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International audience; The quality of electron bunches accelerated by laser wakefields is highly dependant on the temporal and spatial features of the laser driver. Analysis of experiments performed at APOLLON PW-class laser facility shows that spatial instabilities of the focal spot, such as shot-to-shot pointing fluctuations or asymmetry of the transverse fluence, lead to charge and energy degradation of the accelerated electron bunch. It is shown that PIC simulations can reproduce experimental results with a significantly higher accuracy when the measured laser asymmetries are included in the simulated laser's transverse profile, compared to simulations with ideal, symmetric laser profile. A method based on a modified Gerchberg-Saxton iterative algorithm is used to retrieve the laser electric field from fluence measurements in vacuum in the focal volume, and accurately reproduce experimental results using PIC simulations, leading to simulated electron spectra in close agreement with experimental results, for the accelerated charge, energy distribution and pointing of the electron beam at the exit of the plasma.

Laser-driven plasma wakefields can provide hundreds of MeV electron beam in mm-range distances potentially shrinking the dimension of the actual particle accelerators. The plasma density plays a fundamental role in the control and stability of the acceleration process, which is a key development for the future electron injector proposed by EuPRAXIA. A gas cell was designed by LPGP and LIDYL teams, with variable length and backing pressure, to confine the gas and tailor the gas density profile before the arrival of the laser. This cell was used during an experimental campaign with the multi TW-class laser at the Lund Laser Centre. Ionization assisted injection in a tailored density profile is used to tune the electron beam properties. During the experiment, we filled the gas cell with hydrogen mixed with different concentration of nitrogen. We also varied the backing pressure of the gas and the geometrical length of the gas cell. We used a transverse probe to acquire shadowgraphic images of the plasma and to measure the plasma electron density. Methods and results of the analysis with comparisons between shadowgraphic and interferometric images will be discussed., Comment: Approved by JINST

Triploidisation represents several advantages (e.g. sterility) and therefore is routinely applied in aquaculture of several commercially important fish species, including rainbow trout. The comparative transcriptomic analysis of ovaries of triploid (3N) and diploid (2N) female rainbow trout revealed a total of 9 075 differentially expressed genes (DEGs; 4 105 genes upregulated in 2N and 4 970 genes upregulated in 3N ovaries, respectively). Identified clusters for DEGs upregulated in 3N and 2N ovaries were different, including carbohydrate and lipid metabolic process and transport, protein modification, signalling (related to folliculogenesis) and response to stimulus for DEGs upregulated in 2N, and developmental process, signalling (related to apoptosis, cellular senescence and adherence junctions) and regulation of RNA metabolic process for DEGs upregulated in 3N. The enrichment of processes involved in carbohydrate and lipid metabolism in 2N ovaries indicated high metabolism of ovarian tissue and the energy reservoir generation indispensable during the earliest stages of development. Our results highlight the importance of oocyte hydration along with oestrogen, insulin, leptin, fibroblast growth factor, and Notch signalling and pathways related to the regulation of cyclic adenosine monophosphate (cAMP) levels in proper oocyte meiotic maturation prior to ovulation in 2N ovaries. Conversely, triploidisation may lead to an increase in ovarian cellular senescence and apoptosis, which in turn can result in abnormal gonadal morphology and fibrosis. The downregulation of genes responsible for the precise regulation of meiosis and proper chromosome segregation during meiosis probably affects meiotic maturation via irregular meiotic division of chromosomes. The induction of triploidy of the rainbow trout genome resulted in enhanced expression of male-specific genes, genes responsible for re-establishing the transcriptional balance after genome reorganisation and genes involved in regulatory mechanisms, including gene silencing and DNA methylation. To the best of our knowledge, this is the first genome-wide investigation providing in-depth comprehensive and comparative gene expression patterns in the ovary from 2N and 3N rainbow trout females helping in elucidating the molecular mechanisms leading to impaired gonadal development and sterility of female triploids.

