Abstract
Rotary and displacement tuners are described for multistub superconducting rf resonators. The effectiveness of these tuners is made possible because the resonators have low currents between their outer conductors and tuner elements. Computer simulations and experimental data show that the devices provide a tuning range up to 100 kHz with a frequency resolution of about 1 Hz. As well, only a small driving force is required allowing use of a low-backlash drive mechanism. The use of the rotary tuner is limited to the resonators with two loading elements such as the 2-stub quarter wave resonator, the conventional split loop resonator, and the 2-stub, half wave resonator. The displacement tuner is more versatile and can be used for any TEM-like quarter wave resonator or half wave resonator resonators with two or more loading elements.
Highlights
The electromagnetic and mechanical properties of 150 MHz, =4 superconducting accelerating structures, with multiple loading elements, are described in [1,2]
We report two complementary developments at ANU to achieve these design goals: first, a rotary tuner for the 2QWR and a displacement tuner for the 3-QWR
These tuners are only possible because a multistub resonator, in acceleration mode, has low currents between the outer cylinder and the tuner elements
Summary
The electromagnetic and mechanical properties of 150 MHz, =4 superconducting accelerating structures, with multiple loading elements, are described in [1,2]. Since a high driving force is required, it is slow to respond, has poor resolution, and large backlash This is less the case for bellows tuners. Detuning of the resonant frequency on a millisecond time scale can be caused by microphonic noise or rapid fluctuations in helium delivery pressure which need to be compensated. We report two complementary developments at ANU to achieve these design goals: first, a rotary tuner for the 2QWR and a displacement tuner for the 3-QWR These tuners are only possible because a multistub resonator, in acceleration mode, has low currents between the outer cylinder and the tuner elements. The multistub cavity fast tuner must be capable of achieving 1 Hz, frequency resolution within a bandwidth of f1=2 22 Hz. The required Pf is 83 W. Frequency tuning range Frequency resolution Cavity frequency at 4.3 K Cavity frequency at 300 K (air)
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