A Resonantly Coupled, Ferrite-Tuned Buncher-Cavity System for the Los Alamos Proton Storage Ring
Resonantly coupled buncher and ferrite-loaded tuning cavities at 503.125 MHz are separately optimized to provide fast tracking of time-dependent beam current changes in the Los Alamos Proton Storage Ring (PSR) while maximizing radio-frequency (rf) stability and efficiency.
A High-Q Ferrite-Tuned Cavity
Rapid cycling proton synchrotrons, such as the proposed LAMPF II accelerator, require approximately 10 MV per turn rf with 17% tuning range near 50 MHz. The traditional approach to ferrite-tuned cavities uses a ferrite which is longitudinally biased (rf magnetic field parallel to bias field). This method leads to unacceptably high losses in the ferrite. At Los Alamos, we are developing a cavity with transverse bias to the bias field) making use of the tensor permeability of the ferrite. Initial tests of a small (10-cm-diam) quarter-wave singly re-entrant cavity tuned by several different ferrites indicate that the losses in the ferrite can be made negligible compared with the losses due to the surface resistivity of the copper cavity. Details of the test results will be presented.
Measurement of Microwave Dielectric Constants and Tensor Permeabilities of Ferrite Spheres
The Bethe-Schwinger cavity perturbation theory is applied to measurements of the microwave dielectric constants and tensor permeabilities of small spherical samples of ferrites. For the dielectric constant measurements, a cavity opened at a position of minimum transverse wall currents is used. A frequency-shift method is used for measuring the real part of the dielectric constant and a cavity-transmission method is used for measurement of the loss tangent. Circularly-polarized cavity methods yield effective scalar permeabilities of which the real and the imaginary parts are measured in a manner similar to the dielectric measurements. These scalar permeabilities yield sufficient information to describe completely the tensor components. Experimental data are given for a polycrystalline magnesium-manganese ferrite, to illustrate the techniques described.