The smoothing mechanism, that is due to the thermal conductivity in the laser plasma generated by a double pulse, is examined. Plasma preformed by a second harmonics prepulse serves as a low density gradient plasma for impacting the main pulse, the frequency of which was tripled for improving the laser-target coupling. The effect of the preformed plasma on the thermal smoothing of the heating pulse, which was split to create two foci on the target surface, was explored by varying the time delay between the prepulse and the main pulse. The smoothing effect was monitored by a pair of pinhole cameras: one viewing side-on and the other one placed at the rear side of the target. Spatially resolved X-ray emission spectra were recorded to determine the density and temperature distributions in the plasma. The maximum smoothing effect was observed for the time delay t = 0.4–0.7 ns.

X rays emitted from Kr clusters illuminated by a femtosecond laser have been observed over a wide spectral region from 3 keV to 15 keV. The measured spectra are characterized by a broad bremsstrahlung continuum and Kα, β lines at 12.66 keV and 14.1 keV. To the best of the authors' knowledge, this is the first observation of Kα, β emission from laser-heated Kr clusters. The bremsstrahlung continuum arising from collisions in the plasma implies a population of hot electrons consistent with a temperature of several kiloelectron volts. The absolute X-ray yield in the 3–15 keV region is found to be of the order of 107 photons per laser pulse. The plasma temperature, estimated from the continuum part of the spectrum as a function of laser intensity and X-ray yield as a function of laser pulse duration, are studied.

Field emission is identified as the mechanism responsible for high current emission (50 A/cm2 at 300°K) from a dispenser-type cathode. This cathode has advantages for high power operation, and should be suitable for practical applications.

Spherically symmetric shock waves have been produced via Nd3+ laser induced break-down in helium, nitrogen and air at pressures ranging from 760 Torr to 2300 Torr. The measurements are performed at different absorbed laser energies (E0 = 0.05 J to 2 J) at the center of the experimental spherical glass cell where the breakdown of the gas takes place. The temporal evolution of the shock wave followed by a double-pulse, doublewavelength holographic technique is described hydrodynamically well by the point strong explosion theory. The ambient gas counterpressure plays a negligible role in determining the shock wave motion even at low laser energy absorption (E0 ≤, 0.5 J), whereas it has an appreciable effect on the gas density jump at the shock wave itself. The experimental data on temporal evolution of the density jump of the gas and the corresponding theoretical profiles obtained adopting a non-self-similar solution at the same laser absorbed energy are found to be in good mutual agreement.

The minimum irradiance needed to overcome amplified spontaneous emission (ASE) of a seed beam injected into a laser amplifier is evaluated. The treatment is particularly applicable to extreme ultraviolet (EUV) and X-ray laser schemes to inject laser harmonic radiation as a seed into (1) plasma laser amplifiers and (2) free-electron lasers. Simple expressions and calculations are given for the minimum injected irradiance required for amplification of the injected seed beam to exceed ASE from the amplifier, including the effects of gain saturation, assuming one dimensional radiative transfer.

A method to design the composite insulation structures in pulsed power systems is proposed in this paper. The theoretical bases for this method include the Weibull statistical distribution and the empirical insulation formula. A uniform formula to describe the reliability (R) for different insulation media such as solid, liquid, gas, vacuum, and vacuum surface is derived. The dependence curves of the normalized applied field on R are also obtained. These curves show that the normalized applied field decreases rapidly as R increases but the declining rates corresponding to different insulation media are different. In addition, if R is required to be higher than a given level, the normalized applied field should be smaller than a certain value. In practical design, the common range of the applied fields for different insulation media should be chosen to meet a global reliability requirement. In the end, the proposed method is demonstrated with a specific coaxial high-voltage vacuum insulator.

A large-signal theory of bunching of an intense relativistic electron beam with both velocity and density modulation in the triaxial klystron has been derived in this paper. The theory presents both the harmonic current and the transient velocity in the bunching process, and expresses the velocity modulation directly by the modulation voltage that is easier to be attained and controlled in practice. A few checks are performed on the large-signal theory by particle-in-cell simulation that suggested the large-signal theory of bunching can successfully predict the first-order harmonic current and the velocity on a beam, with both velocity and density modulation, after interacting with a modulation voltage on the order of magnitude with the beam voltage. The theory described in this paper can accommodate general situations such as the bunching of a modulated beam after interacting with a buncher cavity of the Triaxial klystron amplifier.

Particle-in-Cell (PIC) simulation is an interpolation-based method on the Newton–Maxwell (N–M) system. Its well-known drawback is its shape/interpolation functions often causing the violation of continuity equations (CEs) at mesh nodes and that of Maxwell equations (MEs) at particles' positions. Whether this drawback can be overcome by choosing/solving suitable shape/interpolation functions is of fundamental importance for the PIC simulation. Until now, these shape/interpolation functions are usually subjectively chosen and, hence, always invoke the drawback. Here, we first investigate whether these shape/interpolation functions can be self-consistently solved by considering under what condition the CEs and the MEs can be satisfied anywhere. Strict mathematical analysis reveals that strict self-consistent shape/interpolation functions are unavailable. Only few approximately self-consistent shape/interpolation functions are luckily found by some authors. This fact drives us to present another universal interpolation-free strict method on the N–M system.

