The RF group is already working on the next generation of solid state amplifier. The existing RF modules in Figure 163 are using LDMOS transistors in class AB push-pull operation, which require balun transformers at the input and the output. These baluns are made with coaxial lines accurately cut to dimension, bent and welded onto the printed circuit board. The ESRF is now developing a new RF module using printed circuit suspended baluns, which should alleviate this tedious fabrication process. Recent results are extremely promising, as 800 W output power was obtained with reasonably low circuit temperatures.

Fig. 164: 75 kW cavity combiner with 22 pallets, each integrating 6 RF modules and their power supplies.

A new type of combiner using a single cavity was developed at the ESRF in collaboration between the RF and Mechanical Engineering Groups. In its ultimate version shown in Figure 164, it couples 132 modules into one 352.2MHz cylindrical cavity. A prototype with only 18 inputs has been built and tested at low level with promising results. The expected advantages are the small footprint as compared to the existing coaxial combiner trees, the possibility of easily adapting the number of modules and good power transfer efficiency.

A research programme was launched to further develop high-power solid-state amplifiers using cavity combiners for particle accelerators. It receives funding from the EU as work package WP7 via the FP7/ESFRI/CRISP programme involving CERN-SLHC, ESS and GSI-FAIR as partners. The deliverables will be a 75 kW prototype amplifier at 352.2 MHz for the ESRF and feasibility studies for CERN, ESS and FAIR at other frequencies.