The power delivered by microwaves is essential for the acceleration of charged particles in most modern particle accelerators. Electromagnetic waves in the range of a hundred MHz to tens of GHz are typically used, hence the names microwave or radio frequency (RF) often used. At the FREIA Laboratory we work typically with frequencies of 352 and 704 MHz (both ESS), 400 MHz (LHC) and 12 GHz (CLIC). The power amplifiers used for the accelerating cavities are the main energy efficiency drivers for linear accelerators. At the FREIA Laboratory we study the energy efficiency optimization of power amplifiers and combiners.
At FREIA we developed 400 kW 352 MHz power amplifiers using tetrode vacuum tubes. They will be used to power the superconducting spoke cavities in the ESS accelerator.
At FREIA we also developed high efficiency amplifier modules using solid-state transistors. Using 8 of these modules a 10 kW power amplifier was developed in combination with a high efficiency planar Gysel combiner. A compact 100 kW cavity combiner was also developed and tested.