Francois Lemery

Generation and Characterization of Electron Bunches with Ramped Current Profiles in a Dual-Frequency Superconducting Linear Accelerator

We report on the successful experimental generation of electron bunches with ramped current profiles. The technique relies on impressing nonlinear correlations in the longitudinal phase space using a superconducing radio frequency linear accelerator operating at two frequencies and a current-enhancing dispersive section. The produced ~700-MeV bunches have peak currents of the order of a kilo-Ampère. Data taken for various accelerator settings demonstrate the versatility of the method and, in particular, its ability to produce current profiles that have a quasilinear dependency on the longitudinal (temporal) coordinate. The measured bunch parameters are shown, via numerical simulations, to produce gigavolt-per-meter peak accelerating electric fields with transformer ratios larger than 2 in dielectric-lined waveguides.

Tailored electron bunches with smooth current profiles for enhanced transformer ratios in beam-driven acceleration

This work was supported by the U.S. Department of Energy contract No. DE-SC0011831 to Northern Illinois University, and the Defense Threat Reduction Agency, Basic Research Award \# HDTRA1-10-1-0051, to Northern Illinois University. P.P. work is also supported by the U.S. Department of Energy under contract DE-AC02-07CH11359 with the Fermi Research Alliance, LLC, and F.L. was partially supported by a dissertation-completion award granted by the Graduate School of Northern Illinois University.

Synchronous acceleration with tapered dielectric-lined waveguides

We present a general concept to accelerate non-relativistic charged particles. Our concept employs an adiabatically-tapered dielectric-lined waveguide which supports accelerating phase velocities for synchronous acceleration. We propose an ansatz for the transient field equations, show it satisfies Maxwells equations under an adiabatic approximation and find excellent agreement with a finite-difference time-domain computer simulation. The fields were implemented into the particle-tracking program {\sc astra} and we present beam dynamics results for an accelerating field with a 1-mm-wavelength and peak electric field of 100~MV/m. The numerical simulations indicate that a

Alternative shapes and shaping techniques for enhanced transformer ratios in beam driven techniques

\sim 200

Passive longitudinal-phase-space tailoring of non-ultrarelativistic beams with dielectric-lined waveguides

-keV electron beam can be accelerated to an energy of

Planned High-gradient Flat-beam-driven Dielectric Wakefield Experiments at the Fermilab’s Advanced Superconducting Test Accelerator

\sim10

Formation of electron bunches with tailored current profiles using multi-frequency linacs

~MeV over

An Adiabatic Phase-Matching Accelerator

\sim 10

Passive Ballistic Microbunching of Non-Ultrarelativistic Electron Bunches using Electromagnetic Wakefields in Dielectric-Lined Waveguides

~cm. The novel scheme is also found to form electron beams with parameters of interest to a wide range of applications including, e.g., future advanced accelerators, and ultra-fast electron diffraction.

Experimental Demonstration of Ballistic Bunching with Dielectric-Lined Waveguides at Pitz

The transformer ratio of collinear beam-driven acceleration techniques can be significantly improved by shaping the current profile of the drive bunch. To date, several current shapes have been proposed to increase the transformer ratio and produce quasi-uniform energy loss within the drive bunch. Some of these tailoring techniques are possible as a result of recent beam-dynamics advances, e.g., transverse-to-longitudinal emittance exchanger. In this paper, we propose an alternative class of longitudinal shapes that enable high transformer ratio and uniform energy loss across the drive bunch. We also suggest a simple method based on photocathode-laser shaping and passive shaping in wakefield structure to realize a shape close to the theoretically optimized current profiles.