A compact high-power ultra-wideband bipolar pulse generator based on a modified Marx circuit is designed, which is mainly composed of a primary power supply, Marx generator, sharpening and cutoff subnanosecond spark gap switches, and coaxial transmission lines. The Marx generator with modified circuit structure has thirty-two stages and is composed of eight disk-like modules. Each module consists of four capacitors, two spark gap switches, four charging inductors, and a mechanical support. To simplify the design of the charging structure and reduce the number of switches, four groups of inductors are used to charge the capacitors of the Marx generator, two of which are used for positive voltage charging and the other two for negative voltage charging. When the capacitor of each stage is charged to 35 kV, the maximum output peak voltage can reach 1 MV when the Marx generator is open circuit. The high-voltage pulse generated by the Marx generator charges the transmission line and forms a bipolar pulse through sharpening and cutoff switches. All transmission lines used for bipolar pulse generation have an impedance of 10 Ω. When the 950 kV pulse voltage generated by the Marx generator is fed into the transmission line, the bipolar pulse peak voltage can reach 390 kV, the center frequency of the pulse is about 400 MHz, and the output peak power is about 15.2 GW.

The topic of proton-boron fusion has recently attracted considerable interest in the scientific community, both for its future perspectives for energy production and for nearer-term possibilities to realize high-brightness α-particle sources. Very interesting experimental results have been obtained, in particular in laser-driven experiments but also using other experimental approaches. The goal of this special issue is to collect the most recent developments in experiments, theory, advanced targetry, diagnostics, and numerical simulation codes.

The stopping power of dense nonideal plasmas is calculated in different approximations. The T-matrix approximation for binary collisions is compared with the random phase approximation (RPA) approximation for dielectric fluctuations. Within a microscopic model, the dynamical evolution of the velocity of the projectile is calculated. It reproduces well experimental values for the stopping of fast heavy ions. Further improvements due to correlations are discussed. Both concepts, cluster decomposition and memory, are compared and it is found that they lead to the same quantum virial corrections of the Beth-Uhlenbeck type in equilibrium. However, memory in the kinetic equation causes an additional renormalization of the effective energy transfer in nonequilibrium.

Since the beginning of the 1960s and up to the present time, laser ablation from metal surfaces under the action of short light pulses has been the topic of many researches. One of the first objects in the early ablation experiments presented thin metal films evaporated by radiation, which were used in lasers with nanosecond pulses as optical gates for Q-switching in resonators or for decoupling in amplifiers. Bleaching of the gates based on metal layers with a time constant τt ≈ 10−8 s observed in a number of experiments, was usually considered as a result of a simple evaporation of matter. We analyze the data of the experiments with a mylar tape [≈0.05 µm aluminum (Al) layer on ≈20 µm lavsan substrate] used as a gate for optical isolation in one of the first Nd: glass laser facilities with a power of ≈1 GW. That gate was irradiated by pulses of Q-switched oscillators: pulse duration 10−7–10−8 s, intensity 107–108 W/cm2. A jump in the transmittance of the expanding Al layer was registered (from ≈0.1 to 50% at τt ≈ 10−9 s). The present study shows that one should consider the metal–insulator phase transition in a superheated liquid metal layer as the mechanism of the fast (up to 10–10–10–11 s) increase in the transmittance of the Al film gate at nanosecond-pulsed laser ablation.

The contribution of different sorts of secondary particles to the preheating of thermonuclear targets driven by heavy-ion beams is analyzed. Two types of illumination geometry are considered: side-on and face-on locations of the fuel with respect to the ion beam. It is shown that a substantial preheating can be expected from (1) nuclear fission fragments for the face-on fuel position and (2) δ-electrons and low-Z nuclear fragments for the side-on fuel location. All the X-ray and gamma photons of various origin are shown to produce a negligible fuel heating.

The main objective of this work is to find analytical formulas for the oscillator strength f of hydrogen-like ions. It is well known that f is proportional to the energy of the transitions between eigenstates (ΔE), and to the square of the R matrix. Therefore, the problem of calculating f can be reduced to finding analytical expressions for both parameters, ΔE and R. Hence these expressions would be in accordance with quantum results based on more sophisticated calculations.

