosmological scales can be predicted within the standard cosmological model, and it depends among others on the (yet unknown) absolute neutrino mass and on the properties of dark matter, whose nature is still a great mystery. The IRFU-DPhP cosmology team strongly contributes to the DESI large spectroscopic sky survey which will provide in the next years an unprecedented cartography of cosmological structures.

This thesis proposes to use observations of the so-called Lyman-alpha forest, which measures the absorption by the intergalactic medium of light from quasars, and provides as of now the best measurement of the matter distribution at "small" (~megaparsec) cosmological scales. State-of-the-art numerical tools will be used to develop a new set of cosmological simulations which include both the hydrodynamics of the intergalactic medium and the hypothetical properties of neutrinos and dark matter. The PhD student will then analyze the first Lyman-alpha forest data from DESI, and by making use of the simulations he/she will be able to derive new measurements on the neutrino mass as well as several dark matter scenarios ("warm dark matter", "fuzzy dark matter",...)

At redshifts of z=2 to 3, the epoch of the peak star formation and black hole activity in the Universe, the first giant dark matter halos were also growing very rapidly, and baryons falling into their deep potential wells induced prodigiously vigorous activity leading to the major phases of galaxy and black hole assembly, often hidden by dust. These early phases for the evolution of galaxies are expected to be crucial to lead to the formation of their dominant early type galaxy population (via quenching mechanisms still poorly understood) and well relaxed hot gas atmospheres, as observed in local massive galaxy clusters (via some sort of yet unknown feedback between galaxies and the hot gas, leading to energy and entropy injection affecting its thermodynamic evolution). The overall physical processes relevant for galaxies and structures evolution in the first forming clusters are still largely poorly mapped, and yet not well understood. But increasing interest and efforts in the community coupled with emerging observational results and prospects for future mission (e.g., JWST, Euclid and Athena) make this research field one of the most hot and promising in the current domain of galaxies and structure formation. I propose a PhD thesis in Saclay in this research field, based on new observations with ALMA, NOEMA, Herschel, HST and Keck of two dense structures discovered by our research groups at z=2 and 2.5 (Gobat et al 2011; 2013; Wang et al 2016) and a new forming cluster found at z=2.91. The student will be responsible of the final reduction, analysis and interpretation of a substantial amount of data we obtained

with the new and revolutionary Keck Cosmic Web Imager, allowing for the first time 3D spectroscopy in the blue over large fields, down to wavelengths not accessible to the MUSE instrument at the VLT. These Keck data have revealed giant clouds of cold gas extending over 100kpc or more at the cluster cores, detected from their Lya emission. The high level goal of the thesis will be to observationally characterise and understand the nature, origin and fate of these giant reservoirs of cold gas. This will be done in particular in connection with galaxy activity present in the clusters, that will be probed by HST multicolour imaging (to reveal morphologies, stellar populations and merging rates possibly connected to galaxy stripping and production of inter cluster material) and with NOEMA, ALMA and Herschel (to study gas reservoirs, star formation hidden by dust and the state of the interstellar medium). The cold gas might eventually result to be a first convincing smoking gun of cold flow accretion to massive dark matter halos required by theory to justify the vigorous galaxy activity present at high redshift. Such smoking gun has long been sought observationally at high redshifts but never convincingly detected yet. Possible evidences leading to this could be connected with the morphology of the Lya gas, large kinematics and metal enrichment, that we will be able to investigate with existing data and with future observations. The student will be, in fact, involved during the PhD in a vigorous effort of proposing for Keck, VLT and ALMA/NOEMA time, to foster this science, with a resulting expertise in all aspects of observational astronomy, including experience with dealing with truly multi-wavelength datasets.

Gamma-Ray Bursts originating from the death of massive stars represent an ideal tool for probing the early Universe and star formation within distant galaxies. However, many questions are still opened on the nature of environments favoring the occurrence of such phenomena, in particular on the differences they show with respect to the entire population of galaxies responsible for star formation throughout cosmic history. We will shed a new light on these questions, thanks to the analysis of high resolution observations of high redshift gamma-ray burst host galaxies obtained on one hand in the near-infrared with the Hubble Space Telescope, and on the other hand with the ALMA millimeter interferometer operating in Chile. These data will allow us constraining the morphology of these galaxies, their star formation surface density, as well as their dust and molecular gas content. Besides, we will infer predictions on the distribution of extinctions in the interstellar medium of distant galaxies such as what will be systematically measured with the gamma-ray bursts to be detected with the future SVOM satellite. This PhD project is proposed in the context of the advent of "time-domain astrophysics" expected for the next decade, and will enable in particular a better assessment of the use of gamma-ray bursts as tracers of massive stars at the scale of cosmological structures.

The Large Hadron Collider (LHC) at CERN is now in exploitation phase. The European physicians on particle physic community has already started the conceptual studies for the Future Circular Collider (FCC) with a collision energy increase to nearly 100 TeV to go deeper in the LHC studies possibility (14 TeV). Such a device would keep the leadership position of the European community in term of high energy physics. In the interaction (IR) area of this accelerator, few specific quadrupole magnets are needed in order to increase the luminosity (the number of collision with time unit) and the statistic related to new particles discovery. Such magnets have to generate a high magnetic field gradient in the largest possible aperture. High Field Superconductors (HFS, also called High Temperature Superconductors: HTS) would find here a use justification considering the higher cost compared to classical Low Temperature Superconductors (LTS).

