Anticorrelation between Ion Acceleration and Nonlinear Coherent Structures from Laser-Underdense Plasma Interaction

In laser-plasma experiments, we observed that ion acceleration from the Coulomb explosion of the plasma channel bored by the laser, is prevented when multiple plasma instabilities such as filamentation and hosing, and nonlinear coherent structures (vortices/post-solitons) appear in the wake of an ultrashort laser pulse. The tailoring of the longitudinal plasma density ramp allows us to control the onset of these insabilities. We deduced that the laser pulse is depleted into these structures in our conditions, when a plasma at about 10% of the critical density exhibits a gradient on the order of 250 {\mu}m (gaussian fit), thus hindering the acceleration. A promising experimental setup with a long pulse is demonstrated enabling the excitation of an isolated coherent structure for polarimetric measurements and, in further perspectives, parametric studies of ion plasma acceleration efficiency.Comment: 4 pages, 5 figure

Short Intense Laser Pulse Collapse in Near-Critical Plasma

It is observed that the interaction of an intense ultra-short laser pulse with an overdense gas jet results in the pulse collapse and the deposition of a significant part of energy in a small and well localized volume in the rising part of the gas jet, where the electrons are efficiently accelerated and heated. A collisionless plasma expansion over 150 microns at a sub-relativistic velocity (~c/3) has been optically monitored in time and space, and attributed to the quasistatic field ionization of the gas associated to the hot electron current. Numerical simulations in good agreement with the observations suggest the acceleration in the collapse region of relativistic electrons, along with the excitation of a sizeable magnetic dipole that sustains the electron current over several picoseconds. Perspectives of ion beam generation at high repetition rate directly from gas jets are discussed

Ion acceleration in underdense plasmas by ultra-short laser pulses

We report on the ion acceleration mechanisms that occur during the interaction of an intense and ultrashort laser pulse ( λ > μ I 2 1018 W cm−2 m2) with an underdense helium plasma produced from an ionized gas jet target. In this unexplored regime, where the laser pulse duration is comparable to the inverse of the electron plasma frequency ωpe, reproducible non-thermal ion bunches have been measured in the radial direction. The two He ion charge states present energy distributions with cutoff energies between 150 and 200 keV, and a striking energy gap around 50 keV appearing consistently for all the shots in a given density range. Fully electromagnetic particle-in-cell simulations explain the experimental behaviors. The acceleration results from a combination of target normal sheath acceleration and Coulomb explosion of a filament formed around the laser pulse propagation axi

Brunel-Dominated Proton Acceleration with a Few-Cycle Laser Pulse

International audienceExperimental measurements of backward accelerated protons are presented. The beam is produced when an ultrashort (5 fs) laser pulse, delivered by a kHz laser system, with a high temporal contrast (10 8), interacts with a thick solid target. Under these conditions, proton cutoff energy dependence with laser parameters, such as pulse energy, polarization (from p to s), and pulse duration (from 5 to 500 fs), is studied. Theoretical model and two-dimensional particle-in-cell simulations, in good agreement with a large set of experimental results, indicate that proton acceleration is directly driven by Brunel electrons, in contrast to conventional target normal sheath acceleration that relies on electron thermal pressure

Persistence of magnetic field driven by relativistic electrons in a plasma

The onset and evolution of magnetic fields in laboratory and astrophysical plasmas is determined by several mechanisms, including instabilities, dynamo effects and ultra-high energy particle flows through gas, plasma and interstellar-media. These processes are relevant over a wide range of conditions, from cosmic ray acceleration and gamma ray bursts to nuclear fusion in stars. The disparate temporal and spatial scales where each operates can be reconciled by scaling parameters that enable to recreate astrophysical conditions in the laboratory. Here we unveil a new mechanism by which the flow of ultra-energetic particles can strongly magnetize the boundary between the plasma and the non-ionized gas to magnetic fields up to 10-100 Tesla (micro Tesla in astrophysical conditions). The physics is observed from the first time-resolved large scale magnetic field measurements obtained in a laser wakefield accelerator. Particle-in-cell simulations capturing the global plasma and field dynamics over the full plasma length confirm the experimental measurements. These results open new paths for the exploration and modelling of ultra high energy particle driven magnetic field generation in the laboratory

Antifibrotic treatment response and prognostic predictors in patients with idiopathic pulmonary fibrosis and exposed to occupational dust

