The high level RF system for transition crossing without RF focusing in the main ring at Fermilab

A new method for crossing transition at the Fermilab Main Ring has been developed. Near transition a third harmonic component is added to the fundamental RF voltage producing a flattened RF waveform. To generate this waveform required the development of a third harmonic system consisting of a 159 MHz cavity, a perpendicularly biased tuner,and a 10 kW power amplifier. The cavity is a modified CERN SPS 200 MHz cavity whose frequency was lowered to 159 MHz by inserting two sleeves at the cavity gap. This cavity is electrically tuned over a 60 kHz range by using an orthogonally biased Iron-Yttrium-Garnet ferrite tuner. The power amplifier is a grid driven tetrode that has a 3/4 λ anode resonator and produces a RF cavity gap voltage of greater than 300 kV. The power amplifier drives the cavity by way of a coupling loop. An overview of this high level RF system and the resulting waveform is given