This article describes computer simulations of a longitudinal instability that affects induction linear accelerators for high-power ion beams. The instability is driven by axial bunching of ions when they interact with acceleration gaps connected to input transmission lines. The process is similar to the longitudinal resistive wall instability in continuous systems. Although bunching instabilities do not appear in existing induction linear accelerators for electrons, they may be important for proposed ion accelerators for heavy ion fusion. The simulation code is a particle-in-cell model that describes a drifting beam crossing discrete acceleration gaps with a self-consistent calculation of axial space charge forces. In present studies with periodic boundaries, the model predicts values for quantities such as the stabilizing axial velocity spread that are in good agreement with analytic theories. The simulations describe the nonlinear growth of the instability and its saturation with increased axial emittance. They show that an initially cold beam is subject to a severe disruption that drives the emittance well above the stabilized saturation levels. The simulation results confirm that axial space charge forces do not reduce axial beam bunching. In fact, space charge effects increase the axial velocity spread required for stability. With simple resistive driving circuits, the model predicts velocity spreads that are too high for heavy ion fusion applications. Several processes currently under study may mitigate this result, including advanced pulsed power switching methods, enhanced gap capacitance, and an energy spread impressed between individual beams of a multibeam transport system.

The possibility of enhancement of the muon transfer process between hydrogen isotopes in the field of an intense electromagnetic wave is discussed. The muon transfer cross section between the ground states of deuterium and tritium under laser irradiation is calculated from a semiclassical model. It is shown in this case that the muon transfer cross section is hardly affected, even at the very large laser intensities of the order of 1016 W/cm2.

We study strongly correlated plasmas far from equilibrium with the ultimate aim of describing the cooling of heavy ion beams by electrons. With the help of molecular dynamics (MD) computer simulations, we conclude that the relaxation of a two-component plasma depends strongly upon the preparation of the initial configuration. If the initial data have no intercomponent correlations, such will build up during the evolution so that the intercomponent potential energy decreases while the kinetic energy increases. These effects become more pronounced for strongly coupled plasmas and limit the efficiency of electron cooling. We cannot confirm certain mean-field predictions on the influence of an external magnetic field on the cooling process. A study of the relaxation of anisotropic velocity distributions for a one-component plasma shows deviations from meanfield results for strongly coupled plasmas.

We report on KrF laser-plasma interaction studies at focused intensities up to 4 × 1014 W/cm2 for pulse durations of 1–2 ns and up to 1015 W/cm2 for pulse duration of 100 ps. The longer-pulse experiments are concerned with quantifying two important features of the ablating plasma. Stimulated Brillouin scattering at moderately large L/λ has been measured in detail as a function of intensity, target Z, and angle of incidence θ to compare with modeling calculations of backscatter in inhomogeneous plasma. In addition, electrodynamic charge analyzer measurements have been made for varying intensity and target Z to compare with hydrodynamic calculations of ion expansion and recombination. In the short-pulse experiments, we report on X-ray conversion measurements for 100-ps laser-irradiated targets of varying Z at laser intensities of 1·5 × 1014 and 1015 W/cm2. In particular, it is shown that higher laser intensity leads to a substantial increase in X-ray conversion efficiency.

Simple circuit models for the terminal properties of a ferromagnetic closing switch are derived under the assumptions that the ferromagnetic material may be described by a hysteresis profile and that the driving H-field quickly becomes large. Comparison with results from a full transmission line model indicates that all but the simplest of these approximate models is extremely accurate for a realistic switch.

We studied the formation of the collector ion flow in magnetically insulated diodes (MID) with plate-, sphere-, and cone-shaped cathodes. The ions are formed as a result of the ionization of residual gas by electron bombardment and are focused into the cathode plasma region. This effect can negatively influence diode operation in the microsecond range of pulse duration.

Experimental treating of hydrodynamic instabilities in laser-accelerated planar targets have pointed out the creation of a mix between a heavy material and a light one. The experiment described here is intended to answer the question: “Is this mix homogeneous or is it an interpenetration of both materials in the form of bubbles and spikes?” The method chosen to study the mix is self-backlighting, that is, backlighting of the target by its own X-ray emission. Comparison of the front and rear X-ray pinhole images of the target allows us to obtain information about the local areal density. Indeed, if 20-μm diameter Au dots are deposited on the target rear face some structures corresponding to these dots are observed on the rear image. The resolution imposed by the pinholes is about 10 μm. By using stable targets Au/CH, we obtained a good coincidence between front and rear pinhole images of the target. By doing the same comparison for unstable targets Au/CH/Au, the coincidence of the images is not significantly different from that obtained with stable targets. Therefore, in this experiment hydrodynamic instabilities do not create structures with dimension larger than 10μm.