International audience; In the design of laser plasma electron injectors for multi-stage laser driven wakefield accelerators, the control of plasma density is a key element to stabilize the acceleration process. A cell with variable parameters is used to confine the gas and tailor the density profile. The gas filling process was characterized both experimentally and by fluid simulations. Results show a good agreement between experiments and simulations. Simulations were also used to study the effect of each of the gas cell parameters on the density distribution and show the possibility to finely control the density profile.

Electron bunches generated by laser driven wakefield acceleration are transported and analyzed using a magnetic line composed of a triplet of quadrupoles and a dipole. Short pulse bunches with a total charge of ≈ 130 p C, and broad band energy spectra in the range 45 to 150 M eV are generated by ionization assisted injection in a gas cell. The electron source is imaged about one meter away from the exit of the gas cell by the magnetic line, delivering electron bunches at a stable position in the image plane where a charge density of ≈ 2 . 9 p C ∕ m m 2 at an energy of 69.4 ± 0 . 6 M eV is achieved. This magnetic line improves dramatically the accuracy of energy determination of this electron source, leading to an energy error as low as 8.6‰ in the 70 M eV range for 5 m rad divergence electron bunch and considering the resolution of the entire detection system. The transport of bunches with improved stability and energy selection paves the way to various applications including multi-stage laser plasma acceleration.

In this paper, the interaction of 10-TW laser pulses, focused at moderately relativistic intensity, with a supersonic he-lium gas-jet has been investigated by varying gas density and jet nozzle. We have successfully tested several advanced diagnostic devices to characterize the plasma and the accelerated electron bunches. Plasma densities have been measured by means of a fem-tosecond high-resolution interferometer, while the electron beams were analyzed with a stack of radiochromic films, a beam-profile monitor, a magnetic spectrometer, and a nuclear activation setup based on gamma-ray generation via electron bremsstrahlung. We present the results as well as the basic features and relevant details of such diagnostics whose performances can fit a large class of experiments.

X-ray spectroscopic diagnostics of laser-cluster interaction at the stage of nonadiabatic scattering of clusters and formation of a spatially uniform plasma channel has been performed. The experimental investigations have been carried out on a Ti:Sa laser setup with a pulse duration of about 65 fs and an energy up to 600 mJ. It has been shown that, within 10 ps from the beginning of a laser femtosecond pulse, the laser-cluster interaction forms a uniform plasma channel with a length of 0.4 to 1 mm with the parameters N e ∼ 1019−1020 cm−3 and T e ∼ 100 eV.

A Robertsonian polymorphism resulting in diploid chromosome number ranging from 59 to 61 and constant chromosome arm number (fundamental number = 104) was observed in the albino rainbow trout ( Oncorhynchus mykiss (Walbaum)) from the yellow color strain. In one individual, 90 mitotic chromosomes and 156 chromosome arms were counted, indicating the fish as a triploid. Morphology of the chromosomes, DAPI staining, and the cytogenetic location of 5S rDNA sequences showed sex-related chromosomal heteromorphism in the specimens. Additionally, length polymorphism of the X chromosome was detected in the studied individuals and two morphs of the X chromosome were described, XLand XS, according to the size of its short arm (p). The XSwas observed in the female as well as male albino rainbow trout; however, among females, no XSXSgenotype was found. After primed in situ labeling with 5S rDNA primers, the p-arms of both types of the X chromosome showed similar hybridization signals. On the other hand, fluorescence in situ hybridization with telomeric PNA (peptide nucleic acid) probe exhibited weak hybridization spots on the p-arm of the XSchromosome compared with the distinct hybridization spots observed on the XLp-arm. This could reflect a different telomere length on the p-arm of the XSand XLchromosomes. Partial translocation and deletion of the X chromosome p-arm are considered to be responsible for the p-arm length difference between the two morphological variants of X chromosome.

International audience; We report on a study on controlled trapping of electrons, by field ionization of nitrogen ions, in laser wakefield accelerators in variable length gas cells. In addition to ionization-induced trapping in the density plateau inside the cells, which results in wide, but stable, electron energy spectra, a regime of ionization-induced trapping localized in the density down-ramp at the exit of the gas cells, is found. The resulting electron energy spectra are peaked, with 10% shot-to-shot fluctuations in peak energy. Ionization-induced trapping of electrons in the density down-ramp is a way to trap and accelerate a large number of electrons, thus improving the efficiency of the laser-driven wakefield acceleration.

