SOLEIL is the French national synchrotron facility, located on the Saclay Plateau near Paris. It is a multi-disciplinary instrument and a research laboratory, whose mission is to run research programs using synchrotron radiation, to develop state-of-the-art instrumentation on the beamlines, and to make those available to the scientific community. SOLEIL, a unique tool for both academic research and industrial applications across a wide range of disciplines including physics, biology, chemistry etc., is used by over 5 000 researchers coming from France and abroad. The facility is a “public” company employing about 500 people, founded by the CNRS and the CEA, and partner of the Paris-Saclay University.
Context of the thesis
SOLEIL is a light source which is in operation since 2006 at Saint Aubin in the Southwest of Paris in France. The facility provides photons of high intensity covering a wide spectral range extending from Infrared to hard X-rays and serves an international community in many fields of science including physics, material science, chemistry and biology. The radiation is produced by 2.75 GeV electrons buckets crossing bending magnets and periodic magnetic devices called insertion devices made of electromagnets or in most cases of permanents magnets. To cover a wide spectral domain in particular in the Soft X-Rays, most of the beamlines are equipped with two insertion devices. The increasing demand of photon brightness has pushed most of the present Synchrotrons in the world to propose new light sources or to upgrade their own storage rings. In 2017, SOLEIL started an Upgrade project of the accelerators and beamlines. The Synchrotron is presently in phase of studying the feasibility to decrease the horizontal emittance with the objective to reach a gain of two orders of magnitude in photon brightness with a very compact new storage ring. However, the increase of the number of guiding magnets has led to a reduction of the space dedicated to insertion (between 30 % and 50 %) and to deliver wide spectral range to insertion beam lines, innovative solutions have been undertaken. The Magnetism and Insertion Device Group of SOLEIL is presently studying the capability of building large spectral domain insertion devices. In the VUV domain, a 5 meter long with large period undulator long will be studied and prototyped whereas in the soft X-Ray two technical solutions are considered. On the one hand, DUAL insertion device made of two independent insertion devices used alternatively by means of a mobile platform. On the other, SOLEIL has also planned to study a magnetic system capable to switch from one magnetic periodicity to its triple value. Both solutions aim at providing photons in a large spectral range.
PhD thesis work
The selected candidate will join the Magnetism and Insertion Device Group and will be trained on magnetic measurements of insertion devices, the use of specific magnetic (RADIA code or TOSCA3D) and radiation (SRW or SPECTRA) softwares.
Insertion device for VUV polarized photons
He/She will focus his/her work in a first step on the study of an undulator dedicated for the DESIRS beamline operating between 5 eV and 40 eV. The candidate will propose a magnetic design in accordance with the experimental needs (spectral range, radiated power, polarization rate) and will evaluate the magnetic, optical performance and the impact on the electron beam dynamics, in particular the additional focusing/defocusing acting on electron bunches, betatron coupling and beta beating. He/She will take in charge a prototype of the undulator be involved in the mechanical studies, specifically by estimating the magnetic forces acting between magnetic arrays which generate mechanical deformation of frame and girders and by evaluating the performance of motors to move arrays to change the photon energy or polarization.
Insertion device for Soft X-Rays polarized photons
Insertion device dedicated for soft X-Rays polarized photons are foreseen to be installed in 4.2 m long straight section (7 meters on present SOLEIL Synchrotron). To continue covering the present spectral range and wider with shorter insertion devices, two period insertion device are to be studied: DUAL undulators and bi-periodic undulators.
DUAL undulators are made of two conventional independent insertion device which can be switched from one to the other by a lateral position change. The main challenge remains in the accuracy of the positioning of each insertion device which may impact the magnetic performance of the system. In accordance with the experimental needs and technical constraints, the candidate will propose a magnetic design by defining the period value, the number of periods, the magnetic field and will evaluate the flux in the required spectral and polarization rate. The candidate will also estimate the magnetic forces, the mechanical deformation and the impact on the magnetic field and optical performances. A prototype using present 1.6-meter long carriage is in phase of construction with the objective of checking the accuracy of lateral position and evaluating the impact of mispositioning on the optical performances and on the beam dynamics. He/She will measure and propose magnetic corrections with a dedicated bench. After qualifying the prototype will be follow by a full-scale study and construction.
Bi-periodic undulators are unique devices made of a special magnet arrangement enabling to switch the magnetic periodicity from one period value to its triple value by means of longitudinal displacement of magnet arrays. This undulator is a compact and innovative insertion device well adapted to spatially limited straight section and can operate alternatively with two magnetic periodicities to extend the spectral range. The candidate will propose a magnetic conception and will evaluate the magnetic performance, the impact on the beam dynamics, the spectral performance.
He/She will compare magnetic and optical performance to a mono-periodic insertion device one and to a DUAL undulator. He/She will take into account the realistic technical constraints related to the operation such as the amount of power caught by vacuum chamber or storage ring equipment or effect on the electron beam. He/she will measure and correct both systems with a dedicated bench with the objective of qualification which will be followed by the construction of a full-scale insertion device which will be operated for dedicated beamline.
The undulator proposed for DESIRS beamline and Soft X-Ray beamlines are a new insertion devices, very compact, without any lateral access to measure the magnetic field. These Insertion devices cannot be measured with the present benches used in the laboratory. The candidate will propose and study a magnetic bench capable to measure field in tiny space.
November, 1rst 2022 – October 30th 2025
Dr. Olivier Marcouillé