We are proposing to demonstrate the feasibility of an interaction quadrupole magnet with a gradient over 150 T/m (1.5 time the FCC IR quadrupole gradient) in an aperture of 210 mm (design FCC). Such magnets will require specific design consideration and optimization, new winding technics and insulation process to be able to protect it against fast resistive transition.

The PhD student will interact with DACM team in order to design a quadrupole magnet corresponding to the accelerators requirement. A design step will be necessary in order to develop the fabrication process. Nevertheless the student will be able to look at specific aspect of the magnet fabrication, like the insulation or the protection aspects in such very high energy magnets.

The Euclid satellite, to be launched in 2022, will observe the sky in the optical and infrared, and will be able to map large scale structures and weak lensing distortions out to high redshifts. Weak gravitational lensing is thought to be one of the most promising tools of cosmology to constrain models. Weak lensing probes the evolution of dark-matter structures and can help distinguish between dark energy and models of modified gravity. Thanks to the shear measurements, we will be able to reconstruct a dark matter mass map of 15000 square degrees. These shear measurements are derived from the galaxy shapes, which are blurred by the PSF (point-spread function) of the optical imaging system. One of the main problems to achieve the scientific goals is therefore the need to model the point spread function (PSF) of the instrument with a very high accuracy. The PSF field can be estimated from the stars contained in the acquired images. It has to take into account the spatial and spectral variation of the PSF. An additional problem to take care of is the subsampling of the images. Once the PSF is correctly modelled, we need to derive the shear from galaxy shapes.

In a recent paper (Schmitz et al 2018) we shown that optimal transport (OT) techniques allow to extremely well represent the evolution of the PSF with the wavelength and on-going work (Morgan et al, 2018) consists in building a 3D Euclid PSF modelling, which takes into account both the spatial variation of the PSF and the PSF wavelength dependency. However even if OT produces beautiful results, its use is extremely limited in practice due to a prohibitive computational cost, and we cannot consider to use our OT PSF modeling for the huge Euclid set.

The goal of the PhD consists first in finding an efficient way to build such a 3D PSF model. A solution could be to use the Deep Wasserstein Embedding technique (Courty, Flamary and Ducoffe, 2017) to get an approximation mechanism that allows to break the complexity. The second step will be to interpolate, from the reconstructed 3D PSFs at stars position, the PSF at any position in the field. This will done by extending to the third dimension the 2D interpolation on a Graph Laplacian we proposed in (Schmitz, Starck and Ngole, 2018), which allows us to interpolate the PSF on the adequate manifold. The final step will be to quantify the modelling errors by studying using simulations the propagation of the reconstructed PSFs errors to cosmological parameters.

With the forthcoming large-scale radio-telescopes, the need for dedicated methods to analyse radio-interferometric data is paramount in signal processing as well as in astrophysics. In this context, the quest for the cosmological signal at the epoch of reionisation mandates the use of tailored component separation methods, whose role is to decompose multi-frequency data into elementary components. Nevertheless, standard methods are not adapted to cope with radio-interferometric data: i) the data are composed of incomplete measurements in the Fourier domain and ii) the sought-after signal is overwhelmed with foreground galactic sources as well as instrumental noise. Consequently, the extraction of the EoR signal mandates the development of dedicated methods that have to tackle both a separation problem and a compressed sensing problem to deal with incomplete measurements. Furthermore, recovering such a weak signal requires designing highly precise component separation methods that account for precise physical models, which are generally parametric and non-linear. Machine Learning methods will be considered to learn complex non-linear models. Finally, as astrophysics enters the Big Data era, a particular attention will be paid to the development of computationaly efficient algorithms.

In order to develop future particle accelerators such as the Future Circular Collider (FCC), high field superconducting electromagnets (higher than 15 T) are necessary. The superconductor Nb3Sn is aimed, however it causes some technical issues yet not solved during its production. The Nb3Sn is produced in the form of cables of the Rutherford type. These cables are then wound to form the coils of the electromagnet. Following winding, the conductor requires a heat treatment at 650°C in order to form the Nb3Sn superconducting phase. It is now established that significant dimensional changes of the strands occur during this phase change, translating in dimensional changes of the cables. If these changes in dimensions are not permitted by the tooling, mechanical stress add up in the coil and the superconducting performances degrade. Currently this issue is dealt with empirically by allowing clearances in central posts, around which are wound the superconducting cables, and by varying iteratively the clearances. However, the thermomechanical behavior of the Nb3Sn cables in a coil during the heat treatment needs to be quantified. The goal of this thesis is to observe and understand the changes of dimensions of this type of Nb3Sn conductors in order to help dimensioning the coil fabrication tooling for future accelerator magnets, and potentially improve their performances.

The experimental and theoretical study of the structure of the nucleon in terms of its elementary components, quarks and gluons, is a research focus at the heart of experimental programmes currently being conducted at Jefferson Lab (US) or CERN. This is one of the major justifications for the construction of a future electron-ion collider (EIC). This theme, at the confluence of special relativity and quantum mechanics, benefits from a well established theoretical framework (Quantum Chromo Dynamics, QCD), and well-defined experimental perspectives. Generalized parton distributions (GPD) and transverse momentum dependent parton distributions (TMD) offer a new perspective on the nucleon: they provide access, for the first time, to complementary three-dimensional information on the nucleon structure.



