Showing papers in "Laser and Particle Beams in 2004"
TL;DR: The 70-year anniversary of the first nuclear fusion reaction of hydrogen isotopes by Oliphant, Harteck, and Rutherford is an opportunity to realize how beam fusion is the path for energy production, including both branches, the magnetic confinement fusion and the inertial fusion energy (IFE).
Abstract: The 70-year anniversary of the first nuclear fusion reaction of hydrogen isotopes by Oliphant, Harteck, and Rutherford is an opportunity to realize how beam fusion is the path for energy production, including both branches, the magnetic confinement fusion and the inertial fusion energy (IFE). It is intriguing that Oliphant's basic concept for igniting controlled fusion reactions by beams has made a comeback even for magnetic confinement plasma, after this beam fusion concept was revealed by the basically nonlinear processes of the well-known alternative of inertial confinement fusion using laser or particle beams. After reviewing the main streams of both directions some results are reported—as an example of possible alternatives—about how experiments with skin layer interaction and avoiding relativistic self-focusing of clean PW–ps laser pulses for IFE may possibly lead to a simplified fusion reactor scheme without the need for special compression of solid deuterium–tritium fuel.
66 citations
63 citations
TL;DR: In this article, the energy dissipation through collective electromagnetic modes (mostly transverse to the incoming beam) of ultra-intense relativistic electrons and nonrelativistic protons interacting with a supercompressed core of deuterium+tritium (DT) thermonuclear fuel was emphasized.
Abstract: This article intends to emphasize out the energy dissipation through collective electromagnetic modes (mostly transverse to the incoming beam) of ultra‐intense relativistic electrons and nonrelativistic protons interacting with a supercompressed core of deuterium+tritium (DT) thermonuclear fuel. This pattern of beam‐plasma interaction documents the fast ignition scenario for inertial confinement fusion. The electronmagnetic weibel instability is considered analytically in a linear approximation. Relevant growth rates parameters then highlight density ratios between target and particle beams, as well as transverse temperatures. Significant refinements include mode‐mode couplings and collisions with target electrons. The former qualify the so‐called quasi‐linear (weakly turbulent) approach. Usually it produces significantly lower growth rates than the linear ones. Collisions enhance them slightly for kc/ωp<1, and dampen them strongly for kc/ωp≥1. Those results simplify rather drastically for the la...
52 citations
TL;DR: In this article, the one-dimensional Poisson-Boltzmann equation is analyzed on a finite spatial interval whose extension is determined by requiring electron energy conservation, resulting in the consistent spatial distributions of the hot electrons created by the laser and of the corresponding electrostatic potential.
Abstract: Effective ion acceleration of picosecond-duration well-collimated bunches in the strong relativistic interaction of a short laser pulse with a thin solid target has been experimentally demonstrated. In this work, with reference to the sharp rear solid–vacuum interface, where ion energization takes place, the one-dimensional Poisson–Boltzmann equation is analytically solved on a finite spatial interval whose extension is determined by requiring electron energy conservation, resulting in the consistent spatial distributions of the hot electrons created by the laser and of the corresponding electrostatic potential. Then, the equation of motions for an ensemble of test ions, initially distributed in a thin layer of the rear target surface, with different initial conditions, is solved and the energy spectrum corresponding to a given initial ion distribution is determined.
51 citations
TL;DR: In this paper, an electron beam with an amplitude of ∼170 A with a duration at FWHM of ∼0.3 ns has been obtained, based on beam temporal characteristics and discharge spatial characteristics, the critical fields were reached at plasma approach to anode.
Abstract: This article reports on experimental studies of subnanosecond electron beams formed in air under atmospheric pressure. An electron beam with an amplitude of ∼170 A with a duration at FWHM of ∼0.3 ns has been obtained. Based on beam temporal characteristics and discharge spatial characteristics, the critical fields were supposed to be reached at plasma approach to anode. Simultaneously, the sharp high-energy pulse of e-beam current is generated. Of critical importance is the cathode type and occurrence on the cathode of plasma protrusions. It is shown that to get maximum amplitude of the electron beam in the gas diode, the discharge in the gas diode should be volumetric.
