Description du sujet de thèse

Superconducting Radio Frequency cavities are the core of future accelerator projects in the post-LHC era. For the high current machines toward high luminosity collisions, namely, FCCee at CERN and PERLE at IJCLab, extremely high-quality factor (Q) is of critical importance to minimize cryogenic power dissipation and thus save liquid helium and electric power consumption. IJCLab is leading the development state-of-the-art high-Q cavities in the international collaboration for sustainable future accelerator projects (iSAS).
In 2024, it has been proven that a clean vacuum furnace at IJCLab could perform advanced heat treatment of a prototype cavity, so-called mid-T baking, and the obtained results reproduced the ones from other laboratories outside France (FNAL, JLAB, KEK, iHEP, DESY). IJCLab is modifying its cavity test stand to be able to measure new cavities under fabrication. For theoretical work, IJCLab established a collaboration with ANL, JLAB, INFN, and KEK to develop nonlinear nonequilibrium models to explain high-Q cavity behaviors under strong RF fields. This is one of the long-lasting fundamental problems of superconductivity and an outstanding challenge in quantum statistical physics.
The successful candidate will work on the measurements and data analysis of prototype high-Q cavities for FCC in IJCLab as well as general cavities. The task includes preparation of cavity testing, cryogenic operations, RF measurement, and data analysis. By using the data, she/he will take part in theoretical modeling of high-Q cavities. In particular, frequency dependence of so-called anti-Q-slope will be compared with newly proposed theories. Moreover, the student will perform systematic comparison of experimental data from different laboratories. From time to time, she/he may participate experiments in other laboratories, such as CERN, KEK, JLAB, INFN, FNAL, etc, as well as providing presentations in international workshop (cf. bi-yearly TTC) and conferences (cf. SRF2027 in Padova). Some of the successfully tested cavities will be installed in the iSAS cryomodule for the new Energy Recovery Linac (ERL) accelerator PERLE at IJCLab. Thus, this project offers a wide range of experience to this student: fundamental understanding of superconductivity, state-of-the-art cavity development, international collaborations, and contributions to a serious accelerator project in France. The objectives of the project include understanding interaction between superconductors and high-field radiofrequency, identifying key parameters that changes cavity performance, contribution to the local accelerator PERLE, provide important insights for the future superconducting accelerator projects (FCC, ...).
The surface resistance of superconductors under RF field is described by the linear response of the BCS theory [1]. Since this is a perturbative theory up to the linear order, nonlinear effects are not included fundamentally. Recently, extremely high-performance superconducting cavities developed for modern particle accelerators show astonishing nonlinear phenomena. In 2014, one model was proposed by using smearing of density of states under strong current [2]; however, its prediction on the nonlinear phenomenon did not agree with the frequency dependence [3]. In 2024, a new theory extending [2] was proposed by introducing Higgs modes [4] and could potentially explain the frequency dependence. There exist completely different approach starting from the 70s by Eliashberg [5] to solve kinetic equations [6] and find characteristic time frequency [7] that enhances nonlinear nonequilibrium effects. Recently, a new calculation [8] based on [6] was developed to model nonlinear behaviour in superconducting devices.
This joint PhD program CNRS-UChicago is led by a team of authors working on nonlinear phenomena in superconducting radiofrequency [8, 9] in collaboration with another theorist [4] aiming at better understanding of this long-lasting problem applied in the accelerator cavities. In 2024, the experimental capability at CNRS was proven [10]. The team is developing numerical codes to analyse the data. Systematic analysis of different data sets taken in the international collaboration may provide insights on important parameters that enables ultra-high performing superconducting cavities.
[1] D. C. Mattis et al., Phys Rev . 111, 412 (1958)
[2] A. Gurevich, Phys. Rev . Lett. 113, 087001 (2014)
[3] M. Martinello, et al, Phys. Rev . Lett. 121 22 224801 (2018)
[4] T. Kubo, Phys. Rev . Applied 22, 044042 (2024)
[5] G. M. Eliashberg, Zh. Eksp. Teor. Fiz. Pis'ma Red. 11, 186 (1970)
[6] J. J. Chang et al, Phys. Rev . B 15, 2651 (1977)
[7] S. B. Kaplan, J. Low Temp. Phys. 37 3 343-365 (1979)
[8] T. Guruswamy , et al, Supercond. Sci. Tech. 28 5 054002 (2015)
[9] A. Miyazaki, et al, Phys. Rev . Accel. Beams 22 7 073101 (2019)
[10] A. Miyazaki, et al., EPJ Web of Conferences 315, 02014 (2024)

