High power experiments of the Prototype Solid State RF System for IFMIF-DONES

Abstract

The current trend in the radiofrequency (RF) power systems of many large scientific facilities is the use of solid-state power amplifiers (SSPAs). When it is feasible, for mid-range power levels at frequencies below 1 or 2 GHz, replacing vacuum technology for solid-state (SS) entails significant advantages. Consequently, SS technology has been also selected for the RF Power System of IFMIF-DONES (International Fusion Materials Irradiation Facility – DEMO (DEMOnstration power plant) Oriented Neutron Source). IFMIF-DONES is one of the central facilities of the European roadmap towards fusion electricity, necessary for the validation and qualification of the materials capable to withstand the harsh conditions inside future fusion reactors. Nevertheless, reaching the high power levels of vacuum technology with SSPAs entails the combination of many SS devices. Hence the search for efficient RF power combination techniques is critical in the development of SSPAs.Resonant cavity combination is an innovative technique that provides a high-power and high-efficient combination in a single step. This minimizes the overall combination losses and reduces the size compared with conventional corporate combination schemes. Two prototype cavity combiners at 175 MHz have been designed and manufactured. The first prototype was validated up to 24 kW in continuous wave (CW) and 100 kW in pulsed mode (duty cycle DC=4 %). The conclusions obtained from those experiments revealed the need for temperature control and/or detuning compensation in the cavity combiner to maintain high efficiency at high-power levels in CW. The second prototype is a water-cooled 160-input cavity combiner capable to combine up to 240 kW in CW. It has been validated at 100 kW in CW, using a witty variant in the experimental test bench that simplifies the experiment. This paper presents the design and small-signal characterization of this 160-input cavity combiner, as well as the results of the high-power validation experiments.