  The Fermilab Accelerator Science and Technology (FAST) facility is currently
in operation with its linac based on TESLA-type superconducting rf cavities.
Using a 3-MHz micropulse repetition rate with a long macropulse composed of up
to 3000 micropulses, and with beam energies demonstrated at 300 MeV and
projected to reach 800 MeV with two additional cryomodules, the feasibilities
for a vacuum ultraviolet (VUV) and an extreme ultraviolet (EUV) free-electron
laser oscillator (FELO) with the two energies are evaluated. We have used both
the GINGER code with an oscillator module and the MINERVA/OPC code to assess
FELO saturation prospects at 120 nm with a 5.0-cm-period undulator of 4.5-m
length and the MINERVA/OPC code to assess the FELO at 13.4 nm with adjusted
parameters. The simulation results support saturation at both of these
wavelengths which are much shorter than the demonstrated shortest wavelength
record of 168.6 nm from a storage-ring-based FELO. This indicates
superconducting rf linac-driven FELOs can be extended into this VUV-EUV
wavelength regime previously only reached with single-pass FEL configurations.
In addition, emittance-dilution effects due to wakefields in the cavities and
the resulting sub-macropulse centroid slew effects on FELO performance are
addressed using MINERVA/OPC simulations for the first time.
