Development of an actively cooled radio-frequency test bench for the ITER ICRF windows

Radio-Frequency (RF) windows (or feedthroughs) are under development for the ITER Ion Cyclotron Range of Frequencies (ICRF) system (40-55 MHz). To test these first of a kind RF window units, an actively cooled radio-frequency coaxial resonator was designed and is currently under construction at CEA/IRFM. This testbed is specified to reach 50 kV peak maximum voltage or 2.5 kA peak maximum current at the middle of the test articles in continuous-wave operation (3600 s RF pulses with a ¼ duty cycle). The operating frequency of the resonator is set to 55 MHz. The conditions of the tests are 0.6 MPa (absolute, dry air) at one side of the RF windows, vacuum (10-4 Pa) environment at the other side of the front window and 0.3 MPa (absolute, dry air) at the rear window. These conditions are representative of the current ITER ICRF environment: the vacuum side simulates the torus vacuum inside the tokamak, and the pressurized side mimics the gas conditions within the transmission lines connecting the RF generators to the antenna. Since it is not possible to maximise both voltage and current at a given position of a resonator, two resonator configurations are foreseen, for each of the front and rear windows (hence 4 different configurations). Each of the front and rear windows will be tested at maximum voltage and maximum current. The test bench was designed to be modular, allowing the positioning of either the rear of the front windows for voltage or current RF test, hence leading to cost reduction. This paper is a description of the RF design, the mechanical design, and a rough description of the ongoing manufacturing phase.