GPD and TMD are two facets of a more general object, the Wigner distribution, which is the quantum and relativistic analogue of the distribution function encountered for example in statistical physics. Together, GPDs and TMDs pave the way for a description of the phase space (positions and momenta) accessible to quarks and gluons within the nucleon. To date, GPDs and TMDs have been at the centre of active, but still largely independent research programmes due to the complexity of each of these topics.



GPDs are accessible through certain exclusive processes (all particles in the final state are detected) such as deeply virtual Compton scattering (DVCS) or deeply virtual meson production (DVMP). TMDs are accessible through other processes, such as semi-inclusive deeply inelastic scattering (SIDIS) or the Drell-Yan process (DY). All these processes are the subject of intense studies, and some of them have already delivered thousands of observables for detailed analysis. Research related to GPDs and TMDs has reached experimental, theoretical and technical maturity, and is at the dawn of an era of precision phenomenology.



The PhD candidate will focus on the construction of new nucleon GPD and TMD models based on common modeling assumptions, and will proceed with the phenomenology associated with these models. It will evaluate the contribution to the description of the 3D structure of the nucleon of this first common analysis of experimental data associated with GPDs and TMDs.

1. Construction of a GPD and TMD model based on light cone wave functions using the general strategy of covariant extension. Particular attention will be paid to the description of the nucleon either in terms of a bound state of a quark and a diquark, or as a bound state of three quarks.

2. Calculations of the different observables associated with these GPDs and TMDs, at least in the DVCS and DY processes using the PARTONS and ArTeMiDe codes, and comparison with existing experimental data. Possible constraints on the wave functions used to build the GPD and TMD models.

3. Study of the 3D structure of the nucleon from the light cone wave functions thus constrained by the experimental data, in particular spin structure, energy, momentum, or longitudinal and transverse pressures.



However, this set of activities may evolve according to theoretical advances on the one hand and the publication of new measurements on the other. Overall, it should be noted that while this subject involves careful programming, most of the effort will be focused on physics. Indeed, most of the IT activity will be handled by a IT professional working within the framework of the 3DPartons virtual access infrastructure funded by the European Union from 2019 to 2023 as part of the STRONG-2020 proposal. This will allow the PhD candidate to focus his or her efforts on modeling, physical analysis and interpretation of results.

The future of hadronic physics lies in the incoming ion-electron collider (EIC) in the United States. Half a century of research has shown that nucleons, i.e. protons and neutrons, are themselves composed of more basic constituents called quarks. Quarks are linked together by gluon exchange that led to the development of the fundamental theory of the strong interaction known as Quantum Chromo-Dynamic (QCD). The EIC's mission is to deepen the knowledge of these fundamental interactions and the emergence of nucleons and nuclei from its constituents.

The EIC R&D program and dedicated research programs on detectors have already begun, in particular with the partnership between IRFU and the Brookhaven National Laboratory (BNL) funded by the Department of Energy (DOE). This research program focuses on the design and improvement of Micro-Pattern Gaseous Detectors (MPGD). While the use of this technology is spreading whithin high energy experiments such as the upgrades of LHC experiments, it is still possible to significantly improve the performance of these detectors. Thanks to our expertise in MPGDs in addition to the idea of an innovative form of segmentation (called "Zigzag") coming from our American partners, and the original use of laser ablation to obtain a exceptional engraving precision; we have already obtained an improvement in the spatial resolution of these detectors by a factor of two.



As part of the proposed thesis, the chosen candidate will: (a) take part in Fermilab proton test beam of current prototypes (b) conduct the analysis of recorded data and the study of their performances (c) starting from this first analysis, the candidate will design of the second generation of 1D then 2D detectors which then will be tested at Fermilab (d) Simulate, design, assemble, and test, a 2D full scale prototype and its possible installation in the SPHNENIX experiment at RHIC (e) Study the performance of the detector in a physics data taking environment.



This thesis subject in instrumentation covers all the stages of the development a modern detection system: from the design to the installation in an experiment.

The atomic nucleus is a quantum system of interacting fermions, protons and neutrons, which can be paired at short range (1 fm, much smaller than their average distance) where the nuclear interaction is poorly known and strongly repulsive. These configurations, called short-range correlations, offer us a unique opportunity to study this regime which is particularly interesting as it corresponds to the transition from a proton/neutron to quark/gluon description of the nucleus. Experiments to characterize short-range correlations have been done on stable nuclei, but the experimental technique used up to now does not allow access to unstable nuclei, where the imbalance between protons and neutrons may affect these correlations. A new technique consisting in studying short-range correlations in exotic nuclei with a proton target is under development.

The candidate will analyze data from the first test experiment that was performed in 2018 using stable beams from the JINR accelerator in Dubna (Russia). He/she will be then strongly involved in the program proposed by the group with the radioactive beams produced by the GSI accelerator (Germany) and a liquid hydrogen target that we are currently developing thanks to a grant from the National Research Agency.

In parallel to the experimental program, he/she will perform simulations to design a new detection system based on tracking of charged particles in a magnetic field. This system will allow increased acceptance for particle identification and momentum measurement of charged particles in future experiments at GSI.

Data analysis and simulations will be performed using the C++-based ROOT and GEANT4 software, respectively, routinely employed in nuclear and subnuclear physics. The thesis will be done at CEA in close collaboration with MIT (USA) and TU Darmstadt (Germany) teams. A long stay in Darmstadt is envisaged.

