L'utilisation des lasers de puissance permet l'étude des propriétés de la matière dans des conditions extrêmes de température et de densité. En effet, l'interaction d'un laser de puissance sur une cible créée un plasma dont la température est suffisamment grande pour atteindre des degrés d'ionisation élevés. Ces conditions peuvent permettre, via divers processus, d'exciter le noyau dans un état nucléaire et notamment dans un état isomère. Un noyau d'intérêt pour étudier ces phénomènes est le 201 Hg. Ce travail de thèse s'inscrit dans le cadre du dimensionnement d'une expérience visant la mise en évidence de l'excitation du 201 Hg dans un plasma laser.La première partie de ce manuscrit présente la détermination des taux d'excitation nucléaire dans les plasmas. Depuis une dizaine d'années les taux d'excitation sont déterminés en utilisant le modèle de l'atome moyen. Afin de valider ce modèle, un code, appelé ADAM (Au-Delà de l'Atome Moyen), a été développé afin de calculer le taux d'excitation nucléaire en DCA (Detailed Conguration Accounting). Il nous permettra d'en déduire un domaine thermodynamique en température et densité où les taux d'excitation déterminés avec le modèle de l'atome moyen sont pertinents.La deuxième partie présente le couplage des taux d'excitation nucléaire avec un code hydrodynamique afin d'en déduire, pour différentes intensités laser, le nombre de noyaux qu'il serait possible d'exciter par tir laser. Enfin, dans une dernière partie,les premières approches expérimentales qui serviront au dimensionnement d'une expérience sur une installation laser sont présentées. Ces approches sont basées sur la détection et la détermination de la quantité d'ions multichargés obtenue loin de la cible (~80 cm). Pour cela, un déviateur électrostatique a été utilisé. / The use of high power lasers allows the study of the properties of matter in extremeconditions of temperature and density. Indeed, the interaction of a power laser and atarget creates a plasma in which the temperature is high enough to reach important degrees of ionization. These conditions can allow the excitation of the nucleus. Anucleus of interest to study the processes of nuclear excitation is the 201 Hg. Thiswork aims to design an experiment where the 201 Hg excitation will be observed in aplasma produced by a high power laser. The first part of this manuscript presents the calculation of the expected nuclear excitation rates in the plasma. For about ten years, nuclear excitation rates have been calculated using the average atom model. To validate this model a code named ADAM (french acronym for Beyond The Average Atom Model) was developed to calculate the nuclear excitation rates under the DCA (Detailed Configuration Accounting) hypothesis. ADAM allows us to deduce the thermo dynamical domain where the nuclear excitation rates determined with the average atom model are relevant. The second part of this manuscript presents the coupling of the excitation rate calculation with a hydrodynamic code to calculate the number of excited nuclei produced in one laser shot for different laser intensity. Finally, in the last part, first experimental approaches which will be used to design an experiment on a laser installation are presented. These approaches are based on the detection and determination of the amount of multicharged ions obtained far from the target (~80 cm). For this purpose, an electrostatic analyzer was used.

The Jupiter Icy Moons Explorer is a planetary exploration mission that aims to study the moons of Jupiter in the planet’s vast magnetosphere. Among the various instruments on board is the Particle Environment Package (PEP), that is led by the Swedish Institute of Space Physics (IRF) in Kiruna. The Jovian plasma Dynamics and Composition analyzer (JDC) is one of six sensors within PEP and focuses on the characterization of positive ions. To be able to measure their three-dimensional distribution and composition, in-situ and in high time resolution, JDC has to cover a large field of view of 2π sr, for the desired energy range, in just a couple of seconds. An electrostatic analyzer within the sensor determines the energy per charge of such particles and a time-of-flight mass spectrometer measures their mass per charge. Constraints on weight and the radiation environment of Jupiter drive the design of the sensor: small and lightweight to allow extra shielding, but still large enough to accomplish measurements in the harsh radiation environment of Jupiter. This work focuses on a new type of compact, electrostatic analyzer using spherical wedges and the start signal generation for the time-of-flight measurement using new venetian blind-type surfaces. Simulations on the electrostatic analyzer showed that the most promising design is a hybrid variant, using an inner shell with spherical wedges and a spheroidal outer shell. A prototype sensor was built and tested with successful results. A reflectron-type time-of-flight cell measures the time it takes for a particle to pass a linear electric field. The time measurement has to be very accurate and requires that all ions enter the reflectron from the same start position. Commonly this is achieved with thin carbon foils of some nanometer thickness to provide a very accurate start position. Upon impact and after leaving a foil, ions generate secondary electrons that act as start signals for the time measurement. Foils require a substantial pre-acceleration of several kilovolts for the ions to penetrate the foil, thus increasing the size and mass of the instrument. When incident ions are reflected at grazing angles from a surface, secondary electrons are released in the same way as with foils. To increase position accuracy during this reflection process, venetian blind-type start surfaces are investigated, where many smaller surfaces replace a large flat surface. The most promising sample was found to be micro pore optics, that were initially designed to focus gamma rays. In several experiments it could be shown that micro pore optics show good reflection properties when used as start surfaces in the time-of-flight measurement. Both improvements allow a more compact and lightweight sensor that can be better shielded against the harsh radiation environment in Jupiter’s system. Jupiter hosts the strongest radiation environment in the solar system, that could kill an unprotected human thousand times over. / JUICE, PEP