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UBC Theses and Dissertations

The generation and control of 1.5 megawatts of RF power for the TRIUMF cyclotron Brackhaus, Karl Heinz

Abstract

This thesis discusses the design of a stable, 1.5 MW, 23.075 MHz, RF system for the TRIDMF cyclotron. A physical description of this EF system; the RF amplifiers, transmission lines, and resonators, is provided. The required characteristics of this system are presented with emphasis on an examination of the amplitude and phase modulation constraints that was carried out as part of the course of study. It is shown that to satisfy the RF system criteria initially proposed, one must reduce RF system disturbances to an absolute minimum, and then further increase system stability by using amplitude and phase regulating feedback systems. A method for reducing one type of system disturbance— the use of dynamic vibration dampers for the resonator hot arm panels—was investigated. The analysis of dampers used for the elimination of vibrations caused by excitation at a single frequency is fairly well known; this thesis presents the method of analysis and design that was developed for systems excited by stochastic signals. To keep the power required by the resonators within the limits imposed by the RF amplifiers, the resonators must be kept closely tuned to the RF driving frequency. The analysis and design of a pneumatic tuning system to accomplish this function is presented. The design of RF feedback regulating systems .requires a knowledge of the response of RF systems to amplitude and phase modulation. Due to the stringent stability requirements imposed on the TRIUMF RF system, it was also considered imperitive to investigate the coupling between amplitude and phase in the same system. To this end, the generalized (matrix) transfer function of a modulated carrier system was derived. This function was then approximated to give the necessary amplitude, phase, and coupling transfer functions. Because it is intended to "square" the RF accelerating voltage waveform by introducing third harmonic power, another problem is introduced. This is, given that the phase relationship between the fundamental and third harmonic RF voltages is to be such that power is fed from the fundamental RF system into the circulating ion beam and from this beam into the third harmonic RF system, will this system be stable? To answer this question the relationships between the instantaneous circulating beam currant and the RF accelerating voltage were derived. The RF system (complete with feedback loops) was then digitally simulated to show that the system is, indeed, stable. The analysis of the required RF feedback loops is presented in this thesis. This analysis is followed by an investigation of the problems of measuring the RF waveform parameters. The design of the RF measurement system is discussed and measurement results are presented.

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