24-082 New Solutions to Control Rf Multipactor

Il y a 2 mois

Brest, France CNES - Centre National d'Etudes Spatiales Temps plein

Doctorat, 36 mois
- Temps plein
- Aucune expérience exigée
- Maitrise, IEP, IUP, Bac+4
- Telecommunications

**Mission**:
The Microwave Devices team of the Lab-STICC are focused on the design and the fabrication of innovative microwave devices for satellite missions on small platforms. For this kind of platform, the miniaturization of RF instruments and equipment, and in particular filters and duplexers is obviously a priority. However, the expected electrical performances and the strong constraints of size reduction are often antagonistic as regards the problematic of power handling and in particular Multipactor thresholds. The reason is a drastic increase of the power density.

The multipactor effect is an electrical discharge process that is triggered in the RF components of satellites under certain conditions. The secondary electronic emission is one of the physical mechanisms which is responsible of the multipactor effect and which must be controlled. Indeed, the walls of a microwave component can, under the impact of residual electrons present in the cavities, produce an electronic cloud by a resonance effect with the guided wave. In certain conditions, it can be the source of destructive discharges (corona).

The solution proposed in this thesis, is a third way and consists in limiting the electron discharges by controlling the electron flow with potential barriers using dielectric or biased voltages. The solution expected in future microwaves components could be a combination of this processes.

This work will be built on previous thesis work, those of Christophe Hallet (2015 -2018), Alejandro Buitrago Bernal (2019 - 2022) and Karim Kouny (2022-2025). These theses based on the synthesis and design of microwave volume filters, have led to the design of two L-band filters, one is a fourth-order filter with an imposed power threshold of 400 W (ESA specifications), the other is a second-order filter with a multipactor threshold of 100 W (CNES specifications).

The electromagnetic design software and the RF measurement devices (VNA Vector Network Analyser) are extremely efficient but it is not the same for the tools addressing the multipactor problematic. Indeed, the electronic emission simulators are not definitively mature and the available test set up are not many in France or Europe, difficult to access for research, mainly for cost issues. Spark3D or CST PIC software offer many advantages, such as the prediction of multipactor trigger thresholds in vacuum, as well as the localization of the different risk zones of a microwave device, such as a Tx filter. However, in these simulation softwares, the effects of dielectric charging or potential barriers cannot be taken into account in the input parameters. To carry out this project, it will be necessary to use the EDGE/MoOra engineering suite to generate the internal particle flux from the external spectrum, with support for different shielding thicknesses, and SPIS (Spacecraft Plasma Interaction Software), developed mainly by ONERA, ARTENUM and Airbus DS, to process the field mapping, including the initial charge state of the dielectrics. This is a 3D modeling tool able to model a large set of phenomenon relative to spacecraft charging (including internal charging), using an advanced 3D electrostatic plasma solver. This tool is able to model the charging of dielectrics of complex and realistic geometries under the effect of strong electromagnetic fields.

Part of the thesis will involve enabling the SPIS software to take RF frequency ranges (GHz) into account. In parallel, it will be necessary to conduct a study on the integration procedure of external electrostatic fields in electromagnetic simulation software such as Ansys HFSS. An important numerical modeling work will allow to couple the different software tools in order to integrate the effects of potential barriers in the simulations of the multipactor effect within a filter representative of a realistic solution. Theses filters will be manufactured and measured. In a second step, new filter solutions adapted to the introduction of potential barriers will be considered. It can be for example filters based on half-wavelength coaxial resonators, with floating conductors.

An accompanying R&T budget of 40k€ will be required for this thesis. This budget includes the construction of filters, the supply of dielectric materials and various tests (SEY characterizations, RF, etc.). A budget will also be devoted to various missions (software, publications, etc.).

=================

**Profil**:
Master or engineer school student with an experience in general physics, solid state physics, plasma and materials physics, microwave (passive devices and filters design). Foreign or French applicants are welcome. In all cases, English is required.

**Nom du Laboratoire**:
Brest - LAB-STICC

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