The interaction of an Nd:YAG laser, operating at 532 nm with 40 ps pulse duration, with human teeth was studied. The results show that teeth were significantly modified at an energy fluence of about 11 J/cm2. Various surface morphologies of enamel and dentine were recorded. Features on enamel include crater (conical form) in the central part and cauliflower morphology at the periphery, whereas on dentine the crater looks like a stretched dome between sharp edges. The behavior of the enamel-dentine junction area showed different morphology with respect to both tooth enamel and dentine alone. Finally, the junction channel showed a removal of collagen fibers and the formation of a needle-like bottom structure. Generally, this investigation showed that the picosecond Nd:YAG laser can ablate a tooth surface practically instantaneously, implying that large tooth surfaces can be processed in short time.

The High Current Experiment (HCX) is being assembled at Lawrence Berkeley National Laboratory as part of the U.S. program to explore heavy ion beam transport at a scale representative of the low-energy end of an induction linac driver for fusion energy production. The primary mission of this experiment is to investigate aperture fill factors acceptable for the transport of space-charge dominated heavy ion beams at high space-charge intensity (line-charge density ∼ 0.2 μC/m) over long pulse durations (>4 μs). This machine will test transport issues at a driver-relevant scale resulting from nonlinear space-charge effects and collective modes, beam centroid alignment and beam steering, matching, image charges, halo, lost-particle induced electron effects, and longitudinal bunch control. We present the first experimental results carried out with the coasting K+ ion beam transported through the first 10 electrostatic transport quadrupoles and associated diagnostics. Later phases of the experiment will include more electrostatic lattice periods to allow more sensitive tests of emittance growth, and also magnetic quadrupoles to explore similar issues in magnetic channels with a full driver scale beam.

In implosion experiments of a cone-guided target using Gekko XII laser, the lasers on the cone side are not irradiated to avoid the irradiation of the cone. In such condition, the implosion process is done highly asymmetrically. Thus we evaluated the effects of the asymmetric implosion on the compression ratio of the fuel in Gekko XII irradiation orientation by three-dimensional hydro simulations. In this paper, we discuss the degradation of the compression ratio by asymmetric implosion and show that the compression ratio can be enhanced by adjusting the laser intensity between each beam to reduce the asymmetry of the implosion.

A high power KrF laser system employing beam multiplexing and stimulated Raman or Brillouin scattering to produce pulses as short as 1 ns and focused intensities on target of 1011 to 1014 W/cm2 has been developed for laser/plasma interaction research. A variety of investigations have been pursued on single and multilayer targets with variable atomic numbers. Absorption, transport, X-ray conversion, ion expansion characteristics, mass ablation and ablation pressure scaling, and stimulated scattering instabilities are among features that have been studied as a function of laser intensity. A wide variety of laser and target diagnostics are employed including focal plane imaging cameras for energy distribution and UV and soft X-ray streak cameras for temporally resolving the incident laser pulse and X-ray emission. Experimental results will be presented and our current understanding of the KrF laser/plasma interaction will be discussed.

Laser-driven relativistic electrons can be focused onto a high-Z convertor for generating high-brightness γ-rays, which in turn can be used to induce photonuclear reactions. In this work, photo-transmutation of long-lived radionuclide 135Cs induced by laser–plasma–interaction-driven electron source is demonstrated using Geant4 simulation (Agostinelli et al., 2003 Nucl. Instrum. Meth. A506, 250). High-energy electron generation, bremsstrahlung, as well as photonuclear reaction are observed at four different laser intensities: 1020, 5 × 1020, 1021, and 5 × 1021 W/cm2. The transmutation efficiency depends on the laser intensity and target size. An optimum laser intensity, namely 1021 W/cm2, was found, with the corresponding photonuclear reaction yield reaching 108 J−1 of the laser energy. Laser-generated electrons can therefore be a promising tool for transmutation reactions. Potential application in nuclear waste management is suggested.

