Investigation of slow collisions for (quasi) symmetric heavy systems: what can be extracted from high resolution X-ray spectra

We present a new experiment on (quasi) symmetric collision systems at low-velocity, namely Ar$^{17+}$ ions ($v=0.53$ a.u.) on gaseous Ar and N$_2$ targets, using low- and high-resolution X-ray spectroscopy. Thanks to an accurate efficiency calibration of the spectrometers, we extract absolute X-ray emission cross sections combining low-resolution X-ray spectroscopy and a complete determination of the ion beam - gas jet target overlap. Values with improved uncertainty are found in agreement with previous results \cite{Tawara2001}. Resolving the whole He-like Ar$^{16+}$ Lyman series from $n=2$ to 10 with our crystal spectrometer enables to determine precisely the distribution ${\mathcal{P}_n}$ of the electron capture probability and the preferential $n_{pref}$ level of the selective single-electron capture. Evaluation of cross sections for this process as well as for the contribution of multiple-capture is carried out. Their sensitivity to the $\ell$-distribution of $n$ levels populated by single-electron capture is clearly demonstrated, providing a stringent benchmark for theories. In addition, the hardness ratio is extracted and the influence of the decay of the metastable $1s2s\ ^3 S_1$ state on this ratio is discussed

PHYSICAL PARAMETER DEPENDENCE OF THE X-RAY GENERATION IN INTENSE LASER – CLUSTER INTERACTION

International audienceStudies on laser – cluster interaction performed on the LUCA facility (French acronym for Ultra Short Tunable Laser, CEA Saclay) allow to observe the production of hard x-rays in the 1 to 5 keV range when rare gas clusters of nanometer sizes are heated by strong optical fields (F > 10^9 V/cm). First complete quantitative measurements of absolute photon emission yields, as well as of charge state distributions of ionic species with inner shell vacancies have been performed as a function of several physical parameters governing the interaction. Our measurements give rise to fundamental results like an optimum heating time and an intensity threshold in the x-ray production. These data provide direct insight into the interaction dynamics and into the heating processes involved

Extension of charge-state-distribution calculations for ion-solid collisions towards low velocities and many-electron ions

Knowledge of the detailed evolution of the whole charge-state distribution of projectile ions colliding with targets is required in several fields of research such as material science and atomic and nuclear physics but also in accelerator physics, and in particular in regard to the several foreseen large-scale facilities. However, there is a lack of data for collisions in the nonperturbative energy domain and that involve many-electron projectiles. Starting from the etacha model we developed [Rozet, Nucl. Instrum. Methods Phys. Res., Sect. B 107, 67 (1996)10.1016/0168-583X(95)00800-4], we present an extension of its validity domain towards lower velocities and larger distortions. Moreover, the system of rate equations is able to take into account ions with up to 60 orbital states of electrons. The computed data from the different new versions of the etacha code are compared to some test collision systems. The improvements made are clearly illustrated by 28.9MeVu-1Pb56+ ions, and laser-generated carbon ion beams of 0.045 to 0.5MeVu-1, passing through carbon or aluminum targets, respectively. Hence, those new developments can efficiently sustain the experimental programs that are currently in progress on the "next-generation" accelerators or laser facilities.Fil: Lamour, E.. Centre National de la Recherche Scientifique; Francia. Universite de Paris; FranciaFil: Fainstein, Pablo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Galassi, Mariel Elisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Prigent, C.. Centre National de la Recherche Scientifique; Francia. Universite de Paris; FranciaFil: Ramirez, C. A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Rivarola, Roberto Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Rozet, J. P.. Centre National de la Recherche Scientifique; Francia. Universite de Paris; FranciaFil: Trassinelli, M.. Centre National de la Recherche Scientifique; Francia. Universite de Paris; FranciaFil: Vernhet, D.. Centre National de la Recherche Scientifique; Francia. Universite de Paris; Franci

Modulating the phase transition temperature of giant magnetocaloric thin films by ion irradiation

