Calculations and observations of the longitudinal instability caused by the ferrite inductors at the Los Alamos Proton Storage Ring (PSR)

The frequency dependence of the complex permeability of the ferrite (at room temperature and 125 °C) used in the inductors at PSR has been determined by comparing the S₁₁ parameters from a jig containing ferrite and a MAFIA (a program package for the computation of electromagnetic fields) simulation of the jig. Both the frequency response and the longitudinal impedance of the inductive inserts were obtained by simulating the inductor cavity in MAFIA using the ferrite properties from the aforementioned fit. Experimental observations of the longitudinal instability caused by the ferrite inductors at room temperature in a bunched coasting beam have been made. Comparisons of observed and simulated growth times, resonant frequencies, and width of the instability will be discussed.