50 citations
50 citations
TL;DR: In this paper, the results concerning the characteristics and the behavior of expanding plasma generated by a Laser Ion Source (LIS) have been reported, which is an efficient means in producing of multi-charged ions utilizing pulsed laser beams.
Abstract: We report on the results concerning the characteristics and the behavior of expanding plasma generated by a Laser Ion Source ~LIS!. The LIS technique is an efficient means in producing of multi-charged ions utilizing pulsed laser beams. In order to extract Cu ions, in this experiment an XeCl excimer UV laser was employed, providing a power density on the target surface up to 5 3 10 8 W0cm 2 . Two typologies of diagnostic systems were developed in order to detect the plasma current and the ion energy. The time-of-flight ~TOF! measurements were performed exploiting either a Faraday cup or an Ion Energy Analyzer ~IEA!. This latter allowed getting quantitative information about the relative ion abundances, their kinetic energy and their charge state. To study the plasma characteristics we measured the total etched material per pulse at 70 mJ. It was 0.235 mg and the overall degree of ionization, 16%. The angular distribution of the ablated material was monitored by optical transmission analysis of the deposited film as a function of the angle with respect to the normal to the target surface. Applying a high voltage to an extraction gap a multi-charged ion beam was obtained; different peaks could be distinguished in the TOF spectrum, resulting from the separation of ions of hydrogen, adsorbed compounds in the target and copper.
48 citations
TL;DR: In this paper, the authors considered ion acceleration at the front surface of overdense plasma by a short laser pulse and showed that the proton acceleration is more effective when they represent only a small dope to the heavy background ions.
Abstract: We consider ion acceleration at the front surface of overdense plasma by a short laser pulse. In this configuration, the laser ponderomotive pressure pushes the background electrons, and a double layer is produced at the boundary of the overdense region. The ions are accelerated by the electrostatic field of the double layer. If the laser intensity is so large that the plasma becomes relativistically transparent, then ion trapping in the running double layer and acceleration to relativistic energies is possible. We study this physics using one-dimensional particle-in-cell simulations. Ion acceleration in one- and two-component plasmas is considered. It is shown that the proton acceleration is more effective when they represent only a small dope to the heavy background ions.
47 citations
TL;DR: In this paper, the authors report on the results of a parameter study that has been carried out to estimate the minimum pulse lengths and the maximum peak powers achievable, using bunch rotation RF gymnastic-including nonlinearities of the RF gap voltage in SIS100, using a longitudinal dynamics particle in cell ~PIC! code, ESME.
Abstract: The Gesellschaft fur Schwerionenforschung ~GSI! Darmstadt has been approved to build a new powerful facility named FAIR ~Facility for Antiprotons and Ion Research! which involves the construction of a new synchrotron ring SIS100. In this paper, we will report on the results of a parameter study that has been carried out to estimate the minimum pulse lengths and the maximum peak powers achievable, using bunch rotation RF gymnastic-including nonlinearities of the RF gap voltage in SIS100, using a longitudinal dynamics particle in cell ~PIC! code, ESME. These calculations have shown that a pulse length of the order of 20 ns may be possible when no prebunching is performed while the pulse length gradually increases with the prebunching voltage. Three different cases, including 0.4 GeV0 u, 1G eV 0u, and 2.7 GeV0u are considered for the particle energy. The worst case is for the kinetic energy of 0.4 GeV0u which leads to a pulse length of about 100 ns for a prebunching voltage of 100 kV ~RF amplitude!. The peak power was found to have a maximum, however, at 0.5‐1.5kV prebunching voltage, depending on the mean kinetic energy of the ions. It is expected that the SIS100 will deliver a beam with an intensity of 1‐2 3 10 12 ions. Availability of such a powerful beam will make it possible to study the properties of high-energy-density ~HED! matter in a parameter range that is very difficult to access by other means. These studies involve irradiation of high density targets by the ion beam for which optimization of the target heating is the key problem. The temperature to which a target can be heated depends on the power that is deposited in the material by the projectile ions. The optimization of the power, however, depends on the interplay of various parameters including beam intensity, beam spot area, and duration of the ion bunch. The purpose of this paper is to determine a set of the above parameters that would lead to an optimized target heating by the future SIS100 beam.
