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UBC Theses and Dissertations

Longitudinal impedance of a prototype kicker magnet system Tran, Hy J.


The longitudinal impedance of a prototype kicker magnet system for the proposed KAON Factory was measured from 0.3 to 200 MHz using the coaxial wire method. The method consists of transforming the aperture of the kicker magnet under test into a coaxial structure by inserting a central conductor so that the transmission coefficient can be measured. The longitudinal impedance was calculated from the transmission coefficient. The measurement was performed in two frequency ranges. From 0.3 to 50 MHz the magnet was transformed into a 50 Ω coaxial line, and from 45 to 200 MHz into a 180 Ω coaxial line. TSD calibration of the measurement assembly was performed in the higher frequency range while HP calibration of the test cables was performed in the lower frequency range. Resonances in the longitudinal impedance are present below the cut-off frequency (30 MHz) of the magnet. The effects on the impedance of a speed-up network and a saturating inductor, installed on the input to the kicker magnet to improve its kick performance, were determined. It was found that a speed-up network damped only the high-frequency resonances whereas a saturating inductor reduced their number. Above the cut-off frequency, other components of the magnet system, such as the speed-up network, the saturating inductor and the cables, were found to have negligible influence on the impedance. The maximum real longitudinal impedance of the magnet was measured to be 32 Ω. The total contribution to the Booster ring is 425 Ω and to the Driver ring is 1184 Ω, respectively. These contributions are small compared with that of rf cavities which have typical values of 10 kΩ. Hence the contribution of kicker magnets is negligible and furthermore any longitudinal instabilities due to kicker magnets can be damped with existing damping systems for the rf cavities except, perhaps, for short bunch (1 ns) operations.

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