Design Of The Fine Tuner For QWR Superconducting Cavity

Superconducting cavity is an important part of the superconducting linear accelerator.Stability of its working frequency at low temperature has an influence on the effect of the particle acceleration.The auto-tuning system composed of tuner and LLRF can smooth out the fluctuations of the frequency of the superconducting cavity caused by the fluctuation of helium pressure,Lorentz detuning,beam loading effect and microphone effect.The cavity type of the accelerator,the working conditions,the tuning accuracy,the responce time etc.should be taken into account in the design of the tuner.The out-of-loop behaviour occurs frequently in the 25 MeV superconducting linear accelerator tuning system,experiments on which was carried out.The linearity,return difference of the tuner and linear unit in CM1,CM2,and CM3 were measured.The mechanical analysis of the lever and scissor structures of the tuner and the electromagnetic simulation of the HWR superconducting cavity under different conditions were performed.The simulation results are in agreement with the experimental results.In this phase of the job,we found the reasons for the out-of-loop behaviour and proposed improvement scheme,which provides technical support for the design of the precision tuner.In this work,the QWR cavity is made of cooper coated niobium.The ? value,the eigen frequency and the bandwidth of it are 0.13,162.5 MHz and 200 Hz,respectively.According to the perturbation theory,we have accomplished the structure design of the precision tuner in the way of synchronous collaboration of the fast-slow tuning on the base of the 25 MeV superconducting linear accelerator tuner,with the goal of stabilizing the frequency of QWR superconducting cavity reached.The tuning range and the maximum tuning force for the 1.1 mm U-turn tuning dial is determined to be 28 kHz and 1500 N respectively by using Solid Works and COMSOL.On this basis,we made selection for the fast tuning driver,piezo,and slow tuning driver,stepping motor.Leadscrew nut was selected for the stepping motor to convert the rotating motion into linear motion.We designed the test tooling of the piezo measure the linearity of piezo.Linearity analyses under different pressures were also presented.Parts of the tuner were mechanically analysed.It was concluded that the parts and the tuning dial have met the working requirement at the maximum tuning force.In the end,we machined the precision tuner,designed the simulating tooling of QWR cavity,built the test platform for the tuner,performed motor-driving tuning test at large scale and at small scale in turn on the tuner and peformed piezo driving test and response test on the tuner.It was showed that return difference was 10 ?m and the response time was 0.2 ms.All results of the tests have met the working requirement of the tuner.