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It is shown that the transverse Rayleigh-Taylor-like (RT) instability in the hole-boring radiation pressure acceleration can be suppressed by using an elliptically polarized (EP) laser. A moderate J×B heating of the EP laser will thermalize the local electrons, which leads to the transverse diffusion of ions, suppressing the short wavelength perturbations of RT instability. A proper condition of polarization ratio is obtained analytically for the given laser intensity and plasma density. The idea is confirmed by two-dimensional particle-in-cell simulations, showing that the ion beam driven by the EP laser is more concentrated and intense compared with that of the circularly polarized laser.

Oscillations of charged dust grains in the sheath region of a radio-frequency plasma containing negative ions are studied using a one-dimensional model for collisional sheaths. The forces on a dust grain in the sheath region are first analyzed and the force-balance conditions found. Oscillations of the levitated dusts are then investigated. Linear lattice waves, including one-dimensional longitudinal and two-dimensional hexagonal transverse lattice waves, as well as the effects of the negative ions and external magnetic field on the waves, are discussed. [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]

Two-dimensional particle-in-cell simulation shows that a target with subwavelength nanolayered front can reduce the reflection and increase the absorption of the energy of an intense short laser pulse. The electrons within the skin depth on the surfaces of the nanolayers are accelerated by J×B heating to relativistic velocities and ejected into the narrow vacuum spaces between the layers. They then propagate forward with most of the absorbed laser energy along the surfaces of the layers. Conversion of the laser energy into electron energy can be enhanced by optimizing the vacuum spacing between the nanolayers since the phase structure of the laser field in the target is modified. The effects of the layer width, length, and spacing on the energy conversion efficiency are investigated. [ABSTRACT FROM AUTHOR]

Two-dimensional particle-in-cell simulation is used to investigate the acceleration of foil ions by the radiation pressure of an ultraintense short laser pulse in the presence of a background plasma of proper density and length behind the foil. It is shown that under appropriate conditions a central foil segment with a transverse dimension ∼σL/2, where σL is the laser spot size, can be stably accelerated. In this plasma backed acceleration scheme, foil electron heating and ion expansion are greatly suppressed by the cool backside electrons that replace the expelled fast electrons in the target, so that a monoenergetic collimated GeV ion sheet is produced. The simulation results agree with that from a physical model for the stably accelerated foil segment. [ABSTRACT FROM AUTHOR]

Energetic proton acceleration from interaction of intense short circularly polarized laser pulse with a sandwich target is investigated using two-dimensional particle-in-cell simulation. The sandwich target consists of a hydrogen-plasma layer surrounded by carbon-plasma layers. It is found that the transverse electric fields generated at the plasma layer interfaces efficiently confine the longitudinally accelerated protons to within the hydrogen-plasma layer such that they are collimated and have smaller energy spread compared with a pure proton layer target. The proton energy spectrum can be controlled by adjusting the target parameters, in particular the width of the hydrogen-plasma layer and the density of the carbon-plasma layer. [ABSTRACT FROM AUTHOR]

Electron acceleration in the low-density preplasma of a thin solid target by a short intense laser pulse is investigated by particle-in-cell simulation. Electrons in the preplasma are trapped and accelerated by the laser ponderomotive force as well as the wake bubble field. When the laser pulse is stopped and reflected by the target, the trapped electrons continue to move forward inertially, passing through the target with small energy spread and emittance. The use of the present scheme in practical applications is discussed. [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 lower-hybrid drift instability (LHDI) in a thin current sheet in the intermediate-wavelength ([formula], where ky, ρe, and ρi are the wave vector and the electron and ion gyroradii, respectively) regime for particles with κ velocity distribution is studied. The latter is more suitable for describing nonthermal distributions with an enhanced high-energy tail and includes the Maxwellian as a limiting case. It is shown that linear electromagnetic LHDI can be excited near the center of the current sheet. The growth rate decreases, but the electromagnetic component of the LHD mode increases with increase in hot particles. [ABSTRACT FROM AUTHOR]

