A series of experiments recently carried out at the Rutherford Appleton Laboratory investigated various aspects of the laser–plasma interaction in the relativistic intensity regime. The propagation of laser pulses through preformed plasmas was studied at intensities exceeding 1019 W/cm2. The transmission of laser energy through long-scale underdense plasmas showed to be inefficient unless a plasma channel is preformed ahead of the main laser pulse. The study of the interaction with overdense plasmas yielded indication of collimated energy transport through the plasma. The production of fast particles during the interaction with solid density targets was also investigated. The measurements revealed the presence of a small-sized directional source of multi-megaelectron volt protons, which was not observed when a plasma was preformed at the back of the solid target. The properties of the source are promising in view of its use in radiographic imaging of dense matter, and preliminary tests were carried out.

The longitudinal dynamics of drift compression and pulse shaping for a space-charge-dominated heavy ion fusion beam is studied. A nonperiodic quadrupole lattice is designed for a beam undergoing drift compression, and an adiabatically matched solution is found for the transverse envelope equations in the nonperiodic lattice.

Based on realistic numerical simulations of the three-dimensional time-dependent Schrödinger equation describing a hydrogen atom interacting with a strong electromagnetic field, the influence of the magnetic component is studied. The same computational techniques can be applied to the case of strong field photoionization as well as to the case of ionization by an incident relativistic heavy ion. One of the main consequences, in the strong-laser-field case, is the presence of true even harmonics of the incoming field. In the heavy ion impact, the asymmetry of the wave function reveals the importance of the nondipole nature of the interaction.

By the interaction of intense (1010 particles/500 ns) relativistic (∼300 MeV/amu) heavy ion beams with solid targets, large volumes (several cubic millimeters) of strongly coupled plasmas are produced at solid-state densities and temperatures of up to 1 eV, with relevance for equation-of-state (EOS) studies of matter at high energy density and heavy ion-beam-driven inertial confinement fusion (ICF). The time and space profile of the ion beams, focused by the plasma lens to diameters of a minimum of 0.5 mm in order to obtain specific energy depositions of up to about 4 kJ/g, were measured to calculate the energy deposition in the target. In the present work, the plasmas created by ion beam interaction with cryogenic gas crystals and metallic targets are studied, among other methods, by backlighting shadowgraphy and electrical conductivity measurements. The experiments are coupled with two-dimensional hydrodynamic simulations.

Progress in heavy ion target design over the past few years has focused on relaxing the target requirements for the driver and for target fabrication. We have designed a plastic (CH) ablator capsule that is easier to fabricate and fill than the beryllium ablator we previously used. In addition, two-dimensional Rayleigh–Taylor instability calculations indicate that this capsule can tolerate ablator surface finishes up to 10 times rougher than the NIF specification. We have also explored the trade-off between surface roughness and yield as a method for finding the optimum capsule. We have also designed two new hohlraums: a “hybrid” target and a large-angle, distributed radiator target. The hybrid target allows a beam spot radius of almost 5 mm while giving gain of 55 from 6.7 MJ of beam energy in integrated Lasnex calculations. To achieve the required symmetry with the large beam spot, internal shields were used in the target to control the P2 and P4 asymmetry. The large-angle, distributed radiator target is a variation on the distributed radiator target that allows large beam entrance angles (up to 24°). Integrated calculations have produced 340 MJ from 6.2 MJ of beam energy in a design that is not quite optimal, In addition, we have done a simple scaling to understand the peak ion beam power required to compress fuel for fast ignition using a short pulse laser.

We have constructed an X-ray photoelectron microscopic system. An X-ray source is a laser-produced plasma in a scheme of an X-ray laser experiment. X rays involving amplified spontaneous emissions (ASE) at 15.47 nm were delivered with a 10-Hz repetition rate from a compact X-ray laser system. X rays were collected and focused by a Schwarzschild optics coated with Mo/Si multilayers for a 15.47-nm X ray. Photoelectron signals due to the Ga 3d and As 3d electrons were observed, when a GaAs wafer was used as a sample. The spatial resolution of about 1 μm was confirmed.

