The GEMpix detector as new soft X-rays diagnostic tool for laser produced plasmas

Laser produced plasmas lend to several interesting applications. The study of X-ray emission from this kind of plasmas is important not only to characterize plasmas itself but also to study the application of these particular plasmas as intense X-ray sources. In particular several emission configurations can be obtained using different kinds of targets and tuning the characteristics of the laser pulse delivered to the target. Typically, laser pulse duration ranges between a few tens of femtoseconds and tens of nanoseconds, with energies from few mJ to tens of kJ. X-ray photon emissions last for times comparable to the laser pulses and during this time a great number of photons can be emitted. The following paper presents a measure of the soft-X-ray emission on the ECLIPSE laser facility realized with a new triple-GEM gas detector (GEMpix). It is a hybrid gas detector with a C-MOS front-end electronics based on Medipix chips. In the present work, different targets have been used in order to test X-rays of different energies. In this paper, in particular, we present results obtained for copper and iron targets. GEMpix is able to realize a 2D imaging of the X-ray emission from plasma with a signal proportional to the energy released in the gas of the detector active volume. Then through a preliminary single photon equalization realized at the NIXT lab (ENEA), also the number of photons reaching the area of the detector has been estimated.

CR-39 track detector calibration for H, He, and C ions from 0.1-0.5 MeV up to 5 MeV for laser-induced nuclear fusion product identification

Laser-accelerated ion beams can be used in many applications and, especially, to initiate nuclear reactions out of thermal equilibrium. We have experimentally studied aneutronic fusion reactions induced by protons accelerated by the Target Normal Sheath Acceleration mechanism, colliding with a boron target. Such experiments require a rigorous method to identify the reaction products (alpha particles) collected in detectors among a few other ion species such as protons or carbon ions, for example. CR-39 track detectors are widely used because they are mostly sensitive to ions and their efficiency is near 100%. We present a complete calibration of CR-39 track detector for protons, alpha particles, and carbon ions. We give measurements of their track diameters for energy ranging from hundreds of keV to a few MeV and for etching times between 1 and 8 h. We used these results to identify alpha particles in our experiments on proton-boron fusion reactions initiated by laser-accelerated protons. We show that their number clearly increases when the boron fuel is preformed in a plasma state.

X-ray grating spectrometer for opacity measurements in the 50 eV to 250 eV spectral range at the LULI 2000 laser facility

An x-ray grating spectrometer was built in order to measure opacities in the 50 eV to 250 eV spectral range with an average spectral resolution <E∕δE> ∼ 50. It has been used at the LULI-2000 laser facility at École Polytechnique (France) to measure the Δn = 0, n = 3 transitions of several elements with neighboring atomic number: Cr, Fe, Ni, and Cu in the same experimental conditions. Hence a spectrometer with a wide spectral range is required. This spectrometer features one line of sight looking through a heated sample at backlighter emission. It is outfitted with one toroidal condensing mirror and several flat mirrors cutting off higher energy photons. The spectral dispersion is obtained with a flatfield grating. Detection consists of a streak camera sensitive to soft x-ray radiation. Some experimental results showing the performance of this spectrometer are presented.

Coincidence measurement of residues and light particles in the reaction 56Fe+p at 1 GeV per nucleon with the spallation reactions setup SPALADIN

The spallation of 56Fe in collisions with hydrogen at 1A GeV has been studied in inverse kinematics with the large-aperture setup SPALADIN at GSI. Coincidences of residues with low-center-of-mass kinetic energy light particles and fragments have been measured allowing the decomposition of the total reaction cross section into the different possible deexcitation channels. Detailed information on the evolution of these deexcitation channels with excitation energy has also been obtained. The comparison of the data with predictions of several deexcitation models coupled to the INCL4 intranuclear cascade model shows that only GEMINI can reasonably account for the bulk of collected results, indicating that in a light system with no compression and little angular momentum, multifragmentation might not be necessary to explain the data.

Dynamics of the 16O(e, e'p) reaction at high missing energies

We measured the cross section and response functions for the quasielastic 16O(e,e'p) reaction for missing energies 25< or =E(m)< or =120 MeV at missing momenta P(m)< or =340 MeV/c. For 25<E(m)<50 MeV and P(m) approximately 60 MeV/c, the reaction is dominated by a single 1s(1/2) proton knockout. At larger P(m), the single-particle aspects are increasingly masked by more complicated processes. Calculations which include pion exchange currents, isobar currents, and short-range correlations account for the shape and the transversity, but for only half of the magnitude of the measured cross section.

First determination of generalized polarizabilities of the proton by a virtual compton scattering experiment

Absolute differential cross sections for the reaction ep-->epgamma have been measured at a four-momentum transfer with virtuality Q2 = 0.33 GeV2 and polarization epsilon = 0.62 in the range 33.6 to 111.5 MeV/c for the momentum of the outgoing photon in the photon-proton center of mass frame. The experiment has been performed with the high-resolution spectrometers at the Mainz Microtron MAMI. From the photon angular distributions, two structure functions which are a linear combination of the generalized polarizabilities have been determined for the first time.

Measurement of tensor polarization in elastic electron-deuteron scattering at large momentum transfer

Tensor polarization observables ( t(20), t(21), and t(22)) have been measured in elastic electron-deuteron scattering for six values of momentum transfer between 0.66 and 1.7 (GeV/c)(2). The experiment was performed at the Jefferson Laboratory in Hall C using the electron High Momentum Spectrometer, a specially designed deuteron magnetic channel and the recoil deuteron polarimeter POLDER. The new data determine to much larger Q2 the deuteron charge form factors G(C) and G(Q). They are in good agreement with relativistic calculations and disagree with perturbative QCD predictions.

[Uveal effusion syndrome. Apropos of a case]

Uveal effusion syndrome is a rare entity. It associates a nonrhegmatogenous retinal detachment, an annular cilio-choroïdal detachment and peripheral vascular anomalies. It is important to differentiate it from the another retinal detachments and the malignant melanoma.