This paper reports results of using High-Frequency Structure Simulator (HFSS) to design a Smythe-type broadband longitudinal HOM damper for the S S U low energy booster (LEB) ferrite-tuned cavity. 'be damper is designed to have a shunt impedance varying from less than 1 kohm between 100-200 MHz to about 3 kobm at 1 GHz. Above 1 GHz, the ferrite should effectively damp all HOM.
The SSC Low-Energy Booster (LEB) cavity must rapidly tune from 47.52 to 59.78 MHz. The cavity tuner will use transversely biased ferrite[ 11 to control the cavity resonance.The thermal expansion of a cavity's materials affects its resonance. There are two other known temperature mechanisms that affect resonance in the water-cooled LEB cavity. The saturation magnetization of the ferrite is a function of temperature, and since the ferrite permeability is dependent on the saturation magnetization, the ferrite permeability is also temperature dependent. The ferrite cooling water is present in the tuner rf field, hence the water permittivity, which is very temperature dependent, also affects cavity resonance.While taking data on the SSC Test Cavity to quantify the effect of temperature on the resonance, we observed that the rf power level also perturbed the resonance, It was readily apparent from the data that the power level affected the resonance much more strongly at low values of control bias than at high values. In fact, when we calculate an apparent modified control-bias H field that produces the observed resonance shift, we noticed an almost perfect, though non-linear, correlation between the ratio of Hrf to H b h and the apparent modified bias field, Happ This paper will present a set of equations to predict the resonance shifts produced by changes in temperature and rf power level. It will also present the techniques, both theoretical and empirical, by which these equations are derived. Finally, some of the methods for dealing with these resonance shifts will be discussed.
The phenomenon of dependence of the resonance shape and frequency on the RF power level in perpendicular biased ferrite-tuned cavities has been observed by G. Hulsey and C. Friednchs in the the SSC test cavity expenment. Thisapaper rsents a theoretical as well as numerical an ysls o thrs phenomenon and compares the results with experimental data. The effect of this nonlinearity on the SSC low energy booster prototype cavity is discussed.
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