Beam-based sub-THz source at the CERN linac electron accelerator for research facility

We report on the radiation studies performed at the CLEAR facility of CERN in the sub-THz range, exploiting picosecond ultrarelativistic electron bunches for the production of coherent radiation. The coherent radiation, produced by different mechanisms (in particular coherent transition radiation), has been fully characterized using different techniques and detectors. The main aim has been that to setup a new beam-based source of radiation in the mm-waves for external users, individuating the performances and the limitations. Moreover the coherent radiation has been used for longitudinal diagnostics, providing reliable bunch length values consistent with other diagnostics. Transverse shaping of the radiation source has been also demonstrated via control of the size and divergence of the electron bunch at the source plane. The mechanism yielding the highest peak-power has been the Cherenkov-Diffraction Radiation, providing ∼0.1  MW. The current performances of the CLEAR THz source seem to be more suitable for high-average-power than high-peak-power applications. Future plans and strategies will look toward the realization of a high-peak-power source, providing ∼10–100  MW THz pulses.