C.R. Prokop

Numerical modeling of a table-top tunable Smith–Purcell terahertz free-electron laser operating in the super-radiant regime

Terahertz (THz) radiation occupies a very large portion of the electromagnetic spectrum and has generated much recent interest due to its ability to penetrate deep into many organic materials without the damage associated with ionizing radiation such as x-rays. One path for generating copious amount of tunable narrow-band THz radiation is based on the Smith-Purcell free-electron laser (SPFEL) effect. In this Letter we propose a simple concept for a compact tunable SPFEL operating in the superradiant regime and demonstrate its capabilities and performances via computer simulation using the conformal finite-difference time-domain electromagnetic solver VORPAL.

Formation of Compressed Flat Electron Beams with High Transverse-Emittance Ratios

Flat beams—beams with asymmetric transverse emittances—have important applications in novel light-source concepts and advanced-acceleration schemes and could possibly alleviate the need for damping rings in lepton colliders. Over the last decade, a flat beam generation technique based on the conversion of an angular-momentum-dominated beam was proposed and experimentally tested. In this paper we explore the production of compressed flat beams. We especially investigate and optimize the flat beam transformation for beams with substantial fractional energy spread. We use as a simulation example the photoinjector of Fermilab’s Advanced Superconducting Test Accelerator. The optimizations of the flat beam generation and compression at Advanced Superconducting Test Accelerator were done via start-to-end numerical simulations for bunch charges of 3.2 nC, 1.0 nC, and 20 pC at ~37 MeV. The optimized emittances of flat beams with different bunch charges were found to be 0.25 μm (emittance ratio is ~400), 0.13 μm, 15 nm before compression, and 0.41 μm, 0.20 μm, 16 nm after full compression, respectively, with peak currents as high as 5.5 kA for a 3.2-nC flat beam. These parameters are consistent with requirements needed to excite wakefields in asymmetric dielectric-lined waveguides or produce significant photon flux using small-gap micro-undulators.

Beam dynamics performances and applications of a low-energy electron-beam magnetic bunch compressor

Many front-end applications of electron linear accelerators rely on the production of temporally compressed bunches. The shortening of electron bunches is often realized with magnetic bunch compressors located in high-energy sections of accelerators. Magnetic compression is subject to collective effects including space charge and self interaction via coherent synchrotron radiation. In this paper we explore the application of magnetic compression to low-energy (∼40MeV), high-charge (nC) electron bunches with low normalized transverse emittances (<5μm).