Behaviour analysis of a capacitive loaded RF cavity for the Iranian Light Source Facility (ILSF)

Synchrotron radiation has numerous applications in science and technology and is considered as one of the most significant research facilities required in Iran in the next 10 years. A key part in each synchrotron machine is its RF cavity. Improving the operation characteristics of the RF cavity will result in radiation quality enhancements. The cavity structure should be designed in a way that not only it can maintain the beam energy to the desired value, but also minimizes the collective instabilities on the beam. The development of the 100 MHz capacitive loaded RF cavity for the Iranian Light Source Facility was initiated in 2016. The main idea was to design a simple structure avoiding complicated fabrication technologies and to put more focus on applying different methods to control and also to minimize the effect of higher order frequency modes. Before engaging in fabrication of the main copper cavity, it was decided to manufacture a smaller aluminum cavity prototype in order to verify our simulations and moreover, improve the measurement methods and investigate the characteristics of the higher order frequency modes. In this paper, the design, simulations, and measurement results of this aluminum cavity prototype is described, two different methods for frequency tuning of the cavity are applied and the effects of these methods on the higher order frequency modes are studied. Contrary to previous experiences in other RF cavities, we propose to use a plunger as a tool for damping or shifting the HOMs instead of tuning the fundamental mode.