Detailed spectroscopic identification and analysis of lines emitted by Ni-like ions may infer on plasma parameters, such as electron density, temperature, and ionization state. Spatially, resolved X-ray spectra of samarium laser produced plasma were recorded in the 7 to10 Å wavelength range. Measured line intensity ratios of Ni-like 3d-5f, 3p-4d, 3p-4s, and 3s-4p transitions were used for electron density diagnostic as a function of the distance from the target. Calculations using Hebrew University Lawrence Livermore Atomic Code show that these ratios are not very sensitive to the electron temperature in the range from 500 to 1000 eV. Self-absorption of some lines is found to be important at electron densities higher than 1021cm−3. The inferred ranges of electron density and temperature are found to be consistent with results of hydrodynamic simulations and models of ionization in plasma.

Both, in the laboratory (specifically the plasma focus) and in astrophysics, charges are accelerated in magnetically pinched current channels. The current channels are annular cylinders, defined by an electric double layer of thickness δrE and radius R due to radial polarization of the plasma. The electric field Er in the double layer and the azimuthal magnetic field Bϕ ensure drifts of charges in the axial direction, but ions do not take up the full drift velocity because their Larmor radius exceeds δrE. Magnetic pinching of the channel reduces the cross sectional area S, and an instability of drift velocity may denude a region of current channel. The inductively maintained current J then cannot be carried by free charges, even with relativistic drift velocity. A displacement current (S/4π) δEz/δt arises, Ez growing until all energy in Bϕ is transferred into Ez. During this transfer Bϕ decreases, so the pinch weakens, permitting discharge of accumulated space charge via a conduction current without reversal of J. Thereafter the cycle repeats quasi-periodically.

In astrophysics acceleration occurs in a pinched magnetic vortex tube (MVT). The difference is that now Bϕ(r, +z) = −Bϕ(r, −z) due to winding of loops of field lines. Hence J reverses across mid-pinch, which implies accumulation of space charge of one sign at mid-pinch and of opposite sign at the ends of the pinch. Now there is reversal of J when the space charge relaxes.

Expressions for the stopping power are derived from the Lenard-Balescu and Boltzmann kinetic equations. Numerical evaluation is carried out for the stopping of light and heavy particles in a multicomponent plasma.

Most of the high-energy laser systems deliver temporally super-Gaussian-shaped laser pulses. The propagation properties of this kind of pulses in a nonlinear medium are studied in this paper. There is Stokes component in the sideband spectrum of super-Gaussian-shaped pulses, and the frequency difference between the Stokes component and the center frequency is equals to the Brillouin frequency of the nonlinear medium. When the laser is reflected by optical elements in the light path, Stokes component in the reflected light can be amplified by the subsequent part of the laser pulse and excite stimulated Brillouin scattering (self-pumped SBS). The self-pumped SBS is studied theoretically and experimentally, and the experimental results agreed well with the calculated results. The simulation results show that lower-order super-Gaussian-shaped pulses are more suitable for suppressing the self-pumped SBS and of great benefit to the energy delivering of the high-power laser pulses. To the best of our knowledge, this is the first time to experimentally demonstrate the self-pumped SBS of high-power super-Gaussian-shaped laser pulses.

This communication presents a comparison of two cases to study the process of laser beam propagation and Stimulated Brillouin Scattering (SBS) in laser plasma interaction. These two cases are, with imposing the restriction of paraxial approximation on the laser beam and, relaxing this restriction up to a certain extent. In this work, the study done by Sharma et al. (2009) using paraxial approximation is extended by taking contribution of the off-axial rays in the laser beam profile. The spitted profile of the laser beam is obtained due to uneven focusing of the off-axial rays and its effect on localization of the ion acoustic wave (IAW) has been studied. Including the off-axial part of the laser beam semi-analytical solution of the nonlinear coupled IAW equation has been found and this is examined that off-axial part affects background densities. The nonlinear coupling between the laser beam and IAW is severely affected by modified profile of the laser beam. Further, it is investigated that the SBS is also influenced by this coupling process. Therefore, the reflectivity of SBS has been compared with and without contribution of off-axial rays. A notable change is found in the magnitude of SBS reflectivity in modified-paraxial case in comparison to the paraxial case.

Improved measurements of ion-correlation effects in a dense shock-compressed plasma are presented. The extended X-ray-absorption fine-structure (EXAFS) technique on the aluminum K edge is used to observe the short-range order within a dense plasma. Densities of about three times solid density were measured with good accuracy. The experimental measurements of density give results that are in good agreement with the MEDUSA onedimensional fluid code predictions. The improved quality of the data enabled us to calculate the ion coupling parameter during the compression and the subsequent heating of the plasma. An estimation of the temperature is given on the basis of published models, and an approximate agreement is obtained with the MEDUSA code predictions.

