Electron-beam guiding and phase-mix damping by a laser-ionized channel

Self-consistent nonstationary processes in phase-mixed electron beams focused by mobile ions

This paper is devoted to the analysis of nonstationary self-consistent processes in electron beam propagation in the presence of mobile ions. This problem is of particular interest for the recently developed plasma-assisted slow-wave oscillators (pasotrons). In pasotrons beam focusing is provided by ions (in contrast to other high-power microwave sources where the beam is focused by a strong external magnetic field). Typically, pasotrons operate in rather long pulses with a pulse duration on the order of 100 micros and larger. In such a time scale, the ion motion can play a significant role, and therefore, the self-consistent nonstationary processes in the beam transport and ion motion become important. In particular, the interaction with beam electrons may result in ion axial acceleration. In the present paper, a theory that describes these nonstationary self-consistent processes is developed, taking account of the phase mixing of electrons having a spread in their initial transverse velocities. The paper also contains some simulation results obtained for typical pasotron parameters.

Synchrotron radiation from electron beams in plasma-focusing channels

Spontaneous radiation emitted from relativistic electrons undergoing betatron motion in a plasma-focusing channel is analyzed, and applications to plasma wake-field accelerator experiments and to the ion-channel laser (ICL) are discussed. Important similarities and differences between a free electron laser (FEL) and an ICL are delineated. It is shown that the frequency of spontaneous radiation is a strong function of the betatron strength parameter a(beta), which plays a role similar to that of the wiggler strength parameter in a conventional FEL. For a(beta) > or approximately 1, radiation is emitted in numerous harmonics. Furthermore, a(beta) is proportional to the amplitude of the betatron orbit, which varies for every electron in the beam. The radiation spectrum emitted from an electron beam is calculated by averaging the single-electron spectrum over the electron distribution. This leads to a frequency broadening of the radiation spectrum, which places serious limits on the possibility of realizing an ICL.

Nonlinear effects on pulsed laser propagation in the atmosphere

Nonlinear effects on the propagation of a high power pulsed laser beam through the earth's atmosphere are modeled. Stimulated Raman scattering in relatively modest power laser beams is estimated to be very significant when extremely long path lengths are considered. Whole beam self-focusing may also seriously affect beam propagation. The observation of these phenomena is likely to be enhanced by wavefront compensation techniques to remove linear refractive-index atmospheric effects such as beam steering and scintillation. Examples of space to ground and ground to space beam propagation are presented.