Contribution Invited Oral
Prospects of an X-ray FEL Oscillator driven by a SCRF linac or on a by-pass of a MBA Storage Ring
An X-ray FEL Oscillator (XFELO), a low-gain device in which an X-ray pulse trapped in a X-ray cavity formed by Bragg crystals receives repeated FEL interaction will broaden the scientific vista for photon science of hard X-rays in areas requiring fully coherent and ultra-fine spectral bandwidth (BW). A 7-8 GeV super-conducting linear accelerator producing a constant stream of electron bunches is an ideal driver for an XFELO. With an optimized injector, it can produce fully coherent X-ray pulses with 3 meV BW and time averaged brightness 1028 photons/s/(mm-mr)2/0.1% BW at 14.4 keV, which is higher by three orders of magnitude expected from LCLS-II-HE. By using a transverse gradient undulator (TGU), an XFELO is also feasible in a bypass of a large storage ring with multi-bend achromats, an “ultimate storage ring (USR) such as PETRA-4. Due to the beam cooling requirement, the ring-based XFELO will need to be operated in a pulsed mode with ~1% duty factor. On the other hand, the X-ray BW could be an order of magnitude smaller than that based on a linac.