Design Of Microwave Reflectometry On HL-2A Tokamak

Microwave reflectometry is now widely used to measure electron density profiles for experiments on tokamaks and other toroidal magnetically confined plasmas. An O-mode microwave reflectometer system has been developed for density profile measurements on the HL-2A tokamak.We have studied about the development and application of the microwave reflectometry on magnetic confined fusion devices, and introduced the basic principle of microwave reflectometry and characteristics of different kinds of microwave reflectometry. We have designed an amplitude modulation reflectometry system with fast-scanning microwave source for density profile measurement on the HL-2A tokamak (R=1.64 m, a=0.4 m,Bt=2.5T, Ne=0.8～4×10¹⁹m^-3). The reflectometer launches microwave power from a very fast-scanning backward wave oscillator in 46-60 GHz to probe the plasma and receive the reflection by the density cutoff layer. The scanning time over the full band of 26.5-40 GHz is about 1ms. It is an ordinary mode reflectometer. The reference signal and the probing signal are obtained by mixing a local oscillator power with the demodulated microwave signals. Comparison is then accomplished by I/Q phase detector.The microwave reflectometry system has been used on HL-2A tokamak for electron density profile, and has given some experiment results.