Institute of research into the fundamental laws of the Universe

Within the CEA-IRFU (Institut de Recherche sur les Lois Fondamentales de l'Univers), the DACM (Département des Accélérateurs, de Cryogénie et de Magnétisme) is a major player at national and international level in the field of particle accelerators. It has actively participated in most of the accelerator projects of the world's leading research centres over the last decades. An important part of these activities concerns the design of accelerators, linear or circular, for high energy physics or any other scientific application. The field of particle accelerator physics requires in-depth knowledge of the beam dynamics in order to control beams perfectly. In this discipline, the DACM has also turned to new laser-plasma acceleration techniques, with a view to designing laser-plasma wakefield accelerators (LWFA) that will make it possible to significantly reduce the size and cost of future accelerators. Collaborations with international (EuPRAXIA, CERN-AWAKE) or national (LPGP-CNRS, IJCLab-CNRS) partners have been initiated for the design of LWFAs in various configurations and applications. The DACM is currently involved in the design of a reliable and compact LWFA to serve as an electron source for the AWAKE collaboration. Such an accelerator would be a world first. In order to prove its viability, the LWFA must generate reproducible high-quality beams. Detailed physical and numerical optimisations from injection to the end user will have to be implemented. The candidate will also be involved in the other LWFA projects of the DACM.



The thesis will focus on the physical and numerical study of plasma acceleration stages and transport lines between plasma stages or to the end user. The core of the studies will be the control of the quality of the particle beam (size characteristics, divergence, energy spread, ...) that results from the laser-plasma interaction and the applied electromagnetic elements. The optimal integration of the acceleration and transport sections will then be determined. At each stage, the fundamental principles for obtaining the best beam parameters will be sought, and then applied to other ALP design projects in which DACM is involved. Optimizations using machine learning algorithms are also envisaged.



The success of these studies is strongly conditioned by a solid understanding of the physical phenomena in question (6D phase space of the beam, wakefields in plasmas subjected to ultra-intense lasers, multipolar field of electromagnets) and by a good use of the corresponding simulation codes.

After the discovery of the Higgs boson at the LHC, particle physics community is exploring and proposing next accelerators, to address the remaining open questions on the underlying mechanisms and on the constituents of the present universe. One of the studied possibilities is FCC (Future Circular Collider), a 100-km-long collider at CERN. The hadron version of FCC (FCC-hh) seems to be the only approach to reach energy levels far beyond the range of the LHC, in the coming decades, providing direct access to new particles with masses up to tens of TeV. The electron version of FCC brings a tremendous increase of production rates for phenomena in the sub-TeV mass range, making precision physics studies possible. A first study has shown no major showstopper in the colliders’ feasibility but has identified several specific challenges for the beam dynamics: large circumference (civil engineering constraints), beam stability with high current, the small geometric emittance, unprecedented collision energy and luminosity, the huge amount of energy stored in the beam, large synchrotron radiation power, plus the injection scenarios. This thesis will focus on the optimization of the hadron option of the future circular collider against linear and non-linear imperfections (i.e. magnets alignments and their field quality). A key point of this thesis is the comparison of current advanced correction schemes to techniques based on machine learning. The application of these techniques to accelerators is one of current hot topics in the field and pursued worldwide.

In order to increase performances of future particle accelerators, high field superconducting electromagnets (higher than 16 T), based on REBCO materials, are being studied. The LEAS at CEA Paris-Saclay already built two dipoles based on these materials through the two major projects EuCARD and EuCARD2. From these magnets we understood that we have to improve the design and protection scheme for such magnets in order to avoid a local damage during resistive transition (from the superconducting state to the resistive state). Indeed during such transition the heat dissipated locally is very high and led to irreversible damages. A possibility is to reuse the technology developed for UHF (Ultra High Field) solenoid like our recent NOUGAT magnet which reached a world record of 32.5 T in 2019 (14.5 T coming from the HTS part and 18 T from a resistive magnet). This MI (Metal-as-Insulation) winding technique allows the current to automatically bypass any local defect and the quench at 32.5 T confirmed that it is efficient to avoid local burning, even at very high Field/current. The PhD candidate will adapt the existing numerical models to the dipole magnets in order to find the best set of windings parameters which allows a good protection and a good magnetic field generation for the purpose of the accelerator magnets. The PhD student will also participate to the design, the fabrication and the tests of one or more prototypes but also needed technological developments.