44 citations
TL;DR: In this article, the authors present recent progress in the direct-drive fusion studies for LMJ and show that non-uniformity can be minimized by repointing the beams.
Abstract: In the context of the French Laser Megajoule (LMJ) fusion research program, direct drive is an alternate to indirect drive to reach ignition and thermonuclear burn. We present recent progress in the direct-drive fusion studies for LMJ. Calculations have shown that the LMJ irradiation uniformity is characterized by long wavelength asymmetries compatible with direct drive requirements. Calculations of the irradiation uniformity in the context of indirect drive beam positioning have been done. We show that non-uniformity can be minimized by repointing the beams. Unfortunately, a time analysis shows that this nonuniformity increases strongly in time above levels usually considered inconsistent for direct drive. Finally, a recent baseline target design is presented and consists of a DT ice shell surrounded by a low-density CH foam wicked with cryogenic DT. This design can potentially reach a gain of 90 with a 1-MJ on-target laser driver. Hydrodynamic stability is increased at the ablation front and the laser–target coupling efficiency achieves 85%.
43 citations
TL;DR: In this article, high-resolution K-shell spectra of a plasma created by superintense laser irradiation of micron-sized Ar clusters have been measured with an intensity above 1019 W/cm2 and a pulse duration of 30 fs.
Abstract: High-resolution K-shell spectra of a plasma created by superintense laser irradiation of micron-sized Ar clusters have been measured with an intensity above 1019 W/cm2 and a pulse duration of 30 fs. The total photon flux of 2 × 108 photons/pulse was achieved for Heα1 resonant line of Ar (λ = 3.9491 A, 3.14 keV). In parallel with X-ray measurements, energy distributions of emitted ions have been measured. The multiply charged ions with kinetic energies up to 800 keV were observed. It is found that hot electrons produced by high contrast laser pulses allow the isochoric heating of clusters and shift the ion balance toward the higher charge states, which enhances both the X-ray line yield of the He-like argon ion and the ion kinetic energy.
TL;DR: In this paper, it was shown that at laser wavelengths of the order of 1 μm, successful fast ignition requires strong anomalous laser beam-pellet coupling, and that the laser beam pressure only causes a more or less deep cone-shaped critical surface that leads to better guidance of the beam and to improved laser-plasma coupling.
Abstract: Hole boring and fast ignition seem to exclude each other: When there is hole boring, no ignition occurs, and vice versa. The laser beam pressure only causes a more or less deep cone-shaped critical surface that leads to better guidance of the beam and to improved laser–plasma coupling. At laser wavelengths of the order of 1 μm, successful fast ignition requires strong anomalous laser beam–pellet coupling.
TL;DR: In this article, the state-of-the-art of optically induced charged particle sources is described and an introduction to the current state of the art is given and possible applications of these optically-induced particle sources are discussed.
Abstract: It is known that relativistic laser plasma interactions can already today induce accelerating fields beyond some TV/m, which are indeed capable to efficiently accelerate plasma background electrons as well as protons. An introduction to the current state of the art will be given and possible applications of these optically induced charged particle sources will be discussed.
TL;DR: In this article, the authors extended the selective resonant tunneling model to other light nucleus fusion reactions, such as d 1 d fusion and d 1 3 He, and derived the features of the astrophysical S-function in terms of this model.
Abstract: The application of selective resonant tunneling model is extended from d 1 t fusion to other light nucleus fusion reactions, such as d 1 d fusion and d 1 3 He. In contrast to traditional formulas, the new formula for the cross-section needs only a few parameters to fit the experimental data in the energy range of interest. The features of the astrophysical S-function are derived in terms of this model. The physics of resonant tunneling is discussed.
TL;DR: In this paper, the authors proposed a specific optimization of the ion beam properties, that is, an appropriate choice of the target design and of the laser pulse intensity, shape, and duration.