© 2016 AIP Publishing LLC. Ionization-induced electron injection was investigated experimentally by focusing a driving laser pulse with a maximum normalized potential of 1.2 at different positions along the plasma density profile inside a gas cell, filled with a gas mixture composed of 99%H2+1%N2. Changing the laser focus position relative to the gas cell entrance controls the accelerated electron bunch properties, such as the spectrum width, maximum energy, and accelerated charge. Simulations performed using the 3D particle-in-cell code WARP with a realistic density profile give results that are in good agreement with the experimental ones. The interest of this regime for optimizing the bunch charge in a selected energy window is discussed.

International audience; The dynamics of ionization-induced electron injection in the high density (~ 1:2 × 1019cm-3) regime of Laser Wakefield Acceleration (LWFA) was investigated by analyzing betatron X-ray emission inside dielectric capillary tubes. A comparative study of the electron and betatron X-ray properties was performed for both self-injection and ionization-induced injection. Direct experimental evidence of early onset of ionization-induced injection into the plasma wave was obtained by mapping the X-ray emission zone inside the plasma. Particle-In-Cell (PIC) simulations showed that the early onset of ionization-induced injection, due to its lower trapping threshold, suppresses self-injection of electrons. An increase of X-ray fluence by at least a factor of two was observed in the case of ionization-induced injection due to an increased trapped charge compared to self-injection mechanism. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Objectives: To estimate the prevalence of and identify risk factors for lipodystrophy syndrome (LS) and body fat abnormality in a population of HIV-infected children and adolescents. Design: Cross-sectional observational study. Methods: HIV-infected subjects aged 2-18 years were recruited from 15 HIV centers in Belgium Italy, and Poland between January 2007 and December 2008. Standardized assessments by the patient's long-term clinician were performed to establish the presence of abnormality. Risk factors were explored in logistic regression models for fat abnormality outcomes and LS (abnormality plus dyslipidemia). Results: Among 426 subjects (70% white), median age was 12.2 years (interquartile range: 9.0-15.0 years) and median duration of antiretroviral therapy was 5.2 years (interquartile range: 2.2-8.8 years). Prevalence was 57% (n = 235) for LS and 42% (n =176) for fat abnormality; 90 subjects with abnormality were affected in ≥3 locations. Lipoatrophy occurred in 28% (n =117) of subjects and lipohypertrophy in 27% (n = 115), most commonly in the face and trunk, respectively. In multivariable analysis, white ethnicity, body mass index, ritonavir/lopinavir, and nonnucleoside reverse transcriptase inhibitors were each associated with an increased risk of LS (P

We demonstrate the influence of the prepulses and ASE of ultrashort pulses interacting with a solid target by addressing the direct comparison of the harmonic spectra generated by reflection onto a solid target with and without the introduction of a plasma mirror system. Harmonics up to the 20th of the fundamental of the Ti-Sa laser are clearly visible in a situation free from any plasma expansion.

The high precision X-ray spectroscopy studies of plasma created from the CO2 clusters in gas jet targets by the ultrashort laser pulses (35 and 60 fs duration) were performed at the intensities IL ∼ 1017–1018 W cm−2. The spectral line shape of the H-like and He-like oxygen ions gains an asymmetry with increasing the laser pulse intensity. Theoretical modeling of the line shape shows that the asymmetry can be explained by absorption of the Doppler-shifted line radiation from the essential fraction of ions (over 10−3) with energies above 1 MeV due to photoionization of inner shells of carbon ions. The results obtained demonstrate measurement capabilities of the X-ray spectral measurements of multicharged ions accelerated during the interaction with a laser radiation.

