AVIS DE SOUTENANCE

Monsieur Julio BALBIN ARIAS

« Sciences pour l'ingénieur : Mécanique, Physique, Micro et Nanoélectronique »

Spécialité « Fusion Magnétique »

Soutiendra publiquement ses travaux de thèse intitulés :

« Investigation of the dependency of separatrix density

of tokamaks as a function of engineering parameters»

Soutenance prévue le mercredi 30 mars 2022 à 15h00

Lieu :   IRFM – Salle des Maquettes - Centre de Cadarache 13115 Saint-Paul-Lez-Durance

et par Skype (voir lien ci-dessous)

Composition du jury proposé :

Mots-clés :

Physique des plasmas, Tokamak, JET, mode-H, base de données, loi d’échelle.

Résumé :

A viable magnetic fusion power plant has to combine very high plasma density and temperature in the core region, in order to maximize fusion reactions, with cold plasma conditions in the peripheral region compatible with long life expectancy of plasma-facing components. In this thesis, we examine this crucial issue for magnetic fusion research by adopting an approach based on the analysis of a large set of experimental data on H-mode plasmas from the JET and TCV tokamaks, in order to obtain a scaling law for the relationship between top pedestal density and separatrix density as a function of engineering parameters. The choice to examine this density ratio is motivated by the fact that, on the one hand, the density at the top pedestal is an indicator of core confinement and device performance, and on the other hand, the separatrix density has a strong impact on divertor conditions, indicating whether safe conditions for divertor targets are achievable or not.

After a brief review of the main parameters of the JET and TCV tokamaks and the diagnostics considered for this study, the data analysis is presented, starting from the method developed for the determination of the separatrix density. As it is well known, this is a very difficult task and many approaches are used to determine this density, which in fact requires locating the position of the separatrix in the measured radial density profile. The method that is developed in this study is based on power balance considerations. This method relies on the choice of the heat flux expression and non-negligible differences in the separatrix densities are observed depending on this choice. In order to estimate the impact on the position of the separatrix and thus on the separatrix density, the power balance method was applied to numerical simulations obtained with the SOLEDGE-EIRENE transport code for a JET configuration considering several heat flux expressions. The position of the separatrix obtained with the power balance method is compared to the known position from the mesh-grid built on a given magnetic equilibrium and used for running the simulation. With this type of verification, it is shown that for typical JET H-mode discharges considered in this study, the power balance method using a kinetically corrected Spitzer expression works very well.

In a second step, the analysis of JET H-mode discharges considered for this work is detailed. A first analysis of the dataset shows that some engineering parameters cannot be considered as independent for our analysis because many discharges were performed considering the same typical values of these parameters, such as the toroidal magnetic field and the plasma current. Thus, two main engineering parameters are first identified and will be used for the scaling law on the ratio of the separatrix density to the top pedestal one, namely the plasma current I_P and the total injected power P_TOTAL. This first scaling law seems to predict the experimental data quite well for low and medium values of the separatrix density, while at high density a strong discrepancy appears. In order to get further insight on such behavior the discharges were analyzed in terms of divertor magnetic configuration. A clear difference is observed between experiments with a corner-corner divertor magnetic configuration compared to the horizontal-vertical ones or vertical-vertical ones. This result suggests the introduction a parameter taking into account the quality of confinement. In this way, a better agreement between predictions and experimental results is obtained for both low and high-density values. Finally, the same type of study is performed on TCV and a scaling law taking into account both devices is derived.

.........................................................................................................................................

Participer à une Réunion Skype       

Vous n’arrivez pas à rejoindre cette réunion ? Essayer l’app web Skype

Participer par téléphone

+33 1 69 35 55 10 (France)                              Français (France)    

Rechercher un numéro local  

ID de conférence : 34046239

 Vous avez oublié votre code confidentiel de connexion ?  |Aide      

Condition d'accès :

• Depuis un Poste CEA équipé de Skype Entreprise (*): Cliquer sur le lien ci-dessus.

• Depuis un navigateur web (sauf Internet Explorer. Le poste n'a pas besoin d'être CEA ni d'être connecté au réseau CEA. Les smartphones et postes Linux sont supportés) : aller à https://vc.cea.fr et appeler 99+ID de conférence . Exemple: ID=1234567--> 991234567

• Depuis une salle de visioconférence CEA : 99+ID de conférence (depuis une salle de visioconférence hors CEA, appeler au préalable sk@vc.cea.fr)

• Pour l'audio seul : Appeler le 0169355510

- Saisir l'ID et valider par la touche #

- Ne pas saisir la touche * et ne pas s'identifier

- Attendre qu'un participant vous autorise à entrer en conférence

* L'usage de l'audio nécessite un micro et un haut-parleur ou un casque/micro

Pour que l'on vous voit (optionnel),votre appareil doit être équipé d'une caméra.

(*) - Seul l'organisateur doit impérativement être raccordé à l'intranet CEA (en direct ou via VPN) pour que la réunion se déroule.

----------------------

Access conditions :

• From a workstation CEA with Skype for Business client installed (*): Click on the link above.

• From a web browser (except Internet Explorer. The workstation does not need to be CEA or to be connected to CEA network. Linux, smartphones and workstations are supported) : go to https://vc.cea.fr and call 99+Conf ID.

• From a CEA videoference room : call 99+Conf ID (from Internet, call sk@vc.cea.fr before)

• From audio only : Call +33 1 69 35 55 10, enter the Conf ID when asked.

- Confirm with the # key.

- Do not enter the * key.

- Simply wait, a participant will authorize you to join the conference.

* Audio experience will be better with an headset but you can use the built-in microphone and speaker of your phone.

In order for you to be seen (optional), your device must be equipped with a camera.

(*) - Only the organizer must be connected to the CEA intranet (directly or via VPN) for the meeting to proceed.

_{[!OC([040c])!]}

.........................................................................................................................................