Abstract: Energetic ion beams are produced during the interaction of ultrahigh-intensity, short laser pulses with plasmas. These laser-produced ion beams have important applications ranging from the fast ignition of thermonuclear targets to proton imaging, deep proton lithography, medical physics, and injectors for conventional accelerators. Although the basic physical mechanisms of ion beam generation in the plasma produced by the laser pulse interaction with the target are common to all these applications, each application requires a specific optimization of the ion beam properties, that is, an appropriate choice of the target design and of the laser pulse intensity, shape, and duration.
TL;DR: In this paper, the electric field in the temporal and spectral domain of coherent diffraction-limited transition radiation is studied, and a general expression for the spatiotemporal electric field is derived, and closed-form solutions for several special cases are given.
Abstract: The electric field in the temporal and spectral domain of coherent diffraction-limited transition radiation is studied. An electron bunch, with arbitrary longitudinal momentum distribution, propagating at normal incidence to a sharp metal-vacuum boundary with finite transverse dimension is considered. A general expression for the spatiotemporal electric field of the transition radiation is derived, and closed-form solutions for several special cases are given. The influence of parameters such as radial boundary size, electron momentum distribution, and angle of observation on the waveform (e.g., radiation pulse length and amplitude) are discussed. For a Gaussian electron bunch, the coherent radiation waveform is shown to have a single-cycle profile. Application to a novel THz source based on a laser-driven accelerator is discussed.
TL;DR: In this article, the fastest ions with high charge number Z, which usually are of megaelectron volt energy following the relativistic self-focusing and nonlinear force acceleration theory, were reduced to less than 50 times lower energies when 1.2 ps laser pulses of about 1 J were incident.
Abstract: Measurements of the ion emission from targets irradiated with neodymium glass and iodine lasers were analyzed and a very significant anomaly observed. The fastest ions with high charge number Z, which usually are of megaelectron volt energy following the relativistic self-focusing and nonlinear-force acceleration theory, were reduced to less than 50 times lower energies when 1.2 ps laser pulses of about 1 J were incident. We clarify this discrepancy by the model of skin depth plasma front interaction in contrast to the relativistic self-focusing with filament generation. This was indicated also from the unique fact that the ion number was independent of the laser intensity. The skin layer theory prescribes prepulse control and lower (near relativistic threshold) laser intensities for nonlinear-force-driven plasma blocks for high-gain ignition similar to light ion beam fusion.
TL;DR: In this paper, the authors report the first results of dosimetric analysis of broad-spectrum, multi-MeV laser accelerated proton beams obtained during experiments at the Rutherford Appleton Laboratory using the Chirped Pulse beam of the Vulcan laser.
Abstract: In this paper, we report the first results of dosimetric analysis of broad-spectrum, multi-MeV laser accelerated proton beams obtained during experiments at the Rutherford Appleton Laboratory using the Chirped Pulse beam of the Vulcan laser. The spectra are retrieved by a numerical analysis that allows the reconstruction of the energetic profile of the proton beam from data obtained using radiochromic film.
TL;DR: In this article, the PARAX code is used to model the laser field in a standard paraxial approximation in three dimensions, and the plasma response is described by single-fluid, two-temperature, fully nonlinear hydrodynamical equations in the plane transverse to the laser propagation axis.
Abstract: The forthcoming laser installations related to inertial confinement fusion, Laser Megajoule (LMJ) (France) and National Ignition Facility (NIF) (USA), require multidimensional numerical simulation tools for interpreting current experimental data and to perform predictive modeling for future experiments. Simulations of macroscopic plasma volumes of the order of 1 mm^3 and laser exposure times of the order of hundreds of picoseconds are necessary. We present recent developments in the PARAX code towards this goal. The laser field is treated in a standard paraxial approximation in three dimensions. The plasma response is described by single-fluid, two-temperature, fully nonlinear hydrodynamical equations in the plane transverse to the laser propagation axis. The code also accounts for the dominant nonlocal transport terms in spectral form originating from a linearized solution to the Fokker–Planck equation. The simulations of interest are hohlraum plasmas in the case of indirect drive or the plasma corona for direct drive. Recent experimental results on plasma-induced smoothing of RPP laser beams are used to validate the code.