Nuclear reactions between a light particle and an atomic nucleus with energies around GeV occur in various domains, namely nuclear waste transmutation, hadron therapy, neutron sources, radiation shielding (accelerators and space), and the study of meteorites. At Irfu/DPhN we develop such a nuclear reaction model.



Our code, INCL (Intranuclear cascade Liège), is developed for more than twenty years with the university of Liège. It is recognized for its sound bases and is implemented in several particle transport codes (Geant4, Phits, MCNPX). Until 2011, its range of application covered projectile energies from ~100 MeV up to 2-3 GeV. It was then extended to 10-20 GeV by adding, first, multiple pion emission channels and, second, strange particles (K, Lambda, Sigma). With the latter particles the goal was not only better manage of the cosmic ray spectrum, but also to get the possibility to produce hypernuclei, which are studied in several facilities (FAIR, JPARC, JLab).



Still related to hypernucleus and cosmic ray, the topic of this thesis will an upgrade of INCL in another direction. Our model treats nucleons , pions an kaons as projectiles, and we are going to add electromagnetic probes and antiprotons. The electromagnetic probe will enable us to study hypernuclei produced at JLab (electron) and to study the impact of muons penetrating deeply the planets. Antiproton spectrum, in cosmic rays, was measured by the PAMELA experiment recently. Although much less numerous compared to protons, their interactions with interstellar bodies will be interesting to investigate. Antiprotons as projectile will be also an opportunity to compare our calculation results to the data measured at FAIR on hypernucleus production. Already available are the data with the antiproton beam from LEAR (Cern) on strange particle and hypernucleus production. Adding Ksi production could be also interesting, since this strange particle will be produced at FAIR, and also JPARC with a Kaon beam, to build S=-2 hypernuclei.



The student will include those new projectiles in INCL. The reaction mechanisms of those particles with nucleons and the nucleus should be studied before, and, after, a careful benchmark will be done to test the reliability. Sound knowledge of hadronic physics, nuclear physics and C++ is required. The new version of INCL will be eventually implemented in Geant4 and the student will be member of the Geant4 collaboration. Considering cosmic ray, he/she will collaborate with I. Leya, University of Berne, expert in interactions between cosmic rays and interstellar bodies.

One of the most fundamental properties of the atomic nucleus is its shape, which is governed by the interplay of macroscopic, liquid-drop like properties of the nuclear matter and microscopic shell effects, which reflect the underlying nuclear interaction. In some cases, configurations corresponding to different shapes may coexist at similar excitation energies, which results in the wave functions of these states mixing. Experimental observables such as quadrupole moments and the electromagnetic transition rates between states are closely related to the nuclear shape. The experimental determination of these observables, therefore, represents a stringent test for theoretical models. This thesis is integrated in our ongoing programme to study nuclear shapes by means of Coulomb excitation and more specifically such an experiment is planned on 100Zr. This method allows to extract the excitation probability for each excited state and to extract a set of electro magnetic matrix elements, and in particular the quadrupole moment which determines the shape of the nucleus. The radioactive 100Zr beam is provided by the ATLAS-CARIBU facility at Argonne National Laboratory (ANL), which is currently the only facility world-wide able to deliver beams of such refractory elements. The programme advisory committee has already accepted the experiment with high priority and we expect it to be scheduled in Q4/2019. The PhD student will participate in the preparation and setting-up of the experiment. It would be advantageous if he/she started already working on the subject already during the stage M2. He/she will be responsible for the data analysis, the presentation of the scientific results (at conferences or workshops) and their publication in a scientific journal. During the thesis work the PhD student may also participate in other experiments of the research group. All experiment(s) take place in international collaborations and may require prolonged stays at foreign laboratories (e.g. 4-6 weeks at ANL, USA).

Positron emission tomography (PET) is a nuclear imaging technique widely used in oncology and neurobiological research. Decay of the radioactive tracer emits positrons, which annihilate in the nearby tissue and emits two back-to-back 511 keV photons. These photons are used to reconstruct the biological activity in the

body.

The precise determination of the position of the positron annihilation vertex is important for an accurate image reconstruction with a good contrast. In particular, it is useful for neuroimaging studies of brain and for pre-clinical

studies with animal models (rodents). The time-of-flight (TOF) technique is used to improve the signal-to-noise ratio in full body scans and therefore the image quality. This technique measures the difference in time between the two annihilation photons in addition to their position.

The ClearMind project at IRFU develops a novel detection technology, which combine the possibility to acquire images with a high spatial precision of several mm3 and time-of-flight capability with precision better than 50 ps (RMS). To obtain these performances, it will be necessary to reconstruct properties of the interaction in the detector volume, from the data acquired on the surface. For this we work on artificial intelligence techniques (Neural Network, Deep Learning etc ...)

After that it is necessary to estimate the quality of images of a foreseen scanner based on our technology.

In this thesis, we propose, first, to work on the algorithms of artificial intelligence necessary for the event reconstruction in the detector, and then

measure its performances. After that contribute to a Monté-Carlo simulation of the foreseen scanner and to the image reconstruction.



