Status of ucla helical permanent-magnet undulator

A helical undulator, utilizing permanent-magnet of cylindrically symmetric (Halbach) geometry has been developed at UCLA’s Neptune Facility. The initial prototype is a short 8.8 cm, 6 periods long helical undulator, designed to test the electron-photon coupling by observing the micro-bunching has been constructed and is currently being tested in the Neptune facility. Coherent Transition Radiation and Coherent Cherenkov Radiation are used for micro-bunching diagnostic. Currently the undulator has been built; magnets were calibrated using magnetic field probe and via pulsed wire method. INTRODUCTION AND SETUP An Inverse Free Electron Laser (IFEL) is an alternative acceleration scheme that lets a laser transfer energy through use of a magnetic undulator to an electron bunch. Previously high-gain IFEL experiments have been successful at UCLA's Neptune facility [1], which utilizes a 100 J CO2 laser and a 15 MeV 0.5 nC Photoinjector linac. All previous undulators used at Neptune had planar symmetry. Using cylindrically symmetric undulator provides better coupling to an electron beam. It also allows separation between adjacent magnets to be bigger, which makes electron propagation through undulator easier. To test cylindrically symmetric undulator IFEL experiment in Neptune we’re building an 8.8 cm, 6 periods long, helical permanent-magnet undulator of Halbach geometry [2]. 10.6 μm CO2 laser light is propagated through the undulator to produce electron micro-bunching. Undulator A structure which has an array of magnets of alternating direction is called an undulator. Period of an undulator can be related to the laser wavelength (see Eq. 1 and Eq. 2). ) 1 ( 2 2 2 u u K + = γ λ λ (1) Where Ku is the undulator constant,