Search Results (4 total)

The interaction between a low-density electron cloud in a circular particle accelerator with a circulating charged particle beam is considered. The particle beam’s space charge attracts the cloud, enhancing the cloud density near the beam axis. It is shown that this enhanced charge and the image charges associated with the cloud charge and the conducting wall of the accelerator may have important consequences for the dynamics of the beam propagation. The tune shift due to the electron cloud is obtained analytically and compared to a new numerical model (QuickPIC) that is described here. Sample numerical results are presented and their significance for current and planned experiments is discussed.

A very intense electron plasma wave is resonantly excited at the top of a broad, flat density profile, by a longitudinal very-high-frequency electric field oscillating at the plasma frequency. Electric field energy densities W=Ẽ ²/4πn_cT_e>10³ are produced, along with copious electrons and ions of kinetic energy K>10³T_e. Reconstruction of the wave, from detailed measurements of electric field amplitude and phase, demonstrates wave breaking and accounts for the observed energetic particles.

Computer simulations of magnetosonic waves, velocity-shell instabilities, and upper-hybrid heating show evidence of a general damping mechanism for large-amplitude electrostatic waves propagating perpendicular to a magnetic field: Particles trapped by a wave of frequency ω and phase velocity V_ph see an electric field V_ph×B, which accelerates them parallel to the wave front until the v×B force is large enough for detrapping. For ω≫ω_c, velocities as large as (ω / 4ω_c)V_ph can be attained, within a time ω_ct≈ω / 4ω_c.

A wave propagating obliquely with respect to a magnetic field has many resonances, located at v_∥=(ω-nΩ) / k_∥. When they overlap, there is a transition between regular and stochastic particle motion, leading to a strong decrease in the final wave amplitude. Simulations confirm this result. In the regime where particle motion is regular, the usual trapping oscillations disappear as the angle of propagation increases, because of phase mixing of the bounce frequencies in different resonances.