PROPOSED WORKS

The foreseen detector registers the 2D spatial coordinates and arrival time of the scintillation and Cherenkov photons produced by the gamma-conversion in the crystal. The Ph.D. study will consist in the development of the detector simulation with Geant 4 software, development and optimization of the coordinates and time reconstruction of the gamma-conversions using artificial intelligence algorithms (neural network, boosted decision tree, etc). Then he/she will contribute to the simulation of a complete scanner using GATE software and estimation of the it performances following NEMA standards.



REQUIREMENT

Excellent academic profile. General knowledge in physics of particle interaction with matter, radioactivity and particle detector principles. Good background in computational mathematics, be comfortable in C++ programming and working

in Unix environment. Background in simulation and artificial intelligence algorithms will be considered an asset.

Muon tomography, or muography, consists in using cosmic muons to perform deep imaging of structures. These highly energetic muons, produced in showers generating from the interaction of cosmic rays with the atmosphere, can indeed cross several hundred meters of stones before being absorbed. The outstanding progress achieved in the last years on particle detectors (spatial resolution, robustness, electronics, etc.) have recently elicited a high interest for muography in many different fields.



A first muon telescope prototype was built and tested in 2015, using Micro-Pattern Gaseous Detectors (Micromegas) with a patented multiplexing scheme. The next year, three new telescopes were deployed around the Khufu's pyramid in Egypt, showing their robustness in extreme conditions (temperature, dust, etc.). Their detection of the "ScanPyramids Big Void" in combination with Japanese instruments located inside the pyramid are a world premiere for outdoors instruments.



These developments triggered the interest of many industrials and researchers for this technology. But like an optical telescope, muon telescopes are quite directional and still not very compact. An elegant solution consists in using a Time Projection Chamber (TPC), which allows for a full trajectory reconstruction with better precision and in a quasi-isotropical way.



The goal of this PhD is then to design, build and test in real conditions such an instrument. One of the main key points concerns the TPC autonomy, in particular the gas consumption, but also its overall stability in outside conditions. A sealed or semi-sealed TPC with a gas purification system, easily transportable and resistant to environmental variations would be a major breakthrough in muon tomography and for gaseous detectors in general.



Through this project, the PhD student will have the opportunity to cover a large spectrum of activities (design, integration, detector characterization, electronics, data analysis, simulation, etc.) and will then acquire skills in multiple aspects of experimental physics. The small size of the team (~6 people) will also ensure a great visibility to his/her work.

The theme of the proposed thesis is the physics of neutrinos emitted by nuclear reactors. A first part of the work will focus on the analysis of data from the STEREO experiment, which aims to test the existence of a sterile neutrino with a mass around 1 eV. The hypothesis of this particle follows work by Irfu on the prediction of reactor neutrino spectra and its comparison with existing data. STEREO is installed near the ILL research reactor in Grenoble. The analysis conducted during the thesis will accumulate all data until the end of the detector's operation in 2020 in order to achieve the final sensitivity in the search for sterile neutrino. The existence of such a particle would be a major discovery and this analysis will be part of a global experimental program supported by 6 ongoing experiments. STEREO will also provide the community with a reference spectrum exclusively from 235U fissions, allowing a complementary test of neutrino spectrum predictions.

This analysis work will be complemented by instrumental work related to the deployment of the Nu-Cleus experiment. The objective is to detect the coherent scattering of neutrinos at the Chooz nuclear power plant, using a bolometer with an extremely low detection threshold (~10 eV) to detect small nuclear recoils induced by neutrinos. Validation of this technology would open up many opportunities: tests of the Standard Model at low-energy, neutron radius of nuclei, application to reactor monitoring. The thesis work will be part of the on-site deployment effort and in particular the study of shielding for the rejection of background noise induced by cosmic-rays, the main limitation of the measurement.

This work offers a very complete training as an experimental physicist as well as a very transversal approach in several fields of physics: nuclear, particle, cosmology.

ATLAS, one of the major experiment at the LHC, is starting the preparation for the expected increase of luminosity for Run3 and HL-LHC. The work of this thesis will initially consist of analysing qualification data for the new muon detectors, which will integrate the experiment from 2020 onwards. The thesis will be followed by a measurement of precision physics in the field of the Z boson with ATLAS data.



In the first year, the student will focus on analyzing the cosmic data from the test bench for a future ATLAS detector at the LHC, the new small wheel (NSW). This detector, based on the Micromegas technology, should be installed from 2020. These new modules are necessary to monitor the expected improvement in the performance of the LHC accelerator by 2020, in terms of brightness and particle flux. Micromegas detectors, for MICRO MEsh GAseous Structure, are gaseous particle detectors, resulting from the development of wire chambers, but allowing high flow operation and simplified construction using processes derived from printed circuit board technology. Invented in 1992 by Georges Charpak and Ioannis Giomataris, Micromegas detectors are mainly used in experimental physics (particle physics, nuclear physics, astrophysics, etc.) but also for imaging projects of large structures or dense objects with cosmic rays. The work will consist in validating the modules by analyzing data on the Saclay cosmic bench and participating in the test beams at CERN.

For the other two years, the subject is focused on electroweak precision physics in ATLAS. The aim is to measure with the best possible precision the electroweak mixing angle, as well as the mass of the Z boson, using Run2 (and possibly Run3) data. The explored channel is that of the Z boson decaying into a muon-antimuon lepton pair. The student will work on muon momentum calibration using J/Psi as the standard candle, and will also reduce, through advanced fitting methods, the uncertainties related to the parton distributions functions (PDFs). These measurements should lead to a high improvement in the electroweak fit and thus significantly constrain the Standard Model, as well as Beyond Standard Model physics.

