Calibration of energy slits and simulation of electron trajectories in the alpha magnet’s 3D field

Abstract

At the PBP-CMU Electron Linac Laboratory, high-brightness electron beams are produced from the radio-frequency (RF) linear accelerator (linac) system that consists of a thermionic RF electron gun, an alpha magnet, a traveling-wave linac structure, quadrupole magnets and steering coils. Several diagnostic devices are installed in the accelerator system to characterize electron beam properties. In this work, we study on measurement of electron beam energy downstream the RF gun using the alpha magnet equipped with energy slits in the vacuum chamber and a current transformer. Calibration of the energy slits’ posit ions for various stepper motor encoder numbers was conducted before installing the slits in the magnet’s vacuum chamber. The calibration result was imported into the energy calculation software that links to the stepper motor encoder and the energy value will then be automatically calculated. Moreover, dynamic simulations using a software ASTRA were performed to investigate electron’s trajectories in the alpha magnet’s field with different initial electron positions and angles. The results from this study will be used to estimate the result and accuracy of energy measurement using the alpha magnet. It was found that, for different initial horizontal and vertical positions at the alpha magnet entrance, the energy of electron will be measured to be lower than its actual energy by around 0.5% and the measured energy will decrease when the initial position is moving away from the middle point. In case of horizontal particle’s angle, the error of energy measurement increases up to 1% at the angle of 3° before the beam hitting the alpha magnet chamber. For the vertical particle’s angle, the electron that has the initial angle less than or larger than 1.5° will hit the vacuum chamber.