Tests at High RF Power of the ESS Medium Beta Cryomodule Demonstrator

CEA is in charge of the 30 elliptical medium and high-beta cryomodules to be installed in the ESS tunnel in Lund, Sweden. Before launching the assembly of the series cryomodules, CEA developed a medium-beta cryomodule technology demonstrator in a collaboration with IPNO, LASA and ESS. This paper briefly presents the cryomodule assembly and summarizes the main results of the high RF power tests performed in 2018 in a dedicated test stand in CEA Saclay. The main ESS requirements were reached: E_{acc} = 16.7 MV/m in cavities, Pforward = 1.1 MW in power couplers, RF pulses length = 3.6 ms at 14 Hz. The piezo tuners efficiently compensated the Lorentz forces detuning and could stabilize the accelerating field better than 1% over the full length of the expected ESS 2.86 ms beam pulse without any LLRF regulation system. Following this successful validation CEA started the assembly of the first ESS medium-beta series cryomodule