Since the first experimental campaign conducted in 2014 with mid field Gated X-ray Imager (GXI) and two quadruplets
(20 kJ at 351 nm) focused on target, the Laser MégaJoule (LMJ) operational capability is still growing up. New plasma
diagnostics have been implemented: a large field 2D GXI, two broadband x-ray spectrometers (called DMX and
miniDMX), a specific soft x-ray spectrometer and a Laser Entrance Hole (LEH) imaging diagnostic. A series of
experiments have been performed leading to more than 60 shots on target. We will present the plasma diagnostics
development status conducted at CEA for experimental purpose. Several diagnostics are now under manufacturing or
development which include a Streaked Soft X-ray Imager (SSXI), an Equation Of State (EOS) diagnostic suite (“EOS
pack”), a Full Aperture BackScattering (FABS) diagnostic, a Near Backscattered Imager (NBI), a high resolution 2D
GXI, a high resolution x-ray spectrometer, a specific set of two polar hard x-ray imagers for LEH characterization and a
set of Neutron Time of Flight (NTOF) detectors. We describe here the diagnostics design and performances in terms of
spatial, temporal and spectral resolutions. Their designs have taken into account the harsh environment (neutron yields,
gamma rays, electromagnetic perturbations, debris and shrapnel) and the safety requirements.
Within the framework of its researches on Inertial Confinement Fusion (ICF), the “Commissariat à l’Énergie Atomique et aux Énergies Alternatives” (CEA) studies and designs advanced X-ray diagnostics in order to probe dense plasmas produced by Laser facilities. The final goal for those diagnostics is to be used during experiments on the Laser Megajoules french facility (LMJ) at Bordeaux.
We present two types of advanced monochromatic High Resolution X-ray Imaging microscopes (HRXI) who have high spatial resolution capability (3-6 μm) and high efficiency.
The first microscope so-called MERSSIX consists of two toroïdals mirrors mounted into a Wolter type geometry and working at grazing incidence. Non-periodic multilayer (depth graded) mirrors were developed with special coatings designed to provide broadband X-ray reflectance in the 1 - 22 keV energy range. Associated to this Wolter microscope a potential monochromatic third mirror coated with a multilayer stack can be used for monochromatic application in that range.
The second microscope is composed of a transmission gold Fresnel Phase Zone Plate (FPZP) and a narrow bandwidth multilayer mirror. We present an experimental study with X-ray plasma-source and a complete characterization of the X-ray optics on the synchrotron radiation facility BESSY II.
Potentialities (a few μspatial resolution monochromatic images) and complementarity of these two monochromatic HRXI are discussed. The design of the MLs for each microscope is detailed.
A new channel of an X-ray broadband spectrometer has been developed for the 2 – 4 keV spectral range. It uses a spectral filtering by using a non-periodic multilayer mirror. This channel is composed by a filter, an aperiodic multilayer mirror and a detector. The design and realization of the optical coating mirror has been defined such as the reflectivity is above 8% in almost the entire bandwidth range 2 – 4 keV and lower than 2% outside. The mirror is optimized for working at 1.9° grazing incidence. The mirror is coated with a stack of 115 chromium / scandium (Cr / Sc) non-periodic layers, between 0.6 nm and 7.3 nm and a 3 nm thick top SiO2 layer to protect the stack from oxidization. To control thin thicknesses, we produced specific multilayer mirrors which consist on a superposition of two periodic Cr / Sc multilayers with the layer to calibrate in between. The mirror and subnanometric layers characterizations were made at the “Laboratoire Charles Fabry” (LCF) with a grazing incidence reflectometer working at 8.048 keV (Cu Kα radiation) and at the synchrotron radiation facility SOLEIL on the hard X-ray branch of the “Metrology” beamline. The reflectivity of the mirrors as a function of the photon energy was obtained in the Physikalisch Technische Bundesanstalt (PTB) laboratory at the synchrotron radiation facility Bessy II.
The path to successful inertial confinement fusion (ICF) requires to observe and control the micro balloon deformations. This will be achieved using X-ray microscope among other diagnostics. A high resolution, high energy X-ray microscope involving state-of-the-art toroidal mirrors and multilayer coatings is described. Years of experiments and experience have led to a small-scale X-ray plasma imager that proves the feasibility of all the features required for a LMJ diagnostic: spatial resolution of 5μm, broad bandwidth, millimetric field of view (FOV). Using the feedback given by this diagnostic, a prototype for the Laser MegaJoule (LMJ) experiments has been designed. The experimental results of the first diagnostic and the concepts of the second are discussed.
