TY - CPAPER AU - Miginsky, S.V. AU - Bae, S. AU - Gudkov, B.A. AU - Jang, K.H. AU - Jeong, Y.U. AU - Kim, H.W. AU - Lee, K. AU - Miginsky, S.V. AU - Mun, J. AU - Park, S. H. AU - Shim, G.I. AU - Vinokurov, N. TI - Waveguide THz FEL Oscillators J2 - Proc. of FEL2015 AB - In today's world there is a significant demand for FEL-based THz radiation sources. They have a wide tuning range, a narrow band of radiation, and comparably high peak and average emission power. There are a significant number of these machines in the world, operating or in the development. The main difference between a long-wave FEL, of THz or a millimeter band, and a conventional one is a too big transverse size of the fundamental mode of an open optical resonator. It claims a large gap in an undulator that dramatically decreases its strength. Both factors sorely decrease the amplification and the efficiency, and often make lasing impossible. The main way to solve this problem is to use a waveguide optical resonator. It decreases and controls the transverse size of the fundamental mode. However, the waveguide causes a number of problems: power absorption in its walls; higher modes generation by inhomogeneities, as it is not ideal; electron beam injection into a FEL is more sophisticated; also outcoupling is more complicated; finally, the resonator detuning control claims some special solutions. The waveguide dispersion relation differs from one in the free space. It shifts up the wavelength of the FEL, changes the optimal detuning, and creates a parasitic mode near the critical wavelength of the waveguide. These problems and possible solutions to them are considered. PB - JACoW CY - Geneva, Switzerland SP - 576 EP - 579 KW - FEL KW - injection KW - electron KW - extraction KW - undulator DA - 2015/12 PY - 2015 SN - 978-3-95450-134-2 DO - 10.18429/JACoW-FEL2015-WEB02 UR - http://accelconf.web.cern.ch/AccelConf/FEL2015/papers/web02.pdf ER -