Long pulse, long range propagation

Summary form only given. An experiment was performed to measure ion hose growth rate using the Troll accelerator (2.5 MeV, 1 kA, 1μs) and a 14-m-long, 1-m-diameter propagation range. The channel was produced by ionization of a background gas with low-energy (400-V) electrons. Beam transverse displacement (x,y) was measured at 11 locations, using dB/dt diagnostics distributed throughout the first 6 m of propagation. The amplitude of transverse oscillations of a given beam segment was seen to grow, saturate, and damp as the segment propagated. For oscillations of less than a channel radius, the amplitude at saturation (d) vs. beam segment (t) grew exponentially according to d=d _o exp(2πGt/t_c), where G is the growth rate and t_c is the characteristic oscillation time of the channel. The next phase of this experiment addressed long-range propagation, and used a 91-m-long, 1-m-diameter propagation range. The channel was produced by laser photoionization of the organic gas trimethylamine (TMA). A KrF laser was used which operates at 248 nm, near an absorption peak of TMA, and produces a 5-J, 2.5-cm-radius beam. The total electron beam current and current density profile were measured about every 15 m throughout the propagation range