MICROWAVE FEL EXPERIMENTS AT CESTA

At CESTA the EUPHROSYNE pulsed generator was used for Ondine 1, our fi rst FEL experiment at 35 GHz. The work was focused on beam creation an d propagation first with an oxide cathode and then with a cold cathode . Typically 1 kA at 2.5 MeV was propagated in single shot operation. A lot of calculations have been done on these problems and we have also developed simulation codes on FEL interaction in both Compton and Ram an regimes, taking into account 3D wiggler field, guiding field, waveg uide modes, and electron beam injection, to obtain trajectories, gain and efficiency. Good agreement with some previous experiments and code s has been found. In the frame of a preliminary superradiant experimen t using a bifilar helical wiggler, we obtained an amplification of the spontaneous emission up to 1 MW in the Kalpha band and 0.2 MW in the 33-36 GHz band. A microwave apparatus has been completed to work in an amplifier configuration: injection magnetron tube (100 kW), amplifica tion line and diagnostics. All these components are compatible of the new Ondine II experiment designed for operation with the LELIA inducti on linac. This experiment is to start at 0.1 Hz with the induction inj ector (1.3 MeV, 1 kA, 50 ns) using the same wiggler technology as Ondi ne 1. In the future we plan to carry out the 35 GHz experiment at 3 Me V by adding an accelerating module to the LELIA injector. An hybrid pl anar wiggler with parabolic pole faces is being studied for further ex periments.