The proposed thesis focuses on the detection of neutrinos emitted by nuclear reactors according to the coherent diffusion process, first demonstrated in 2017 with neutrinos from a spallation source of a few tens of MeV[1]. The Nu-Cleus experiment[2], which is the subject of the thesis, is currently at the end of its design phase. It will be deployed at the Chooz nuclear power plant from 2019. A new detection site, located between the two cores of the plant, will be used for the measurement. Detection will be done with mini-bolometers with an extremely low detection threshold, in the order of 10 eV, in order to observe small nuclear retreats induced by neutrinos[3]. A first phase of the experiment, between 2020 and 2021, will use a detector mass of around 10 grams. This reduction in fiduciary mass will represent a technological breakthrough in neutrino physics. A network of around 100 bolometers will then be used to conduct an innovative physics programme: standard model tests and research into new low-energy physics (including sterile neutrinos), weak nucleus shape factors, application to reactor monitoring.



The main thesis work will involve the development of a simulation chain and analysis of experience data. This chain will be used to optimize detection, to carry out sensitivity studies, and finally to analyze and publish the results of the measurements. The student will also participate in the integration of the on-site experience, scheduled for 2020, followed by the commissioning of the detectors. This work will be done in close collaboration with the University of Munich, the Irfu Nuclear Physics Department, and the CNPE Chooz teams.



Irfu is firmly involved in the theme of low-energy neutrinos, with the measurement of theta-13 mixing angle by the Double Chooz experiment[4], non-proliferation applications by the Nucifer experiment[5], and sterile neutrino research by the Stereo[6] and KATRIN[7] experiments.



REFERENCES



[1] D. Akimov et al., Science 03 Aug 2017

[2] Strauss, R., Rothe, J., Angloher, G. et al. Eur. Phys. J. C (2017) 77: 506

[3] J. Bill J.Phys. G44 (2017) no.10, 105101

[4] M. Kaneda, Phys. Part. Nucl. 49 (2018)

[5] M. Pequignot, Nucl. P. P. Proc. 265-266 2015

[6] H. Almazan et al., arXiv:1806.02096

[7] M. Kleesiek, arXiv:1806.00369

The proposed PhD thesis subject consists in designing and building Micromegas detectors to equip the sPHENIX TPC. The detectors must provide a good enough spacial resolution in order to accurately measure the momentum of the produced charged particles. At the same time, it must minimize the presence of positive charges (ions) in the TPC volume. These charges could create local distortions to the electric field in the TPC and ruin its ability to properly reconstruct the particle's trajectory.



Micromegas detectors are parallel plate gas detectors that consist of two stages: (i) a drift stage that coincides with the TPC drift volume and (ii) an amplification stage delimited by the printed circuit board that collects the signal and a mesh. The electric field in the amplification stage is very large, resulting in an avalanche process when entered by an electron coming from the drift stage. The positive ions resulting from this avalanche are the ones that could cause electric field distortions in the TPC. The student's job during his/her PhD will be to study the possibility to add one or several extra meshes on top of the amplification mesh in order to capture these ions before they enter the drift volume. This will require the design and characterization of smaller size detector prototypes, the precise simulation of their properties and the test of these detectors in realistic conditions.



Regarding data analysis, the student will study bottomonium production in heavy-ion collisions, based on data collected by ALICE during LHC Run-2 (2015-2018). Possible analysis topics include: measuring bottomonium production as a function of particle multiplicity in proton-proton, proton-led and led-led collisions; measuring the bottomonium nuclear modification factor, or the bottomonium elliptic flow. Such studies are complementary to the ones that will be carried out in the future with sPHENIX.

On 14 August 2017, the ATLAS experiment at CERN has published in Nature Physics [1] the first direct evidence of high-energy photon-photon elastic scattering, thereby confirming one of the oldest predictions of quantum electrodynamics (QED). The experimental observation of this process is difficult. Indeed, this phenomenon is only possible in intense electromagnetic (EM) field with an electric field of at least 10^18 V / m. The ATLAS experiment used 2.5 TeV high energy ion beams per nucleon to produce these intense fields. The interaction of the EM fields of the 2 lead ion beams (of opposite directions) makes it possible to carry out the appropriate experimental conditions. Then, the publication of 14 August 2017 has reported 13 events identified as elastic collisions of photons (with 2.7 events of background). From mid-November 2018 to the beginning of December 2018, a new data taking is underway which should allow this number of events to be increased by a factor of 4 to 5, allowing more detailed studies than a simple observation.

The aim of the thesis will be to participate in this new analysis. The student will contribute to the general understanding of the data and will focus on a few specific points: for example, to study in depth the systematic uncertainties on the cross section of the 4-photon interaction as a function of the invariant mass of the 2 incident photons, such as the uncertainties on the photon reconstruction identification efficiencies. The mass spectrum of photon-photon elastic scattering events is also essential for another innovative aspect of the thesis. Thus, at first, the student will work on measuring the cross section of the photon-photon elastic scattering. With more data, it will be possible to search for new particles that can be produced in photon-photon collisions, in particular a scalar particle called Axion [2] which plays an important role in the theory of strong interactions and which could also to be a source of dark matter in astrophysics. With a good understanding of the mass spectrum described above, we can start to search for resonances in this spectrum (for each accessible Axion mass) and, failing that, to extract limits for the effective cross sections of the spectrum. 'Axions. This approach, the feasibility of which has been demonstrated [2], will have to be undertaken by the student on the data recorded at the end of 2018. To conclude, let us mention that the contribution of the CEA Saclay group to the first publication of ATLAS [1] was decisive. and that, on this momentum, the environment within the group is favorable so that the student can play an important role in what will follow.



