RF test benches for electron cloud studies

In the framework of the CERN program on the electron cloud effects in existing and future accelerators, a coaxial multipacting test stand was built. It consists of a 100 mm diameter vacuum chamber forming the outer conductor and 6 wires cage-aerial-type as the inner conductor. In order to simulate the bunched beam, this test stand is submitted to short RF pulses. The available field strength in a travelling wave mode allows to trigger electron multipacting in as received or baked stainless steel surfaces, but not in chambers treated to reduce the secondary emission yield. Thus a number of upgrades in the bench set-up have been pursued, mainly in two directions. The first one is a general improvement on mismatches and losses. Second, instead of dumping the pulsed power into a load, it is re-circulated in a multiple frequency ring resonator. For this purpose, we designed a directional coupler with several kV DC isolation, very low transmission losses and a four octave bandwidth. In this paper, we give an overview of the present status of the set-up highlighting the latest improvements.