The SEPAGE spectrometer (Spectromètre Electrons Protons A Grandes Energies) was realized within the PETAL+ project funded by the French ANR (French National Agency for Research). This plasma diagnostic, installed on the LMJ-PETAL laser facility, is dedicated to the measurement of charged particle energy spectra generated by experiments using PETAL (PETawatt Aquitaine Laser). SEPAGE is inserted inside the 10-meter diameter LMJ experimental chamber with a SID (Diagnostic Insertion System) in order to be close enough to the target. It is composed of two Thomson Parabola measuring ion spectra and more particularly proton spectra ranging from 0.1 to 20 MeV and from 8 to 200 MeV for the low and high energy channels respectively. The electron spectrum is also measured with an energy range between 0.1 and 150 MeV. The front part of the diagnostic carries a film stack that can be placed as close as 100 mm from the target center chamber. This stack allows a spatial and spectral characterization of the entire proton beam. It can also be used to realize proton radiographies.
This paper presents the goals and some of the results of experiments conducted within the Working Package 10 (Fusion
Experimental Programme) of the HiPER Project. These experiments concern the study of the physics connected to
"Advanced Ignition Schemes", i.e. the Fast Ignition and the Shock Ignition Approaches to Inertial Fusion. Such schemes
are aimed at achieving a higher gain, as compared to the classical approach which is used in NIF, as required for future
reactors, and making fusion possible with smaller facilities.
In particular, a series of experiments related to Fast Ignition were performed at the RAL (UK) and LULI (France)
Laboratories and were addressed to study the propagation of fast electrons (created by a short-pulse ultra-high-intensity
beam) in compressed matter, created either by cylindrical implosions or by compression of planar targets by (planar)
laser-driven shock waves. A more recent experiment was performed at PALS and investigated the laser-plasma coupling
in the 1016 W/cm2 intensity regime of interest for Shock Ignition.
Inertial Confinement Fusion with Shock Ignition relies on a very strong shock created by a laser pulse at an intensity of
the order of 1016W/cm2. In this context, an experimental campaign at the Prague Asterix Laser System (PALS) has been
carried out within the frame of the HiPER project. Two beams have been used, the first to create an extended preformed
plasma (scale length of the order of hundreds of micrometers) on a planar target, the second to generate a strong shock
wave. Different diagnostics were used to study both the shock breakout at the rear surface of the target and the laserplasma
coupling and parametric instabilities. This paper is focused on back-scattering analysis to measure the backreflected
energy and to characterize parametric instabilities such as stimulated Brillouin and Raman scattering. Our
experimental data show that parametric instabilities do not play a strong role in the laser plasma coupling. Moreover,
preliminary analysis of the back reflected light from the interaction region shows that less than 5% of the total incident
laser energy was back-reflected, with only a small fraction of that light was originating from parametric instabilities.
L. Volpe, D. Batani, B. Vauzour, Ph. Nicolai, J. Santos, F. Dorchies, C. Fourment, S. Hulin, C. Regan, F. Perez, S. Baton, M. Koenig, K. Lancaster, M. Galimberti, R. Heathcote, M. Tolley, Ch. Spindloe, P. Koester, L. Labate, L. Gizzi, C. Benedetti, A. Sgattoni, M. Richetta
Generation of high intensity and well collimated multi energetic proton beams from laser-matter
interaction extend the possibility to use protons as a diagnostic to image imploding target in Inertial
Confinement Fusion experiments. An experiment was done at the Rutherford Appleton Laboratory
(Vulcan Laser Petawatt laser) to study fast electron propagation in cylindrically compressed targets,
a subject of interest for fast ignition. This was performed in the framework of the experimental road
map of HiPER (the European High Power laser Energy Research facility Project). In the experiment,
protons accelerated by a ps-laser pulse were used to radiograph a 220 m diameter cylinder (20 m wall,
filled with low density foam), imploded with 200 J of green laser light in 4 symmetrically incident
beams of pulse length 1 ns. Point projection proton backlighting was used to get the compression
history and the stagnation time. Detailed comparison with 2D numerical hydro simulations has
been done using a Monte Carlo code adapted to describe multiple scattering and plasma effects
and with those from hard X-ray radiography. These analysis shows that due to the very large mass
densities reached during implosion processes, protons traveling through the target undergo a very large
number of collisions which deviate protons from their original trajectory reducing proton radiography
resolution. Here we present a simple analytical model to study the proton radiography diagnostic
performance as a function of the main experimental parameters such as proton beam energy and target
areal density. This approach leads to define two different criteria for PR resolution (called "strong"
and "weak" condition) describing different experimental conditions. Finally numerical simulations
using both hydrodynamic and Monte Carlo codes are presented to validate analytical predictions.
