WEA03
ANL, Argonne, Ilinois, USA
SLAC, Menlo Park, California, USA
An x-ray FEL oscillator (XFELO) will produce hard x-ray pulses of ultra-fine spectral resolution (~ meV) that combines FEL brightness with storage ring stability [1]. Thus, for example, the long-standing problem of high-TC superconductivity could be solved by inelastic x-ray scattering. In addition, an x-ray spectral comb can in principle be generated, vastly expanding the reach of experimental x-ray quantum optics. The accelerator for an XFELO should optimally be of the CW superconducting type. The linac for the European XFEL can be operated in CW mode without adding more cooling capacity if the energy is lowered from 14 to 7 GeV [2]. It is also possible to drive a hard x-ray XFELO at lower than 7 GeV, if a higher harmonic is chosen as the operating wavelength [3]. We have studied XFELO for 1 Å x-rays operating at the third or fifth harmonic using the 4 GeV SCRF linac planned for LCLS-II. Assuming bunch charge=50 pC, normalized rms emittance=0.2 mm-mrad, rms energy spread=500 keV, rms bunch length=190 fs, and undulator period length=2.6 cm, the gain at 1 Å as a 5th harmonic is found to be about 40%, sufficient for lasing allowing for the various losses.
[1] K.-J. Kim, Y. Shvyd’ko, and S. Reiche, Phys. Rev. Lett. 100,244802 (2008)
[2] J.K. Sekutowicz, et al., 2013 FEL Conf.(2013)
[3] J. Dai, H. Deng, and Z. Dai, Phys. Rev. Lett. 108,034802(2012)
