A Compact Soft X-ray Free-Electron Laser Facility based on a Dielectric Wakefield Accelerator

X-ray free-electron lasers (FELs) are expensive instruments with the accelerator holding the largest portion of the cost of the entire facility. Using a highenergy gain dielectric wakefield accelerator (DWA) instead of the conventional accelerator may reduce the facility size and, significantly, its cost. We show that a collinear dielectric wakefield accelerator can, in principle, accelerate low charge and high peak current electron bunches to a few GeV energy with up to 100-kHz bunch repetition rate. Several such accelerators can share the same tunnel and cw superconducting linac (operating with a few-MHz bunch repetition rate), whose sole purpose is feeding the DWAs with wake producing low-energy, high-charge electron bunches with the desired periodicity. Then, ten or more x-ray FELs can operate independently, each using its own linac. In this paper, we present an initial case study of a single-stage 850-GHz DWA based on a quartz tube with a ~100-MV/m loaded gradient sufficient to accelerate a 50-pC main electron beam to 2.4 GeV at a 100-kHz bunch repetition rate in just under 30 meters. While the accelerated electron beam has a large energy chirp, we show that FEL gain can be maintained by appropriately tapering the undulator, although other schemes may also be possible.