Studies On Beam Based Alignment Technology

Free Electron Laser as a novel light source has the great advantages of coherentradiation, high brightness and tunable wavelength, which enable its extensive potentials inphysics, material and bioscience. In order to generate FEL radiation, the linac is used toprovide high-energy electron beams, and then transmitted in to undulators that consist ofperiodic magnets. High coherent free electron laser will be generated by the interactionsbetween electron beam and electromagnetic field.Various kinds of effects caused by element errors will be met if the electron beam doesnot go through the magnet center of elements. And since transverse dispersion changesoff-energy particle trajectories and increases the effective beam size, dispersion must becontrolled. The traditional mechanical alignment technology is insufficient considering thestringent demands for FEL process on the transverse trajectory and size of the electronbeam.In order to improve the performance of orbit correction, the Beam Based Alignment(BBA) technology has been proposed and studied since1980s. In this dissertation,theoretical and simulation studies of quadrupole scan method and global correction methodare presented for Shanghai XFEL facility and Dalian Coherent Light Source, respectively.As a novel BBA scheme, Dispersion Free Steering (DFS) method uses large deliberateenergy variations of the electron beam to detect quadrupole magnet and beam positionmonitor (BPM) transverse offsets simultaneously. Simulation studies of DFS on ILC andFLASH undulator are shown, which confirm the capabilities of this scheme. Experimentsof BBA on FLASH are also presented.In addition, development of virtual accelerator environment for beam diagnostics isdescribed. Beam measurement and orbit control tools are verified under this virtualenvironment and it will greatly speed up the development of machine commissioning tools.The design concept and current development status are presented.