Recent direct drive implosion experiments, performed on the OMEGA laser, have been analyzed by comparing full two-dimensional (2D) and one-dimensional (1D) numerical simulations. The 2D simulations result in a fusion yield higher than experimental results. A simple full-mixing model, leaving only the clean region, overestimates yield degradation. Fully turbulent mixing is expected to develop in most of the mixing region; however regions slightly beyond the radius of the most penetrating spike are expected to remain clean and to contribute to fusion yield. One can correct the mixing model by redefining the clean region. Accounting for this unmixed region results in improved agreement with experimental results. Differences in central pressure, density, temperature, and fusion rate in implosions dominated by low mode number perturbations imply that mix effects might not be limited to the mix region, and that 2D simulations are necessary to describe the large scale flow affecting the central region. The same analysis has been undertaken for implosions with different convergence ratios, but with similar initial perturbation spectra. These implosions should be compared to implosions dominated by high mode number perturbations, which might be described by models based on 1D simulations.

The stopping at low (V < Vth) and high (V ≤ Vth) velocity, of N strongly correlated ion debris is investigated for the case of a dense and classical electron target. The considered topologies of cluster projectile charges are taken cubic like, and circular, respectively. A specific emphasis is given to the N-dependence, and also to the topological features of the corresponding enhanced correlated stopping.

The irradiation of cylindrical targets by intense heavy ion beams was studied using a two-dimensional numerical simulation code including radiation effects on the hydrodynamical flow. Solid and hollow Aluminum targets as well as gas tubes are studied for various beam configurations with a view to identifying the characteristic features of the flow and possible observables, especially the emitted radiation from Xenon gas tubes.

A model for the hydrodynamics of a layer-structured target impinged by an intense ion beam is presented. For some power law time pulses, the flow in the absorber region, which is entirely different from that in the tamper, becomes self-similar for planar geometries. Scaling laws for the ablation pressure and the implosion velocity have been obtained from the analysis.

The paper reports on a method of producing spherical targets with a light ablator layer having a density of 0·2g/cm3 and a thickness 10μm. This method for obtaining polystyrene microballoons and polyethylene microballs works for hemispheres made from plastics and metals with diameters from 600 to 1200 μm and wall thicknesses from 10 to 50 μm. It also provides a way to assemble cascade targets.

For the guarantee of the long-distance transport of the bunches of China Initiative Accelerator Driven System (CIADS), a new scheme is proposed that extra magnetic field is used in the accelerator-target coupling section before the windowless target to minimize the self-modulation (SM) mechanism. Particle-in-cell simulations are carried out to study the influence of the solenoidal magnetic field on the self-modulation mechanism when long proton bunches move in the background plasmas. The long proton bunches used in the simulations are similar to these in the linear accelerator of CIADS. It is found that the presence of the solenoidal magnetic field will significantly inhibit the self-modulation process. For the strong magnetic field, the longitudinal separation and transverse focusing of the long bunches disappear. We attribute these phenomena to the reason that the strong solenoidal magnetic field restricts the transverse movement of plasma electrons. Thus, there are not enough electrons around the bunch to compensate the space charge effect. Moreover, without transverse current, the longitudinal pinched effect disappears, and the long bunch can not be separated into small pulses anymore.

KrF and other short wavelength lasers are ideal candidates for producing hot dense plasmas since the laser energy can be absorbed with high efficiency by classical mechanisms, thereby virtually eliminating anomalous absorption and the production of non-thermal electrons. A high power KrF laser system employing optical beam multiplexing and stimulated Brillouin scattering to produce pulses as short as 1 ns and focused intensities on target of 1011−1014 W/cm2 has been developed for producing such plasmas and studying laser/plasma interaction phenomena. A variety of studies on absorption, transport, ablation, X-ray conversion and stimulated scattering instabilities have been pursued with this ¼ μm laser on single atomic number and multi-layer targets. This paper briefly describes some of the features of the KrF laser system and highlights some of the characteristics of the hot dense plasmas produced.

Spectroscopic study of plasma produced through bombardment of the 1 × 3 mm2 area on the surface of a solid Mg target with Kr+ ions is carried out. Spectral lines of Mg I and Mg II ions were observed in the visible range (200–600 nm). The plasma parameters Ne = 1.4.1017 cm−3 and Te = 0.8 eV are calculated from electron impact broadening of the 4f–3d line of Mg II and from the ratio of intensities for the 4f–3d and 4s–3p lines of Mg II. The ionic composition of the plasma is determined. The detected X-ray emission is shown to be the characteristic emission of the target.

