Using a combination of laser–plasma interactions and magnetic confinement configurations, a conceptual fusion reactor is proposed in this paper. Our reactor consists of the following: (1) A background plasma of boron11 and hydrogen ions, plus electrons, is generated and kept for a certain time, with densities of the order of a mg/cm3 and temperatures of tens of eV. Both the radiation level and the plasma thermal pressure are thus very low. (2) A plasma channel is induced in a solid target by irradiation with a high power laser that creates a very intense shock wave. This mechanism conveys the acceleration of protons in the laser direction. The mechanisms must be tuned for the protons to reach a kinetic energy of 300–1200 keV where the pB11 fusion cross section is significantly large (note that this value is not a temperature). (3) Those ultra-fast protons enter the background plasma and collide with boron11 to produce three alphas. Fusion born alphas collide with protons of the plasma and accelerate them causing a chain reaction. (4) A combination of an induction current and a magnetic bottle keeps the chain reaction process going on, for a pulse long enough to get a high energy gain. (5) Materials for the background plasma and the laser target must be replaced for starting a new chain reaction cycle.

The formation of a collisional shock wave by the light pressure of a short-laser pulse at intensities in the range of 1018–1023 W/cm2 is considered. In this regime the thermodynamic parameters of the equilibrium states, before and after the shock transition, are related to the relativistic Rankine–Hugoniot equations. The electron and ion temperatures associated with these shock waves are calculated. It is shown that if the time scale of energy dissipation is shorter than the laser pulse duration a collisional shock is formed. The electrons and the ions in the shock-heated layer may have equal or different temperatures, depending on the laser pulse duration, the material density and the laser intensity. This shock wave may serve as a heating mechanism in a fast ignition scheme.

After achieving significant research results on laser-driven boron fusion, the essential facts are presented how the classical very low-energy gains of the initially known thermal ignition conditions for fusion of hydrogen (H) with the boron isotope 11 (HB11 fusion) were bridged by nine orders of magnitudes in agreement with experiments. This is possible under extreme non-thermal equilibrium conditions for ignition by >10 PW-ps laser pulses of extreme power and nonlinear conditions. This low-temperature clean and low-cost fusion energy generation is in crucial contrast to local thermal equilibrium conditions with the advantage to avoid the difficulties of the usual problems with extremely high temperatures.

This paper considers the heating of a target in a shock wave created in a planar geometry by the ponderomotive force induced by a short laser pulse with intensity higher than 1018 W/cm2. The shock parameters were calculated using the relativistic Rankine–Hugoniot equations coupled to a laser piston model. The temperatures of the electrons and the ions were calculated as a function of time by using the energy conservation separately for ions and electrons. These equations are supplemented by the ideal gas equations of state (with one or three degrees of freedom) separately for ions and electrons. The efficiency of the transition of the work done by the laser piston into internal thermal energy is calculated in the context of the Hugoniot equations by taking into account the binary collisions during the shock wave formation from the target initial condition to the compressed domain. It is shown that for each laser intensity there is threshold pulse duration for the formation of a shock wave. The explicit calculations are done for an aluminum target.

Exceptionally high reaction gains of hydrogen protons measured with the boron isotope 11 are compared with other fusion reactions. This is leading to the conclusion that secondary avalanche reactions are happening and confirming the results of high-gain, neutron-free, clean, safe, low-cost, and long-term available energy. The essential basis is the unusual non-thermal block-ignition scheme with picosecond laser pulses of extremely high powers above the petawatt range.

A criterion for a two temperature plasma nuclear fusion ignition is derived by using a common model. In particular, deuterium-tritium (DT) and proton–boron11 (pB11) are considered for pre-compressed plasma. The ignition criterion is described by a surface in the three-dimensional space defined by the electron and ion temperatures Te, Ti, and the plasma density times the hot spot dimension, ρ·R. The appropriate fusion ion temperatures Ti are larger than 10 keV for DT and 150 keV for pB11. The required value of ρ·R for pB11 ignition is larger by a factor of 50 or more than for DT, depending on the electron temperature. Furthermore, our ignition criterion obtained here for pB11 fusion is practically impossible for equal electron and ion temperatures. In this paper it is suggested to use a two temperature laser induced shock wave in the intermediate domain between relativistic and non-relativistic shock waves. The laser parameters required for fast ignition are calculated. In particular, we find that for DT case one needs a 3 kJ/1 ps laser to ignite a pre-compressed target at about 600 g/cm3. For pB11 ignition it is necessary to use more than three orders of magnitude of laser energy for the same laser pulse duration.