The numerical simulation of the driving beams in a heavy ion fusion power plant is a challenging task, and simulation of the power plant as a whole, or even of the driver, is not yet possible. Despite the rapid progress in computer power, past and anticipated, one must consider the use of the most advanced numerical techniques, if we are to reach our goal expeditiously. One of the difficulties of these simulations resides in the disparity of scales, in time and in space, which must be resolved. When these disparities are in distinctive zones of the simulation region, a method which has proven to be effective in other areas (e.g., fluid dynamics simulations) is the mesh refinement technique. We discuss the challenges posed by the implementation of this technique into plasma simulations (due to the presence of particles and electromagnetic waves). We present the prospects for and projected benefits of its application to heavy ion fusion, in particular to the simulation of the ion source and the final beam propagation in the chamber. A collaboration project is under way at Lawrence Berkeley National Laboratory between the Applied Numerical Algorithms Group (ANAG) and the Heavy Ion Fusion group to couple the adaptive mesh refinement library CHOMBO developed by the ANAG group to the particle-in-cell accelerator code WARP developed by the Heavy Ion Fusion–Virtual National Laboratory. We describe our progress and present our initial findings.

Recently, two novel techniques for the extraction of the phase-shift map (Tomassini et al. (2001). Applied Optics40, 35) and the electronic density map estimation (Tomassini P. & Giulietti A. (2001). Optics Communication199, 143–148) have been proposed. In this article, we apply both methods to a sample laser–plasma interferogram obtained with femtoseconds probe pulse, in an experimental setup devoted to laser particle acceleration studies.

The Heavy Ion Fusion Virtual National Laboratory High Current Experiment (HCX) is exploring transport issues such as dynamic aperture, effects of quadrupole rotation, and the effects on the beam of nonideal distribution function, mismatch, and electrons, using one driver-scale 0.2 μC/m, 2–10 μs coasting K+ beam. Two- and three-dimensional simulations are being done, using the particle-in-cell code WARP to study these phenomena. We present results which predict that the dynamic aperture in the electrostatic focusing transport section will be set by particle loss.

The absolutely calibrated K-shell spectra emitted from short-living aluminum plasmas at laser intensities of 5 × 1015–4 × 1018 W/cm2 are reported. The experiments performed with the constant energy, variable-length laser pulses (1.5 ps–1 ns) are modeled by the one-dimensional (1D) hydrodynamics code, including nonlinear resonance absorption of the laser radiation, fast electron acceleration, and energy transfer into the target. The characteristic features of the measured and the postprocessed spectra are outlined. The spatial and temporal profiles of the emitted spectra are presented; the scaling rules for the conversion efficiency of the laser radiation into the line X-ray emission are discussed.

Recent experiments undertaken at the Rutherford Appleton Laboratory to produce X-ray lasing over the 5–30 nm wavelength range are reviewed. The efficiency of lasing is optimized when the main pumping pulse interacts with a preformed plasma. Experiments using double 75-ps pulses and picosecond pulses superimposed on 300-ps background pulses are described. The use of travelling wave pumping with the approximately picosecond pulse experiments is necessary as the gain duration becomes comparable to the time for the X-ray laser pulse to propagate along the target length. Results from a model taking account of laser saturation and deviations from the speed of light c of the travelling wave and X-ray laser group velocity are presented. We show that X-ray laser pulses as short as 2–3 ps can be produced with optical pumping pulses of ≈1-ps.

A possibility is analyzed to use direct drive cylindrical targets in the fast ignition mode irradiated by beams of nearly relativistic heavy ions with long ranges in matter. The minimum beam energy required to compress the DT fuel in a 1-cm-long target to (ρR)DT = 0.5 g/cm2, ρDT = 100 g/cm3 is found to lie in the range 10–15 MJ. Ignition and axial burn propagation is achieved with a 0.2-ns, 0.4-MJ pulse of 100-GeV heavy ions. Thermonuclear energy gains in the range 50–150 appear to be possible.

We report soft X-ray spectra (4–18 nm) produced by the interaction of 25–100-fs laser pulses at an intensity of up to 7 × 1016 W/cm2 with a cryogenically cooled Ar gas jet. New spectral lines from Ar8+, Ar9+, and Ar10+ charge states appeared with decreasing preexpansion gas temperature. A nonlinear increase of X-ray line emission from Ar7+, Ar8+, and Ar9+ was observed with cooling, which saturated below a certain temperature. The drastic change in the spectrum is attributed to efficient collisional heating and collisional ionization of growing, small- to medium-sized (102–103 atoms) Ar clusters from the cooled jet. When the laser pulse was extended from 25 to 100 fs we observed considerably stronger emission on lines from high charge states, such as Ar8+, Ar9+, and Ar10+, which suggests that the resonance absorption condition could be reached for the 100-fs pulse.

