The problem of initial thermal velocity and the space charge effect of electron guns in numerical simulations have been investigated deeply. In general, the current software can meet the engineering requirements. However, the electron's initial thermal velocity and the space charge effect lack sufficient consideration. The above two factors significantly limit the performances of electron guns. Moreover, the parameters of electron guns are approximated based on a limited number of electron trajectories. Thus, the statistical distribution of the beam electron resulting from its initial thermal velocity is not considered adequately in present software. This paper introduces the equivalent meridional projected trajectory equation and the curvilinear axis evolution theory of the current density of toroidal electron sub-beam, and subsequently the current and charge density distributions in electron guns can be derived through iteration calculation. Based upon, the virtual crossover of an electron gun is determined by its current density distribution. As well as, a relevant numerical algorithm is developed and the related program is modified based on the popular commercial software SOURCE. Tungsten cathode guns, LaB6 cathode guns, field mission guns and Pierce guns are simulated respectively by examples. The calculations prove that the modified software is effective and practical.

X-ray spectroscopy is a widely used means of diagnosing densities and temperature within laser-produced plasmas. At X-ray energies above approximately 1 keV, Bragg crystal spectrometers are routinely used to record X-ray spectra. Quantitative measurements of plasma conditions can be obtained with a knowledge of crystal reflectivity and film or detector response. In such data analysis it is always assumed that the crystal response is constant in time. However, we show that under certain adverse experimental conditions the X-ray fluxes incident on the crystal are so high as to significantly transiently modify the reflection characteristics of the crystal. Such degradation need not necessarily be accompanied by a loss of observed spectral solution. The transient (nanosecond-time-scale) change in crystal reflectivity is due to a change from dynamical to more kinematic diffraction caused by an X-ray-induced thermal strain gradient in the surface layer of the crystal. The decay time of this strain is typically several nanoseconds. Calculations of some specific crystal reflectivities and rocking curves under such conditions are presented, and methods of minimizing the effect by appropriate filtering are discussed.

All of mankind, not only the readers of this Journal, is now fascinated by the laser. The process of many preceding physics discoveries beginning with Einstein (Zürich lecture, printed 1916, see A. Held, General Relativity and Gravitation One Hundred Years after the Birth of Einstein, Plenum, New York, 1980, Vol. 1, p. 17–21) and how this earth shattering discovery was not recognized by the giants in science is really a process of “how it happened” and the fact is: Charles Townes is its creator. Since there were some dark clouds through which this discovery of our century (next to the quantum theory and the theory of relativity) had to finally shine through, it is a revelation to now read what its creator has to say; modest, quiet, but true and fascinating.

It is shown that large gainlengths of amplified spontaneous emission (ASE) together with collisional effects in plasmas are liable to generate modifications in population inversions and then in observed gain values. In the case of the Ne-like Se24+ ion, one can expect a significant reduction of the J = 0–1 transition gain value at the wavelength of 18.24 nm.

A physical-mathematical model for the development of the boundary instability of a spherical incompressible-liquid shell, with due regard for the ablation effect, is considered.

The phase diagram of high density (1023 ˜ 1027/cm3) deuterium is obtained by calculation. The values of specific heat, electrical resistivity and thermal conductivity in the metallic state are estimated over a wide range of temperature (10−2 ˜ 104 eV). The temperature dependences of these properties are shown in figures with the density. When T ≤ Tf (Tf: the Fermi temperature of electrons), the behavior is very similar to those of normal metals. At high temperatures where T ≥ Tf, the behavior is similar to that of completely ionized classical plasma.

This fundamental data for deuterium will help us understand the properties of fuel in inertial-confinement fusion and to solve the fluid equations for efficient compression of fuel pellets.

The bubble regime acceleration of electrons by a short pulse laser in a carbon nanotube (CNT) embedded plasma is investigated, employing two-dimensional Particle-in-Cell simulations. The laser converts the CNT placed on the laser axis into dense plasma and expels the electrons out, to form a co-moving positive charged sheet inside the bubble. The additional field generated due to sheet enhances the energy of the monoenergetic bunch by about 5% and their number by 5–20%. For a typical 40 fs, 7.5 × 1019 Wcm−2 pulse in an underdense plasma of density n0, CNT of thickness 25 nm and electron density 30n0, produces a monoenergetic bunch of 115 MeV with 5% energy spread. When CNT density is raised to 90n0, the energy gain, energy spread and accelerated charge increases further. The analytical framework supports these features.

Two complementary models invoking ion heating are presented which, together with pump depletion, quantitatively account for the principal observations (reflectivity, spectral shape, saturation) of stimulated Brillouin scattering (SBS) in a CO2 laser/plasma interaction experiment. A simple energy balance model, which incorporates ion heating and includes a consistent calculation of ion wave damping, is applicable for steady state convective growth of the ion waves (long interaction times). A more refined model, which includes a calculation of the trapped ion fraction (along with heating), is applicable for SBS in a transient regime. Strong ion wave damping has been consistently observed in both cases in our high intensity CO2 laser/plasma scattering experiments. A variety of measurements have been made to investigate the basic features of SBS and associated density fluctuations for both long pulse (40 ns) and short pulse (2 ns) CO2 laser irradiation. Measured parameters reported here include plasma density, temperature, density scalelength, SBS reflectivity, and spectral characteristics. Together with previous measurements of density fluctuations (amplitude, wavenumber spectra, spatial and temporal information), the observed behavior confirms that Brillouin scattering is dominated by strong ion trapping, heating and ion wave damping for the laser/plasma parameters prevailing in these experiments.