A portable (200 � 100 � 100 mm 3 ), high-luminosity, spherically bent crystal spectrometer was designed to measure very low emissivity X-ray spectra of different elements with spatial resolution in a wide spectral range (1.2� 19.6 ( A). A large (50 � 15 mm 2 ) open aperture mica spherically bent crystal with R ¼ 150 mm was used as dispersive and focusing element. This spectrometer was associated with a large sensitive area (f ¼ 40 mm) micro-channel plates assembly. This apparatus provides simultaneously high spectral (l=dlB1800) and spatial (100–200mm) resolutions. Its large tunability allowed, without any adjustment of the spectrometer set-up, to record spectra in the 1.38–17.5 ( A wavelength range. We used the X-ray emission of femtosecond laser-produced plasmas from different materials ((CF2)n, CaF2, Cu, Al) to test the spectrometer. Thanks to the high sensitivity (high collection efficiency) of the system, high quality space-resolved X-ray spectra of Fluorine and Aluminum plasmas were obtained on a single laser shot. r 2001 Elsevier Science B.V. All rights reserved.

International audience; The stability of beams of laser wakefield accelerated electrons in dielectric capillary tubes is experimentally investigated. These beams are found to be more stable in charge and pointing than the corresponding beams of electrons accelerated in a gas jet. Electron beams with an average charge of 43 pC and a standard deviation of 14% are generated. The fluctuations in charge are partly correlated to fluctuations in laser pulse energy. The pointing scatter of the electron beams is measured to be as low as 0.8 mrad (rms). High laser beam pointing stability improved the stability of the electron beams.

The stability of accelerated electron beams produced by self injection of plasma electrons into the wakefield driven by a laser pulse guided inside capillary tubes is analyzed statistically in relation to laser and plasma parameters, and compared to results obtained in a gas jet. The analysis shows that reproducible electron beams are achieved with a charge of 66 pC +/- 11%, a FWHM beam divergence of 9 mrad +/- 14%, a maximum energy of 120 MeV +/- 10% and pointing fluctuations of 2.3 mrad using 10 mm long, 178 mu m diameter capillary tubes at an electron density of (10.0 +/- 1.5) x 10(18) cm(-3). Active stabilization of the laser pointing was used and laser parameters were recorded on each shot. Although the shot-to-shot laser energy fluctuations can account for a fraction of the electrons fluctuations, gas density fluctuations are suspected to be a more important source of instability. (C) 2013 Elsevier B.V. All rights reserved.

Atomic argon clusters were created using various types of nozzles and gas jet backing pressures. High temperature plasmas were created by irradiating the clusters with high intensity 35 fs laser pulses. The data obtained from these experiments were compared with each other as well as an experiment using a longer pulse ( 60 fs ) higher flux density laser. Detailed spectroscopic analysis of high resolution X-ray data near the Heα,Heβ, and Lyα lines of Ar was consistent with a two-temperature collisional-radiative model incorporating the effects of highly energetic electrons. Each variation has an effect on the rate of cluster expansion; therefore, results of the analysis provide useful insight into the behavior of such plasmas over short time scales. It was demonstrated for the first time, that by using sufficiently large clusters, hydrogen-like ions of Ar with an ionization potential of approximately 4120 eV could be obtained with a 35 fs laser pulse with a relatively low flux density of 1×10 17 W/cm 2 .

A study on the interaction of a 10 TW, 60 fs, Ti–Sapphire laser with a high-density long-scale pulsed nitrogen gas jet is reported. Experimental data on the laser propagation are analyzed with the help of a ray-tracing model. The plasma dynamics is investigated by means of time-resolved shadowgraphy and time-integrated high-resolution x-ray spectroscopy. Shadowgrams show that the plasma does not expand during the first 55 ps, while x-ray spectra exhibit an unusual continuum-like structure attributed to hollow atoms produced by charge exchange process between bare nuclei expelled from the plasma and molecules of the surrounding gas. The interpretation of the results is supported by particle-in-cell simulations. The question of x-ray lasing is also examined using a hydrodynamic code to simulate the long lasting regime of recombination.

Progress of a four-wave sum difference frequency generation scheme to convert coherent soft X-ray radiation to shorter wavelengths, using a plasma medium is discussed. Results are presented from a preliminary experiment, involving the Ne-like Ni XRL (λ XRL = 0.023 μm) mixed in phase-matched mode with a Nd:glass laser (λ OPT = 1.054 μm) in a Na-like Argon plasma. A 25 mm single slab target of Ni pumped with ∼ 200 J of energy from 5 optical beams has routinely produced ∼ 3 mJ of XRL energy at 23.1 nm. The XRL was split and recombined and information from fringe visibility measurements has been used to estimate the degree of spatial coherence in the XRL. Characterisation of the gas jet mixing medium has been carried out through emission spectroscopy and optical interferometry.