Nitrogen lasers have been used for many years to make dye solutions lase. A nitrogen laser, which transverse electrical discharge in gas at atmospheric pressure has been built in our laboratory. It has been characterized and applied to pump different dyes: Rhodamine 6G, Coumarin 440, DOTCI, and pyranine in simple “on axis” geometric configuration. It has been shown that pyranine can lase in the absence of any optical external mirror cavity, this happens at very low threshold, and in different solvents. Dyes under consideration can be grouped into two major classes according to their lasing behavior independently on their concentration in the solvent: Rhodamine 6G and DOTCI can lase both axially or transversally and Coumarin 440 and pyranine can lase only axially. Other intriguing features have been observed that span from simultaneous multiple beam generation, to super fluorescence and to distribute axial pumping of dye solutions. A preliminary basis for understanding and controlling such processes is the spatial energy distribution and the energy density of the beam.

Suprathermal electrons produced by laser–plasma interactions at 0.53-μm laser wavelength have been investigated using 19 electron spectrometers. The targets were 2- and 10-μm-thick Al foils, while the laser average intensities were 2 × 1013 and 7 × 1014 W/cm2. A double temperature distribution was observed in the electron energy spectrum: the lower electron temperature was below 25 keV, whereas the higher was ~50 keV. The angular distribution of the total suprathermal electron energy approximately obeyed the Gaussian distribution, peaking along the k vector of the incident laser beam for perpendicular incidence. Furthermore, the conversion rate of laser energy into escaped suprathermal electron energy over the π sr solid angle was ~10−4 at $\sim \!\!10^{14} \; {\rm W}/{\rm c}{\rm m}^{\rm 2}$, increasing almost linearly with the laser intensity.

Dependence of quasistatic Wakefield and high harmonic generation on the pulse-shape of an ultrashort, intense, few-cycle laser in the reflected radiation from a thin dense plasma layer is investigated. The pulse envelopes considered are Gaussian, Lorentzian, and hyperbolic secant having identical full width at half maximum of intensity. The reflected radiation from the strongly driven surface plasma layer embodies a quasistatic Wakefield, which exists after the main pulse is passed over. A phase modulation is also experienced by the laser light upon reflection from plasma surface motion. As a result harmonics of center carrier frequency of the laser-pulse are generated in the reflected signal. Intensity of the laser harmonics and magnitude of the Wakefield in the reflected radiation are found to depend on the pulse-shape, number of cycles, carrier envelope phase difference, plasma density, angle of incidence, and intensity of the incident pulse.

Laser beat wave heating of magnetized plasma via electron cyclotron damping is proposed and analyzed. A plasma density ripple is presumed to exist across the magnetic field. Two collinear lasers propagating along the magnetic field exert a beat frequency ponderomotive force on electrons, driving a large amplitude Bernstein quasi-mode which suffers cyclotron damping on electrons. Finite Larmor radius effects play an important role in the heating. Electron temperature initially rises linearly with time. As the temperature rises cyclotron damping becomes stronger and temperature rises rapidly. The process, however, requires ripple wavelength shorter than the wavelength of the beat wave.

The inertial confinement fusion (ICF) research has remarkably developed in the last 10 years, which enables us to scope the fusion ignition and burn in the near future. Following the recent progress in the ICF, the perspectives of the inertial fusion energy (IFE) are presented. International collaboration is highly expected.

A scheme of generating ultra-intense attosecond pulses in ultra-relativistic laser interaction with under-dense plasmas is proposed. The attosecond pulse emission is caused by an oscillating transverse current sheet formed by an electron density spike composed of trapped electrons in the laser wakefield and the residual transverse momentum of electrons left behind the laser pulse when its front is strongly modulated. As soon as the attosecond pulse emerges, it tends to feed back to further enhance the transverse electron momentum and the transverse current. Consequently, the attosecond pulse is enhanced and developed into a few cycles later until the density spike is depleted out due to the pump laser depletion. To control the formation of the transverse current sheet, a non-uniform plasma slab with an up-ramp density profile in front of a uniform region is adopted, which enables one to obtain attosecond pulses with higher amplitudes than that in a uniform plasma slab.