Characterization of a CCD array for Bragg spectroscopy

The average pixel distance as well as the relative orientation of an array of 6 CCD detectors have been measured with accuracies of about 0.5 nm and 50 $\mu$rad, respectively. Such a precision satisfies the needs of modern crystal spectroscopy experiments in the field of exotic atoms and highly charged ions. Two different measurements have been performed by illuminating masks in front of the detector array by remote sources of radiation. In one case, an aluminum mask was irradiated with X-rays and in a second attempt, a nanometric quartz wafer was illuminated by a light bulb. Both methods gave consistent results with a smaller error for the optical method. In addition, the thermal expansion of the CCD detectors was characterized between -105 C and -40 C.Comment: Submitted to Review of Scientific Instrument

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

High Resolution He-like Argon And Sulfur Spectra From The PSI ECRIT

We present new results on the X-ray spectroscopy of multicharged argon, sulfur and chlorine obtained with the Electron Cyclotron Resonance Ion Trap (ECRIT) in operation at the Paul Scherrer Institut (Villigen, Switzerland). We used a Johann-type Bragg spectrometer with a spherically-bent crystal, with an energy resolution of about 0.4 eV. The ECRIT itself is of a hybrid type, with a superconducting split coil magnet, special iron inserts which provides the mirror field, and a permanent magnetic hexapole. The high frequency was provided by a 6.4 GHz microwave emitter. We obtained high intensity X-ray spectra of multicharged F-like to He-like argon, sulfur and chlorine with one 1s hole. In particular, we observed the 1s2s^{3}S_1 \to 1s^2^{1}S_0 M1 and 1s2p^{3}P_2 \to 1s^2^{1}S_0 M2 transitions in He-like argon, sulfur and chlorine with unprecedented statistics and resolution. The energies of the observed lines are being determined with good accuracy using the He-like M1 line as a reference

Magnetic properties changes of MnAs thin films irradiated with highly charged ions

We present the first investigation on the effect of highly charged ion bombardment on a manganese arsenide thin film. The MnAs films, 150 nm thick, are irradiated with 90 keV Ne$^{9+}$ ions with a dose varying from $1.6\times10^{12}$ to $1.6\times10^{15}$ ions/cm$^2$. The structural and magnetic properties of the film after irradiation are investigated using different techniques, namely, X-ray diffraction, magneto-optic Kerr effect and magnetic force microscope. Preliminary results are presented. From the study of the lattice spacing, we measure a change on the film structure that depends on the received dose, similarly to previous studies with other materials. Investigations on the surface show a strong modification of its magnetic properties

High-resolution x-ray spectroscopy to probe quantum dynamics in collisions of Ar17+, 18(+) ions with atoms and solids, towards clusters

International audienceWe report on studies of projectile excited states produced by electron capture in both low and high velocity regimes, and when highly charged ions (HCIs) collide either with dilute or dense matter. Quantum effects in the interaction dynamics are probed via high-resolution x-ray spectroscopy for Ar17+ at 7 keV u(-1) and for Ar18+ at 13.6 MeV u(-1) on Ar, N-2 or CH4 gas targets and on carbon solid foils. Relevant comparison between those two collision velocity regimes, and between gaseous and solid targets reveal specific features. In particular, the effect of multiple capture process occurring within a single-collision with gaseous target can be compared with the consequence of multistep collisions arising at surfaces and in solid-bulk at low velocity. At high velocity, beside evidence for collective response of the target electrons due to the wake field induced by HCI passing through the solid-bulk, we demonstrate that excitation and ionization collision processes damp the populations of projectile excited states for long ion transit times. The evolution of the np population as a function of n in solid is at variance from the 1/n(3) law found in gas, and the disagreement increases with solid target thickness. We have also tackled studies of HCIs in collision with clusters showing that x-ray spectroscopy provides a powerful tool to sign the presence of clusters in a supersonic gas jet

Improvement of the ETACHA Code towards low velocities and many-electron ions

International audienceKnowledge 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, atomic, plasma and nuclear physics, in particular in regards of the several foreseen large scale facilities. Starting from the previous ETACHA model [1], we present extension of its validity domain towards lower velocities and larger distortions. Moreover, the system of rate equations is now able to take into account ions with up to 60 electrons

Role of the laser wavelength in the X-ray production for clusters under intense laser pulses

International audienceIn case of laser-rare gas cluster interaction, precise evolution of the intensity threshold in the keV Xray production with pulse duration has been determined at 400 and 800 nm. These measurements demonstrate that doubling the laser frequency does not increase the efficiency of the X-ray yield per cluster

A vacuum double-crystal spectrometer for reference-free X-ray spectroscopy of highly charged ions

International audienceWe have built a vacuum double crystal spectrometer, which coupled to an electron-cyclotron resonance ion source, allows absolute measurements of low-energy X-ray transitions in highly charged ions with accuracies of the order of a few parts per million. We describe in detail the instrument and its performance. Furthermore, we present a few spectra of n = 2 -> n = 1 transitions in Ar14+, Ar15+ and Ar16+. We have developed an ab initio simulation code that allows us to obtain accurate line profiles. It can reproduce experimental spectra with unprecedented accuracy. The quality of the profiles allows the direct determination of line width

Low energy Ne ion beam induced-modifications of magnetic properties in MnAs thin films

International audienceInvestigations of the complex behavior of the magnetization of manganese arsenide thin films due to defects induced by irradiation of slow heavy ions are presented. In addition to the thermal hysteresis suppression already highlighted in M. Trassinelli et al., Appl. Phys. Lett. 104, 081906 (2014), we report here on new local magnetic features recorded by a magnetic force microscope at different temperatures close to the characteristic sample phase transition. Complementary measurements of the global magnetization measurements in different conditions (applied magnetic field and temperatures) enable to complete the film characterization. The obtained results suggest that the ion bombardment produces regions where the local mechanical constraints are significantly different from the average, promoting the local presence of magneto-structural phases far from the equilibrium. These regions could be responsible for the thermal hysteresis suppression previously reported, irradiation-induced defects acting as seeds in the phase transition