Receiver circuit improvement of dual frequency-comb ka-band Doppler backscattering system in the large helical device (LHD)

Abstract

Doppler-backscattering (DBS) has been used in several fusion plasma devices because it can measure the perpendicular velocity of electron density perturbation v⊥, the radial electric field E r, and the perpendicular wavenumber spectrum S( k⊥) with high wavenumber and spatial resolution. In particular, recently constructed frequency comb DBS systems enable observation of turbulent phenomena at multiple observation points in the radial direction. A dual-comb microwave DBS system has been developed for the large helical device plasma measurement. Since it is desirable to control the gain of each frequency-comb separately, a frequency-comb DBS system was developed with a function to adjust the gain of the scattered signal intensity of each channel separately. A correction processing method was also developed to correct the amplitude ratio and the phase difference between the in-phase and quadrature-phase signals of the scattered signals. As a result, the error in Doppler-shift estimation required to observe vertical velocity and the radial electric field was reduced, which enables more precise measurements.

The investigation of edge-localized modes on the Globus-M2 tokamak using Doppler backscattering

“…DBS, sometimes referred to as Doppler reflectometry, is a method which involves the detection of the backscattered radiation by means of introducing a microwave beam at oblique incidence into the plasma. DBS is currently installed on most modern tokamaks [14][15][16][17][18][19][20][21][22][23][24][25] and stellarators [26][27][28][29][30], and is also being developed for new devices, such as JT60-SA [31] and ITER [32].…”