[1] Nature Physics 13, 852–858 (2017)

[2] ATL-COM-PHYS-2018-1113

The neutrino, as only particle of mater without electrical charge, could be a Majorana particle, i.e. identical to its antiparticle. In this case a new phenomenon should appear for a few radioactive atomic nuclei: the neutrinoless double beta decay. The violation of the leptonic number which follows, forbidden by the Standard Model, would be a major discovery and one of the required conditions to explain the mater-antimatter asymmetry in the Universe.



The PandaX-III experiment aims to measure the kinematics of double-beta decays of Xenon 136 in a large volume of 10 bar gaseous Xenon. This experiment could detect double-beta decays without emission of neutrinos and distinguish them from backgrounds like usual double-beta decays with neutrino emission, gammas from radioactive contamination, or cosmics. These rare processes will be detected in gaseous Xenon inside large Time Projection Chambers (TPC) with a detection of ionization electrons based on Micromegas Microbulk micro-pattern gaseous detectors. The TPC will operate under a pressure of up to 10 bar. An excellent resolution of electron energy measurement and a very good reconstruction of the event topology is required to separate neutrinoless double-beta decays from the various backgrounds. A high radiological purity of the experimental set-up is also necessary to limit the gamma background contamination. This experiment will take place in the Jinping underground laboratory (Sichuan province, China) which presents the lowest residual cosmics rate in the world. A first 150 to 200kg-Xenon TPC chamber will be installed by the beginning of 2020, and 5 modules will be installed in the following years to reach a level of 1t of Xenon.



Associated with the PandaX-III team at DPhN and DEDIP (detector, electronics and computing laboratory for physics) the student will participate to the development of high pressure Micromegas detectors with high energy resolution and their associated read-out electronics. R&D will be conducted on several types of Micromegas detectors, in order to reach 1% energy resolution at 2.5 MeV. This work will include performance measurements of the different prototypes in high pressure gaseous environment, in association with our partners at Zaragoza and Shanghai universities. In parallel the student will work on algorithms of TPC data reconstruction in view of the analysis of the data to be taken with the future experiment. The goal of these developments is to be able to measure and to determine the characteristics of double-beta decays (energy, kinematics, event topology) and to distinguish them from the gamma background events, in order to reduce their impact by a factor 100. Test set-up data as well as Monte Carlo simulations will be studied for that goal. The student will participate to the analysis of the first data of the PandaX-III experiment from mid-2020 in order to determine a first limit on the production of neutrinoless double-beta decays.

A few microseconds after the Big Bang, the Universe was in a quark gluon plasma (QGP) state. Such state is predicted by Quantum Chromodynamics, which is the theory of strong interactions, and should be reached at very high temperature or energy density. Such conditions are reproduced in ultra-relativistic heavy ion collisions at the LHC at CERN. Among the various QGP observables, the study of hadrons with heavy-flavor quarks (charm c or beauty b) and quarkonia (c-cbar or b- bbar bound states) is particularly important to understand the properties of the QGP.



Quarkonia are rare and heavy particles that are produced in the initial stages of the collision, even before the QGP is formed, and are therefore ideal probes of the plasma properties. As they traverse the hadronic matter, the binding of quark/anti-quark pairs will get screened by the color field of the many free quarks and gluons in the QGP, and the quarkonium states might be dissociated. This color screening mechanism therefore leads to the quarkonia suppression in the QGP. Since the various quarkonium states have different binding energies, each state will have a different probability of being dissociated. This results in a sequential suppression pattern of the quarkonium states. Additionally, if the initial number of produced quark/anti-quark pairs is large and if heavy quarks do thermalise in the QGP, then new quarkonia could be produced in the QGP by recombination of heavy quarks. This mechanism is known as regeneration. At the LHC, Upsilon (b-bbar) and J/psi (c-cbar) are complementary. The former is thought to be more suited to address the sequential suppression, while the latter should allow to study possible regeneration mechanisms. Quarkonia are measured via their dimuon decay channel with the muons being reconstructed in the muon spectrometer of ALICE.



Following the successful Run1+2 data taking, the ALICE apparatus will be upgraded to increase the interaction rate capabilities from 8 kHz to 50 kHz for Pb-Pb collisions. Combined with a novel self-triggered data acquisition mode, this will result in a statistics of heavy-ion collisions for Run 3 roughly 100 times larger than Run 1+2. In the quarkonium sector, this will allow us to investigate J/psi suppression and regeneration with much better statistical precision, as well as to access quarkonium states with smaller production cross-sections. The addition of a new silicon-pixel based tracker (MFT) in front of the muon spectrometer will open the possibility to separate the prompt and non-prompt (from decays of b hadrons) J/psi contributions.