We present the idea of intensified attosecond X-ray generation based on nonlinear Thomson backscattering of an intense laser pulse by electrons trapped in plasma-vacuum boundary. Two frequency up-conversions due to the relativistic Doppler effect and longitudinal γ-spike effect are analyzed, respectively, where γ is the relativistic factor of the plasma surface. Relativistic resonance heating conditions should be used as a criterion for the experimental design to obtain efficient high-order harmonics and energetic electrons' generation at relatively low laser intensities. Shaping the laser field by proposing a detuned second-harmonic can generate a single attosecond pulse without spectral filtering.

Experiments have been performed to investigate the transport and stability of microsecond-pulselength intense relativistic electron beams in the ‘ion-focused regime’ (IFR) in low-pressure neutral gas and laser-preionized channels. Beams have been generated by the Michigan Electron Long Beam Accelerator (MELBA) which operates with parameters: voltage = −0·7 to −1 MV electrically compensated for collapsing diode impedance over the first 1·5 μs, pulselength = 0·1 to 4μs limited by diode closure, and current = 0·2 to 30 kA.

Long pulse beam propagation experiments have demonstrated the following effects:

1) At pressures of 1–230 m Torr in air and helium with no laser-preionized channel:

a) the electron-beam transport efficiency peaks after times longer than the time calculated for beam-induced ionization to reach fe. = 1. Up to 100% efficient transport occurs during short spikes over a 1 m propagation distance.

b) Within 100 ns of efficient transport the propagated beam exhibits rapid beam cutoff in air and helium. This initial pulse of propagated current is followed by a series of 10 ns to 60 ns duration spikes for the remainder of the injected beam pulse. At higher gas pressures usually less current is propagated in the later peaks. At the lowest pressure for which significant current is propagated (7·6 m Torr air, 14 m Torr helium) the maximum transported current occurs in one of the later peaks.

2) In initial experiments with excimer-laser-ionized channels in diethylaniline at pressures of 3–8 × 10−4 Torr the electron-beam transport over 1·2 m is efficient (80% to 100%) for at least the first 0·5 μs and does not exhibit the erratic transport observed in the electron-beam induced channels. For fixed laser energy, a narrow pressure window exists for efficient and stable long pulse electron-beam transport. Pressures below optimal give inefficient transport while higher pressures cause ejection of the beam from the ionized channel at later times.

We present the current status-of-the-art in Stark broadening theory as a theoretical basis for diagnostics of low temperature plasmas in gas discharges, and of high temperature laser produced or z-pinch dense plasmas. The diagnostics abilities vary depending on the parameters of the gas discharges, or on the range of intensity, and duration of the laser or z-pinch pulses. In the case of high temperature plasmas, besides the conventional diagnostics based on the Stark broadening, the contemporary possibilities of UV and XUV interferometry for plasma density measurements and of tomography reconstruction of the macroscopic gradients of temperature and densities in laser produced plasmas are discussed.

An experimental investigation into inertial properties of the developed Rayleigh–Taylor instability with the different initial values of the kinetic energy of turbulence has been performed. The experiments were performed by using two fluids having different densities with density ration n = 3. Fluids were placed in an ampoule. At the unstable stage of motion, the ampoule was moving under an acceleration. At a certain instant of time the acceleration was removed and the ampoule moved under the force of inertia. By means of pulsed X-ray photography, the mixing region size and the time-space distributionof the average density of matter in the turbulent mixing region have been determined at different instants of time. The time-space distributions are compared with those obtained by semiempirical theories of mixing.

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.

