Beam dynamics in the spiral-line induction accelerator

The 3-D electrostatic particle/field simulation code SPIRAL is used to trace electron trajectories through a 180° bend in a spiral-line induction accelerator. Two specific issues were addressed. First, the vertical field coils were tested for their design quality by tracking single-particle orbits through the fields resulting from the coils. One important point was that the field index was relatively constant to about 3 cm from the reference orbit position, which indicated that the cosine φ coil positioning was well designed. Another point was that the proper placement of the vertical field terminations significantly reduces beam disruption as the beam traverses the transition into the vertical coils. The second issue addressed was that of the effect of stellarator fields on beam quality due to energy mismatch. It was found that the beam was not seriously degraded by an energy mismatch of up to 10%, and that the beam centroid motion due to the mismatch was tolerable