Beam impedance of ferrite kicker magnets

The longitudinal beam impedance of a typical pulsed magnet that will be used in the Advanced Light Source was measured. The magnets are of a ferrite window-frame design with a single plate conductor on each side. Two separate power supplies are used to derive current in opposite directions in the two conductors. The continuity of the ferrite yoke is interrupted by two copper plates 1 mm thick in the center of the top and bottom of the window frame. This increases the reluctance of the magnetic path, and thus decreases the flux which couples the beam. The measurements were made by exciting a 1/8-in. rod along the beam path through the magnet. This makes a 185-Ω transmission line, and it was terminated in a resistive divider at the exist end. A 3-GHz network and analyzer was used to measure S₂₁ through the magnet, and longitudinal beam impedance was calculated from these data. The impedance is dominated by two low-frequency resonances in the magnet winding and drive circuit