Fast Resonant Extraction from the CERN SPS

Two different modes of fast resonant extraction are used at the SPS: non-coherent half-integer extraction with a spill duration from 1 ms to 3 ms and coherent half-integer extraction with a spill duration from about 70 ¿s (two 23 ¿s bursts separated by a 23 ¿s interval) to 1 ms. A special requirement is to stop a 2 ms spill after extraction of part of the beam. The remaining beam is then accelerated to higher energies and can be extracted by any of the other extraction modes in operation at the SPS. The duration of a coherent spill is generally adjusted by choosing a suitable strength of the fast ferrite kicker which kicks the beam into the unstable region in phase space after it has been brought close to the resonance. The shortest coherent spill was studied in some detail. Excellent agreement was found between theoretical predictions and measurements.