Self-generated magnetic dipoles in weakly magnetized beam-plasma system.

A self-generation mechanism of magnetic dipoles and the anomalous energy dissipation of fast electrons in a magnetized beam-plasma system are presented. Based on two-dimensional particle-in-cell simulations, it is found that the magnetic dipoles are self-organized and play important roles in the beam electron energy dissipation. These dipoles drift slowly in the direction of the return flow with a quasisteady velocity, which depends upon the magnetic amplitude of the dipole and the imposed external magnetic field. This dipole formation provides a mechanism for the anomalous energy dissipation of a relativistic electron beam, which would play an important role in collisionless shock and ion shock acceleration.

Autocorrelation measurement of fast electron pulses emitted through the interaction of femtosecond laser pulses with a solid target.

We report the first direct measurement of the emission duration of laser-accelerated fast electrons from the surface of a solid target irradiated by a high-intensity femtosecond laser pulse. The emission duration is determined by autocorrelation measurement using the Coulomb repulsive forces that act on two equivalent electron pulses. The emission duration depends on the laser pulse duration for laser pulses of 200-690 fs. Numerical modeling of three-dimensional charged particle dynamics indicates that the emission duration of fast electrons is almost equal to the duration of the laser pulse.

Particle in cell analysis of a laser-cluster interaction including collision and ionization processes.

A new particle-in-cell (PIC) code which includes collisional and ionization processes has been developed to study laser-plasma interaction. Using the new code, the dynamics of a cluster plasma in a strong laser field has been analyzed and the threshold intensity of the resonant heating, which was previously predicted is accurately evaluated. The angular dependence of ion energy spectrum has also been simulated. As a result, it is found that the anisotropic energy spectrum depends strongly on the presence or absence of collisional processes.

Resonant heating of a cluster plasma by intense laser light.

The heating of a single argon (Ar) cluster by a strong laser field is studied using an electrostatic particle-in-cell code for a range of intensities and cluster sizes. Heating is dominated by a nonlinear resonant absorption process involving energetic electrons transiting through the cluster. This process gives rise to a threshold in field strength for strong absorption and controls the dielectric properties of the cluster.