Magnetic refrigeration based on the magnetocaloric effect at room temperature is one of the most attractive alternative to the current gas compression/expansion method routinely employed. Nevertheless, in giant magnetocaloric materials, optimal refrigeration is restricted to the narrow temperature window of the phase transition (Tc). In this work, we present the possibility of varying this transition temperature into a same giant magnetocaloric material by ion irradiation. We demonstrate that the transition temperature of iron rhodium thin films can be tuned by the bombardment of ions of Ne 5+ with varying fluences up to 10 14 ions cm --2 , leading to optimal refrigeration over a large 270--380 K temperature window. The Tc modification is found to be due to the ion-induced disorder and to the density of new point-like defects. The variation of the phase transition temperature with the number of incident ions opens new perspectives in the conception of devices using giant magnetocaloric materials

Suppression of the thermal hysteresis in magnetocaloric MnAs thin film by highly charged ion bombardment

We present the investigation on the modifications of structural and magnetic properties of MnAs thin film epitaxially grown on GaAs induced by slow highly charged ions bombardment under well-controlled conditions. The ion-induced defects facilitate the nucleation of one phase with respect to the other in the first-order magneto-structural MnAs transition with a consequent suppression of thermal hysteresis without any significant perturbation on the other structural and magnetic properties. In particular, the irradiated film keeps the giant magnetocaloric effect at room temperature opening new perspective on magnetic refrigeration technology for everyday use

Source X par agrégats : contrôle et optimisation des paramètres gouvernant línteraction laser de puissance - agrégats de gaz rare

National audienceLes expériences que nous avons réalisées sur le Laser Ultra Court Accordable du CEA Saclay permettent dóbserver l\'émission de photons X dans la gamme 1-5 keV lors de lírradiation dágrégats de gaz rare (Ar, Kr et Xe comprenant entre 10^3 et 10^6 atomes par agrégat) avec un laser femtoseconde de puissance (Ipic jusqu\'à 10^17 W/cm²). En plus de la distribution des états de charge des ions responsables de l\'émission X, la technique de spectroscopie X que nous utilisons permet de mesurer les taux absolus de photons émis dans 4π par impulsion laser en fonction des paramètres gouvernant línteraction dans des conditions contrôlées. Nous avons déterminé la sensibilité des paramètres physiques régissant la production du rayonnement X pendant línteraction, ce qui permet dáccéder à lóptimisation de cette source. Cet article est plus particulièrement dédié aux résultas relatifs à l\'évolution du taux d\'X avec l\'éclairement laser, dúne part, et avec la durée de límpulsion laser, dáutre part

Electronic temperatures, densities and plasma X-ray emission of a 14.5 GHz Electron-Cyclotron Resonance Ion Source

We have performed a systematic study of the Bremsstrahlung emission from the electrons in the plasma of a commercial 14.5 GHz Electron-Cyclotron Resonance Ion Source. The electronic spectral temperature and the product of ionic and electronic densities of the plasma are measured by analyzing the Bremsstrahlung spectra recorded for several rare gases (Ar, Kr, Xe) as a function of the injected power. Within our uncertainty, we find an average temperature of ? 48 keV above 100W, with a weak dependency on the injected power and gas composition. Charge state distributions of extracted ion beams have been determined as well, providing a way to disentangle the ionic density from the electronic density. Moreover X-ray emission from highly charged argon ions in the plasma has been observed with a high-resolution mosaic crystal spectrometer, demonstrating the feasibility for high-precision measurements of transition energies of highly charged ions, in particular of the magnetic dipole (M1) transition of He-like of argon ions

Émission X(L) du xénon par interaction laser -agrégats

National audienceNous avons étudié le rayonnement X provenant d'ions fortement multichargés (" 24+) présentant des lacunes en couche L produits lors de l'irradiation d'agrégats de xénon par des impulsions lumineuses issues d'un laser femtoseconde de puissance. Les résultats obtenus lors de la toute dernière campagne d'expériences réalisée auprès du serveur LUCA du SPAM/DRECAM au CEA/Saclay mettent en cause certains travaux antérieurs. Des divergences marquées apparaissent tant au niveau de l'interprétation des spectres X que sur la variation du taux d'émission en fonction de l'éclairement et de la longueur d'onde