We present the results of an experiment concerning laser-plasma interaction in the regime relevant to shock ignition. The
interaction of high-intensity frequency tripled laser pulse with CH plasma preformed by lower intensity pre-pulse on
fundamental wavelength of the kJ-class iodine laser was investigated in the planar geometry in order to estimate the
coupling of the laser energy to the shock wave or parametric instabilities such as stimulated Raman or Brillouin
scattering, or to the fast electrons. First the complete characterization of the hydrodynamic parameters of preformed
plasma was made using crystal spectrometer to estimate the electron temperature and XUV probe to resolve the electron
density profile close to the critical density region. The other part of the experiment consisted of the shock chronometry,
calorimetry of the back-scattered light and hard X-ray spectrometry to evaluate the coupling to different processes. The
preliminary analysis of the measurements showed rather low energy transfer of the high-intensity pulse to back-scattered
light (< 5%) and no traces of any significant hot electron production were found in the X-ray spectra.
HiPER (High Power laser Energy Research) is the first European plan for international cooperation in
developing inertial fusion energy. ICF activities are ongoing in a number of nations and the first ignition
experiments are underway at the National Ignition Facility (NIF) in the USA. Although HiPER is still in the
preparatory phase, it is appropriate for Europe to commence planning for future inertial fusion activities that
leverage the demonstration of ignition. In this paper we shall detail some of the key points of the laser design
and the way this design is connected to the capsule requirements.
In this paper we describe the experimental validation of the technique of correction of wavefront aberration in the middle of the laser amplifying chain. This technique allows the correction of the aberrations from the first part of the laser system, and the pre-compensation of the aberrations built in the second part. This approach will allow an effective aberration management in the laser chain, to protect the optical surfaces and optimize performances, and is the only possible approach for multi-Petawatt laser system from the technical and economical point of view. This approach is now possible after the introduction of new deformable mirrors with lower static aberrations and higher dynamic than the standard devices.
Hydrodynamic regimes of KrF laser interaction with solid and thin-film targets in atmospheric and reduced pressure air were investigated at high-energy GARPUN installation. These experiments were performed with 100-J, 100-ns laser pulses in planar focusing geometry and compared with numerical simulations with ATLANT code to verify the concept of laser-driven shock tube (LST), which could accelerate a gas to hypersonic velocity and produce strong shock waves (SW). Laser beam was focused by a prism raster optical system that provided very uniform intensity distribution at moderate laser intensities q ≤ 1 GW/cm2 over a square spot of ~ 1-cm size. Dynamics of laser-produced plasma and SW in a surrounding gas were investigated by means of high-speed photo-chronograph and streak camera in combination with shadow or schlieren techniques, time and space resolved spectroscopy in a visible spectral range. Both experiments and simulations confirmed that target evaporation and blow-up of expanding plasma are the main mechanisms of UV laser-target interaction in a surrounding gas. Planar shock waves with velocities up to 7 km/s towards the laser beam were observed in a normal density air and up to 30 km/s in a rarefied air. Acceleration of thin CH films of 1 to 50-μm thickness was investigated both in a free-expansion and plasma-confined regimes with the highest achieved velocities up to 4 km/s. The SW damping law in a free space independently on laser intensity and air pressure could be approximated by a power law x ~ tn with a power indexes n1 = 0.85 - 0.95 at the initial stage and n2 = 0.5 - 0.6 later, when a distance of the SW front from a target became comparable with a size of the irradiated spot. Instability growth at contact interfaces between ablative plasma and accelerated film, as well as between plasma and compressed air were observed and compared for various initial irradiation non-uniformities. They were introduced by a grid, which was set in front of the film target.
