A new technology for generating high quality and powerful terahertz (THz) synchrotron radiation based on a low energy tabletop storage ring is presented. The ring has been designed to provide coherent synchrotron radiation (CSR) from a bending magnet of 156 mm bending radius with the acceptance angle of 264 (H) × 198 (V) mrad2. The THz emission is forced by an exactly circular mirror, named photon storage ring (PhSR), placed around the electron orbit. In this system, synchrotron radiations are reflected back by the mirror to intersect the electron orbit again, and are consequently accumulated within the PhSR. The accumulated synchrotron radiations can be fully extracted through a simple opening on the mirror surface. The optimum optical system has been determined by using ray trace simulation code ZEMAX. The expected THz output is of the order of 100 W.