Author: Jeon, M.Y.
Paper Title Page
MOP030 Performance Analysis of Variable-Period Helical Undulator with Permanent Magnet for a KAERI THz FEL 84
  • J. Mun, K.H. Jang, Y.U. Jeong, K. Lee, S. H. Park, N. Vinokurov
    KAERI, Daejon, Republic of Korea
  • M.Y. Jeon
    Chungnam National University, Daejoen, Republic of Korea
  Funding: This work was supported by the World Class Institute Program of the National Research Foundation of Korea(NRF) funded by the Ministry of Science, ICT and Future Planning.(NRF Grant Number:WCI2011-001)
We realized a variable-period permanent-magnet helical undulator with high (~1 T) field amplitude, which is almost constant over undulator periods of 23–26 mm. Each undulator period has 4 modular sections of iron poles and permanent magnets embedded in non-magnetic disks with holes along the undulator axis. Modular plates undergo a longitudinal repulsive force from the magnetic field pressure and the spring coils between modular plates. The undulator period can thus be controlled by mechanically changing of the end plate longitudinal position. This compact design is suitable for a table-top terahertz free electron lasers. The measured on-axis field is about 0.97 T with the deviation less than 1% through the whole range of the undulator period variation. The measured spread of the longitudinal coordinates of the undulator field component maxima is less than 1%, and the measured field distribution meets the requirement for our terahertz FEL. The field reproducibility was checked by six measurements of the undulator field after the period variation for the 26 mm period. The r. m. s. phase errors is 3.7 degrees.