Emittance measurement and Laser Wire
The next generation of electron synchrotron light sources and high-energy electron-position accelerators will have unprecedented properties. The particle density will be sufficiently large that any solid object placed in the beam path will be almost immediately destroyed. The normal technique for measuring beam sizes relies on placing a wire or screen target in beam and so cannot be used. The laser-wire uses the interaction between a high power laser beam and the charged particle beam. The laser-photons are Compton scattered to high energies (gamma-rays) by the electrons. By moving the position of the laser beam whilst measuring the rate of Compton gamma rays gives a detailed picture of the charge density within a particle beam.
The laser-wire collaboration is between the John Adams Institute in Royal Holloway and Oxford and international laboratories (DESY and KEK). We have verified the operation of a near diffraction limited laser-wire system that can measure beam sizes of order 1 micrometer in transverse size. Our developments and expertise can now be deployed at various international facilities, including light sources, to enhance the beam measurement and control.