Beam Dynamics And Key Technology Studies Of A Compact Low Energy Electron Storage Ring Dedicated To Thomson Scattering

Tsinghua Thomson Scattering X Ray Source Phase ?(TTX-?)is a light source based on the original Tsinghua Thomson Scattering X Ray Source(TTX).Using TTX as an injector,TTX-? stores low energy electrons accelerated by TTX,which collide with laser beams to generate X-rays.This work focuses around the TTX-? storage ring.The lattice design of the ring and designs of key components are presented with theoretical analysis and simulation calculation on beam injection,collective effects and equilibrium parameters.TTX-? has a circumference of 5.668 m and consists of four dipoles and six quadrupoles.The fringe fields of the short dipole magnets will increase the vertical chromaticity.By optimizing the parameters of the dipole magnets by parameter scanning,the natural chromaticity can be controlled within a relatively reasonable range.Due to the compactness of the ring,conventional sextupole correction scheme can not effectively change the chromaticity to be positive.The bunch will suffer head-tail instability under the condition of negative chromaticity and positive slip factor.Through theoretical analysis and particle tracking simulation,it is found that the initial emittance of the bunch can be increased by the fringe field injection system,and the bunch has sufficient tune spreads by the nonlinear components of dipole and quadrupole magnets.Landau damping can successfully suppress the instability.The design of injection and extraction system is an important part of storage ring design.Due to the limited space,the dipole fringe field is used instead of septum magnets to inject and extract the beam,and the phase space evolution of the bunch during injection and extraction process is simulated.It is found that the nonlinearity of dipole magnets will increase beam emittance,which helps suppressing collective effects.The bunch length of the electron beam generated by TTX is only 1mm,and the bending radius of the dipole magnets of TTX-? is short,so strong coherent synchrotron radiation occurs after injection.The bunch length is not negligible compared with dipole length,so non-steadystate coherent synchrotron radiation also occurs at the edge of dipole magnets.Based on the Liénard–Wiechert formula,a fast simulation algorithm for steady-state and transiant coherent synchrotron radiation at dipole edges in storage rings is presented.Multi-particle multi-particle tracking simulation of the beam phase space evolution after beam injection is carried out.Coherent synchrotron radiation increases the synchrotron frequency of the bunch,which speeds up the filamentization process and increases the energy spread and length of the bunch.RF cavities are used for longitudinal focusing in the storage ring.Eigenmodes of RF cavities may induce Robinson instability.With the high revolution frequency of the compact storage ring and the Landau damping introduced by the nonlinearity of the components in the ring,a safety zone of at least 40 MHz wide defined by Landau damping and Robinson damping can be determined in the frequency spectrum.According to this safety zone,The eigenmodes of the RF cavity can optimized to suppress Robinson instability without HOM dampers.