THE CAPACITANCE OF FERRITE LOADED CAVITIES

> We have recently measured the capacitance of the coaxial quarter wave-length cavity. The object of the investigation is t o determine the effect of the ferrite discs and cooling plates on the distributed capacitance of the cavity. The variations of the cavity capacitance were observed as a function of the number of ferrite rings. Experimental results showed that the capacitance decreased as the number of the ferrite discs increases. And the existence of the metallic cooling plates seemed to enhance the distributed capacitance of the cavity. Floating of the cooling plates, as compared t o grounding, produced a smaller value of distributed capacitance. The experimental results were also compared with the results calculated from the Superfkh code and the results were very consistent. INTRODUCTION The ferrite loaded cavity consists of several materials distributed along the longitudinal directionfl]. The impedance of the cavity can be calculated by means of a distributed constant analysis. It is well-known that the inductive part of impedance is due mainly to the inductance of the ferrite discs because of their high magnetic permeability. The inductance can be analytically calculated very well, but it is very difficult t o estimate the distributed capacitance of the cavity. The barrier cavity requires the smallest value of capacitance consistent with tuning of the ferrite inductance to keep the drive current as low as possible. To increase the barrier voltage per unit length, a multi-gap rf-station, which is made up of several short re-entrant cavities, has been considered as an AGS barrier system, Generally, when the re-entrant cavity is filled with a uniform material the electromagnetic field is a transverse mode (TEM). However, in practically, as the ferrite stack is interleaved with thin metallic plates for cooling, the electric field around the metals should turn direction locally so as to cross perpendicular to their surface. Then, it seems as if the parallel-plate capacitors are in series along the co-axial cavity because of the high ferrite