Inverse bremsstrahlung absorption in the spherical, quasi-steady corona of a weakly nonuniform laser-irradiated target is considered. Here we have assumed that laser irradiation is almost spherical, justifying a linear analysis in terms of spherical harmonics. Our analysis is applicable for low intensities and short wavelength pulses. Complete results for ablation pressure, mass flow rate, and critical surface location are given in terms of Legendre index.

We have developed a new soft x-ray spectrometer covering the photon energy range 50–500 eV. It employs a free-standing transmission grating coupled to a microchannelplate detector. The performance of the device was tested by using radiation from a synchrotron with a continuous spectrum. The detector shows a rather flat response over most of the useful spectral range, with an abrupt decrease in the sensitivity at the short-wavelength end. Its simplicity of operation makes the device attractive for such applications as the study of soft x-ray emission from laser-produced plasmas.

A mechanism of trapping and entrainment of electromagnetic (EM) field pulses into supercritical regions of an inhomogeneous plasma by ion-acoustic waves is considered.

In terms of energy conservation and vector matching relations, the dynamic process of the second harmonic emission from a laser plasma has been analyzed in this article for the first time. Then, considering the Langmuir wave spectrum which reflects the second harmonic spectrum, we derive the kinetic equation of the Langmuir wave. After a numerical Fourier analysis, the spectrum profiles are obtained, which coincide well with the experiments.

In order to calculate more generally the space-charge limited current between two points of different voltage, modern differential geometrical methods are applied. This problem was first treated by Child (1911) and later by Langmuir (1913). It is possible, for example, to account for effects due to more than one charge component as well as the influence of a neutral background gas (which causes ionization and scattering of charge carriers). A systematic derivation of the self-consistent representation based on a Hamilton theory for density functions is given, and solution methods are discussed. The concept is designed to investigate ion and electron diodes with very intense currents, but it may also be useful for treating space charge problems in a stationary plasma.

The mass ablation rate and ablation pressure on laser-irradiated spherical microshells were measured using the space-resolved X-ray spectroscopy. A new method for the study of the ablation by means of the Doppler shifted X-ray images is proposed. The time-resolved measurements of X-ray emission from layered microtargets allow us to determine the heat front penetration through the microshell wall.

Experimental studies of the ablative acceleration of thin foils as carried out on the “Mishen” device (Nd laser, λ = 1·06μm, 3 nsec pulses) are reported. The plasma corona in the range of power densities 1013–1014 W/cm2 is shown to absorb 80–90% of the laser beam energy, the classical collisional absorption mechanism being the main one. Jet-like and filamentary structures are observed in the laser-plasma interaction; however, the main plasma parameters are found to be independent of the presence (or absence) of such structures. The measured hydrodynamic efficiency of stable ablative acceleration in plane geometry is ≲5%. The production of high-speed cumulative jets with irradiated thin-wall hollow conical targets is reported as an example of a non-traditional ablative acceleration geometry.

We studied the electron beam generation in high-current diode with various cathode shapes and the beam propagation through vacuum or plasma delivered to metallic drift tube. The combined effect of external longitudinal and self-consistent azimuthal magnetic fields with the accelerating electric field is discussed. We are interested in obtaining the diode efficiency and beam characteristic in stationary state.

Scattered emission from the laser plasma created in shell target heating experiments using the Delfin-1 laser has been studied. It is shown that the ω0 spherical harmonics can be used to determine both the plasma temperature in the nc/4 region and also the plasma flow through this region.

The characteristics of a laser plasma created by a high intensity UV excimer laser were investigated. The UV laser plasma was used as a switch for control of the laser pulse duration for the first time. An X-ray preionized XeCl laser pulse duration can be changed from 10 to 85 ns. This technique is useful for many applications of excimer lasers requiring various pulse durations.

