ENERGY AND FREQUENCY MEASUREMENTS ON THE TWENTE RAMAN FREE-ELECTRON LASER

Results of energy and frequency measurements on the Twente Raman FEL a re presented and discussed. A highest energy of 230 mJ was measured us ing a joule meter. The spectrum was determined using waveguide cutoff filters. These measurements generally showed a broad spectrum containi ng two or more peaks. Far from magneto-resonance this indicates that t he radiation field grows at the upper as well as at the lower interact ion of the slow space-charge wave with the the electromagnetic wavegui de modes. Near magneto-resonance, the analysis of the spectra shows th e presence of the cyclotron instability together with the FEL instabil ity. The two instabilities are resonant with different waveguide modes . The latter was confirmed by a measurement of the radial profile of t he emitted radiation for a single setting of the guide and undulator f ield.