We propose to study the production of prompt quarkonium states in p-p collisions, using the first data collected at higher interaction rates. In Pb-Pb collisions, the separation of prompt and non-prompt J/psi allow to differentiate among the QGP effects acting over the c quark from that over the b quark. In p-p collisions, besides providing the proper reference for Pb-Pb studies, it enables a rigorous comparison with the calculations of quarkonium production models. Through the analysis work, the student will become familiar with the grid computing tools and the simulation, reconstruction and data analysis software of the ALICE Collaboration. In particular, he/she will have the possibility to actively participate in the development of the new online/offline event reconstruction software, as well as to participate in the commissioning phase of the upgraded ALICE detector.

Future experiments on linear colliders (e+e-) with low hadronic background require improvements in the spatial resolution of pixel vertex detectors to the micron range, in order to determine precisely the primary and secondary vertices for particles with a high transverse momentum. This kind of detector is set closest to the interaction point. This will provide the opportunity to make precision lifetime measurements of short-lived charged particles. We need to develop pixels arrays with a pixel dimension below the micron squared. The proposed technologies (DOTPIX: Quantum Dot Pixels) should give a significant advance in particle tracking and vertexing. Although the principle of these new devices has been already been studied in IRFU (see reference), this doctoral work should focus on the study of real devices which should then be fabricated using nanotechnologies in collaboration with other Institutes. This should require the use of simulation codes and the fabrication of test structures. Applications outside basics physics are X ray imaging and optimum resolution sensors for visible light holographic cameras.

Neutrino physics has made enormous progress in the last decades, in particular with the discovery of neutrino oscillations. This indicates that neutrinos have non-zero masses, requiring ingredients beyond the particles and interactions presently known. Moreover, the relatively large value of the theta13 angle open the possibility to probe CP violating phenomena in the leptonic sector. This might be related to the observed matter-antimatter asymmetry in the Universe.

These studies require very intense neutrino beams and large underground detectors, like the project DUNE, now in construction in USA. Within DUNE, the team at IRFU is building a large demonstrator of a new technology for liquid argon Time Projection Chamber, offering superior detector performance. This 300-tonnes demonstrator will be exposed to cosmic rays in 2019 and to a charged-particle beam in 2021. The thesis work will consist in the analysis of the data to understand the detector response and to develop the algorithms for track and shower reconstruction. The student will also participate to a R&D of the gas detectors (Large Electron Multipliers, LEM) to improve the performance toward DUNE.

Since their discoveries at the beginning of the twentieth century, the unique properties of superconductivity have been used in a wide variety of applications from powerful electromagnets used in MRIs and fusion reactors, to next generation electronic fast digital circuits (Quantum-bits) and particle accelerators. Major causes for performance limitations in a superconductor originate from its interaction with external electro-magnetic fields which are responsible for the entire electromagnetic behavior of applied superconducting materials. We propose an original approach to mitigate the superconducting dissipation originating from deleterious vortices: a new superconducting multilayer as efficient screening structure to inhibit vortices entry into the bulk superconductor. The synthesis and design of these nano hetero-structures by Atomic Layer Deposition will be optimized and tailored to drastically improve the performance of a superconductor-based device: superconducting radio frequency (SRF) cavities.

The PhD student will be an important active part of the synergistic approach between synthesis, design, characterization and performance tests of the most effective screening hetero-structures based on the superconducting nitride alloys NbN, NbTiN, MoN and insulating materials AlN, MgO, SrTiO3 in order to provide a technological breakthrough towards unprecedented superconductor performances for superconducting resonators. This 3 years program will focus on three research thrusts or work packages:

1- Explore synthetic routes to deposit innovative hetero-structures. Years 1-2.

2- Tailor hetero-structure properties to optimize superconductor performances. Years 2-3

3- Test optimized hetero-structure on superconducting Nb resonators. Year 3.

Quantum mechanical contextuality has been studied in recent years as a resource that allows for measurement-based quantum computation, enabling non-classical performance. Contextuality has also been studied in the framework of resource theories using topological approaches. Fully grasping the power of contextuality as a resource in this general setting remains an open problem. It has been suggested that the partition of a physical system into subsystems supplies a crucial element for the increase in computational power. Devising and exploring a mathematical setting where this partition can be studied computationally will be the main goal of this dissertation.

Nowadays, superconducting magnets are more and more used for applications related to the future energy. Indeed, they represent one main component of the so-called "Tokamak" machines which goal is to produce one day electricity from thermonuclear fusion energy. In order be in a superconducting state and to transport high current densities, these magnets are cooled by supercritical helium at a temperature of 5 K. However, a disturbance or fault in the machine could induce a heat deposition on the conductor and make it transit from his superconducting state to a normal resistive state. Once the conductor is resistive, the high current passing in it induces high heat deposition by joule effect and thus a transition of the conductor lengths close by. This transition chain reaction of the conductor from its superconducting state to its normal state is called "Quench". In the Framework of a collaboration between Europe and Japan, 20 superconducting magnets of the JT60SA Tokamak were tested by CEA under their nominal operating conditions (25 kA and 5 K). Quench experiments have been performed on each one of them. The PhD work will consist first in the physical analysis of the data obtained during quench experiments and the identification of the physical phenomena taking place during a quench. Then the PhD student may propose and carry out new complementary experiments allowing him to better understand the main thermo-hydraulic phenomena taking place. Finally, the PhD student will have to build a numerical model that reproduces and predicts the behavior of the magnets during a quench experiment. This model will be implemented in and existing industrial software.