The achievement of ignition from an Inertial Confinement Fusion capsule will require a detailed understanding of a wide range of high energy density phenomena. This paper presents some recent work aimed at improving our knowledge of the strength and equation of state characteristics of low-Z materials, and outlines data which will provide quantitative benchmarks against which our predictive radiation hydrodynamics capabilities can be tested. Improvements to our understanding in these areas are required if reproducible and predictable fusion energy production is to be achieved on the next generation of laser facilities.

In particular, the HELEN laser at AWE has been used to create a thermal X-ray source with 140 eV peak radiation temperature and 3% instantaneous flux uniformity to allow measurements of the Equation of State of materials at pressures up to 20 Mbar to an accuracy of <±2% in shock velocity. The same laser has been used to investigate the onset of spallation upon the release of a strong shock at a metal-vacuum boundary, with dynamic radiography used to image the spalled material in flight for the first time. Finally, a range of experiments have been performed to generate quantitative radiation hydrodynamics data on the evolution of gross target defects, driven in both planar and imploding geometry. X-ray radiography was used to record the evolving target deformation in a system where the X-ray drive and unperturbed target response were sufficiently characterized to permit meaningful analysis. The results have been compared to preshot predictions made using a wide variety of fluid codes, highlighting substantial differences between the various approaches, and indicating significant discrepancies with the experimental reality. The techniques developed to allow quantitative comparisons are allowing the causes of the discrepancies to be identified, and are guiding the development of new simulation techniques.

Stark broadening of Lyman lines in high density plasmas is treated theoretically to study the effects of the fields inside the plasmas, the microfield, and the oscillating fields from Langmuir waves. Resonance features are expected to be observed from the line profiles, especially about the microfield.

The properties of heavy-ion induced fusion targets with two-sided illumination and with the converters placed completely inside the Hohlraum have been investigated using integrated simulations based on the SATURN and MIMOZA code packages in order to check the results obtained with the view-factor method in previous work, which is briefly reviewed. Separate converter simulations show the importance of an accurate treatment of radiation transport but also demonstrate that a converter efficiency of 40–80% can be achieved easily depending on the detailed converter material and geometry. For the complete target, a gas fill is shown to be necessary, and it turned out to be very important to allow some of the radiation shields to become partially transparent during the evolution. In the most favorable case, an asymmetry in the temperature on the capsule of about 5% was achieved, leading to a reduction of the neutron yield by a factor of 7 compared to an ideally symmetric situation.

A review of structural materials choices under irradiation in fusion environments is presented. Results on the neutron source term and the intensities in the structural materials as a function of pulse time, energy, and protection is given. The role of multiscale modeling for understanding the basic physics in irradiated materials is explained, and simulations of metals under pulse irradiation and SiC are reported.

A paraxial ray formalism is developed to study the evolution of an on axis intensity spike on a Gaussian laser beam in a plasma dominated by relativistic and ponderomotive non-linearities. Ion motion is taken to be frozen. A single beam width parameter characterizes the evolution of the spike. The spike introduces two competing influences: diffraction divergence and self-convergence. The former grows with the reduction in spot size of the spike, while the latter depends on the gradient in non-linear permittivity. Parameter δ = (ωpr00/c) a00/(3.5 r00/r01) characterizes the relative importance of the two, where r01 and r00 are the spike and main beam radii, ωp is the plasma frequency, and a00 is the normalized laser amplitude. For δ > 1, the intensity ripple causes faster self-focusing of the beam; higher the ripple amplitude stronger the focusing. In the opposite limit, diffraction divergence increases more rapidly, slowing down the self-focusing of the beam. As the beam intensity rises due to self-focusing, it causes stronger generation of the third harmonic.

We have analyzed the effects of the wiggler error due to the electron beam's emittance, energy spreads, and higher-order modes in a free-electron laser (FEL) oscillator by using two electron beams of different energies based on the proposed FEL facility which is operated at a far-infrared and infrared regions. The three-dimensional (3D) effects in a FEL oscillator due to the wiggler error were calculated and an evaluation of the effect of the beam's emittance and energy spread was performed for the case of the coupled two-beam oscillator for phase shift errors and wiggler errors. The mode construction was studied on the higher-order modes of the wiggler for the various wiggler error parameters for FEL performance which is required for the high-quality electron beam. The radiation intensity at the fundamental mode was calculated for the rms phase shake in wiggler errors with sinus type, constant type, and parabolic type in the two-beam oscillator system using the 3D calculations. The results are compared with those of the fundamental modes without wiggler errors.

On the average, intergalactic space contains a component of gas, dust, and plasma. The numerical density of this medium depends very strongly on what the actual distance is to objects of intermediate and high redshifts. The average density could be enormously higher than currently assumed. In addition, there is the problem of how the material outside the galaxies is distributed. X-ray emission observed in clouds exterior to galaxies as well as in diffuse backgrounds in clusters of galaxies also attest to the radiation of hot plasmas between galaxies. The sizes of these X-ray emitting regions scale with their distances.

An experiment on Al-Cu impedance-match targets, carried out at the Shenguang highpower laser facility, is described. The shock adiabat of Cu in the pressure region 0.4- 0.8 TPa, measured experimentally, is close to the extrapolated results of the data at lower pressure obtained with a high-explosive loading facility and also is in agreement with the data at high pressure measured in the underground nuclear test environment.

The present 28th ECLIM in Rome is a continuation of the series of conferences that started in Frascati, Italy in 1966. These conferences deal with the interdisciplinary subjects of laser interaction with matter, related not only to basic science but also to a wide range of applications. ECLIM is an independent scientific conference, free of any institutional or political influence, keeping science without boundaries.

