The High Voltage Radio Frequency Test Facility
(HVRFTF) is a flexible experiment
developed to characterize the low pressure
electrical insolation of componets
operating at radio frequency.
The goal is to verify the design criteria of the RF (Radio Frequency) circuit and its special components installed in the ion source of SPIDER
The neutral beam injector (NBI) ion source for the ITER experiment is studied in the SPIDER and MITICA experiments. This consists in particular of a plasma source fed at a frequency of 1 MHz with powers up to 800 kW.
The radio frequency circuit on the source board is composed of both commercial components such as vacuum capacitors, and special components, called drivers, developed to transfer up to 100 kW (8 drivers are present in the ion source) to the generated plasma.
The atmosphere in which the radio frequency components operate is around 60 mPa in H2, and the estimated voltages reach 16 kV. In this environment, the radio frequency voltage holding is critical, as experimentally verified, and discharges are possible with consequences that have a serious impact in the experiment, limiting the operating space. To avoid these phenomena, a dedicated study was launched aimed at the experimental verification of the design criteria of the radio frequency circuit and of the special components installed, and to identify strategies to limit the interaction of the RF circuit with the different systems (diagnostics, other electrical circuits necessary for the operation of the source) and nearby structures.
HVRFTF consists of a vacuum chamber capable of containing different types of “device under test” (DUT), electrodes to which the test voltage is applied; a gas injection and pumping system capable of providing operating pressures up to 10-5 Pa with different types of gas (H2, N2, Ar, He); a radio frequency circuit, designed internally by Consorzio RFX, to produce test voltages up to 17 kV in the frequency range 0.9 – 1.1 MHz.