Summary report of Working Group 3: Laser and high-gradient structure-based acceleration

Working Group (WG) 3 assessed current challenges in developing advanced accelerators based on RF and laser-driven electromagnetic (EM) structures and surveyed the state-of-the-art research and methods addressing these challenges. A critical challenge for EM structures is the gradient limitation imposed by RF breakdown, pulsed heating, dark current, quench, thermal breakdown and other factors, depending on structure type, pulse width, duty cycle and regime of operation. Other challenges include developing approaches to reduce cost and size while at the same time greatly increasing performance. WG 3 examined a variety of approaches to the improve gradient, cost, size, and performance of advanced accelerators including dielectric loaded structures, photonic bandgap structures, solid-state crystal structures, terahertz generation technologies, inverse FELs and undulators, micro-accelerators and light sources, high gradient structures, and RF sources. These approaches cover a large range of frequencies and span a considerable parameter space including room temperature and superconducting devices, THz and optical EM, and dielectric-based structures. The state of the art was surveyed in RF source and component development, materials development, advanced micro-and nano-fabrication technologies, and surface coatings for accelerator applications. WG 3 also attempted to address challenges beyond gradient limitation, including simulation challenges, high order mode characterization, measurement, and damping, field distributions producing low emittance, power efficiency, and impact of fabrication tolerances.