RRCAT, Indore (M.P.), India
Feedback control system plays important role for proper injection and acceleration of beam in particle accelerators by providing the required amplitude and phase stability of RF fields in accelerating structures. Advanced digital technologies allow development of control systems for RF applications. Digital LLRF system offers inherent advantages like flexibility, adaptability, good repeatability and low drift errors compared to analog system. For feedback control algorithm, I/Q control scheme is used. Properly sampling of down converted IF generates accurate feedback signal and eliminates the need of separate detector for amplitude and phase. Controller is implemented in Vertex-4 FPGA with proper control algorithm which offers fast correction with good accuracy and also controls the amplitude and phase in all four quadrants. Single I/Q modulator work as common correctors for both amplitude and phase. LO signal is derived from RF signal itself to achieve synchronization between RF, LO and FPGA clock. Control system has been successfully tested in laboratory with phase and amplitude stability better then ± 1% and ±1°. With minor modification same systems can be used at any frequencies.
RRCAT, Indore (M.P.), India
The Indus-2 synchrotron radiation source has four RF stations along with their feedback control systems. For higher beam energy and current operation, amplitude and phase feedback control systems of Indus-2 are being upgraded. To understand the behavior of amplitude and phase control loop under different operating conditions, modeling and simulation of RF feedback control system is done. RF cavity base band quadrature domain model has been created due to its close correspondence with actual implementation and better computational efficiency which make the simulation faster. Correspondence between base band and actual RF cavity model is confirmed by comparing their simulation results. Base band Cavity model was studied under different operating conditions. LLRF feed back control system simulation is done using the same cavity model. Error signals are intentionally generated and response of the closed loops system is observed. With implementation of feedback control loop, broadening in the RF cavity bandwidth was also observed in terms of reduction in cavity fill time. Simulation will help us in optimizing parameters of upgraded LLRF system for higher beam energy and current operation.
