Free-electron lasers driven by supercurrent

We propose new concepts of free-electron lasers which are based on using the DC current in superconductors as a driver. It is found that these FEL-type devices are very promising due to the high critical current density and quantum coherence of the condensate in superconductors. Cherenkov and resotron (based on the dissipative instability) schemes driven by supercurrent are considered, the small-signal exponential gain is calculated.