Rare gas or lead clusters of several hundreds to many thousands of atoms per cluster were irradiated by intense laser pulses producing peak intensities up to 1017W/cm2. Fast, highly charged fragment ions were observed by means of standard TOF mass spectrometry as well as a magnetic deflection TOF device (MDTOF). Charge states of up to Xe30+ or Pb18+ were detected with maximum kinetic energies reaching far beyond 100 keV for Xe. A strong dependence of the charging and heating process on the laser pulse duration was found. While the resulting ionic fragment spectra are qualitatively similar for rare gas and lead clusters, the kinetic energies for the metal clusters seem to be significantly lower.

Summary The colour genes controlling the palomino and albino phenotype in the spring spawning rainbow trout [Oncorhynchus mykiss (Walbaum 1792)] strain reared at the Department of Salmonid Research Rutki, Poland were found to have strong detrimental pleiotropic effects on growth and vitality. After 5 and 9 months of rearing, the differences in mean body weights in albino, palomino and wild-coloured trout were statistically highly significant, with albino showing the poorest, palomino as the intermediate and wild-coloured trout having the highest growth. An identical ranking of colour phenotypes was observed for survival. The influence of colour phenotypes on both traits showed a diminishing tendency with increasing age of fish. It is concluded that alleles controlling palomino and albino colouration cannot be recommended as genetic markers. If reference groups are needed, instead of albino trout, palomino trout should be used since their pleiotropic effects are less pronounced.

The x-ray spectra of a plasma generated by heating CO2 and Ar clusters with high-intensity femtosecond laser pulses with q las≃1018 W/cm2 are investigated. Spatially resolved x-ray spectra of a cluster plasma are obtained for the first time. Photoionization absorption is observed to influence the spectral line profiles. The recorded features of the x-ray emission spectra definitely indicate the existence of a large relative number of excited ions (≃10−2–10−3) with energies of 0.1–1 MeV in such a plasma. Possible mechanisms underlying the acceleration of ions to high energies are discussed. It is shown that the experimental results can be attributed to the influence of ponderomotive forces in standing waves generated by the reflection of laser radiation from the clusters.

The x-ray spectra of a plasma produced by heating CO2 clusters with intense femtosecond laser pulses with λ=0.8 μm and λ=0.4 μm are investigated. Spatially resolved x-ray spectra of the cluster plasma are obtained. The observed characteristic features of the x-ray emission spectra show unequivocally that such a plasma contains quite a large relative number of ions (≃10−2–10−3) with energies of 0.1–1 MeV. The contour of the OVIII Lyα line is found to have characteristic features that are especially conspicuous when the clusters are heated with second-harmonic pulses. These features cannot be explained by any mechanisms known to the authors.

We have studied the ionic outcome from the interaction of intense laser light with large argon and xenon clusters. Ions with initial energies of several 100 keV are charge and energy selected using a magnetic deflection time-of-flight mass spectrometer. For argon clusters, Coulomb repulsion is the key process in the explosion mechanism, whereas for xenon we observe a mixture of Coulomb repulsion and hydrodynamic expansion. Coulomb explosion is the preferred decay channel for smaller clusters and it is also responsible for the production of the most energetic ions. Our results can be understood on the basis of a charged sphere model of cluster-sized plasmas.

International audience; The dynamics of ionization-induced electron injection in high density (~1.2 × 1019 cm-3) regime of laser wakefield acceleration is investigated by analyzing the betatron X-ray emission. In such high density operation, the laser normalized vector potential exceeds the injection-thresholds of both ionization-injection and self-injection due to self-focusing. In this regime, direct experimental evidence of early on-set of ionization-induced injection into the plasma wave is given by mapping the X-ray emission zone inside the plasma. Particle-In-Cell simulations show that this early on-set of ionization-induced injection, due to its lower trapping threshold, suppresses the trapping of self-injected electrons. A comparative study of the electron and X-ray properties is performed for both self-injection and ionization-induced injection. An increase of X-ray fluence by at least a factor of two is observed in the case of ionization-induced injection due to increased trapped charge compared to self-injection mechanism.