BACKGROUND: Idiopathic Pulmonary Fibrosis (IPF) is an aggressive interstitial lung disease with an unpredictable course. Occupational dust exposure may contribute to IPF onset, but its impact on antifibrotic treatment and disease prognosis is still unknown. We evaluated clinical characteristics, respiratory function and prognostic predictors at diagnosis and at 12 month treatment of pirfenidone or nintedanib in IPF patients according to occupational dust exposure. METHODS: A total of 115 IPF patients were recruited. At diagnosis, we collected demographic, clinical characteristics, occupational history. Pulmonary function tests were performed and two prognostic indices [Gender, Age, Physiology (GAP) and Composite Physiologic Index (CPI)] calculated, both at diagnosis and after the 12 month treatment. The date of long-term oxygen therapy (LTOT) initiation was recorded during the entire follow-up (mean = 37.85, range 12-60 months). RESULTS: At baseline, patients exposed to occupational dust [≥ 10 years (n = 62)] showed a lower percentage of graduates (19.3% vs 54.7%; p = 0.04) and a higher percentage of asbestos exposure (46.8% vs 18.9%; p 0.002) than patients not exposed [< 10 years (n = 53)]. Both at diagnosis and after 12 months of antifibrotics, no significant differences for respiratory function and prognostic predictors were found. The multivariate analysis confirmed that occupational dust exposure did not affect neither FVC and DLCO after 12 month therapy nor the timing of LTOT initiation. CONCLUSION: Occupational dust exposure lasting 10 years or more does not seem to influence the therapeutic effects of antifibrotics and the prognostic predictors in patients with IPF

Fetal brain hemodynamics in pregnancies at term: correlation with gestational age, birthweight and clinical outcome

Introduction: The primary aim of this study was to ascertain the strength of association between cerebral blood flow assessed in anterior (ACA), middle (MCA), and posterior (PCA) cerebral arteries and the following clinical outcomes: small for gestational age (SGA), induction of labor (IOL) for oligohydramnios and caesarean section (CS) for nonreassuring fetal status (NRFS) during labor. Material and methods: Retrospective analysis of prospectively collected data on consecutive singleton pregnancies from 40 0/7 to 41 6/7 week of gestation. UA, ACA, MCA, PCA pulsatility index (PI) were measured from 40 weeks of gestations. Furthermore, the ratios between cerebral blood flow and UA (CPR, ACA/UA and PCA/UA) were calculated and correlated with the observed outcomes. Results: Two hundred twenty-four singleton pregnancies were included in the study. Mean PI of either ACA (p = .04), MCA (p = .008), and PCA (p = .003) were lower in the SGA compared to non-SGA group; furthermore, mean PCA PI was significantly lower than MCA PI (p = .04). Furthermore, CPR (p = .016), ACA/UA (p = .02), and PCA/UA (p = .003) were significantly lower in the SGA group compared to controls. UA, ACA, MCA, and PCA PI were higher in women undergoing IOL for oligohydramnios compared to controls. Logistic regression analysis showed that CPR and PCA/UA ratio were independently associated with SGA. SGA, ACA PI, and ACA/UA were independently associated with CS for NRFS. Finally, birthweight centile, were independently associated with IOL oligohydramnios. Despite this, the predictive accuracy of Doppler in detecting any of the explored outcome was only poor to moderate. Conclusion: Redistribution of cerebral blood flow at term is significantly associated with SGA, IOL for oligohydramnios and CS for NRFS in labor. However, the predictive accuracy of Doppler at term is only poor to moderate, thus advising against its use in clinical practice as a standalone screening test for adverse perinatal outcome in pregnancies at term. Key Message Redistribution of cerebral blood flow at term is significantly associated with SGA, IOL for oligohydramnios and CS for NRFS in labor

Spectral and spatial shaping of a laser-produced ion beam for radiation-biology experiments

International audience; The study of radiation biology on laser-based accelerators is most interesting due to the unique irradiation conditions they can produce, in terms of peak current and duration of the irradiation. In this paper we present the implementation of a beam transport system to transport and shape the proton beam generated by laser-target interaction for in vitro irradiation of biological samples. A set of four permanent magnet quadrupoles is used to transport and focus the beam, efficiently shaping the spectrum and providing a large and relatively uniform irradiation surface. Real time, absolutely calibrated, dosimetry is installed on the beam line, to enable shot-to-shot control of dose deposition in the irradiated volume. Preliminary results of cell sample irradiation are presented to validate the robustness of the full system

Effects of laser prepulses on laser-induced proton generation

Low-intensity laser prepulses (<10(13) W cm(-2), nanosecond duration) are a major issue in experiments on laser-induced generation of protons, often limiting the performances of proton sources produced by high-intensity lasers (approximate to 10(19) W cm(-2), picosecond or femtosecond duration). Depending on the intensity regime, several effects may be associated with the prepulse, some of which are discussed in this paper: (i) destruction of thin foil targets by the shock generated by the laser prepulse; (ii) creation of preplasma on the target front side affecting laser absorption; (iii) deformation of the target rear side; and (iv) whole displacement of thin foil targets affecting the focusing condition. In particular, we show that under oblique high-intensity irradiation and for low prepulse intensities, the proton beam is directed away from the target normal. Deviation is towards the laser forward direction, with an angle that increases with the level and duration of the ASE pedestal. Also, for a given laser pulse, the beam deviation increases with proton energy. The observations are discussed in terms of target normal sheath acceleration, in combination with a laser-controllable shock wave locally deforming the target surface