Investigation on stable operational regions for SPIDER RF oscillators

The Radio-Frequency generators of the SPIDER experiment are devoted to the ignition and heating up of the ion source plasma. Such generators are 4 free-excited oscillators based on vacuum tubes technology (tetrodes), which work at a frequency of 1 MHz ± 0.1 MHz. In this paper the behaviour of such system is deeply investigated also thanks to the developed models, which have been able to reproduce instabilities observed in other similar RF ion sources and in SPIDER first operation.