TL;DR: The PLEIADES (Picosecond Laser-Electron Interaction for the Dynamical Evaluation of Structures) facility at Lawrence Livermore National Laboratory as discussed by the authors was the first X-ray source with a high-brightness, relativistic electron beam.
Abstract: The Compton scattering of a terawatt-class, femtosecond laser pulse by a high-brightness, relativistic electron beam has been demonstrated as a viable approach toward compact, tunable sources of bright, femtosecond, hard X-ray flashes. The main focus of this article is a detailed description of such a novel X-ray source, namely the PLEIADES (Picosecond Laser–Electron Inter-Action for the Dynamical Evaluation of Structures) facility at Lawrence Livermore National Laboratory. PLEIADES has produced first light at 70 keV, thus enabling critical applications, such as advanced backlighting for the National Ignition Facility and in situ time-resolved studies of high- Z materials. To date, the electron beam has been focused down to σ x = σ y = 27 μm rms, at 57 MeV, with 266 pC of charge, a relative energy spread of 0.2%, a normalized horizontal emittance of 3.5 mm·mrad, a normalized vertical emittance of 11 mm·mrad, and a duration of 3 ps rms. The compressed laser pulse energy at focus is 480 mJ, the pulse duration 54 fs Intensity Full Width at Half-Maximum (IFWHM), and the 1/ e 2 radius 36 μm. Initial X rays produced by head-on collisions between the laser and electron beams at a repetition rate of 10 Hz were captured with a cooled CCD using a CsI scintillator; the peak photon energy was approximately 78 keV, and the observed angular distribution was found to agree very well with three-dimensional codes. The current X-ray dose is 3 × 10 6 photons per pulse, and the inferred peak brightness exceeds 10 15 photons/(mm 2 × mrad 2 × s × 0.1% bandwidth). Spectral measurements using calibrated foils of variable thickness are consistent with theory. Measurements of the X-ray dose as a function of the delay between the laser and electron beams show a 24-ps full width at half maximum (FWHM) window, as predicted by theory, in contrast with a measured timing jitter of 1.2 ps, which contributes to the stability of the source. In addition, K -edge radiographs of a Ta foil obtained at different electron beam energies clearly demonstrate the γ 2 -tunability of the source and show very good agreement with the theoretical divergence-angle dependence of the X-ray spectrum. Finally, electron bunch shortening experiments using velocity compression have also been performed and durations as short as 300 fs rms have been observed using coherent transition radiation; the corresponding inferred peak X-ray flux approaches 10 19 photons/s.
TL;DR: In this paper, the authors used the one-dimensional PIC code for the description of the laser interaction with the plasma layer at the target surface and treated fast electron transport into the target by a newly developed Monte Carlo code with temporal resolution.
Abstract: K-α emission is an intense short-pulse line source well suited for X-ray diagnostic techniques with subpicosecond and micrometer resolution. Numerical simulations are performed here in a search for laser–target interaction regimes where both high efficiency of laser energy transformation to X-ray emission and ultrashort X-ray pulses are achieved. We use the one-dimensional PIC code for the description of the laser interaction with the plasma layer at the target surface. Fast electron transport into the target is treated by our newly developed Monte Carlo code with temporal resolution that is described here in detail. Our simulations reveal extremely short ∼200 fs FWHM bright K-α X-ray pulses emitted from targets heated by 120-fs pulses of a table-top laser. Laser energy conversion efficiency to K-α line emission as high as 6 × 10−5 is noticed. Integration of the emitted energy over the focal spot is carried out to improve the simulation accord with published experimental data. Negligible impact of self-induced electric fields on K-α emission is found for conducting target materials at moderate laser intensities [lsim ]1017 W/cm2.
TL;DR: In this article, an analysis and simulations of fast particles produced by a high-intensity short laser pulse interacting with a foil target are performed. And the authors analyze the mechanism of ion acceleration in the foil plasma and the influence of the density gradient and other laser and plasma parameters on ion acceleration.
