Research On The Phase And Power Control System For ICRH In EAST

Ion Cyclotron Wave Resonant Heating(ICRH)is one of the most important auxiliary methods to heat plasma in Experimental Advanced Superconducting Tokamak(EAST).It is considered as the preferred choice for core plasma heating and current drive.Ion cyclotron wave can not only heat the electrons and ions,but also control the spatial distribution of some important parameters of the plasma,and can be used for generation of plasma poloidal current.Theoretical calculations and experimental studies show that the ICRH antenna has better heating efficiency and produces relatively small impurities operating in the dipole phase.In addition,the antenna can drive current by inducing an asymmetric spectrum in the monopole phase.In the future,ion cyclotron current drive will serve as an important means to drive the core current on the ITER.Thus the measurement and accurate control of the antenna phase is important for both ion cyclotron heating and research of current drive.If the phase between antenna straps cannot be accurately measured and controlled,it will cause power imbalance between the antenna straps and have deleterious impact on the waves coupling efficiency.The plasma impedance always changes at any time in the EAST experiments,which results in the fluctuation of RF power in the ICRH system.In previous experiments on ICRH system,we manually set the control signal to adjust the actual injecting power and phase with the needed ones.The control signals were fixed constantly during a discharge and thus lead to the randomly variation of injecting power and phase.So we can not achieve the precise control of power.Our main objective is the establishment of a real-time data acquisition and feedback control system for phase and power in this paper.Several different measurement methods of phase and power are compared,then we present a new phase detector mainly composed of analog chip(HMC439)on the basis of AD8302.The new phase detector has wider measurement range(up to 720°)and ultra low phase noise.Moreover,it has good linearity,which brings convenience for following data processing.Feedback control systems for both phase and power is composed of signal acquisition board and feedback control board based on Field Programmable Gate Array(FPGA).Signal acquisition board is responsible for the signal conditioning of phase and power as well as analog to digital conversion.Finally,the data fitting and calculation is completed in FPGA.The feedback control board performs the communication with the host PC and fulfills the feedback control of phase and power.We use the Labview software to develop the host computer program,and the data transmission between the host computer and the control cabinet is realized by USB protocol.Through the design of hardware and software and the optimization of the feedback algorithm,the feedback control system was tested using both a matched dummy load and plasma load,and it was successful in stable operations on 2016 EAST campaign.Phase and power remained stable at the value we set,constantly adapting to the antenna loading variations,which lays the foundation for the development of power and phase modulation experiments.