Design of Ultra-low Emittance Ring with Multi-bend Lattice on a Torus-knot

Abstract

We proposed a torus knot type synchrotron radiation ring in that the beam orbit does not close in one turn but closes after multiple turns around the ring. Currently, we are designing a new ring based on the shape of a (11, 3) torus knot for our future plan ‘HiSOR-II.’ This ring is mid-low energy light source ring with beam energy of 700 MeV. Recently some light source rings are achieving very low emittance that reaches a diffraction limited light by adopting a multi-bend scheme to the arc section of the ring. It is not difficult for low-mid energy VUV-SX light source ring because the electron beam less than 10 nmrad can provide the diffraction limited light in the energy less than 10eV. However the multi-bend lattice has many families of the magnets, therefore it is not easy to decide the parameters of the lattice. Especially, it is difficult for the torus knot type SR ring because there is a lot of geometric limitation around the cross points of orbits. We present the details of the designing procedure and the specifications of the ultra-low emittance light source ring having innovatively odd shape.