In order to develop a high repetition rate X-ray lasers, the longitudinal-pumped transient collisional excitation (TCE) X-ray laser is one of the most effective pumping schemes. The high directive Ni-like Mo 18.9 nm soft X-ray laser pumped by modest laser energy has already been demonstrated by using the tabletop size Ti:sapphire/Nd:glass laser system that delivering energy of 150 mJ in 475 fs at the center wavelength of 1054 nm. The total energy in the pre-pulse and the main pulse was 150 mJ, which will make possible multi-hertz operation. To pursue the high repetition rate of the laser-driven TCE X-ray laser, we have designed a new 20 TW Ti:Sapphire laser system (600 mJ, 30 fs, 10 Hz). Special attention was paid to improve the contrast ratio, control of pulse shape as well as phase by an acoustic optic programmable dispersive filter (AOPDF) and 1 kHz preamplifier. Preliminary data have shown good laser characteristics. As the preliminary experiments, we have investigated high order harmonics generation from low-density laser plasma by using the solid target irradiated by a femtosecond laser pulse. The highest order was the 51st. harmonic at wavelength of 15.61 nm.

The studies of laser ablation have lead to a new theory of nuclei, endothermic nuclei generation, and quark-gluon plasmas. The surface of ablated plasma expanding into vacuum after high power laser irradiation of targets contains an electric double layer having the thickness of the Debye length. This led to the discovery of surface tension in plasmas, and led to the internal dynamic electric fields in all inhomogeneous plasmas. The surface tension causes stabilization by short length surface wave smoothing the expanding plasma plume and to stabilization against the Rayleigh–Taylor instability. Generalizing this to the degenerate electrons in a metal with the Fermi energy instead of the temperature resulted in the first quantum theory of surface tension of metals in agreement with measurements. Taking the Fermi energy in the Debye length for nucleons results in a theory of nuclei with stable confinement of protons and neutrons just at the well-known nuclear density, and the Debye lengths equal to the Hofstadter decay of the nuclear surface. Increasing the nuclear density by a factor of 10 leads to a change of the Fermi energy into its relativistic branch where no surface energy is possible and the particle mass is not defined, permitting the quark gluon plasma. Expansion of this higher density at the big bang or in super-nova results in nucleation and element generation. The Boltzmann equilibrium permits the synthesis of nuclei even in the endothermic range, however with the limit to about uranium. A relation for the magic numbers leads to a quark structure of nuclear shells that can be understood as a duality property of nuclei with respect to nucleons and quarks

Plasmas of high reproducibility that are suitable for beam-plasma experiments are generated by a pulsed-power z-pinch discharge. The z-pinch device is designed as a plasma target for the investigation of ion beam-plasma interactions. The dynamic plasma state is characterized by the electron density, the electron temperature, and the magnetic field distribution, which are observed using time-resolved diagnostics. For z-pinch discharges in hydrogen, average electron densities of up to (2.6 ± 0.1) × 1018 electrons/cm3 were measured interferometrically. Electron temperatures in the range 2–7 eV are determined by time-resolved spectroscopy. The reproducibility of the electron density of the z-pinch discharge in terms of shot-to-shot fluctuations is estimated to be better than 3%. This is a favorable condition for performing beam-plasma experiments.

The present paper proposes a model for the generation of Terahertz (THz) radiation by self-focused hollow Gaussian beam (HGB) in collisionless magnetized rippled density plasma. At high intensities, the change in the electron mass occurs due to relativistic effect, introducing a nonlinearity in the plasma leading to the self-focusing of the HGB. The nonlinear interaction of this highly intense self-focused HGB with the electron plasma wave in the rippled density plasma, satisfying proper phase matching conditions, results in the resonant excitation of THz radiations at the beat frequency. We have studied the dependence of generated THz radiations on the order of the HGB as well as on the static background magnetic field. The results show that the intensity of the generated radiations is highly sensitive to both of these parameters. For the current scheme the power of the generated THz waves comes out to be of the order of Gigawatts.

A construction and exploitation of a comparatively large I photodissociation laser system (Perun) is reported. This system was constructed in cooperation between the Institute of Physics of Czechoslovak Academy of Science in Prague and the Lebedev Institute of Physics of Soviet Academy of Science in Moscow. The laser produces subnanosecond pulses of maximum 50 J and 0·5 ns in duration. Although the pumping time by Xe flashlamps is long enough for an acoustic disturbance released in the active medium to introduce an optical inhomogeneity across the whole cross section of the laser tube, the radiation can be focused in a focal spot of a power density exceeding 1014 W/cm2, enough for meaningful laser target experiments both for a laser plasma production or a modification of solid surfaces. The repetition time of the shots is about 10 min.

