Longitudinal impedance simulations in ORBIT: benchmarking and application to the SNS extraction kicker

Longitudinal and transverse impedances have been incorporated into the ORBIT particle beam dynamics code. This paper deals with longitudinal impedance calculations. The model has been validated for low harmonic number ring stability calculations. Successful benchmarking with the ESME code, for a case without space charge, and with analytical instability thresholds, for coasting beams with and without space charge, has been carried out. The model was then applied to the SNS ring using the measured impedance of the proposed extraction kicker, and it was found that the instability threshold occurred at about four times the proposed current for 2 MW operation.