With regards to the future Laser Megajoules french facility (LMJ), our laboratory is developing advanced time-resolved
High Resolution X-ray Imaging (HRXI) systems to diagnose laser produced plasma. Shrapnel and X-ray
loading on this laser imposes to place any HRXI as far away from the source as possible. Grazing incidence X-ray
microscopes are the best solution to overpass this limitation. These imagers combine therefore grazing X-ray
microscope and camera. We designed imaging diagnostics, mainly with a long working distance (> 50 cm) and high
spatial resolution. All of them are composed of single or multi-toroïdal(s) mirror(s).
To increase the bandwidth of reflectivity of all these mirrors, multilayer coatings have been deposited. We present
mainly microscopes using non-periodic W/SiC multilayer coatings (Supermirrors), developed in collaboration with
Supermirrors were designed for a first set of diagnostics to work at 0.7° grazing incidence. Secondly, we have
implemented this supermirror on a Wolter-type microscope used at a smaller grazing incidence (0.6° angle) in order
to increase the bandwidth of reflectivity up to 12 keV.
Metrology for x-ray reflectance in the whole range on the synchrotron radiation facility BESSY II is also presented.
X-ray imaging technology is highly developed to meet the needs of high-energy physics and diagnostics of inertial
confinement fusion. In this paper, we describe the design of a non coplanar toroïdal mirrors microscope. It consists of
three off-axis revolution concave toroïdal mirrors working at grazing incidence. Non-periodic W/SiC multilayer coatings
have been deposited on each mirror, in order to increase until 10 keV the bandpass of reflectivity of the microscope.
These super mirrors have been designed to work at 0.6° grazing incidence angle and display a reflectivity better than
40% in the entire energy range 2-10 keV. Concerning the imaging performances, we have almost achieved 5 μm of
spatial resolution in a field of 500 μm. Regarding to these results, this prototype of microscope, the so-called "Plasma
Imageur X pour les Experiences Laser Mega Joule" (PIXEL), will be used for 2D spatial and 1D time resolved imaging
of dense plasmas produced during inertial confinement fusion experiments at the future Laser Mega Joule French facility
Metrology of XUV beams and more specifically X-ray laser (XRL) beam is of crucial importance for development of applications. We have then developed several new optical systems enabling to measure the x-ray laser optical properties. By use of a Michelson interferometer working as a Fourier-Transform spectrometer, the line shapes of different x-ray lasers have been measured with an unprecedented accuracy (δλ/λ~10-6). Achievement of the first XUV wavefront sensor has enable to measure the beam quality of laser-pumped as well as discharge pumped x-ray lasers. Capillary discharge XRL has demonstrated a very good wavefront allowing to achieve intensity as high 3*1014 Wcm-2 by focusing with a f = 5 cm mirror. The measured sensor accuracy is as good as λ/120 at 13 nm. Commercial developments are under way.
Experiments were performed in indirect drive at the Phebus laser facility to study the ablation front Rayleigh-Taylor instability. Brominated plastic targets with sinusoidal modulations were accelerated with a temporally shaped soft x-ray pulse created in a hohlraum. The growth of the perturbations was observed by face-on radiography using a new Wolter-like microscope and the acceleration was derived from separate side-on velocity measurements.
Advanced Wolter X-ray microscope is developed to diagnose laser-produced plasmas and for the researching Inertial Confinement Fusion (ICF). The microscope is composed of two aspherical mirrors. We present X-ray Imaging Diagnostic and imaging studies we have performed with two kinds of X-ray source: an x-ray generator and a plasma laser x-ray source obtained with a power laser facility at 'Centre d'etudes de Limeil-Valenton,' France. A spatial resolution of better than 4 micrometer has been obtained in the 1 - 5 keV range over a field of 500 micrometer and for different magnifications varying from 15 to 40.
Spectral characteristics of plane multilayer amplitude molybdenum-silicon diffraction gratings (1000 and 2000 lines/mm, d-spacing of 115 angstrom), fabricated by electron- beam lithography, were determined using a laser-produced plasma XUV radiation source. The gratings were studied at near-normal incidence and at an angle of incidence of 36 degrees in stigmatic and quasi-stigmatic spectrograph systems with moderate dispersion. The task of focusing radiation was imposed on either a grazing-incidence toroidal mirror or a normal-incidence Mo-Si multilayer mirror with a d-spacing of 115 angstrom. The spectral profile of resonance reflection by the gratings was determined in the first and second Bragg orders of the multilayer structure for different angles of incidence. Line spectra of multiply charged F, Na, Mg, and Cl ions were recorded in the 160 - 230 angstrom range by means of these multilayer gratings, and the resolving power of the gratings was determined.