Abstract: Analysis and simulations of fast particles produced by a high-intensity short laser pulse interacting with a foil target are performed Initially, the plasma density distribution of the foil target has a smooth gradient with the scale length of plasma density varying across it The absorbed laser energy is transferred to fast electrons, which penetrate in the foil and are partially ejected from the foil rear These electrons produce an electric field that causes an ion beam to be emitted from the foil We analyze the mechanism of ion acceleration in the foil plasma and the influence of the density gradient and other laser and plasma parameters on ion acceleration The angular distributions of the ejected electrons and ions are calculated
TL;DR: In this paper, the effects of foam heterogeneity leads to increased shock velocity and reduced compressibility, and evidence of this effect is obtained using two-dimensional adaptive mesh refinement Eulerian numerical simulations.
Abstract: Foams are an important component of various inertial confinement fusion target schemes. The propagation of shock waves in foams is also an important issue for many other laser experiments (e.g., laboratory astrophysics experiments). The usual approach is to assume that the foam can be considered as a homogeneous mixture. Taking into account the effects of foam heterogeneity leads to increased shock velocity and reduced compressibility. Evidence of this effect is obtained using two-dimensional adaptive mesh refinement Eulerian numerical simulations. Nonetheless, for the very low density foams filled with DT ice used in recent direct drive target designs, the homogeneous mixture model provides adequate shock timing, density, and pressure profiles.
TL;DR: In this paper, a plan to simulate the whole of fast ignition self-consistently with four individual codes is presented, and four codes are integrated into one big system in the Fast Ignition Integrated Interconnecting code project.
Abstract: Relativistic laser–plasma interaction, subsequent superhot electron transport, superhot electron energy deposition, and the overall implosion process are key subjects for fast ignition. All these phenomena couple with each other, and more studies by simulations are essential. We have a plan to simulate the whole of fast ignition self-consistently with four individual codes. Four codes are integrated into one big system in the Fast Ignition Integrated Interconnecting code project. In a first stage of this project, we integrate the Arbitrary Lagrangian Eulerian (ALE) hydro code with the collective particle in cell (PIC) code. The PIC code obtains density profile at maximum compression from the ALE hydro code to introduce imploded plasma into a PIC system, and we can simulate interaction between ignition laser and realistic plasma. We have evaluated reflected laser spectrum and electron energy distribution, and found many differences between the realistic plasma profile and the conventional one in PIC simulations.
TL;DR: In this article, the authors presented some experimental results on X-ray spectra obtained from plasmas produced using a compact Nd:YAG laser system and both high resolution and low resolution X-rayspectra were recorded.
Abstract: We present some experimental results on X-ray spectra obtained from plasmas produced using a compact Nd:YAG lasersystem. The beam was focused on different targets~Cu,Al,Ge,...!and both high resolution and low resolution X-rayspectra were recorded.Keywords: ps laser; X-ray plasma sources; X-ray spectroscopy 1. INTRODUCTIONLaser-plasma sources are very powerful laboratory-scaleX-raydeviceswherewavelengthtunabilityisfeasiblebecauseof the comparatively free choice of target material, laserwavelength, and intensity. They have already been success-fully applied for radiobiology ~Turcu et al., 1994a; Masiniet al., 1999; Milani et al., 1999; Bortolotto et al., 2000!,X-ray microscopy~Batani et al., 2000, 2002; Desai et al.2003;Polettietal.,2004!,micro-lithography~Bijkerketal.,1992; Turcu et al., 1994b!. For all these applications theknowledgeofX-rayspectraisveryimportant,eitherdirectlyorbecauseenergydepositionandradiationdosearestronglyenergy dependent.For instance in micro-lithography;1-keVX-ray photonsare required to achieve efficient radiation transfer throughthe X-ray mask membrane and sufficient energy depositiononto the resist coated Si wafer.In radiobiology, laser-plasma X-ray sources were used toirradiate biological specimens: V-79 Chinese hamster cells~Turcu et al., 1994a!, and study DNA damage, DNA repairand repair inhibition, or Saccharomices Cerevisiae yeastcells ~Masini et al., 1999; Milani et al., 1999! and studymetabolic damages. In the first case, X-rays at hn’1.2 keVwere produced using L-shell emission from Cu targets,which could guaranty