We propose a new approach to the calculation of ion populations in the LTE dense plasmas in the superconfiguration approximation. The screening of plasma ions is obtained using the same free-electron chemical potential for each ion charge. This chemical potential is determined by iteration keeping the total density constant and varying the volume of each ion. In such a way our approach not only gives the charge neutrality of the plasma, but also assures that the free-electron density is equal in the vicinity of each ion. The resulting ion charge distribution is different with respect to the one obtained without imposing the constraint of equal chemical potential. For instance, the effective charge is a little bit higher, which can change the shape of the absorption spectra, especially at higher densities. Examples of absorption spectra of medium-Z plasmas in a temperature and density range close to the present opacity measurements are shown.

Between the accelerator and fusion chamber, the heavy ion beams are subject to a dramatic but vital series of manipulations, some of which are carried out simultaneously and involve large space charge forces. The beams' quality must be maintained at a level sufficient for the fusion application; this general requirement significantly impacts beam line design, especially in the considerations of momentum dispersion. Immediately prior to final focus onto a fusion target, heavy ion driver beams are compressed in length by typically an order of magnitude. This process is simultaneous with bending through large angles to achieve the required target illumination configuration. The large increase in beam current is accommodated by a combination of decreased lattice period, increased beam radius, and increased strength of the beamline quadrupoles. However, the large head-to-tail momentum tilt (up to 5%) needed to compress the pulse results in a very significant dispersion of the pulse centroid from the design axis. General design features are discussed. A principal design goal is to minimize the magnitude of the dispersion while maintaining approximate first order achromaticity through the complete compression/bend system. Configurations of bends and quadrupoles, which achieve this goal while simultaneously maintaining a locally matched beam-envelope, are analyzed.

The so-called fast ignition mode is one way to ignite the thermonuclear fuel in systems of inertial fusion and decrease of the necessary energy of the driver. In the present work the second stage of the process—the heating, the thermonuclear burning initiation under the influence of a powerful ion pulse, and distribution of the burning all over the rest of the cylindrical system—is studied. The main purpose of the presented calculations was to determine the threshold of the fast ignition of the cylindrical DT cord by a heavy ion beam.

The characteristics of a fast ignition heavy ion fusion (FIHIF) power plant are preliminarily evaluated. The reactor chamber consists of two sections: The upper smaller part is the microexplosion section proper; the lower bigger part is the condensation section, in which sprayed jets of coolant are injected. The first surface of the blanket is of generally accepted wetted porous design. The coolant is lithium-lead eutectic with an initial surface temperature of 820 K. The mass of the evaporated coolant just after the explosion is evaluated as 4 kg. Computation of neutronics results in blanket energy deposition with maximum density of the order of 108 J/m3 at the first wall. The heat conversion system consisting of three coolant loops provides a net efficiency of the FIHIF power plant of 0.37.

Plasmas irradiated by an intense laser beam have recently been demonstrated to be sources for particles (electrons, ions, positrons). During this interaction, it has been found that these charged particles can be efficiently accelerated. An overview of these results as well as some perspectives are presented here.

This article extends previous numerical studies of the stability properties of intense nonneutral charged particle beams with large temperature anisotropy (T⊥b >> T∥b) to allow for nonaxisymmetric perturbations with ∂/∂θ ≠ 0. The most unstable modes are identified, and their eigenfrequencies, radial mode structure, and nonlinear dynamics are determined.

The generation of coherent soft X rays is studied using a terawatt picosecond Nd:glass laser system. Two different methods are investigated as candidates for efficient generation of such radiation, namely, longitudinally pumped transient collisional excitation nickel-like molybdenum X-ray laser, and high-harmonic generation from solid–vacuum interfaces. In the course of experiments on longitudinally pumped X-ray lasers, unexpected jetlike structures are observed in the visible emission of the molybdenum plasma, extending over a length of several millimeters. An interesting characteristic of this phenomena is that clear jets are observed only for longitudinal pump intensities between 5 × 1014 and 7 × 1014 W/cm2. The effects of a finite scale length density gradient on surface harmonics is also investigated. The efficiency of harmonic generation from near-solid density plasma is found to increase by a factor of 2 to 3 when using prepulses. The scale length of the preplasma is simulated using a one-dimensional hydrodynamic code, and the increase in efficiency is verified to be in accordance with particle-in-cell simulation results.