Stability of relativistic electron beams in density channels - II

In a series of experiments we have observed the interaction of an intense relativistic electron beam (REB) with reduced density channels. The time history of the REB pulse approximated a half-sine wave with amplitude ∼8 kA and half-period ∼40 ns. The energy of the REB was ∼1 MeV and the diameter at injection into the channel was 2.3 cm. Interaction experiments took place in a large chamber filled with ammonia gas (NH3) to a pressure of 40 Torr. Channels were formed in the ammonia by absorption of the high energy beam (∼ 300 J) from a pulsed CO2 laser. To create simple channels (on axis density minimum) the laser beam passed through a simple aperture that limited the channel to 4 cm diameter at the REB injection point. To create annular channels (density minimum in an annulus off-axis) the laser beam passed through an annular mask that limited the channel to 2.3 cm inner diameter, 4 cm diameter outer diameter at the REB injection point. In both cases the minimum density in the channel was approximately one fourth the chamber filling density. The REB was injected into these channels coaxially. The presence of either type channel caused the REB trajectory to deflect away from the channel.