The formation of a double layer is proposed as the mechanism which produces the critical velocity phenomenon. We examine this hypothesis, qualitatively, and find that the double layer can be a very efficient mechanism for transferring the kinetic energy of the neutral gas into the kinetic energy of electrons which, in turn, will ionize the neutral gas if the critical velocity has been reached or exceeded.

Time and space-resolved emission spectroscopy measurements were performed to investigate plasma dynamics during laser evaporation of a graphite target in an ambient inert atmosphere. Intense molecular emission is found to occur behind a front separating the plasma from the foreign gas. Two stages of expansion are found and are well described, using a viscous drag force model for the first one and a delayed ideal blast wave model for the second. The vibrational temperature estimated using the Swan band in helium at different pressures is presented.

The goal of the experiments on “Module A-5” and S-300 machines for some 15 years was to study the “liner-converter” inertial confinement fusion (ICF) scheme. A new class of fast instabilities of z pinches was studied both in experiments and in analytical theory. Stabilization of the light liner has been achieved by means of an extrinsic magnetic field. Formation of thin overheated current-carrying shells has been predicted analytically and seems to be really observed. Both theory and simulations predict growing Te and heat flux onto the converter by using heterogeneous z pinches with spatially separated regions of efficient energy exchange and of efficient heat conductivity. In our first experiments of this kind, impurities were inserted by means of placing thin glass fibers into a He jet. Growing intensity of the spectral lines of He-like chlorine from the cathode surface confirms the growth of heat flux. Theoretical investigations and 2.5-D simulations were devoted to some basic points of this program.

We theoretically and experimentally investigate the conditions of obtaining a narrowband flat-top Brillouin gain spectrum (BGS) based on single-frequency and multi-frequency phase modulations. Using the unequal-amplitude spectral lines, the flat-top BGS can be realized by controlling the intensity ratio and the frequency separation between them. In experiment, we obtain the flat-top gain spectra with the bandwidths of 40 MHz and 125 MHz, and with the top fluctuation of less than 0.21 dB. Based on this, we also achieve low distortion Brillouin amplification of a probe signal pulse and spectrum.

An injection-locking excimer laser beam with a pulse duration of 25 ns is focused on the surface of a polymide film. The laser beam that passes through the etching film is shorter than the original one. By optimizing the thickness of the film and the beam powerdensity, a pulse with a 3-ns pulse duration can be obtained using this switch technology.

The acceleration of transparent charged macroparticles by the repeated radiation pressure of a laser beam is considered. A radial electric field allows a motion along a closed path, on a stable orbit. For macroparticles made out of carborundum, of radius r = 0.5 μm, velocities above 100 km/s look feasible, allowing the production of high densities of energy.

A simple model in two dimensions is developed and solved analytically taking into account the electric and magnetic fields in laser produced plasmas. The electric potential in this model is described by the non-linear differential equation

ψ = eφ/T, where eφ is the electric potential energy and T is the temperature in energy units. The physical branch ψ < 1, defined by the electron density n = no exp ψ, boundary conditions n (x = 0) = const and n (x = +∞) = 0, introduces a typical electrostatic double layer. The stationary solution of this model is consistent for − 3 ≲ ψ < 1, with electron temperatures in the KeV region and a ratio of the electric (E) to magnetic (B) fields of [E/106 v/cm]/[B/MGauss] ∼ 1.

A conical-pinched electron-beam diode has been studied with the objective of increasing the brightness of this inherently high current ion beam. Experiments and calculations are described that suggest it may be possible to obtain powers as high as 1013W/cm2 at 4MV from a carefully designed insulated-anode-type pinched-electron beam diode.

A high performance, fully controlled picosecond laser system has been designed and built with the aid of a numerical code capable of simulating the temporal behavior of the laser system, including each active and passive component. The laser performance was characterized with an optical streak camera, equivalent plane monitor, and calorimeter measurements. The laser pulse was focused on 150-nm thick foils to investigate plasma formation and the related transmittivity of the laser light. The experimental data are in very good agreement with the predictions of a simple, 2D analytical model that takes into account the actual shot-to-shot features of the laser pulse. The temporal profile of the pulse and the intensity distribution in the focal spot were found to play a key role in determining the transmission properties of the laser-irradiated foil. This work may be relevant to a wide class of laser exploded foil plasma experiments.

We present some experimental results which demonstrate the presence of electric inhibition in the propagation of relativistic electrons generated by intense laser pulses, depending on target conductivity. The use of transparent targets and shadowgraphic techniques has made it possible to evidence electron jets moving at the speed of light, an indication of the presence of self-generated strong magnetic fields.

A nonequilibrium kinetic model is used for predicting the time evolution of the Li atom concentrations (ground and excited states) in the plasma produced by excimer laser ablation of a LiNbO3 target. The model predicts a very high ionization degree (∼0.97) that agrees well with the one obtained experimentally (∼1). These results together with the prediction of high (and close to local thermodynamic equilibrium) population densities of the electronically excited Li upper energy levels provide an indirect support for an electronic rather than thermal ablation mechanism of Li atoms.