Dimitri Batani, F. Strati, H. Stabile, M. Tomasini, C. Olivotto, Tara Desai, G. Lucchini, Michel Koenig, A. Benuzzi-Mounaix, Hiroaki Nishimura, Yoshihiro Ochi, Jiri Ullschmied, Jiri Skala, Bozena Kralikova, Miroslav Pfeifer, Christelle Kadlec, Tomas Mocek, A. Praeg, T. Hall, Paolo Milani, E. Barborini, P. Piseri
Experiments on the Equation of State (EOS) of Carbon were performed at the PALS and LULI laboratories. We used Carbon samples with two different value of initial density, in order to explore a wider region of the phase diagram. We obtain experimental data for carbon Hugoniot at Megabar pressures induced by laser-driven shock waves. The target rear side emissivity due to the shock unloading was recorded from (two-materials two-steps) targets (Al-C) with
space and time resolution. By applying the impedance mismatch method, a direct determination of relative EOS points was obtained. Experimental data are compared with previous experiments and with theoretical models. Our results indicate a higher compressibility of carbon at Megabar pressures compared to theoretical models.
Here we discuss the results of the experiments performed using the Prague Asterix Laser System (PALS) of wavelength 0.44 μm (3ω of Iodine laser) and energy ≈ 250 J in 450 ps (FWHM). Two sets of experiments were carried out, firstly, generation of high quality shocks which were steady in time and uniform in space using Phase Zone Plates (PZP), to establish the scaling laws of shock pressure Vs. laser intensity for aluminum foil target of thickness 8 μm. Our results show a good agreement with the delocalized laser absorption model. Secondly, measurements of the Equation of State of carbon compressed by shocks at megabars of pressure have been realized. Equation of State were obtained for carbon using the impedance mismatch technique. Step targets allowed the simultaneous measurements of shock velocity in two different materials. Aluminum was used as a reference material and relative EOS data for carbon have been obtained up to ≈ 14 Mbar pressure.
Giulio Poletti, Franceasco Orsini, Jiri Ullschmied, Jiri Skala, Bozena Kralikova, Miroslav Pfeifer, Christelle Kadlec, Tomas Mocek, A. Prag, F. Cotelli, C. Lora Lamia, Dimitri Batani, A. Bernardinello, Tara Desai, A. Zullini
An experiment on Soft X-ray Contact Microscopy (SXCM) performed on Caenorhabditis elegans nematodes is discussed. This sample has been selected since it is a well studied case used as model in many biological contexts. The experiment has been performed using the iodine PALS laser source to generate pulsed soft X-rays from laser-plasma interaction, using molybdenum and gold as targets. Typical intensities on the targets exceeded 1014 W/cm2. The SXCM imprints have been recorded on Polymethilmetacrylate (PMMA) photo resists which have been chemically developed and analyzed with an Atomic Force Microscope (AFM) operating in constant force mode. The use of error signal AFM
images together with topography AFM images, did allow an easier recognition of biological patterns, and the identification of observed structures with internal organs. Several organs were identified in the SXCM images, including cuticle annuli, alae, pharynx, and three different types of cell nuclei. These are the first SXCM images of multi-cellular complex organisms.
In all recently proposed schemes for laser-driven Fast Ignition (FI) of Inertial Confinement Fusion (ICF) targets, two key elements are the conversion of the energy of a Petawatt laser pulse into a beam of strongly relativistic electrons and its transport through a dense plasma or a solid target. The electron beam may either drive ignition directly or be exploited to acccelerate a proton beam which in turn is used to ignite the target. Both approaches to FI involve a number of physical processes that are challenging for theory and simulation. In this paper, theoretical and numerical investigations are presented concerning several fundamental issues of relevance to FI, including electron beam instabilities, electron transport in solid-density materials, and requirements for proton beam driven ignition.
Targets containing foams have always been in demand in ICF and HDE experiments. These foams are usually quite different and highly specialized. These foams are at the edge of current foam knowledge with the combination of low density and small pore sizes are a challenge to all chemists. The science and property of these materials are still not fully understood and investigated. The low-density materials and the production methods of various types of foams are reviewed and the limitations of each discussed.
