Half-Integer Resonance Extraction for the NAL Accelerator

The slow extraction from the main ring at NAL utilizes the half-integer resonance at ¿x = 41/2. Extraction elements are three quadrupoles and one octupole. Two quadrupoles control the tune during the extraction while the third one is used to compensate for the tune fluctuation, thereby reducing the amount of the beam intensity modulation. The turn separation is produced by the average octupole field in the ring as well as by the special octupole which is located in phase with extraction quadrupoles. The size of turn separation is also controlled by a local bump in the closed orbit near the extraction septum. The beam has been extracted with the spill time up to 700 ms and with the efficiency of 85-90%. Together with a pinger, it is also possible to extract over 90% of the beam in less than 400 ¿s.