Physics Commons^™

Generating quasi-monochromatic, femtosecond gamma-ray pulses via Thomson scattering (TS) demands exceptional electron beam (e-beam) quality, such as percent scale energy spread and five-dimensional brightness over 10^16 A/m^2. We show that near-GeV e-beams with these metrics can be accelerated in a cavity of electron density, driven with an incoherent stack of Joule-scale laser pulses through a mm-size, dense plasma (n ~ 10^19 cm^-􀀀3). Changing the time delay, frequency difference, and energy ratio of the stack components controls the e-beam phase space on the femtosecond scale, while the modest energy of the optical driver helps afford kHz-scale repetition rate at manageable average …