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 Spherical Pinch (SP) is a particular variation of the inertial confinement scheme, in that the two criteria required for plasma fusion breakeven condition, namely the attainment of a sufficiently high plasma temperature and of a product nτ in excess of 1014 cm-3. sec, are satisfied through two separate mechanisms. The advantage of this approach is that the scaling laws for breakeven are easier to satisfy than in the classical inertial confinement scheme. The first derivation of the scaling laws for spherical pinch experiments (Panarella & Savic 1983; Panarella 1987) was obtained under the simplifying assumption of an infinitely small central plasma in a sphere reaching the required high temperature for fusion, and of an undefined time delay Δt between the creation of such central plasma and the launching of the peripheral shock waves used to contain the central plasma. The analysis reported in this paper removes these assumptions and derives scaling laws which are generalized in their parameters, in that they explicitly contain the radius Rp of the central plasma and the time delay Δt.

The paper describes a technique for operative control of the high-intensity pulsed ion beam parameters. The time-of-flight diagnostics uses one high-speed Faraday cup sensor with magnetic cut-off of low-energy electrons. The technique makes it possible to determine the composition of the beam (the type of ions and the degree of ionization), the absolute values of the current density of ions and the energy spectrum for each type of ions with an error of <±10%. The technique was tested at different pulsed ion accelerators and ion diodes both with self-magnetic insulation (accelerating voltage of 200–250 kV, ion current density of 20–300 A/cm2) and external magnetic insulation of the electrons (400–500 kV, 200 A/cm2). The article presents a comparative analysis of two types of Faraday cups with magnetic cut-off of the electrons and with electric bias.

In this work, extreme ultraviolet (EUV) emission, from EUV induced, low-temperature microplasmas, were investigated. To perform temporal measurements of the EUV pulses of low intensity, in a medium vacuum, under the pressure of the order of 0.1–0.01 mbar a special detection system was prepared. The system was based on an EUV collector and a semiconductor detector, sensitive for the EUV photons. The collector consisted of two identical grazing incidence, paraboloidal mirrors, and allowed to focus a part of the radiation emitted from the microplasma onto the detector surface. An absorption filter, mounted between the collector and the detector, allowed for selection of an interesting wavelength range. Plasmas were created by irradiation of small portions of gases, injected into the vacuum chamber, using a laser produced plasma EUV source. Three gases were used for the EUV induced plasma formation: neon, krypton, and xenon. Low-temperature plasmas, created in these gases, contained multiply charged ions, emitting radiation in similar wavelength ranges. Two detectors, AXUV20HS1 and AXUVHS5, were used for the measurements. It was shown that differences between the corresponding signal profiles, obtained using both detectors, were not very significant. Moreover, it was demonstrated that the duration of the EUV emission from plasmas, created in different gases, were comparable with the duration of the driving EUV pulse. The longest EUV emission was observed for Kr plasmas, approximately 1.5 times the full width half maximum of the driving EUV pulse.

The interaction of an intense laser field with a thin foil is studied within the framework of a 1D capacitor model with mobile negative point-charges. The model describes the excitation of plane electrostatic oscillations, taking into account the effects of particle–particle crossings and the presence of vacuum boundaries. It is demonstrated how vacuum excursions of particles cause wavebreaking within the foil. From wavebreaking points, charge density discontinuities are shown to propagate further along particle caustics. Absorption is calculated as a function of laser intensity and frequency. It is found that a thin overdense foil can absorb about 5 times more energy than a corresponding surface of an extended solid. This is explained by the doubling of surface charges and by electron heating in the potential well of the foil. A further absorption maximum is obtained below the plasma frequency due to resonance absorption.