The spatial distribution of chlorine ions in the focal spot of intense 130 fs laser pulses is studied. To this end a one-colour pump - probe experiment is performed, where the pump pulse produces multiply ionized molecules exploding into energetic fragments and the probe induces additional ionization of these fragments shortly after their creation. Our method is based on the simulation of the recorded experimental pump - probe spectra, using tunnel ionization theory to describe the further ionization of the fragments by the probe. The ionization process is shown to strongly depend on the spatial distribution of the molecular ions produced in the focus of the pump. Comparison of the simulated and experimental spectra strongly suggests a pyramid-like distribution within the laser focus, thereby allowing us to discard onion- or potato-like distributions as observed for atoms.

A novel one-colour pump - probe scheme with 130 fs pulses is used to study the fragments arising from the multi-electron dissociative ionization of molecular chlorine. This approach allows us to demonstrate the coexistence of nascent fragments and those fragments which are further ionized by the probe pulse. A simple model, based on tunnel ionization theory, accounts well for the observed population transfer of the ionic fragments. In contrast, only nascent fragments are observed for intense 2 ps pulses. Our results show that the absence of post-dissociation ionization in most experiments is not due to the strong decrease of the ionization rates beyond the critical distance. A possible explanation is laser-field induced screening of the nuclei by electrons leading to a `retarded' Coulomb repulsion. The multiple ionization of the molecule followed by dissociation would then occur later in the pulse where the intensity increase is not sufficient to induce post-dissociation ionization.

Argon ions with charge states of at least up to q = 9 are produced with 30 ps laser light pulses at 1064 nm from neutral clusters, whereas only can be produced from monomers. Irradiation of cluster targets leads to ions with remarkably high kinetic energies exceeding 4.8 keV, depending on the ion charge state. The experimental results are understood in terms of cluster-sized nanoplasmas with internal electron temperatures of approximately which are heated by collisional electron - ion absorption. From these thermalized superdense nanoplasmas highly charged ions are ejected isotropically with the corresponding ion sound velocity. A simple Coulomb explosion model cannot account for the observed ion energies.

The first experiments on the National Ignition Facility (NIF) in the US started and will be followed by the Laser MegaJoule (LMJ) in France. Such facilities will provide unique tools for inertial confinement fusion (ICF) physics & for basic science. A petawatt short pulse laser (ps) is being added to the ns pulse beams of the LMJ. This is PETAL (PETawatt Aquitaine Laser), under construction on the LMJ site near Bordeaux (France). The Petal+ project is aiming at the design and construction of diagnostics dedicated to experiments with PETAL and LMJ laser beams. Within Petal+, three types of diagnostics are under study: a proton spectrometer, an electron spectrometer and a large-band X-ray spectrometer. The first goal of these diagnostics will be to characterize the secondary radiation and particle sources produced with PETAL. They will also be used for experiments using both ns and ps beams. In the present paper emphasis is put on the charged-particle diagnostics.

A 65-fs, 800-nm, 2-TW laser pulse propagating through a nitrogen gas jet has been experimentally studied by 90 degrees Thomson scattering. Time-integrated spectra of scattered light show unprecedented broadening towards the blue which exceeds 300 nm. Images of the scattering region provide for the first time a space-and time-resolved description of the process leading quite regularly to such a large upshift. The mean shifting rate was as high as delta lambda/delta t approximate to 3 angstrom/fs, never observed before. Interferometry shows that it occurs after partial laser defocusing. Numerical simulations prove that such an upshift is consistent with a laser-gas late interaction, when laser intensity has decreased well below relativistic values (a(0) << 1) and ionization process involves most of the laser pulse. This kind of interaction makes spectral tuning of ultrashort intense laser pulses possible in a large spectral range. (C) 2013 AIP Publishing LLC.