HSRC, Higashi-Hiroshima, Japan
We proposed a new scheme of lattice design for a compact storage ring in which a design orbit of electron beam closes after completing multiple turns.* This new lattice can be made by placing necessary accelerator components at certain positions on a projected torus knot in the horizontal orbit plane. In a storage ring having this type of lattice, the beam trajectory crosses in bending magnets, i.e. each bending magnet accepts two beam orbits. For example, in the ring having the (11, 3) torus knot lattice with 11 bending magnets, a bunch goes through bending magnets 22-times to complete its 3-turn closed orbit. Since the maximum output laser power is proportional to the synchrotron radiation loss in the complete turn round a closed orbit starting from the optical resonator section,** the maximum laser power from the projected torus knot storage ring FEL can be doubled for 2-turn lattice and tripled for 3-turn lattice compared with that from a conventional storage ring FEL. The new lattice scheme may contribute to more stable operation of a compact storage ring FEL. Some realistic parameters and achievable performance for UV-FEL are discussed in the presentation.
*S. Sasaki and A. Miyamoto, Proceedings of IPAC'11, San Sebastian, September 2011, TUPO010, p.1467 (2011).
**R. Bartolini, et al, Phys. Rev. E 69, 036501 (2004).