penetration of X-rays to the cellnucleus, so that absorbed dose was really related to DNAdamage. In the second case, it was essential to produce lowenergy X-ray photons, which would mainly deposit the doseatthecellwall,inordertoproducedamagesatthemetaboliclevel without touching the cell nucleus.Finally in X-ray microscopy, the spectrum is importantbecause only X-rays in the “water window” ~between 22and 44 A ! will contribute to the formation of a clean image,being absorbed by biological material but not by water. Thepresence of other X-ray lines will diminish the image con-trast dramatically.Besides all this, the study of X-ray spectra from plasmasis very important in itself and it is a well developed field inphysics. Indeed on one side, X-ray spectra are very impor-tant for atomic physics because by recording X-ray emis-sion lines, it is possible to access the energy levels in atomsand in multi-charged ions~Rosmej et al., 1997; Stepanovet al., 1997; Vergunova et al., 1997; Biemont et al., 2000!.On the other side, X-ray spectroscopy is a key technique inplasma diagnostics ~Koenig et al., 1997; Magunov et al.,1998; Batani et al., 1999! since from measurements ofX-ray spectra we can calculate the plasma parameters: elec-tron density, electron temperature, ion charges, and evendeduce important information on plasma opacities and onthe exact shape of the electron distribution function~includ-ing the presence of fast electrons!A key problem for applications and for X-ray spectros-copy, would be the development of very compact X-raysources which would be cheap ~and be reproduced in many
TL;DR: In this paper, the authors present simulations taking into account two different mechanisms generating the gain: (1) photoionization with subsequent three-body recombination, which takes advantage of the monochromaticity of the pump radiation to generate very cold electrons; (2) inner-shell ionization in which transient inversion is obtained by generating a hole in an otherwise completely filled shell.
Abstract: Within the next few years X-ray free-electron lasers (XFELs) now under construction are expected to generate highly collimated XUV pulses with 1013 photons and a duration of 100 fs. Focusing this radiation to a spot some 10 μm in diameter generates intensities of up to 1016 W/cm2. Such pump intensities make feasible the investigation of photopumped XUV lasers using this radiation. We present simulations taking into account two different mechanisms generating the gain: (1) photoionization with subsequent three-body recombination, which takes advantage of the monochromaticity of the pump radiation to generate very cold electrons; (2) inner-shell ionization in which transient inversion is obtained by generating a hole in an otherwise completely filled shell. The simulations show that under appropriate conditions both mechanisms generate very high gain. However, a number of further issues must be considered, such as the propagation of the pump pulse in the medium to be pumped.
TL;DR: In this paper, the results of 25D PIC simulations, showing the production of an electron bunch with reduced energy spread, are reported also, a possible method to produce the required plasma density transition by laser explosion of a suitable couple of thin foils is discussed.
Abstract: Laser Wake Field Acceleration of relativistic electron bunches is a promising method to produce a large amount of energetic particles with table top equipment One of the possible methods to inject particles in the appropriate acceleration phase of the wake behind the pulse takes advantage of the partial longitudinal breaking of the wake crests across a density downramp In this paper results of 25D PIC simulations, showing the production of an electron bunch with reduced energy spread, are reported Also, a possible method to produce the required plasma density transition by laser explosion of a suitable couple of thin foils is discussed
TL;DR: In this paper, the collective absorption of intense laser pulses by atomic clusters is studied by PIC simulations, and the absorbed energy per electron reaches a maximum of about Wmax = mωp2D2 (ωp: plasma frequency, m: electron mass), where ionization saturates.
Abstract: Collective absorption of intense laser pulses by atomic clusters is studied by PIC simulations. The cluster is modeled in two-dimensional calculations as a cylindrical plasma column with a diameter of D = 6.4 nm and an initial electron density of ne0 = 1023 cm−3. The frequency and intensity dependence of absorption is discussed. It is found that nonresonant absorption by electron emission increases as a power law with the laser intensity. The absorbed energy per electron reaches a maximum of about Wmax = mωp2D2 (ωp: plasma frequency, m: electron mass) at the intensity where ionization saturates.