Since DT laser fusion with 10-MJ laser pulses for 1000-MJ output now offers the physics solution for an economical fusion energy reactor, the conditions are evaluated assuming that controlled ICF reactions will become possible in the future using clean nuclear fusion fuel such as deuterium-helium(3) or hydrogen-boron(11). Using the transparent physics mechanisms of volume ignition of the fuel capsules, we show that the volume ignition for strong reduction of the optimum initial temperature can be reached for both types of fuels if a compression about 100 times higher than those in present-day laser compression experiments is attained in the future. Helium(3) laser-pulse energies are then in the same range as for DT, but ten times higher energies will be required for hydrogenboron(11).

The many years' of difficulty with laser fusion owing to the complexity of the interaction with the plasma has been clarified experimentally from the 10-ps pulsation of the interaction. The theoretical understanding of this pulsation is presented here from a hydrodynamic simulation of the interaction in which the generation of partial standing waves and the subsequent nonlinear-force-produced density ripple produces ideal Bragg reflection in the outermost part of the plasma. This all decays within about 10 ps hydrodynamically. The theory explains immediately why the 2-ps coherence at induced spatial incoherence avoids the pulsation and arrives at a smooth interaction similar to the random-phase plate or the use of broad-band laser spectrum irradiation.

The article reviews experiments on flash X radiography of laser-accelerated foils. The spatial resolution, sensitivity, spectral range, and signal-to-noise ratio of measurements were carefully optimized and characterized. The method was used at the Mishen facility to measure a distribution of mass ablative rate across the focal spot and for observation of the transverse plasma flows during the drive laser pulse.

Dye lasers with bleaching wave (LBW) are the first condensed state lasers where the restriction on energy and duration of optical exciting pulses are practically removed. This gives an opportunity to create tunable lasers in the visible range with average powers significantly higher than that of any available laser of this type. Physical principles and current experimental results along with prospects of future LBW development are presented.

When focusing light ions with intense light ion-beam diodes, problems occur with ions emitted at the edge of the anode plasma. Numerical studies investigating this well-known experimental observation are presented. Going beyond the computational simulations introduced by Westermann (1991 Appl. Phys. Lett. 58, 696), two suggestions for the case of the self-magnetically Bθ-insulated ion diode are presented to focus the beamlets emitted from outer parts of the anode. The first one is based upon the idea of changing nonemitting parts of the anode surface and the second one of shifting the emitting anode surface into the anode body.

This article presents the tendency of the changes of Nd-laser plasma parameters in dependence upon increasing target atomic numbers. In the experiment, the following targets — (C8H8)n, SiO2, Al, Cu, Ta, and Au — were investigated. For targets with Z higher than 13, the two-temperature plasma is observed with temperatures Te =500–600 eV and Te≅ 100 eV. Energy carried by ions from the low-temperature plasma can be higher than half the total energy carried by ions. The number of ions from low-temperature, X-ray-heated plasma can be by an order of magnitude higher than the number of ions from thermal plasma (Te = 500–600 eV).

Laser pulses are focused in the interior of a human eye in areas of opacity to produce there an optical breakdown resulting in a high-temperature plasma, after which the filling up with liquid results in a transparent area. The empirically given limits for Q-switch laser pulses in the nanosecond range and for mode-locked pulses in the picosecond range are analyzed, and it is shown that these limits are below the self-focusing condition of laser beams in plasmas. A further analysis evaluates theoretically where the maximum limits are given in order to provide the parameters for the highest possible pulse energy that avoids damage in the eye by self-focusing.

Massive carbon targets were irradiated with a pulsed ruby laser and the laser-produced plasma electron densities were simultaneously evaluated using Nomarski interferometry and the refractive fringe diagnostic. An agreement of half an order of magnitude between the two diagnostics was obtained.

The energy spectra of electrons emitted radially from a CO2 laser focus originating from the ionization of K and Xe atoms of tenuous gas pressure are measured. We simultaneously measured the cases in which medium laser intensities and high laser intensities are applied, fitting the ADK tunneling theory.

Experimental and theoretical studies on the evolution of shock waves in air plasma induced by laser spark have been carried out. The systematic study of the shock wave has been performed experimentally and 1-D numerical code of radiation hydrodynamics (1-DRHC) has been used to simulate the later stage of laser spark in air. The numerical results on the propagation of shock waves and the expansion of hot plasma are presented and subsequent results on the first divergent and convergent shock waves are found to be in good agreement with the experimental data.