We have studied the shock induced pressures due to the interaction of soft X-ray thermal radiation with foam-layered metal targets. Thermal X-ray radiation was produced by focusing a high energy laser inside a small size hohlraum. Experiments were performed using a 3ω converted (λ=0.44 μm) Iodine laser of τ≈450 ps (FWHM) duration. An increase in shock pressure was observed with the foam layered targets as compared to bare metal targets. Results are analyzed on the basis of the role of foam density and thickness.
Eugene Henry, Dimitri Batani, A. Morelli, M. Bernasconi, Michel Koenig, A. Benuzzi-Mounaix, I. Masclet, B. Marchet, M. Rebec, Charles Reverdin, Peter Celliers, Luiz Da Silva, Robert Cauble, G. Collins, T. Hall, C. Cavazzoni
In recent years, shock waves driven by high power lasers have become a reliable tool for the study of the equation of state (EOS) of material sin the Megabar pressure range, where they become strongly correlated, degenerate, dense plasmas. The EOS of water at very high pressures plays a very important role in astrophysics. In particular, the large magnetic field measured on Uranus and Neptune by Voyager 2 is assumed to be generated in the 'ice' layers where pressures up to 6 Mbar are reached. Recent calculations predict an insulator-metallic phase transition of water in this regime. Here, we present some preliminary results form a recent experiment on water EOS performed with the laser PHEBUS and funded by the European Union in the framework of the 'Access to Large Scale Facilities' program. In the experiment, structured targets made of an Aluminium step followed by a water layer are irradiated by the laser at an intensity approximately equals 4.1014 W.cm-2 to generate a shock wave. Velocities are measured in the two materials using a VISAR interferometric diagnostic for water, and a streak camera to measure target emission for Al. EOS points for water are obtained with the impedance mismatch method using Al EOS as a reference. Water reflectivity was also measured.
Focused Ion Beam (FIB) is a novel technique that allows easy target cell selection, fast operation, high resolution, 3D imaging and sample manipulation during imaging. The FIB technique of microscopy and nanomachining, that is widely spread in semiconductor technology, is reshuffled to open new horizons in the field oflife sciences at cellular and subcellular level. FIB is a source ofions which can be precisely oriented and focused on the sample, supported also by an electron source. The resolution can be as low as I 5nm. Two different operation modes are available: "cutting" and "etching" operations of very high precision and at the same time the resulting secondary ions and electrons provide follow up sample imaging. FIB tomography ability has been tested to provide information on cell characterisation, cell division time sequence, view of inner structures and investigation of membrane structural properties. We compare the performances and the advantages of different high-resolution microscopy techniques: Soft X-ray Contact Microscopy (SXCM), Focused Ion Beam (FIB) and Transmission Electron Microscopy (TEM). These have been used to image Saccharoniyces cerevisiae yeast cells, a rather well known sample of great biological interest. TEM is an established technique used as a benchmark for comparison.
An overall approach into the differential investigation of membrane/cytoplasm related metabolism and of cell-cycle of yeast cells after two color soft X-ray irradiation is presented; the soft X-rays being generated in trains of picosecond pulses by laser-plasma interaction. The two color X-ray differential technique is based on the generation of approximately 0.6 KeV X-rays which are deposited only in the membrane-wall complex switching off the anaerobic (fermentative) activity of yeast cells and on the generation of approximately 1.2 KeV X-rays which are mainly deposited in the cytoplasm, mitochondria and nucleus of yeast cells, mainly affecting the aerobic metabolism. A synergetic analysis of the metabolism is discussed, mainly founded on the recording of different correlated metabolic parameters, both on-line and delayed. Among the relevant access, pressure monitoring in batch samples acquire a dominant role allowing the identification of metabolic oscillation, that represent a marker of physical and chemical actions performed on the samples at different times. The experience acquired on yeast cells metabolism is being used to investigate lymphocytes metabolism and the related oscillatory properties of relevant enzymatic complexes. Actually even if it is not exactly the same as the mammalian situation, it should really propel the whole field forward.
