关键词: HL-2M 装置；固态亚毫米波干涉仪；全相位快速傅里叶转换 

Abstract: A solid state submillimeter wave heterodyne interferometry system and a phase processing method 
based on all phase Fast Fourier Transform (apFFT) are developed to measure electron density during the HL-2M 
first plasma discharges. This system produces the detection wave with the power above 0.1MW and the frequency 
of 306.9GHz by high order frequency multiplication to low frequency phase locked microwave source via planar 
diode frequency multiplying technology. A numeral algorithm for phase calculation based on apFFT is introduced, 
which is able to obtain phase information from raw signals and alleviate phase jump induced by possible high 
lever density fluctuation. The time resolution for the system is 5μs while the lower and upper limits of electron 
density measurement are1016m−3and 1020m−3 respectively. During the HL-2M initial discharges, the system is 
installed on the mid-plane while interferometric measurement is realized by reflection of the metal inner wall, and 
the line-averaged electron densities have been measured. 

Key words: HL-2M tokamak, Solid state sub-millimeter wave interferometer, All phase fast Fourier transform