Author: Kim, E.-S.
Paper Title Page
Development of an S-band Cavity-type Beam Position Monitor for a Table-top Terahertz Free-electron Laser  
  • S.Y. Noh, E.-S. Kim
    Kyungpook National University, Daegu, Republic of Korea
  • S. Bae, K.H. Jang, Y.U. Jeong, H.W. Kim, K. Lee, J. Mun, S. H. Park, N. Vinokurov
    KAERI, Daejon, Republic of Korea
  A cavity-type beam position monitor (BPM) has been developed for a compact terahertz (THz) free-electron laser (FEL) system and ultrashort-pulsed electron linac system at the Korea Atomic Energy research Institute (KAERI). The cavity-type BPM has higher sensitivity and faster response time even at low charges, comparing with other types of BPMs. The designed position resolution of the cavity BPM is less than 10 μm. The material of the BPM is aluminium and the vacuum could be kept by indium sealing without brazing process, which result in easy modification and saving cost. The resonance frequency of the cavity BPM is 2.801 GHz and has a dimension of 200 x 220 mm (length x height) with a pipe radius of 38 mm. When electron beam passing through the cavity BPM with an offset, the amplitude of a dipole mode which depends linearly on the beam offset inside the cavity BPM is excited. With the KAERI THz FEL, signals from the BPM was measured by using an oscilloscope as a function of the beam offset. The position sensitivity was calculated to be 6.19 mV/mm/mA. By measuring the thermal noise of the system, position resolution of the cavity BPM was estimated to be less than 1 μm.