Aldo Conti, Dimitri Batani, Cesare Botto, Alessandra Masini, A. Bernardinello, Fulvia Bortolotto, M. Moret, G. Poletti, S. Piccoli, F. Cotelli, C. Lora Lamia Donin, Anthony Stead, A. Marranca, Klaus Eidmann, Francesco Flora, Libero Palladino, Lucia Reale
The use of a high energy laser source for soft x-ray contact microscopy is discussed. Several different targets were used and their emission spectra compared. The x-ray emission, inside and outside the Water Window, was characterized in detail by means of many diagnostics, including pin hole and streak cameras. Up to 12 samples holders per shot were exposed thanks to the large x-ray flux and the geometry of the interaction chamber. Images of several biological samples were obtained, including Chlamydomonas and Crethidia green algae, fish and boar sperms and Saccharomyces Cerevisiae yeast cells. A 50 nm resolution was reached on the images of boar sperm. Original information concerning the density of inner structures of Crethidia green algae were obtained.
A toroidal crystal spectrometer was designed with the purpose of measuring the aluminum K-absorption edge shift, in the wavelength range around 7.9 angstroms, in highly compressed matter. The expected shift is about 100 mA (approximately 20 eV). The x-ray reflected from the crystal are focused onto a streak camera slit of 16 mm high and 100 micrometers width, to obtain a time resolved spectrum. High resolution value and dispersion of about 1 angstrom/16 mm on the detection window is hence required. A crystal with a toroidal surface is used to enhance the focusing power in the spatial dimension as in the spectral one. Numerical simulations are performed by means of 1D and 2D codes for the determination of the crystal characteristics like the dimension and the curvature radius with respect to the geometric constraints. Some results will be presented concerning the obtained spectra.
Saccharomyces Cerevisiae yeast cells were irradiated using the soft X-ray laser-plasma source at Rutherford Laboratory. The aim was to produce a selective damage of enzyme metabolic activity at the wall and membrane level (responsible for fermentation) without interfering with respiration (taking place in mitochondria) and with nuclear and DNA activity. The source was calibrated by PIN diodes and X-ray spectrometers. Teflon stripes were chosen as targets for the UV laser, emitting X-rays at about 0.9 keV, characterized by a very large decay exponent in biological matter. X-ray doses to the different cell compartments were calculated following a Lambert-Bouguet-Beer law. After irradiation, the selective damage to metabolic activity at the membrane level was measured by monitoring CO2 production with pressure silicon detectors. Preliminary results gave evidence of pressure reduction for irradiated samples and non-linear response to doses. Also metabolic oscillations were evidenced in cell suspensions and it was shown that X-ray irradiation changed the oscillation frequency.
A procedure is presented to release soft x-rays onto yeast cell membrane allegedly damaging the resident enzymatic processes connected with fermentation. The damage is expected to be restricted to regulating fermentation processes without interference with respiration. By this technique fermentation is followed leading to CO2 production, and respiration resulting in global pressure measurements. A solid state pressure sensor system has been developed linked to a data acquisition system. Yeast cells cultures have been investigated at different concentrations and with different nutrients. A non-monotone response in CO2 production as a function of the delivered x-ray dose is observed.
A large volume long pulse excimer laser ((lambda) equals 308 nm) is used to generate a soft x- ray plasma source with long heating time at a power density in the order of 1012 - 1014 W/cm2. The characteristics of the plasma source for different laser pulse time evolution in the range 10-120 ns and for different target materials are investigated. In particular the most suitable source conditions (spectral energy distribution, time duration, etc.) for specific applications are analyzed.
Soft x-ray contact microscopy (SXCM), using a pulsed x-ray source, offers the possibility of imaging the ultrastructure of living biological systems at sub-50nm resolution. We have developed a pulsed plasma x-ray source for this application, generated by the large volume XeCl laser 'Hercules'. Various unstable optical resonator configurations were employed to achieve a high laser intensity to increase the conversion efficiency to 'water window' x-rays (280-530eV). Optimum plasma conditions for SXCM are discussed, including the effect of pulse duration on image resolution. Soft x-ray contact images of Chlamydomonas dysosmos (unicellular alga) and the cyanobacteria Leptolyngbya are shown. In addition, the potential of producing a 'movie film' of the development of x-ray images within the photoresist (acting as the recording medium) is discussed, following the resist development while viewing by atomic force microscopy.
