Challenges in operation of low level RF system of Indus-2 synchrotron radiation source

Indus-2 is a 2.5 GeV Synchrotron Radiation Source. RF system (505.8 MHz) of Indus-2 was designed with four bell shaped RF cavities, RF amplifiers and Low Level RF (LLRF) controls. Initially RF system was installed with analog LLRF system that worked satisfactorily for many years. High power amplifiers of Indus-2 were upgraded that required optimization of operating parameters of RF system after every upgrade. Under these conditions digital systems are more suitable due to their advantages of flexibility and adaptability. Considering this Digital LLRF control systems for all RF stations of Indus-2 employing FPGA have been designed, developed and commissioned in phased manner. Digital LLRF systems were built on PXI platform and codes for fast feedback control were prepared in LabView. Recently a fifth RF station with digital LLRF system has been installed to cater RF power requirement for Insertion Devices. Digital LLRF system has RF Processing Unit (RFPU) that perform the function of down conversion of RF to IF, synchronized clock generation and amplitude/phase control of RF drive to high power amplifier. Presently five digital LLRF control systems have been installed with RF system of Indus-2, providing phase and amplitude stability better then ±0.5° and ± 0.5% respectively and Indus-2 is being operated successfully in round the clock manner at designed energy of 2.5 GeV/200 mA. Challenges faced, experience gained and lessons learnt in the development and operation of Low Level RF system of Indus-2 will be presented in this paper. (author)