Atomic processes in X-ray laser interaction plasmas are investigated by using a collisional-radiative model. Population inversions on free-bound transitions can be produced by photoionization above a threshold of incident X-ray laser intensity and lead to stimulated free-bound emission (SFBE). Free-bound lasers pumped by intense X-ray lasers are proposed and their feasibility is investigated simply considering X-ray laser interaction plasmas.

Electron dynamics in an axially localized large amplitude electron Bernstein mode in a magnetic mirror is studied. The mode is localized due to plasma density and magnetic field profiles and could be driven by an electron cyclotron wave, launched from outside, via linear mode conversion. Energetic electrons of finite gyro-radius resonantly interact with the mode and gain primarily transverse energy favoring stronger mirror confinement. At Bernstein wave normalized amplitude of A00 = 0.01 and for other normalized parameters Zn0 = 40, k⊥c/ω = 10, ${L}^{\prime}_m = 215$, ωc0/ω = 0.9, ψn0 = 3π/2, the electrons can gain energy in the hundreds of keV range.

We studied the behavior of porous carbon compressed by laser-generated shock waves. In particular, we developed a new design for targets, optimized for the investigation of carbon reflectivity at hundred-GPa pressures and eV/k temperatures. Specially designed “two-layer-two materials” targets, comprising porous carbon on transparent substrates, allowed the probing of carbon reflectivity and a quite accurate determination of the position in the P, T plane. This was achieved by the simultaneous measurement of shock breakout times, sample temperature (by optical pyrometry) and uid velocity. The experiments proved the new scheme is reliable and appropriate for reflectivity measurements of thermodynamical states lying out of the standard graphite or diamond hugoniot. An increase of reflectivity in carbon has been observed at 260 GPa and 14,000 K while no increase in reflectivity is found at 200 GPa and 20,000 K. We also discuss the role of numerical simulations in the optimization of target parameters and in clarifying shock dynamics.

Inertial confinement fusion (ICF) has made great progress. In fact several significant scientific firsts have been achieved in the last year. These developments have presented the ICF community with an opportunity to embark on a new phase in ICF research. The key issues of laser fusion are to attain a high absorption of laser light in a plasma, to prevent preheating of fuel during the compression, and to achieve highly efficient implosion by uniform compression of fuel due to the homogeneous deposition of laser energy on the pellet surface. Direct drive and indirect drive have been investigated. The progress in both schemes is remarkable. The neutron yield by the stagnation free compression of the LHART target has attained 1013 which corresponds to a pellet gain of 1/500. The plastic shell target has reached a fuel density as large as 600 times the liquid density which is measured by the Si activation method as well as the D knockon method. A cryogenic foam target is now under investigation.

We generate self-phase-stabilized pulses by difference-frequency generation of a hollow-fibre broadened supercontinuum followed by two-stage optical parametric amplification. This system allows the production of broadband pulses widely tuneable in the near-IR wavelength region. Energies up to 0.2 mJ with 15 fs pulse width are demonstrated. These characteristics make this source suitable as a driver for attosecond pulse generation.

This paper examines the reliability of a widely used method for temperature determination by multi-wavelength pyrometry. In recent warm dense matter experiments with ion-beam heated metal foils, we found that the statistical quality of the fit to the measured data is not necessarily a measure of the accuracy of the inferred temperature. We found a specific example where a second-best fit leads to a more realistic temperature value. The physics issue is the wavelength-dependent emissivity of the hot surface. We discuss improvements of the multi-frequency pyrometry technique, which will give a more reliable determination of the temperature from emission data.

The possibility of enhancement of molecular formation by strong electromagnetic fields is discussed. The electron screening of the laser is considered. Rate production of ddμ and dtμ molecules in the presence of a laser field is estimated as a function of the resonance detuning.

Effects of external static magnetic field (applied in $\hat y$-direction) on resonant excitation of surface plasma waves (SPW) have been investigated over the metal free space interface. The high power laser $({\rm \omega} _0,\;\vec k_{0z})$ is incident over the metal surface and exerts a ponderomotive force on the metal electrons in the skin layer. The ponderomotive force disturbs the quasi-neutrality of plasma which results into the excitation of space charge field at the frequency 2ω0. The electron density perturbation at frequency 2ω0 driven by self-consistent space charge potential couples with the oscillatory velocity due to the seed SPW $({\rm \omega}, \;\vec k_z)$ and produces nonlinear current to drive another counter propagating SPW $({\rm \omega} _1,\;\vec k_{1z})$ at the phase matching conditions of frequency ω = ω1 − 2ω0 and wavenumber $\vec k_z = \vec k_{1z} - 2\vec k{}_{0z}$ (by feedback mechanism). The parametric process becomes resonant at 2ω0 ≈ ωp and the maximum growth rate is achieved for an incidence angle of laser θ = 40°. The growth rate of the process reduces to half on increasing the magnetic field from 0.49 to 2.45 MG. The present study may be significant to the laser absorption experiments where surface rippling can strongly affect the laser energy absorption.

A s-polarized short-pulse laser impinged obliquely on an overdense plasma slab is shown to produce very significant second harmonic in the direction of specular reflection and transmission. The laser induces a non-linear current on electrons, which is curl free. However, with sharp plasma boundary, it gives rise to electromagnetic radiation at the second harmonic. Our formalism includes multiple reflections of the incident and second-harmonic waves from both the front and rear surfaces. The present work includes finiteness of the slab. The normalized second-harmonic amplitude acquires a sharp peak at some specific angle of incidence for a particular set of parameters dependent on thickness of the slab and plasma density.