We propose a Photon Storage Ring (PhSR), which is a novel free-electron laser (FEL) composed of a compact synchrotron radiation (SR) source and a cylindrical mirror surrounding the electron orbit. The SR source is an exactly circular type and the mirror is concentric to the electron orbit. In this scheme SR is reflected back tangentially to the electron orbit by the cylindrical mirror and interacts with the electrons, leading to the laser oscillation. The PhSR posesses many ideal features: since SR is confined by the mirror then all the radiations emitted at an angle to the electron orbit exibit good coherency; since the interaction occurs continiously along the electron orbit, a large gain is expected; and since all radiations are extracted through a simple opening, an extraction efficiency is fairly high. Compared with a conventional FEL, PhSR is capable of generating a high laser power by using a relatively small accelerator with a small electron beam current.
