Effects of Sextupolar Undulator Magnetic Field Contributions on Inverse Free Electron Laser Accelerator

In this paper, we include the important effects of sextupolar field contributions on saturation gain and length of a linear polarized undulator driven inverse free electron laser (IFEL) that arise when the electrons are injected off axis. The modified IFEL equations are derived and analyzed. Both the accelerating gradient and the saturation length of the IFEL are influenced by the imperfect beam trajectory. For a fixed laser wavelength, the effects are more pronounced in the case of short period undulator in comparison with a larger period undulator IFEL. A useful empirical fit is prescribed to estimate the tolerance of the IFEL for imperfect beam trajectory.

I. Introduction

In recent years, there exists an interest in laser driven accelerator for acceleration of electrons to energies of the order of gigaelectronvolts. The schematic of using free electron laser (FEL) mechanism to accelerate electrons called as inverse FEL (IFEL) is based on [1]. In this schematic, the relativistic electrons move through an undulator magnet in the presence of an electromagnetic wave parallel to the relativistic electron beam. The undulator magnet produces a small transverse velocity in a direction parallel to the electric field vector of the electromagnetic wave and energy transfer from the laser to the electron takes place at the resonant condition. Due to availability of very high-peak-power lasers with mature and novel undulator technology, IFEL has emerged as an advanced promising accelerator scheme to provide table top gigaelectronvolt-level accelerator for many applications in applied modern physics and FELs.