Search

Terahertz (THz) radiation from a plasma cylinder with embedded radial electric and axial magnetic fields is investigated. The plasma density and the electric and magnetic fields are such that the electron plasma frequency is near the electron cyclotron frequency and in the THz regime. Two-dimensional particle-in-cell simulations show that the plasma electrons oscillate not only in the azimuthal direction but also in the radial direction. Spectral analysis shows that the resulting oscillating current pattern has a clearly defined characteristic frequency near the electron cyclotron frequency, suggesting resonance between the cyclotron and plasma oscillations. The resulting far-field THz radiation in the axial direction is also discussed. [ABSTRACT FROM AUTHOR]

The magnetic reconnection (MR) configuration was constructed by using two approaching laser-produced plasma bubbles. The characteristics of the MR current sheet were investigated. The driving energy of the laser pulse affects the type of the current sheet. The experiments present “Y-type” and “X-type” current sheets for larger and smaller driving energy, respectively. The energetic electrons were found to be well-collimated. The formation and ejection of plasmoid from the “Y-type” current sheet was expected to enhance the number of accelerated electrons. [ABSTRACT FROM PUBLISHER]

Nonlinear coupling of the motion in the three spatial degrees of freedom of a cold fluid electron-positron plasma is investigated. Exact solutions describing expanding flows with oscillations are obtained. It is found that the energy in the irrotational flow component is in general transferred to the rotational components, but not in the reversed direction. Furthermore, since the density evolution need not be related to all the three flow components, oscillations in one or two of the flow fields can be purely electromagnetic and are not accompanied by density oscillations. [ABSTRACT FROM AUTHOR]

Fully nonlinear electrostatic waves in a plasma containing electrons, positrons, and ions are investigated by solving the governing equations exactly. It is found that both smooth and spiky quasistationary waves exist, and large-amplitude waves necessarily have large-phase velocities, but small-amplitude waves can be both fast and slow. [ABSTRACT FROM AUTHOR]

Collimated proton beams from laser interaction with a slab having a hole on its backside are investigated using particle-in-cell simulation. The hot target electrons driven by the laser expand rapidly into the hole. However, at the hole's corners the electrons are strongly compressed and an intense electron jet is emitted from each corner, tightly followed by the ions. The plasma jets focus and collimate along the axis of the hole and can propagate without divergence within the hole. The effect of the hole diameter on the collimated proton beam is considered. [ABSTRACT FROM AUTHOR]

It is shown that an intense laser pulse can be focused by a conical channel. This anomalous light focusing can be attributed to a hitherto ignored effect in nonlinear optics, namely that the boundary response depends on the light intensity: the inner cone surface is ionized and the laser pulse is in turn modified by the resulting boundary plasma. The interaction creates a new self-consistently evolving light-plasma boundary, which greatly reduces reflection and enhances forward propagation of the light pulse. The hollow cone can thus be used for attaining extremely high light intensities for applications in strongfield and high energy-density physics and other areas. [ABSTRACT FROM AUTHOR]

The acceleration of a micrometer-sized plasma pellet at 100 critical densities (1023 cm-3) by consecutive application of ultra-short ultra-intense laser pulses is studied using two-dimensional particle-in-cell simulation. It is shown that due to the repeated actions of the laser ponderomotive force, a small dense plasma pellet can be efficiently accelerated, with a considerable fraction of the plasma ions accelerated to high speeds. The proposed scheme can provide a high-density flux of energetic ions, which should be valuable in many practical applications. [ABSTRACT FROM AUTHOR]

Monoenegetic ion beam generation from circularly polarized laser-pulse interaction with a double-layer target is considered. The front layer consists of heavy-ion plasma, and the rear layer is a small thin coating of light-ion plasma. Particle-in-cell simulation shows that the multi-dimensional effects in the ion radiation pressure acceleration are avoided and a highly monoenergetic light-ion beam can be produced. Our simulations reveal that the charge-mass ratio of heavy ions in the front layer and the thicknesses of both layers can strongly affect the proton energy spectra. [ABSTRACT FROM AUTHOR]

The formation of collisionless electrostatic shock (CES) and ion acceleration in thin foils irradiated by intense laser pulse is investigated using particle-in-cell simulation. The CES can appear in the expanding plasma behind the foil when self-induced transparency occurs. The transmitting laser pulse can expel target-interior electrons, in addition to the electrons from the front target surface. The additional hot electrons lead to an enhanced and spatially-extended sheath field behind the foil. As the CES propagates in the plasma, it also continuously forward-reflects many of the upstream ions to higher energies. The latter ions are further accelerated by the enhanced sheath field and can overtake and shield the target-normal sheath accelerated ions. The energy gain of the CES accelerated ions can thus be considerably higher than that of the latter. [ABSTRACT FROM AUTHOR]

The campaign for one-child families in the People's Republic of China has created world-wide interest. This study compares the general rates of single-child families in China and in 60 other countries and shows that China's current rate (12.5) is relatively low in comparison with some developed countries, e.g. Hungary (25.0). The mean age-specific single-child rate for 54 less developed countries shows a different pattern from that for seven developed countries; this is likely to be due to the later age of marriage and longer birth intervals of women in the developed countries. [ABSTRACT FROM PUBLISHER]

This paper reports the results of a June 1980 survey of 1069 children in Changsha, Hunan Province. The data have been unavailable previously either in Chinese or in English. In general, they suggest that comparisons of single children with children from multiple-child families in China regarding quality of life, intellectual development, and behavioural traits are similar to comparisons conducted in the United States and other western countries. As in many western studies, single children in China appear to have a better quality of life than children with siblings. Regarding intellectual development, single children in China perform better than those with siblings, a finding which is consonant with the family intactness model of Falbo. Single children in Changsha are little different from ones from multiple-child families on various aspects of behaviour, and are more co-operative and less hostile. These findings are the opposite of those of the Shanghai study, the other major analysis of single children in China; the Shanghai survey indicated that single children were not as well-behaved as those with siblings, a finding that caused some concern among Chinese social scientists. To the extent that the findings of the Changsha study, and not those of the Shanghai study, reflect the situation of single children in China, this could mean that the one-child family planning campaign may not be having a negative impact on children's behaviour. [ABSTRACT FROM PUBLISHER]

This paper examines rates of marital childlessness in the developing countries of the world and separates them into voluntary, involuntary and related components through a decision-tree model based on fecundity, contraceptive behaviour, pregnancy status, age, years married, and other variables. The principal data are taken from World Fertility Surveys. The conclusion is reached that virtually all of the permanent childlessness in the developing countries examined is involuntary. [ABSTRACT FROM PUBLISHER]

The transient, growth and nonlinear saturation stages in the evolution of the electrostatic two-stream instabilities as described by the Vlasov–Poisson system are reconsidered by numerically following the evolution of the total wave energy of the plasma oscillations excited from (numerical) noise. Except for peculiarities related to the necessarily finite (even though very small) magnitude of the perturbations in the numerical simulation, the existence and initial growth properties of the instabilities from the numerical results are found to be consistent with those from linear normal mode analysis and the Penrose criteria. However, contradictory to the traditional point of view, the growth of instability before saturation is not always linear. The initial stage of the growth can exhibit fine structures that can be attributed to the harmonics of the excited plasma oscillations, whose wavelengths are determined by the system size and the numerical noise. As expected, saturation of the unstable oscillations is due to electron trapping when they reach sufficiently large amplitudes. [ABSTRACT FROM PUBLISHER]