• C.H. Chen, K.Y. Huang, Y.-C. Huang
  NTHU, Hsinchu
• W.K. Lau, A.P. Lee
  NSRRC, Hsinchu

A THz-pulse-train photoinjector is under construction at the High-energy OPtics and Electronics (HOPE) Lab. at National Tsinghua University, Taiwan. This photoinjector is believed to be useful for generating high-power THz radiation, as well as for driving or loading a plasma-wave accelerator. A THz laser beat wave with full tunability in its beat frequency is employed to induce the emission of the THz electron pulses from the photoinjector. We show in our study that such a photoinjector is capable of generating periodically bunched MeV electrons with a bunching factor larger than 0.1 at THz frequencies for a total amount of 1nC charges in a 10-ps time duration. We will also present a driver laser technology that can tune the electron bunch frequency with ease and help the growth of the high harmonics in the bunching spectrum of accelerated electrons. Experimental progress on this photoinjector will be reported in the conference. The authors gratefully acknowledge funding supports from National Scienc Council under Contract NSC 97-2112-M-007-018 -MY2, National Synchrotron Radiation Research Center under Project 955LRF01N, and National Tsinghua University under Project 98N2534·10¹.

• Y.-C. Huang, C.H. Chen
  NTHU, Hsinchu

We study a desktop MW superradiance free-electron laser (FEL) at THz frequencies. By using some nominal beam parameters from a THz-pulse-train electron gun, we show in theory and simulation that 10-MW-level radiation power at THz frequencies is achievable from a meter long undulator in one single electron transit through the undulator. The proposed THz superradiance FEL is directly attached to the emittance compensating coil of the photoinjector without using any additional beam-fucusing element in between. This compact design allows the construction of a 10-MW FEL at THz frequencies on an ordinary desk. We will also show the usefulness of a tapered undulator for a superradiance FEL. With a 20% linearly tapered undulator, the FEL radiation power can be increased by more than 30%. This FEL is being constructed at the High-energy OPtics and Electronics (HOPE) Laboratory, National Tsinghua University, Taiwan. Experimental progress of this ultracompact, high-power single-pass superradiance FEL will be reported in the conference.