Modeling the APLE injector solenoid magnetic field with the Biot-Savart Law

摘要

The APLE (Average Power Laser Experiment) photoinjector accelerates electrons to 5 MeV with four cavities. A solenoid placed between the first two cavities focuses the low energy (1.2 MeV) electron beam. The beam transport and the beam quality of the injector depend on the detailed field profile of the solenoid. To describe the solenoid magnetic field accurately, we integrate the fields from each section of the solenoid using the Biot-Savart's Law. This integration can produce an accurate model of the solenoid field installed in the APLE injector. The solenoid consists of three layers with a shared axis. Each layer is connected by spirals, and the ends are terminated with the leads. We evaluate the magnetic field from each component of solenoid and study the asymmetric transverse field along the beam axis that was observed in the experiment. We determine the angle of the solenoid axis by a best match of transverse field components measured on the beam axis z.The Biot-Savart algorithm is implemented in the particle simulation code PARMELA, and the injector optimization was performed.