Progress of the Cesta RKA experiment

Summary form only given. During the ICOPS 2005 conference, we presented the preparation of a relativistic-klystron amplifier experiment (RKA) at CESTA. Our purpose is to understand the physics of such a device by using a large number of diagnostics and to compare the results they give with the predictions from the PIC code MAGIC. We present here the first experimental results where only two pill-box cavities are installed in the RKA. The first cavity is fed by a small part of the microwave emission produced by an external vircator. An alternating voltage at 2.28 GHz is then induced in the gap of this cavity which then modulates the 2 kA, 400 keV annular e-beam emitted by the RK cathode. The second cavity enhances this beam current modulation which is observed using B-dot probes. The measurement of the emission of the vircator enables us to monitor the power level entering the first cavity, both in time and frequency. We compare the observed bunching modulation at various positions on the RKA beam propagation line with the MAGIC predictions