Contexte de travail

The Irène Joliot-Curie Physics Laboratory of 2 Infinities (IJCLab) is a UMR under the supervision of the CNRS (IN2P3), the University of Paris-Saclay and the University of Paris is located on the campus of the University of Paris -Saclay in Orsay. The laboratory is located on the campus of the Université Paris-Sud, Université Paris-Saclay in Orsay. The campus is located 20 km south of Paris and easily accessible by RER in 35 minutes.
IJCLab was born in 2020 from the merger of five units (CSNSM, IMNC, IPN, LAL, LPT). The staff is made up of nearly 560 permanent (340 engineers, technicians and administrators and 220 researchers and teacher-researchers) and approximately 200 non-permanent including 120 doctoral students. The research themes of the laboratory are nuclear physics, high energy physics, theoretical physics, astroparticles, astrophysics and cosmology, particle accelerators, energy and the environment and health. IJCLab has very significant technical capacities (around 280 IT) in all the major fields required to design, develop / implement the experimental devices necessary for its scientific activity, as well as the design, development and use of instruments. .
The PhD student will work in the accelerator group of the Laboratory which is involved in multiple developing superconducting accelerating cavity projects, such as Spiral2, ESS, MYRRHA, PIPII, and more recently PERLE, FCC, and ILC.
The group includes around 90 physicists and engineers(permanent researchers, post-docs and doctoral students).
This project is an international collaboration with University of Chicago and national laboratories in the Chicago region. The collaboration expands more globally, including CEA, CERN, DESY, INFN, KEK, IHEP, FNAL, JLAB, etc, in order to perform systematic analysis of data taken in each lab and models developed and implemented by external collaborators.

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.

Contraintes et risques

Constraints and specific features of the post, possible travel requirements
“The successful candidate shall be enrolled on a PhD programme of the PHENICS doctoral school. Travel to University of Chicago (FNAL + ANL) in the US, CERN in Switzerland, KEK in Japan should be expected. Depending on the progress of the research, traveling to other institutions and join their experiments can be considered.”

Informations complémentaires

- basic knowledge in general physics (electrodynamics, thermodynamics, quantum theory , statistical physics)
- programming skills for data analysis (python, Julia, C++, MATLAB, ...)
- passion in learning interdisciplinary subjects is mandatory
- open communication in true international environment is mandatory
- basic knowledge in condensed matter physics (superconductivity) is a plus
- experiences in microwave measurement (oscilloscope, spectrum analyser, network analyser) is a plus

Other Documents
(if it's requested in addition to CVs and LMs, to attach letters of recommendation, names and contact details, if applicable, of former supervisors / teachers, etc.)
Submit a covering letter and CV without any break in date showing diplomas, titles and work and professional experience.
Example:
The candidate must have a Masters in physics. The post requires sound knowledge of basic physics (quantum physics, statistical physics, classical electrodynamics, etc), a high level of communication skills, both oral and written (English required) to be able to present at conferences and write articles in scientific publications, and sound knowledge of IT and data processing. We are looking for a PhD fellow who will be able to become fully involved with the project, with a thirst for knowledge, a certain independence of thought and strong motivation to develop skills in numerical calculation and data analysis in the field of nonequilibrium superconductors under radiofrequency. In addition, the candidate must be able to work in a team on multi-disciplinary projects.
Applications must include a detailed CV; at least two references (people who may be contac-ted); a cover letter of one page; a one-page résumé of the dissertation for the Masters; grades for the Masters 1 or 2).
The closing date for sending applications is 31/06/2025.