A beam-slice algorithm for transport of the darht-2 accelerator

A beam-slice algorithm has been implemented into the LSP particle-in-cell (PIC) code to allow for efficient simulation of beam electron transport through a long accelerator. The slice algorithm pushes beam particles along a virtual axial dimension and performs a field solve on a transverse grid which moves with the particle slice. External electric and magnetic fields are also applied to the slice at each time step. For an axisymmetric beam the slice algorithm is very fast compared to full 2-D r-z PIC simulations. The algorithm calculates beam emittance growth due to mismatch oscillations, in contrast to standard envelope codes which assume constant emittance. Using the slice algorithm we are able to simulate beam transport in the DARHT-2 accelerator at LANL from the region just downstream of the diode to the end of the accelerator, a distance of about 55 meters. Results from the slice simulation are compared to both 2-D PIC simulations in LSP and the beam envelope code LAMDA. The sensitivity of the final emittance to imperfect tuning of the transport solenoids is calculated.