In this paper we consider laser intensities greater than $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}10^{16}\ \mathrm{W\ cm}^{-2}$ where the ablation pressure is negligible in comparison with the radiation pressure. The radiation pressure is caused by the ponderomotive force acting mainly on the electrons that are separated from the ions to create a double layer (DL). This DL is accelerated into the target, like a piston that pushes the matter in such a way that a shock wave is created. Here we discuss two novel ideas. Firstly, the transition domain between the relativistic and non-relativistic laser-induced shock waves. Our solution is based on relativistic hydrodynamics also for the above transition domain. The relativistic shock wave parameters, such as compression, pressure, shock wave and particle flow velocities, sound velocity and rarefaction wave velocity in the compressed target, and temperature are calculated. Secondly, we would like to use this transition domain for shock-wave-induced ultrafast ignition of a pre-compressed target. The laser parameters for these purposes are calculated and the main advantages of this scheme are described. If this scheme is successful a new source of energy in large quantities may become feasible.

This paper analyzes the one dimensional shock wave created in a planar target by the ponderomotive force induced by very high laser irradiance. The laser-induced relativistic shock wave parameters, such as compression, pressure, shock wave and particle flow velocities, sound velocity and temperature are calculated here for the first time in the context of relativistic hydrodynamics. For solid targets and laser irradiance of about 2 × 1024 W/cm2, the shock wave velocity is larger than 50% of the speed of light, the shock wave compression is larger than 4 (usually of the order of 10) and the targets have a pressure of the order of 1015 atmospheres. The estimated temperature can be larger than 1 MeV in energy units and therefore very excited physics (like electron positron formation) is expected in the shocked area. Although the next generation of lasers might allow obtaining relativistic shock waves in the laboratory this possibility is suggested in this paper for the first time.

It is shown that it is possible to accelerate micro-foils to velocities from 108 cm/s up to relativistic velocities without the disturbance of the Rayleigh-Taylor instability. The acceleration occurs due to the radiation pressure of proper high power lasers. In these systems, the ablation force is negligible relative to the ponderomotive force that dominates the acceleration. The laser irradiances of 1017 W/cm2 < IL < 1021 W/cm2 with a pulse duration of the order of 10 picoseconds can accelerate a micro-foil by the laser radiation pressure to velocities as high as 109 cm/s before breaking by Rayleigh Taylor (RT) instability. Similarly, laser irradiances of IL > 1021 W/cm2 with pulse duration of the order of 10 femtoseconds can accelerate a micro-foil to relativistic velocities without RT breaking. Due to the nature of the accelerating ponderomotive force, in both the relativistic and non-relativistic cases, the structure of the accelerated target contains a double layer (DL) at the interface of the laser-target interaction. The DL acts as a piston during the acceleration process. The influence of the DL surface tension on the RT instability is also analyzed in this paper.

An accelerated micro-foil is used to ignite a pre-compressed cylindrical shell containing deuterium–tritium fuel. The well-known shock wave ignition criterion and a novel criterion based on heat wave ignition are developed in this work. It is shown that for heat ignition very high impact velocities are required. It is suggested that a multi-petawatt laser can accelerate a micro-foil to relativistic velocities in a very short time duration (˜picosecond) of the laser pulse. The cylindrical geometry suggested here for the fast ignition approach has the advantage of geometrically separating the nanosecond lasers that compress the target from the picosecond laser that accelerates the foil. The present model suggests that nuclear fusion by micro-foil impact ignition could be attained with currently existing technology.

Due to the recent developments in high power lasers in the multi-petawatt domain it seems now feasible to accelerate a micro-foil to relativistic velocities. In this paper, we calculate analytically the high velocities achieved by the ponderomotive force of the irradiating laser. The accelerated foil collides with a second foil resulting in the creation of the relativistic shock waves. The density, pressure, temperature, and shock wave velocities are calculated within the context of relativistic fluid dynamics. The calculated thermodynamic parameters that are achieved in these collisions are enormous.

In this work, it is suggested that the ponderomotive force, induced by a multi-petawatt laser on the interface of a vacuum with solid target, can accelerate a micro-foil to relativistic velocities. The extremely high velocities of the micro-foil can be achieved due to the very short time duration (about a picosecond) of the laser pulse. This accelerated micro-foil is used to ignite a pre-compressed cylindrical shell containing the deuterium tritium fuel. The fast ignition is induced by a heat wave produced during the collision of the accelerated foil with the pre-compressed target. This approach has the advantage of separating geometrically the nanoseconds lasers that compress the target with the picosecond laser that accelerates the foil.

