Christopher M. S. Sears

Dielectric laser accelerators

We describe recent advances in the study of particle acceleration using dielectric near-field structures driven by infrared lasers, which we refer to as Dielectric Laser Accelerators. Implications for high energy physics and other applications are discussed.

Designing photonic bandgap fibers for particle acceleration

Photonic bandgap (PBG) fibers with hollow core defects have been suggested for use as laser driven accelerator structures. The modes of a photonic crystal fiber lie in a set of allowed bands. A fiber with a central vacuum defect can support so-called defect modes with frequencies in the bandgap and electromagnetic fields confined spatially near the defect. A defect mode suitable for relativistic particle acceleration must have a longitudinal electric field in the central defect and a phase velocity at the speed of light (SOL). We explore the design of the defect geometry to support well confined accelerating modes in such PBG fibers. The dispersion diagram of an accelerating mode must cross the SOL line, and such modes form a special class of defect modes known as surface modes, which are lattice modes of the original PBG crystal that have been perturbed into the bandgap. The details of the surface boundary separating the defect from the surrounding PBG matrix are found to be the critical ingredients for optimizing the accelerator mode properties.

Beam Coupling to Optical Scale Accelerating Structures

Current research efforts into structure based laser acceleration of electrons utilize beams from standard RF linacs. These beams must be coupled into very small structures with transverse dimensions comparable to the laser wavelength. To obtain decent transmission, a permanent magnet quadrupole (PMQ) triplet with a focusing gradient of 560 T/m is used to focus into the structure. Also of interest is the induced wakefield from the structure, useful for diagnosing potential accelerator structures or as novel radiation sources.

Structure Loaded Vacuum Laser‐Driven Particle Acceleration Experiments at SLAC

We present an overview of the future laser‐driven particle acceleration experiments. These will be carried out at the E163 facility at SLAC. Our objectives include a reconfirmation of the proof‐of‐principle experiment, a staged buncher laser‐accelerator experiment, and longer‐term future experiments that employ dielectric laser‐accelerator microstructures.

An electron source for a laser accelerator

Laser accelerators offer the promise of producing attosecond electron bunches from a compact accelerator. Electron source requirements for laser accelerators are challenging in several respects, but are achievable. We discuss these requirements, and propose an injector design. Simulation and design work for essential components for a laser accelerator electron source suitable for a high energy physics machine will be presented. Near-term plans to test key technical components of the laser injector will also be discussed.

High-Harmonic Inverse Free-Electron-Laser Interaction at 800 NM

The inverse Free Electron Laser (IFEL) interaction has recently been proposed and used as a short wavelength modulator for micro bunching of beams for laser acceleration experiments [1,2]. These experiments utilized the fundamental of the interaction between the laser field and electron bunch. In the current experiment, we explore the higher order resonances of the IFEL interaction from a 3 period, 1.8 centimeter wavelength undulator with a picosecond, 0.5 mJ/pulse laser at 800nm. The resonances are observed by adjusting the gap of the undulator while keeping the beam energy constant. We also compare the experimental results to a simple analytic model that describes coupling to high order harmonics of the interaction.

IFEL‐Chicane Based Microbuncher at 800nm

As a first stage to net acceleration in a laser based EM structure RF electron pulses must be microbunched to match the laser wavelength. We report on the design of an undulator and chicane for microbunching at 800nm using an inverse free electron laser (IFEL) interaction. This includes design considerations for the hardware itself, the laser IFEL interaction and bunching performance, and a full 3D particle tracking simulation to study the focusing effects and possible emittance growth due to the fringe fields of the magnets. The talk will close with a discussion of laser‐electron beam diagnostics for overlap in the undulator and for diagnosing microbunching performance.