ACCELERATOR CHALLENGES BEYOND LCLS: DEVELOPMENT OF ULTRA-HIGH-BRIGHTNESS GUN*

Abstract where γ is the electron energy in units of its rest energy and λ is the x-ray wavelength. For λ = 1 Å and γ = 104, we have εn = 0.1 mm-mrad, which is lower by an order of magnitude than the current state of the art. A lower emittance at a fixed current implies higher brightness. Thus we see that the optimal e-beam brightness of an x-ray-FEL-based future light source is an order of magnitude higher than currently feasible. Cost and complexities of next-generation light sources based on high-gain x-ray free-electron lasers (FELs) can be reduced significantly if the beam brightness can be increased by an order of magnitude than what is feasible today. We discuss the benefits of such ultra-high-brightness beams and possible R&D paths towards producing them