I. C. Edmond Turcu, Ian Ross, P. Trenda, C. Wharton, R. Meldrum, Hiroyuki Daido, M. Schulz, P. Fluck, Alan Michette, A. Juna, Juan Maldonado, Harry Shields, Gregory Tallents, L. Dwivedi, J. Krishnan, D. Stevens, T. Jenner, Dimitri Batani, H. Goodson
At Rutherford Appleton Laboratory we developed a high repetition rate, picosecond, excimer laser system which generates a high temperature and density plasma source emitting approximately 200 mW (78 mW/sr) x ray average power at h(nu) approximately 1.2 KeV or 0.28 KeV < h(nu) < 0.53 KeV (the `water window'). At 3.37 nm wavelength the spectral brightness of the source is approximately 9 X 1011 photons/s/mm2/mrad2/0.1% bandwidth. The x-ray source serves a large user community for applications such as: scanning and holographic microscopy, the study of the biochemistry of DNA damage and repair, microlithography and spectroscopy.
A large volume XeCl laser has been equipped with a confocal positive branch unstable resonator (CPBUR), obtaining a near diffraction-limited beam, with a brightness of > 1014W/(cm2sr). Focusing the radiation, an intensity of about 1012W/cm2 is reached on a copper target, generating an x-ray emitting plasma in the region of 100 eV, with pulse length up to 100 ns.
The Rutherford Appleton Laboratory Repetitive Laser-Plasma X-ray Source has been scaled to repetition rates of up to 100 Hz. An average power of 40 mW/sr has been measured from mylar tape targets in the spectral region 0.28 < h(upsilon) < 0.53 keV (the `water window') with approximately 30% of the emission in the hydrogen-like carbon ion L(alpha) (h(upsilon) equals 368 eV) line. A scanning transmission x-ray microscope (STXM) was used for the first time with a laser-plasma source to generate test images. The source was also run with Cu and Fe targets to generate h(upsilon) approximately equals 1 keV x-rays in atmospheric pressure helium, yielding at 30 Hz an average power of approximately 9 mW/sr. Proximity x-ray microlithography images in 1.2 micrometers thick photoresist have accurately reproduced features of approximately 0.3 micrometers.
Laser based x-ray sources at h(upsilon) approximately equals 0.9 - 1.2 keV (Fe to Cu L-shell) developed for applications are studied from the point of view of x-ray emission spectra. X-ray spectra obtained with different laser intensities and wavelengths using Nd and KrF lasers are described. Results are qualitatively compared with the predictions of simple analytical models for plasma temperature Te and average ionization Z*. When using KrF lasers it is possible to introduce a He atmosphere in the interaction chamber to reduce the debris problem. X-ray spectra at different He pressures were recorded and x-ray L-shell emission of Fe and Cu were shown to be largely independent of the pressure.
A repetitively pulsed (5Hz) KrF laser-based X-ray source producing photons at
i-ru 1.1 keV (copper, L-shell) from a copper coated rotating target has been used to
study soft X-ray induced DNA damage effects in Chinese hamster cells. The source
was computer controlled for accurate delivery to the biological material of pre-set
doses. DNA damage was induced by exposures lasting 7s for V79 cells and 40s for AA8
cells. To minimise the debris from the laser-plasma source and for convenient
handling of biological specimens, the target chamber contained helium at 1
atmosphere with a slow flow. The X-ray yield of the source decreased by only at
most 10-20% compared to vacuum operation and a further 16% of X-rays were absorbed
in helium between target and the biological material placed outside the target
chamber behind a beryllium filter. The measured spectral and spatial distribution
of the copper X-ray emission was found to be largely independent of the ambient
helium pressure. The time resolved X-ray signal lasted for only 3 ns starting at
the beginning of the 2lns laser pulse and its shape was independent of helium
pressure in the target chamber.
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