Recent laser guided transport calculations

Laser-guided transport has been simulated in axisymmetry for intense electron beams at energies ranging from 3 to 45 MeV for currents of 2 to 5 kA. The simulation includes time variation of guiding channel formation and the time evolution of channel ion oscillations. Expressions are derived which determine when electrons are captured in a simple z independent model. In the same approximation, ignoring the spectrum of ion masses, the ion collapse time is calculated. For typical ATA (Advanced Test Accelerator) currents of 2 to 5 kA, the collapse occurs near the end of the pulse. Thus, any adverse emittance growth effects caused by ion collapse would be expected near the end of the pulse. The occurrence of unstable radial oscillations was demonstrated for extreme ion channel λ_i variation. The DPC code has been used to simulate laser guided transport for a complete pulse the entire length of ATA. The variation of channel radius throughout the beam pulse has been confirmed and emittance growth has been demonstrated at the end of the ATA accelerator