Using three dimensional test particle simulations, the characteristics and essential conditions under which an electron, in a vacuum laser beam, can undergo a capture and acceleration scenario (CAS) have been examined. When $a_0\text{≳100}$ the electron can be captured and violently accelerated to energies ≳1 GeV, with an acceleration gradient ≳10 GeV/cm, where $a_0{\mathrm{=eE}}_0{\mathrm{/m}}_e\mathrm{\omega c}$ is the normalized laser field amplitude. The physical mechanism behind the CAS is that diffraction of the focused laser beam leads to a slowing down of the effective wave phase velocity along the captured electron trajectory, such that the electron can be trapped in the acceleration phase of the wave for a longer time and thus gain significant energy from the field.

Rarefactive ion-acoustic solitons have been observed in a two-electron-temperature plasma. Some of the characteristics can be interpreted by the solution of the Kortweg–de Vries (K–dV) equation. The Mach number of the solitons is a function of the temperature ratio of hot and cold components.

A plasma lens for 18-MeV round-shaped electron beams was experimentally studied; the lens is based on self-focusing due to shielding of the space charge of a particle beam by a quiescent plasma. A differential pumping technique was applied to separate the plasma chamber from the linac acceleration duct. It is shown that overdense plasmas successfully focus the electron beams. Another finding is that the plasmas appear to reduce the transverse emittance.

The nonlinear evolution of oblique collisions is investigated experimentally on plane ion-acoustic solitons in two-dimensional space. Many of the observed characteristics of inelastic collisions of solitons are found to be similar to those of resonance interactions described by nonlinear ion-acoustic waves.

Experimental observations on the partial reflection of a planar ion-acoustic soliton from a plane rigid boundary with sharp density gradients are presented. The reflected wave attenuates rapidly, forming a spherical wave front apart from a small reflector. The reflection coefficient of about 25% at the boundary has no apparent dependence on the incident wave amplitude and the sheath thickness in front of the reflector in the case of the disk reflector, while it has a dependence in the case of the mesh reflector, having even larger values of up to about 50%.

Using a gas-jet flow, via the interaction between an ultrashort high-intensity laser pulse and plasma in the presence of a perpendicular external dc magnetic field, the short pulse radiation from a magnetized plasma wakefield has been observed. Different nozzles are used in order to generate different densities and gas profiles. The neutral density of the gas-jet flow measured with a Mach-Zehnder interferometer is found to be proportional to back pressure of the gas jet in the range of 1 to 8 atm. Strength of the applied dc magnetic field varies from 0 to 8 kG at the interaction region. The frequency of the emitted radiation with the pulse width of 200 ps (detection limit) is in the millimeter wave range. Polarization and spatial distributions of the experimental data are measured to be in good agreement with the theory based on the ${\mathbf{V}}_{\mathbf{p}}\times \mathbf{B}$ radiation scheme, where ${\mathbf{V}}_{\mathbf{p}}$ is the phase velocity of the electron plasma wave and $\mathbf{B}$ is the steady magnetic field intensity. Characteristics of the radiation are extensively studied as a function of plasma density and magnetic field strength. These experiments should contribute to the development of a new kind of millimeter wavelength radiation source that is tunable in frequency, pulse duration, and intensity.