The Parker Solar Probe (PSP) mission, launched in 2018, has given us an unprecedented view of the inner heliosphere, revealing a solar atmosphere that is much more structured than expected. Starting in 2024, the spacecraft will fly as close as 9.8 solar radii from the Sun, making it the first to literally penetrate a stellar atmosphere.

Among the phenomena that are currently receiving a great deal of attention are the so-called Type III solar radio bursts. These are generated by a multistage process in which an energetic electron beam emitted by the Sun is expected to generate Langmuir waves, which are then converted into electromagnetic waves by nonlinear processes in which electron density fluctuations play an important role.

What makes PSP truly unique compared to all other missions is its ability to directly observe this nonlinear conversion process in situ, before the beam has begun to relax. Interestingly, PSP is equipped with two sets of instruments that provide high-quality observations of these Type III radio bursts and their local signature: electric field antennas and the SCM search-coil magnetometer built and used by LPC2E. The latter has a high-frequency sensor covering the frequency range of the waves of interest (0.01-2 MHz).

In a recent series of articles, members of our team have provided the first unambiguous evidence for the existence of a slow electromagnetic mode that is a by-product of this mode conversion process [Larosa et al, ApJL (2022) doi:10.3847/1538-4357/ac4e85], a detailed analysis of the harmonics in the Type III radio bursts and their polarisation properties, which are essential for a full understanding of their emission and their interaction processes [Jebaraj et al., ApJL (2023) doi: 10.3847/2041-8213/acf857], and the key role played by processes acting at the front of the population of injected energetic particles [Krasnoselskikh et al., AGU Fall meeting, 2024].

These studies have benefited greatly from observations made with the SCM search coil. Indeed, these observations allow the mode of the primary waves to be determined, and in addition allow electrostatic and electromagnetic waves to be separated when observed in situ. The bursty nature of the generation mechanisms leads to an energy dissipation and a modification of the particle distribution function that is very different from what conventional quasilinear theory of beam-plasma interactions provides.

The main objective of this work is precisely to study this relaxation process. This will be done by a detailed analysis of the polarisation properties of Type III radio bursts. The analysis will be based mainly on PSP observations (due to its proximity to the Sun). However, observations from the Solar Orbiter mission, which carries the same set of instruments (including an SCM magnetometer from LPC2E), will also be considered, as there are only a few events so far where an electron beam happens to pass close to the spacecraft.

The three supervisors of this thesis have complementary expertise: Säm Krucker (SSL Berkeley, and Univ. of Applied Sciences Northwestern Switzerland) will bring his expertise in the measurement and analysis of energetic particle distributions from both missions; Vladimir Krasnoselskikh (LPC2E, Orléans) will bring his expertise in the theoretical modelling of beam-plasma interactions, and Thierry Dudok de Wit (LPC2E, Orléans, and ISSI, Bern) will bring his expertise in the data analysis. All are CoI or lead-CoI on the two missions.

This thesis aims to provide the Ph.D. student with a complete training, including practical aspects such as data retrieval and preprocessing, the development of multi-instrument analysis skills, and a solid understanding of the physical processes that play a key role in both heliospheric and astrophysical plasmas.

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For more Information about the topics and the co-financial partner (found by the lab !); 

contact Directeur de thèse - ddwit@cnrs-orleans.fr

Then, prepare a resume, a recent transcript and a reference letter from your M2 supervisor/ engineering school director and you will be ready to apply online  before March 14th, 2025 Midnight Paris time !