Backlighting is extensively used as a diagnostic tool in experiments relative to Inertial Confinement Fusion. Thus, beam and target nonuniformities effects on hydrodynamic instabilities growth and imprinting, shock propagation in solid materials and foil acceleration are studied in planar geometry. Spherical or cylindrical implosions measurements are relative to hydrodynamic instabilities, feedthrough and fuel-pusher mixing, in-flight aspect ratio, implosion velocity, symmetry and peak compression densities. With the laser mega-joule very high laser power and energy will be reached that will give access to new density and temperature domains. Correlatively, diagnostics survivability has to be considered taking the large X-ray, neutron and debris emissions into account. The X-ray induced shocks or neutron induced radioactivity will constitute limitations to measurements inside the target chamber. The experimental program on its route towards ignition and gain will anyway still require backlighters to optimize the targets parameters (the microballoon wall thickness, the ablator nature) and allow the adjustment of not well known quantities as opacities and equations of state.
The multi-image framing camera based on gated MicroChannel Plates (MCPs), used in ICF programs, allows to obtain a sequence of 2D images in the x-ray range with gating times smaller than 100 ps and spatial resolution better than 20 pl/mm. After using such devices from different factories, we decided to build our own tube. Our choice is motivated by the great fragility of the tube, consequent to both bad vacuum during the experiment and moisture due to frequent air launching, and by the mastery of the technology which is necessary to repair rapidly such apparatuses. The characteristics of the tube, particularly shutter time and spectral response, must be known as exactly as possible. Consequently we describe in these pages the method used to measure a shutter time of about 75 ps and we appraise the errors due to the FWHM and the spatial unstability of the UV laser pulse employed to illuminate the front side of the MCP. The measurement of the spectral sensitivity, determined by experiments with synchrotron radiation on the storage ring SUPERACO in Orsay (France), shows a response in the energy band 2 - 5 keV different from the one measured with the gold vacuum-deposited photocathode on the MCP.
We give an experimental study of soft x-ray diffraction by various laminar multilayer amplitude grating mirrors made by electron beam lithography. The +1, 0, -1 diffraction order efficiencies in the grating rule scan model and their positions were measured using synchrotron radiation on the Super-Aco at L.U.R.E in the X-UV region, particularly above the silicon L edge. These efficiencies were compared with values obtained in the detector scan mode. Their diffraction pattern were analyzed and discussed with a model. We describe a modular X-UV spectrogoniometer (0 - 20 goniometer).
Carbon alternated with metallic elements such as Ni, Co, Cr, Rh, Fe, W, or Ti offers the best potentialities in terms of soft X-ray reflection in the range 44 - 100 A. Deposition of this type of device requires a very accurate control of nanometric film deposition with a high regularity and sharp interfaces. We have made a precise investigation of the influence of the deposition conditions on the nanostructure of these systems using ultrahigh vacuum rf-sputtering technique. Conventional plasma conditions such as pressure and power levels have been investigated and also more unusual conditions such as target resistivity or sample temperature. It appears that the optimization process always results in a reduction of the amount of energy applied to the surface during growth. Medium argon pressure, low power levels, low target autobias and deposition at low temperature give the best structural quality and the best performance at the carbon K-alpha line. Metallic layer crystallization and the parasitic etching process are limited especially for the most sensitive Ni/C and Rh/C systems. The second part of the study is devoted to the comparison of Ni, Rh, Co, Fe, Cr, Ti, and W alternated with carbon. Thermal stability of the different systems is evaluated and related to the nanostructural behavior. When carbide formation is thermodynamically favorable, parasitics effects due to the crystallization are limited and the thermal stability is improved.
Two types of linear multilayer gratings have been investigated with special attention on the influence of the fabrication method on performance. Rh/C and Mo/Si systems have been realized for use above the carbon K-edge at 43.6 A and the silicon L3 edge at 125 A, respectively. We analyzed in detail the performance of the multilayer coatings in relation with their structural behavior. Mo/Si amplitude gratings were manufactured by suppressing the soft X-ray reflectivity of the multilayer mirror in selective areas with gold coating and lift off process. This method provides a well-defined 3 micron period Au grating. The soft X-ray reflectivity of the multilayer alone reached a maximum of 45 percent at normal incidence, whereas it was measured around 12.5 percent after Au grating deposition. Up to 13 grating orders were detected in the grating scan and detector scan showing the very good quality of these structures. A more unusual method was applied to manufacture Rh/C multilayer gratings. A carbon grating was first patterned on a silicon substrate and the multilayer was deposited at the end of the process. Measured reflectivity around 60 A in conventional 0 - 20 scan shows a reduction of the performances by a factor three. This is probably due to the surface roughness of the carbon grating prior to the multilayer deposition.