The impact of a laser-accelerated micron-size projectile on a dense plasma target is studied using two-dimensional particle-in-cell simulations. The projectile is first accelerated by an ultraintense laser. It then impinges on the dense plasma target and merges with the latter. Part of the kinetic energy of the laser-accelerated ions in the projectile is deposited in the fused target, and an extremely high concentration of plasma ions with a mean kinetic energy needed for fusion reaction is induced. The interaction is thus useful for laser-driven impact fusion and as a compact neutron source. [ABSTRACT FROM AUTHOR]

Ion acceleration by ultrashort circularly polarized laser pulse in a solid-density target is investigated using two-dimensional particle-in-cell simulation. The ions are accelerated and compressed by the continuously extending space-charge field created by the evacuation and compression of the target electrons by the laser light pressure. For a sufficiently thin target, the accelerated and compressed ions can reach and exit from the rear surface as a high-density high-energy ion bunch. The peak ion energy depends on the target thickness and reaches maximum when the compressed ion layer can just reach the rear target surface. The compressed ion layer exhibits lateral striation which can be suppressed by using a sharp-rising laser pulse. [ABSTRACT FROM AUTHOR]

The interaction of an ultraintense laser pulse with parabolic concave target is studied using two-dimensional particle-in-cell simulation. It is found that ions at the back of the concave target can be accelerated more effectively than that with a plane target because of a large electrostatic field on the propagation axis induced by focusing of the laser expelled electrons. A highly collimated ion bunch with high particle and current densities appears. The dependence of the quality of ion acceleration and bunching on the width of the concave cavity is examined. It is found that the maximum ion energy is greatly enhanced when the width of the cavity attains a threshold, and an optimum width for generating a high-quality ion bunch exists. The results should be useful in the design of targets used in producing highly collimated energetic ions in high-energy-density physics. [ABSTRACT FROM AUTHOR]

The effect of plasma temperature on electrostatic shock generated by a circularly polarized laser pulse in overdense plasma is studied by particle-in-cell simulation. Ion reflection and transmission in the collisionless electrostatic shock (CES) are investigated analytically. As the initial ion temperature is varied, a distinct transition from the laser-driven piston scenario with all ions being reflected to the CES scenario with partial ion reflection is found. The results show that at low but finite temperatures the ions are much more accelerated than if they were cold. [ABSTRACT FROM AUTHOR]

The electric and the positive- and negative-ion drag forces on a dust grain in an electronegative complex plasma are investigated. It is shown that the number of locations where the drag forces balance the electric force is considerably larger than that in an electropositive plasma. The balance occurs in the so-called oscillation regime where the electric field oscillates in space. The effect of the negative-ion drag force on the dust grain can be substantial in a certain parameter range. [ABSTRACT FROM AUTHOR]

The spatial distribution of the ion flux at the substrate or work surface in inductively coupled plasma source is studied experimentally and theoretically. The theoretical study is based on a two-dimensional fluid model and the well-known global model. The spatial profiles of the electron density and temperature, as well as the ion flux density, are obtained. The theoretical results are compared with the experimental data obtained using a plate probe. It is found that at high pressures the temperature dependence of the electron-neutral collision rate can be important. For argon, maximum uniformity of the ion flux at the work surface occurs for p∼20 mTorr, with the induction coils located on the cylindrical sidewall of the discharge chamber. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The interaction of two energetic electron bunches generated in the wakefields of two intense intersecting laser pulses in rarefied plasmas is investigated using particle-in-cell simulations. It is found that, with suitable intersection angle between the two laser pulses, the initially independent wakefield accelerated electron bunches can merged into a single one with high charge, energy, and narrow energy spread. The dynamics of the laser-pulse intersection and wake-bubble merging process is also investigated, and the crucial roles of the intersection angle are pointed out and analyzed. [ABSTRACT FROM AUTHOR]