Phase and amplitude stabilization of superconducting resonators

• Main Author: Delayen, Jean Roger
• Format: Others
• Published: 1978
• Online Access: https://thesis.library.caltech.edu/867/1/Delayen_jr_1978.pdf; Delayen, Jean Roger (1978) Phase and amplitude stabilization of superconducting resonators. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/ZS1J-1E35. https://resolver.caltech.edu/CaltechETD:etd-03042008-083340 <https://resolver.caltech.edu/CaltechETD:etd-03042008-083340>

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. This thesis, which stemmed from the superconducting heavy-ion accelerator project at Caltech, deals with the problem of phase and amplitude stabilization of the fields in superconducting resonators. The problem arises from the fast ([...]50 Hz) resonator eigenfrequency modulation of magnitude ([...]100 Hz) which is much larger than the resonator bandwidth ([...]10 Hz). The problem is compounded by the fact that the coupling between the electrical and mechanical modes of the resonator can lead to instabilities (ponderomotive instabilities). The solution suggested involves operating the resonators in self-excited loops, and electronically modifying the loop parameters in order to lock the loop oscillations to an external phase and amplitude reference without attempt to modify the instantaneous resonator eigenfrequency. It is found that this method of phase stabilization is well suited to resonators with small energy contents and small eigenfrequency deviations since the power required is equal to their product; this occurs when the loaded bandwidth of the resonator is twice the maximum eigenfrequency deviation to be compensated for. It is also found that when the loop is free-running, the field amplitude is stable and no ponderomotive instabilities are present as long as the non-ideal effects are limited. When the loop is locked to an external phase and amplitude reference, ponderomotive instabilities can occur; however, the loop can be made stable by adjustment of the loop phase shift, and the stable range can be increased by using high amplitude and phase feedback gains. It is also found that under certain feedback conditions, the error on the particle energy gain can be made to vanish, although residual phase and amplitude errors are still present. A microprocessor-controlled feedback system based on this analysis is then described and results of experiments performed in conjunction with a 150 MHz lead (Pb) plated superconducting split-ring resonator are presented. The experiments show excellent agreement with the analysis.