The Laboratory Microfusion Facility (LMF) has been proposed to study Inertial Confinement Fusion (ICF) targets with reactor-grade gains. An advanced solid-state laser is the prime candidate as the driver for the LMF. However, here we present a conceptual design for an alternate approach using a Nuclear Pumped Laser (NPL).

A pulsed fission reactor is used to excite an oxygen-iodine laser in this design, based on preliminary data on nuclear pumping of O2(1δ). Although a working NPL of this specific type has not yet been assembled, we believe this concept holds great potential, both as a test facility driver and as a future power reactor.

The interaction of ultrashort laser pulses with a fully ionized plasma is investigated in the plane geometry by means of numerical simulation. The impact of the space oscillations in the amplitude of the laser electric field on the shape of the electron distribution function, on laser beam absorption, and on electron heat transport is demonstrated. Oscillations in the absorption rate of laser radiation with the minima coincident to the maxima of the laser electric field lead to a further decrease in the absorption of laser radiation. Heat flux in the direction of increasing temperature in the underdense region is caused by the modification of the electron distribution function and by the density gradient. A limitation of heat flux to the overdense plasma isobserved with the flux limiter in range 0.03–0.08, growing moderately with the intensity 1014–1016 W/cm2 of the incident 1.2-ps laser pulse.

In the Ampfion diode, an ion beam is extracted from an anode plasma that is being pushed away from the cathode by a rising magnetic field. There is concern that ion heating in the anode plasma sheath may result in a significant ion beam divergence. To investigate this possibility, a comparison of Z pinches, θ pinches, and Ampfion is made. Ampfion sheath scenarios are examined and a simple argument is presented that indicates that an anomalous resistivity should develop. An upper bound estimate of the ion divergence is calculated, and examples are given for PBFA-II parameters. For a small radius diode with a high density anode plasma, it is shown that ion beam divergence due to plasma heating should not be a problem. For a large radius diode with a low density anode plasma, it is shown that ion beam divergence due to plasma heating is a problem, but that an Ampfion filtering mechanism should select a cool portion of the heated ions and help to alleviate this problem.

The possibility of using the analytical wave functions in hydrogen-like and semiclassical approximations for self-consistent Hartree-Fock-Slater model is considered. The usage of analytical wave functions simplifies the obtaining of self-consistent field and yields the suitable expressions for calculation various characteristics of high-temperature plasmas—cross sections of radiative processes, Rosseland mean opacities, and equation of state.

Two concepts have been applied to the classical problem of accelerators for the ignition of indirectly driven inertial fusion. The first is the use of non-Liouvillian stacking based on photoionisation of a singly charged ion beam. A special FEL appears the most suited device to generate the appropriate light beam intensity at the required wavelength. The second is based on the use of a large number of (>1000) beamlets–or “beam straws”–all focussed by an appropriate magnetic structure and concentrated on the same spot on the pellet. The use of a large number of beams–each with a relatively low-current density–elegantly circumvents the problems of space charge, making use of the non-Liouvillian nature of the stopping power of the material of the pellet. The present conceptual design is based on a low-current (〈i〉 ≈ 50 mA) heavy-ion beam accelerated with a standard LINAC structure and accumulated in a stack of rings with the help of photoionisation. Beams are then extracted simultaneously from all the rings and further subdivided with the help of a switchyard of alternate paths separating and synchronising the many bunches from each ring before they hit the pellet. Single beam straws carry a reasonable number of ions: Beams and technology are directly relatable to the ones presently employed, for instance, at the CERN-PS. Space-charge-dominated conditions arise only during the last few turns before extraction and in the beam transport channel to the reaction chamber. In a practical example, we aim at a peak power of 500 TW delivered to the pellet for a duration of 10–15 ns. High-energy (10 GeV) beam straws of Ba doubly ionised ions are concentrated on several (four) focal spots of a radius of about 1 mm. The power density deposited on these tiny cylindrical absorbers inside a hermetic “hohlraum” is about 2.5 × 1016 w/g. These conditions are believed to be optimal for X-ray conversion, i.e., with an estimated conversion efficiency of about 90%.

Recent progress in laser-plasma accelerators has matured a concept of particle acceleration as a possible next-generation particle accelerator promising ultrahigh accelerating gradients in a compact size. Four major concepts of laser-plasma accelerators—the plasma beat wave accelerator, the laser wakefield accelerator, the self-modulated laser wakefield accelerator, and the plasma wakefield accelerator—are reviewed on accelerator physics issues and experiments demonstrating the basic mechanisms of their concepts. As a perspective to the future practical application, a design of 5-TeV linear colliders based on the laser wakefield accelerator is discussed.