1-D computer simulations have been performed to study the influence of X-rays preheating on the compression of spherical laser-produced plasmas. The targets are glass microballoons filled with Neon at the initial pressure 10 bars. It is assumed that the only significant absorption process in the Neon is by inverse bremsstrahlung absorption. The results indicate that the radiative preheating energy has a nonnegligible effect on the compression, and a study of the Lawson criterion shows that this effect is more important for high-Z target shell materials and for thicker shells.

It has been recently suggested (Hora & Miley 1984) that in the cannonball scheme of laser compression the pellet may be considered to be compressed by the ‘brute force’ of the radiation pressure. For such a radiation-driven compression, this paper applies an energy balance method to give an equation fixing the radius compression ratio κ which is a key parameter for such intense compressions. A shock model is used to yield specific results. For a square-pulse driving power compressing a spherical pellet with a specific heat ratio of 5/3, a density compression ratio Γ of 27 is computed. Double (stepped) pulsing with linearly rising power enhances Γ to 1750. The value of Γ is not dependent on the absolute magnitude of the piston power, as long as this is large enough. Further enhancement of compression by multiple (stepped) pulsing becomes obvious. The enhanced compression increases the energy gain factor G for a 100 μm DT pellet driven by radiation power of 1016 W from 6 for a square pulse power with 0·5 MJ absorbed energy to 90 for a double (stepped) linearly rising pulse with absorbed energy of 0·4 MJ assuming perfect coupling efficiency.

A nonlinear relaxation is observed when an electron beam interacts with plasma in an external magnetic field. An acceleration of electrons to energies which are more than twice that of the initial beam energy is observed. The acceleration mechanism is connected with the modulation instability of the plasma waves which is excited when the beam relaxes.

Experiments have been performed at the Central Laser Facility, Rutherford Appleton Lab., UK. using novel techniques in which laser produced plasmas have been diagnosed by measurements of the charged thermonuclear reaction products. Two types of experiment are being reported here. Firstly, thermonuclear alpha particles from an exploding pusher target have been used to determine the growth of the Rayleigh–Taylor instability in a separate laser driven planar foil. The resulting alpha particle range loss distributions provide a direct measurement of the foil thickness distribution and hence the instability. The R–T instability has been observed in a number of foils with range losses varying between almost zero to over lOμm. Secondly, a thermonuclear particle backlighting technique has been used in the measurement of the stopping power of hot plasma for different materials. The ratio of plasma stopping power to that of the cold material is measured and compared to a value obtained from theoretical modelling. The solid state nuclear track detector CR–39 has been used as a diagnostic for these experiments. A sophisticated image analysis system has been developed to enhance and improve data recovery.

The problem of heavy-ion beam energy conversion into the plasma self-radiation of the spherical target is considered by using the radiative conductivity approximation. It is shown that there is a single parameter γ which determines the spherical ‘corona’ structure and has the meaning of the ratio: the ion range/the effective heat range. The conversion coefficient increases with the increase in the parameter γ and becomes ∼ 1, when γ ≃ 102. Typical beam and target parameters of modern HIF designs correspond to γ ≃ 10 and conversion coefficients >50%. Thus, at quasistationary stage of the ‘corona’ expansion the target acceleration and implosion regime is basically the radiative one.

The evolution of rf-accelerator technology toward high-power, high-current, lowemittance beams produces an ever-increasing demand for efficient, very high power microwave power sources. The present klystron technology has performed very well but is not expected to produce reliable gigawatt peak-power units in the 1- to 10-GHz regime. Further major advancements must involve other types of sources. The reflexing-electron class of sources can produce microwave powers at the gigawatt level and has demonstrated operation from 800-MHz to 40-GHz. The pulse length appears to be limited by diode closure, and reflexing-electron devices have been operated in a repetitively pulsed mode. A design is presented for a reflexing electron microwave amplifier that is frequency and phase locked. In this design, the generated microwave power can be efficiently coupled to one or several accelerator loads. Frequency and phase-locking capability may permit parallel-source operation for higher power. The low-frequency (500-MHz to 10-GHz) operation at very high power required by present and proposed microwave particle accelerators makes an amplifier, based on reflexing electron phenomena, a candidate for the development of new accelerator power sources.