The shock waves in laser plasma interaction have played an important role in the study of inertial fusion energy (IFE) since the 1970's and perhaps earlier. The interaction of laser, or any other high power beam, induced shock waves with matter was one of the foundations of the target design in IFE. Even the importance of shock wave collision was studied and its importance forgotten. In due course, the shock waves were taken as granted and became “second fiddle” in IFE scenario. The analysis of the shock wave in the context of IFE is revived in this paper. At the forefront of the past decade the concept of fast ignition was introduced. The different ideas of fast ignition are summarized with special emphasis on shock wave fast ignition. The ignition is achieved by launching a shock wave during the final stages of the implosion. In this paper, a possible instability in the propagation of the igniting shock wave is analyzed. The idea of combining the fast ignition fusion with an impact shock wave is suggested and analyzed. This is achieved by launching a shock wave by an accelerated foil during the final stage of the implosion in order to ignite the compressed fuel. In this scheme, like other fast ignition schemes, a significant reduction of the driver energy in comparison with standard IFE scenarios is required for the same high gain fusion.

We study the details of a gradual change in electron properties from those of a nearly-free-electron (NFE) metal to those of a strongly-coupled plasma, in ultrashort pulse energy deposition in solid metal targets. Time scales shorter than those of a target surface layer expansion are considered. Both the case of an optical laser (visible or near infrared wavelengths range) and of a free electron laser (vacuum ultraviolet or X-ray) are treated. The mechanisms responsible for the change in electron behavior are isochoric melting, lattice charge disordering, and electron mean free path reduction. We find that the transition from metal to plasma usually occurs via an intermediate stage of a charge-disordered solid (solid plasma), in which ions are at their lattice sites but the ionization stages of individual ions differ due to ionization from localized bound states. Charge disordered state formation is very rapid (typically, few femtoseconds or few tens of femtoseconds). Pathway to charge-disordered state differs in simple metals and in noble metals. Probabilities are derived for electron impact ionization and 3-body recombination of a bound ionic state in solid-density medium, applicable both in metal and in plasma regime. An evolution of energy coupling between electron and ion subsystems, from metallic electron-phonon (e-ph) to plasma electron-ion (e-i) coupling, is considered. Substantial increase in coupling parameter is expected as a result of charge disorder.

Very high plasma densities can be obtained at the end of the implosion phase in inertial fusion targets, particularly in the so-called fast-ignition scheme (Tabak et al., 1994; Mulser & Bauer, 2004), where a central hot spark is not needed at all. By properly tailoring the fuel compression stage, degenerate states can be reached (Azechi et al., 1991; Nakai et al., 1991; McCory, 1998). In that case, most of the relevant energy transfer mechanisms involving electrons are affected (Honrubia & Tikhonchuk, 2004; Bibi & Matte, 2004; Bibi et al., 2004). For instance, bremsstrahlung emission is highly suppressed (Eliezer et al., 2003). In fact, a low ignition-temperature regime appears at very high plasma densities, due to radiation leakage reduction (León et al., 2001). Stopping power and ion-electron coulomb collisions are also changed in this case, which are important mechanisms to trigger ignition by the incoming fast jet, and to launch the fusion wave from the igniting region into the colder, degenerate plasma. All these points are reviewed in this paper. Although degenerate states would not be easy to obtain by target implosion, they present a very interesting upper limit that deserves more attention in order to complete the understanding on the different domains for inertial confinement fusion.

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.

Bremsstrahlung is one of the most important energy loss mechanisms in achieving ignition, which is only possible above a threshold in temperature for a given fusion reaction and plasma conditions. A detailed analysis of the bremsstrahlung process in degenerate plasma points out that radiation energy loss is much smaller than the value given by the classical formulation. This fact seems not useful to relax ignition requirements in self-ignited targets, because it is only relevant at extremely high densities. On the contrary, it can be very positive in the fast ignition scheme, where the target is compressed to very high densities at a minimum temperature, before the igniting beamlet is sent in.

The approach to the ultimate strength of metals is determined experimentally. The strength of the materials and the strain rate were determined from the free surface velocity time history, which was measured with an optically recording velocity interferometer system. The dynamic strength was measured at strain rates in the domain of 5·106 to 5·108 s−1. The necessary tension to break the metal (spall) and the very high strain rates were achieved using high-powered lasers in nanosecond and picosecond regimes. The measurements at strain rates larger than 108 s−1 were achieved for the first time. The ultimate strength of metals was calculated using a realistic wide-range equation of state. Our experiments indicate that under very fast tension processes, the dynamic strength of materials is determined not by the macroscopic defects but by atomic quantum mechanical processes described by the equation of state of the material. The rate of the process is described by the strain rate, and at strain rates higher than 5·107 s−1, the atomic forces are dominating the dynamic strength of materials.

A high-irradiance short pulsed laser was used to generate hemispherical shock waves in planar targets. A linear relationship was obtained between the laser energy for threshold spall conditions (EL) and the cubic target thickness (d): EL = 45.3d3 + 4.9, where EL is in J and d is in mm. It is found that the laser-induced ablation pressure decays with the distance to a power slightly greater than 2.